Specification of Selected Performance Monitoring and Commissioning Verification Algorithms for CHP Systems

Transcription

1 PNNL Specfcaton of Selected Performance Montorng and Commssonng Verfcaton Algorthms for CHP Systems MR Brambley S Katpamula October 2006 Prepared for the U.S. Department of Energy under Contract DE-AC05-76RL01830

2 DISCLAIMER Ths report was prepared as an account of work sponsored by an agency of the Unted States Government. Nether the Unted States Government nor any agency thereof, nor Battelle Memoral Insttute, nor any of ther employees, makes any warranty, express or mpled, or assumes any legal lablty or responsblty for the accuracy, completeness, or usefulness of any nformaton, apparatus, product, or process dsclosed, or represents that ts use would not nfrnge prvately owned rghts. Reference heren to any specfc commercal product, process, or servce by trade name, trademark, manufacturer, or otherwse does not necessarly consttute or mply ts endorsement, recommendaton, or favorng by the Unted States Government or any agency thereof, or Battelle Memoral Insttute. The vews and opnons of authors expressed heren do not necessarly state or reflect those of the Unted States Government or any agency thereof. PACIFIC NORTHWEST NATIONAL LABORATORY operated by BATTELLE for the UNITED STATES DEPARTMENT OF ENERGY under Contract DE-AC05-76RL01830 Prnted n the Unted States of Amerca Avalable to DOE and DOE contractors from the Offce of Scentfc and Techncal Informaton, P.O. Box 62, Oak Rdge, TN ; ph: (865) fax: (865) emal: [email protected] Avalable to the publc from the Natonal Techncal Informaton Servce, U.S. Department of Commerce, 5285 Port Royal Rd., Sprngfeld, VA ph: (800) fax: (703) emal: [email protected] onlne orderng:

3 Specfcaton of Selected Performance Montorng and Commssonng Verfcaton Algorthms for CHP Systems MR Brambley S Katpamula October 2006 Prepared for the U.S. Department of Energy under Contract DE-AC05-76RL01830 Pacfc Northwest Natonal Laboratory Rchland, Washngton 99352

4 Acknowledgements Ths work was supported the Dstrbuted Energy Program of the Offce of Electrcty Delvery and Energy Relablty of the U.S. Department of Energy. The authors wsh to thank Maro Scull, Program Manager at the Natonal Energy Technology Laboratory, and Debbe Haught, the DOE Program Manager, for ther support and gudance n the performance of ths work. Members of the project advsory panel also provded valuable nput through ther revew of project plans and reports. Ther gudance s crtcal to the successful performance of ths project. Project Advsory Panel Todd Amundson, Bonnevlle Power Admnstraton Gordon Bloomqust, Washngton State Unversty Extenson Program and Northwest CHP Applcaton Center Mchael O Callaghan, Unted Technologes Research Center Joe Haley, UTC Power Steve Gable, Honeywell Carlos Haad, Southern Calforna Edson Sumt Ray, Trammell Crow Randy Hudson II, Oak Rdge Natonal Laboratory Abd Zaltash, Oak Rdge Natonal Laboratory Chrs Marnay, Lawrence Berkeley Natonal Laboratory

5 Executve Summary Pacfc Northwest Natonal Laboratory (PNNL) s assstng the U.S. Department of Energy (DOE) Dstrbuted Energy (DE) Program by developng advanced control algorthms that provde the bass upon whch tools to enhance performance and relablty, and reduce emssons of dstrbuted energy technologes, ncludng combned heat and power (CHP) technologes, could be developed. The prmary objectve of ths multyear project s to develop algorthms for combned heat and power systems. These algorthms wll ensure optmal performance, ncrease relablty, and lead to the goal of clean, effcent, relable and affordable next generaton energy systems. Ths document provdes detaled functonal specfcatons for the algorthms for CHP system performance montorng and commssonng verfcaton that are applcable to both exstng and new CHP systems. The report dentfes 7 generc CHP system confguratons for whch algorthms wll be developed from a total of 10 orgnally dentfed n the Scope Specfcaton (Katpamula and Brambley 2006). The report then provdes specfcatons for montorng ndvdual components present n the seven selected CHP confguratons. Each specfcaton ncludes equatons for calculatng performance metrcs and a dagram showng all fxed nputs, measured nputs, and outputs for the algorthms. An analogous specfcaton s also provded for performance montorng at the system level. Commssonng and performance verfcaton are then dscussed n some detal. A method to model system performance and detect degradatons s presented along wth equatons and an nput/output dagram. Verfcaton of commssonng s accomplshed essentally by comparng actual measured performance to benchmarks for performance provded by the system ntegrator and/or component manufacturers. The results of these comparsons are then automatcally nterpreted to provde conclusons regardng whether the CHP system and ts components have been properly commssoned and where problems are found, gudance s provded for correctons. The report then presents an example of how the montorng algorthms could be deployed as a stand-alone software package. Scenaros are also provded llustratng how the algorthms could be used for performance montorng durng operaton of a CHP system and as a means for verfyng proper commssonng of a CHP system durng ntal start-up or restart. The report concludes by dentfyng the next steps n the project.

6 Varables Physcal Varable Coeffcent of performance Cost Densty Value-weghted energy utlzaton factor Specfc enthalpy Fuel energy flow rate Heat loss rate Hgher heatng value Lower heatng value Mass flow rate Power Pressure Specfc heat Temperature Volumetrc flow rate Effcency Effectveness Electrc power Prce Thermal power Unt monetary value Subscrpts Parameter Components Absorpton chller generator Absorpton chller Chller (electrc) Condenser Coolng tower Desccant system Evaporator Fan Gear box Heat recovery steam generator Heat recovery unt Prme Movers Mcro-turbne Recprocatng engne Pump Notaton Notaton COP Cost ρ EUF VW H Q Fuel L HHV LHV m& W P c p T v& η ε W Elec Prce Q th Y Subscrpt Notaton gen AbChller Chller cond CT D evap Fan gearbox HRSG HRU Turbne engne Pump v

7 Parameter Substances Ar Coolng water Exhaust gases Fuel Hot water Steam Water Flow Drecton Input Output Forms of Energy Electrcty Thermal Fuel Other Actual value Commssonng baselne Dscharge Electrc generaton Mnmum Maxmum Sucton Wet bulb Subscrpt Notaton A cw ex F or Fuel hotwater S or steam w o Elec th F or Fuel a Cxb dscharge EE mn max sucton wb v

8 Contents Executve Summary... Introducton... 1 Scope... 2 Defntons and Approach... 8 Performance Montorng... 8 Commssonng Verfcaton... 9 Component Montorng Prme Movers Effcency of Prme Movers Prme Mover Input/Output Dagram Heat Recovery Unt Effectveness of Heat Recovery System Heat Recovery Unt Input/Output Dagram Heat Recovery Steam Generator Effectveness of Heat Recovery Steam Generator Heat Recovery Steam Generator Input/Output Dagram Absorpton Chller Effcency of Absorpton Chller Absorpton Chller Input/Output Dagram Coolng Tower Effcency of Coolng Towers Coolng Tower Input/Output Dagram Pumps Effcency of Pumps Pump Input/Output Dagram Fans Effcency of Fans Fan Input/Output Dagram Desccant System Effcency of Desccant System Desccant System Input/Output Dagram System Level Montorng System-Level Performance CHP System-Level Input/Output Dagram Commssonng and Performance Verfcaton CHP System Commssonng Approach to Commssonng and Performance Verfcaton A Bn-Based Method for Baselne Performance Input/Output Dagrams Commssonng Verfcaton Input/Output Dagrams Performance Verfcaton Input/Output Dagrams CHP Performance Montorng (PM) and Commssonng Verfcaton (CxV): Algorthm Deployment Scenaro CHP Performance Montorng and Commssonng Verfcaton: Applcaton Scenaros Summary v

9 Next Steps References v

10 Introducton Pacfc Northwest Natonal Laboratory (PNNL) s assstng the U.S. Department of Energy (DOE) Dstrbuted Energy (DE) Program by developng advanced control algorthms that would lead to development of tools to enhance performance and relablty, and reduce emssons of dstrbuted energy technologes, ncludng combned heat and power (CHP) technologes 1. The prmary objectve of ths multyear project s to develop algorthms for combned heat and power systems. These algorthms wll ensure optmal performance, ncrease relablty, and lead to the goal of clean, effcent, relable and affordable next generaton energy systems. As part of the project, n late FY2005, an expert project advsory panel (PAP) was formed to help gude and revew progress of the proposed multyear research effort. The advsory panel ncluded representatves from: 1) Honeywell Labs, 2) Unted Technologes Research Center (UTRC), 3) Northwest CHP Applcaton Center, 4) Bonnevlle Power Admnstraton (BPA) and 5) Southern Calforna Edson (SCE). Ths panel met to revew project objectves, scope and plans n December The next phase of the project focused on defnng the potental breadth of advanced controls for CHP systems and then defned from that the specfc scope for ths project. The results of that phase are documented n a report ttled Advanced CHP Control Algorthms: Scope Specfcaton (Katpamula and Brambley 2006). The current report documents the next phase of work, provdng a detaled functonal specfcaton for algorthms for performance montorng and commssonng verfcaton that are applcable to both exstng and new CHP systems. The report dentfes the systems for whch algorthms wll be developed, the specfc functons of each algorthm, metrcs that the algorthms wll output, and nputs requred by each algorthm. Specfcatons of algorthms for montorng the performance of ndvdual CHP components are developed frst, followed by algorthms for montorng specfc CHP system confguratons. That s followed by specfcaton of the algorthms for commssonng verfcaton, whch use the outputs of performance montorng as nputs to verfy that performance meets expectatons. Ths nformaton forms the bass for development of the algorthms n the next phase of the project. The report then provdes a scenaro for deployment and use of the algorthms to help the reader better understand how the algorthms would be deployed n software and used to support CHP system operatons. We conclude the report by brefly descrbng the focus of the next phase of the project, whch wll nvolve developng the algorthms for performance montorng and commssonng verfcaton. 1 In the open lterature, several dfferent terms are used for combned heat and power systems, ncludng buldng combned heat and power (BCHP), combned coolng, heatng and power (CCHP), combned heat and power for buldngs, and ntegrated energy systems. See Katpamula and Brambley (2006) for addtonal dscusson of termnology and the overall scope of ths project. 1

11 Scope In ths secton, we dentfy the specfc capabltes to be developed under FY2006 fundng and the systems for whch they wll be developed. Fgure 1 shows the full scope of capabltes to be developed n ths project, as orgnally proposed. Of these, performance montorng and commssonng verfcaton wll be developed under fundng provded n FY2006 (shown n black). 2 Ths ncludes performance montorng and commssonng verfcaton. Algorthms for the other capabltes (e.g., automated fault detecton and dagnostcs and supervsory controls, shown as red dashed lnes) wll be developed under fundng provded n years after FY2006. Although most of the automated fault detecton and dagnostc (AFDD) capabltes wll be developed under future fundng, some of the AFDD algorthms that operate drectly on performance montorng data wll be developed under FY2006 fundng to the extent that resources permt (e.g. automated detecton of degradaton of performance metrcs). Rather than try to cover all possble CHP system confguratons, we have selected a manageable subset for whch to develop the algorthms. Ths subset of confguratons represents those commonly used for CHP systems of less than 1 MWe 3 capacty and sutable for applcatons n commercal buldngs (although some are sutable for agrcultural, ndustral and other applcatons as well). As stated n the overall scope specfcaton document (Katpamula and Brambley 2006), ths project wll focus on CHP systems that use the followng components: small gas turbnes 4 and recprocatng engnes for prmer movers, heat recovery heat exchangers, absorpton chllers, coolng towers, desccant systems, pumps and fans. System confguratons based on these components are shown n Fgure 2 through Fgure 8. Fgure 2 shows a smple CHP system usng a small turbne to power an electrc generator. Exhaust gases pass through a heat recovery heat exchanger, where heat s transferred to ar or water, producng hot water, steam or hot ar for space heatng or other thermal applcatons. An electrcally drven pump or fan mparts flow to the water or ar, whch s heated n the heat recovery unt. The heat recovery unt may also have a fuel-fred auxlary heater (duct-burner) to meet the demand for steam, hot ar or water at tmes when the heat n the exhaust gases cannot meet the entre load. Turbne exhaust generally contans 16% or greater oxygen, whch enables co-frng (unlke exhaust from recprocatng engnes, whch contans 1% to 6% oxygen and does not). When hot water s produced, supplemental heatng of the hot water drectly, rather than by use of a duct heater, leads to hgher effcences. Useful outputs of the system nclude the electrcty produced and hot water or ar for thermal applcatons such as space heatng. A system smlar to the one shown n Fgure 2, except wth a recprocatng engne used as the prme mover for the electrc generator, s shown n Fgure 3. In addton to recoverng heat from 2 Although the fundng for these actvtes was provded n FY2006, because fundng was not authorzed untl md- FY2006, some of the correspondng work wll be completed n the frst half of FY MWe s used to desgnate 1 MW of electrc generaton capacty. 4 The terms small turbnes and turbnes are used nterchangeably n ths report to represent all mcro-turbnes, mn-turbnes, and small gas turbnes used n CHP systems wth up to about 1 MW elec output. 2

12 Fgure 1 Major categores of advanced CHP control capabltes wth those for whch algorthms wll be developed by ths project n FY2006 shown n sold black lnes; algorthm categores for future work are shown n red dashed lnes. Exhaust Gases Pump/Fan Cold Ar/ Water Duct Burner Heat Recovery Unt/Steam Generator Hot Ar/ Water/ Steam Exhaust Auxlary Fuel Input Fuel Input Small Turbne Generator Electrcty Output Fgure 2 A smple CHP system usng a small turbne generator wth exhaust gas heat recovery. 3

13 Fgure 3 CHP system usng a recprocatng engne for electrcty generaton wth engne jacket and exhaustgas heat recovery. Hot Water Out Cold Water In Fuel Input Recprocatng Engne Electrcty Output Exhaust Gases Fgure 4 CHP system usng a recprocatng engne for electrcty generaton wth heat recovery from the engne jacket s coolng water. the engne exhaust gases, heat s also recovered from the engne by crculatng coolng water through the engne jacket. The resultng preheated water s then passed through the heat recovery unt, where t s brought to the temperature requred by applcatons. The output of the heat recovery process may be hot water or steam wth auxlary fuel-fred heatng as necessary to meet thermal loads. 4

14 Pump Auxlary Fuel Input Fuel Input Water In Duct Burner Exhaust Gases Small Turbne Generator Heat Recovery Unt/Steam Generator Electrcty Output Hot Water/ Steam Out Hot Exhaust Coolng Water Chlled Water Return Absorpton Chller Cooled Coolng Water Chlled Water Supply Pump Coolng Tower Fgure 5 CHP system usng a small turbne generator wth exhaust-gas heat recovery and an absorpton chller wth a coolng tower. Fuel Input Exhaust Gases Auxlary Fuel Input Small Turbne Generator Duct Burner Chlled Water Return Absorpton Chller Hot Coolng Water Cooled Coolng Water Exhaust Most Ar Chlled Water Supply Desccant System Dry Ar Exhaust Electrcty Output Pump Coolng Tower Fgure 6 CHP system usng a small turbne generator wth an absorpton chller drect-fred wth hot turbne exhaust gases and a desccant system. 5

15 Fgure 7 CHP system usng a small turbne generator wth heat recovery heat exchanger, hot-water or steam-fred absorpton chller wth a coolng tower and drect-fred desccant system. Fgure 8 CHP system that uses a recprocatng-engne generator wth both jacket and exhaust-gas heat recovery, a hot-water or steam-fred absorpton chller wth a coolng tower, and drect-fred desccant system for ar dryng. 6

16 Fgure 4 shows a smple CHP system wth heat recovery from the hot recprocatng engne coolng water only. Hot exhaust gases are dumped to the ambent envronment wth no heat recovery. The recprocatng engne serves as the prme mover for the electrc generator. Useful energy flows from the system are the electrcty generated and hot water at a temperature of 160 o F to 180 o F. The CHP confguraton shown n Fgure 5 uses a small turbne wth exhaust-gas heat recovery and a hot-water or steam-fred absorpton chller 5 and a coolng tower. In most cases, the absorpton system s lmted to sngle-effect lthum bromde and water. Addtonal fuel can be used n the heat recovery system to meet addtonal thermal demand. The output of the heat recovery may be hot water or steam. Ths confguraton s most suted for commercal and nsttutonal buldngs and s commonly used n such buldngs. Fgure 6 shows a CHP system wth a small turbne used for electrcty generaton. Hot turbne exhaust gases are used to drect-fre 6 an absorpton chller, whch produces chlled water. Supplemental drect heat s provded to the chller wth auxlary fuel (e.g., natural gas) when heat from turbne exhaust gases s nsuffcent to meet chller demands. Exhaust gases extng the absorpton chller are used to regenerate desccant used to dry ar. Ths confguraton s commonly used n commercal buldngs applcatons. Because hot exhaust gases are used drectly n the absorpton chller, double- and trple-effect absorpton systems (e.g., lthumbromde/water) can be used. Fgure 7 shows a confguraton wth a small turbne, heat-recovery heat exchanger, hot-waterfred/steam-fred absorpton chller wth coolng tower and a desccant system that s drect-fred. The heat recovery unt can be desgned to produce ether hot water or steam. To ncrease the coolng or dehumdfcaton capacty, auxlary fuel can be used to supplement waste heat recovered from the prme mover to produce more hot water. Ths confguraton s most suted for commercal buldngs wth sgnfcant latent loads buldngs such as restaurants, assembly facltes, and schools. A common varaton on the confguraton n Fgure 7 splts the exhaust gas nto two parallel flows before the heat recovery unt, wth one flow gong to the heat recovery unt (HRU) and the other drectly to the desccant system. The system confguraton shown n Fgure 8 s very smlar to the one shown n Fgure 7 except for the use of a recprocatng engne as the prme mover for electrcty generaton. Moreover, heat from the engne jacket s used to preheat water before t enters the heat recovery unt, where t s further heated to produce hot water or steam for use by the absorpton chller. Heat remanng n the exhaust gases after leavng the heat recovery unt regenerates desccant used for dryng ar. Ths confguraton s most suted for commercal buldngs wth sgnfcant latent loads. As wth the system n Fgure 7, a varaton of t splts the exhaust gas nto two parallel flows before the heat recovery unt, wth one flow gong to the HRU and the other gong drectly to the desccant system. 5 Absorpton systems could be used as heat pumps or chller/heaters for both heatng and coolng, but only absorpton chllers are consdered n ths study. 6 Drect-fred refers to the waste heat n exhaust gases beng drectly used to regenerate workng flud from soluton n the absorpton chller. 7

17 Defntons and Approach In ths secton, we explan the purpose of and general approach to performance montorng and commssonng verfcaton to establsh the context for the specfcatons provded n the sectons that follow. Performance Montorng The performance of CHP systems can be categorzed accordng to the outcome of prmary nterest. CHP systems have the objectve of provdng both electrc power and useful heat at the lowest cost possble, whle meetng other requrements such as constrants on envronmental emssons. Once the physcal system s desgned and bult, operatng costs can be controlled by mantanng effcent operaton. Ths nvolves both operatng the system well (deally optmally) and mantanng the system so that t can perform effcently. Effcency should be maxmzed to mnmze fuel use (and fuel cost) subject to external constrants on meetng (but not exceedng) loads and prces, whch determne the value of the electrcty and the heat produced. Of course, ths must be balanced aganst the cost of each addtonal mantenance actvty. The algorthms to be developed n FY2006 focus on provdng nformaton to CHP system operators so they can ntally ensure that the performance of ther CHP systems and ther ndvdual components meet performance expectatons establshed by the desgner or manufacturer(s) (through commssonng verfcaton) and then montor performance to quckly spot degradatons n effcency suffcent to warrant changes n operaton or mantenance acton. Performance montorng wll then serve as the bass for correctons to operaton and ntaton of mantenance (or condton-based operaton and mantenance). A later phase of the project (n FY2007 and possbly beyond) wll provde supervsory control, whch wll enable system operators to balance the costs of varous control strateges and mantenance actons to mnmze the total cost of operatng and ownng the CHP faclty, as descrbed n the precedng paragraph. To enable operators to track CHP system performance and detect problems wth t, we propose to develop algorthms for montorng the performance of the overall effcency of the CHP system and the effcency of each of the ndvdual components. The overall effcency s an ndcator of how well the system s convertng fuel nto electrcty and useful heat. Sgnfcant degradatons n system effcency would ndcate both a loss n the capacty to generate these useful forms of energy and an ncrease n fuel use per unt of useful output energy. The latter would lead to ncreased fuel costs. Emssons of gaseous pollutants to the atmosphere are controlled by regulaton. Exceedng emssons lmts can result n fnes and the need to shut down the system (decrease emssons to zero by not operatng) for a tme perod necessary to brng the system back nto complance wth regulatons. Whle not operatng, the captal nvested n the CHP system sts dle, provdng no return on that nvestment. Ths gravely affects the economcs of a CHP system. To help operators ensure complance wth emsson regulatons, algorthms should be developed for trackng envronmentally mportant CHP system emssons as an ad to dentfy when emsson rates ncrease above normal operaton, possbly requrng operaton changes or mantenance acton, but ths s beyond the scope of ths project. 8

18 We propose to use the fuel utlzaton effcency ( η F ), defned as (Katpamula and Brambley 2006) WElec + Qth, j j η F =. Q Fuel Eq. (1) as the metrc for overall CHP system performance. Here, W Elec s the net electrcal power output, Q th,j represents the net rate of useful thermal energy output from thermal recovery process j wth the sum beng over all thermal recovery processes n the system, and Q Fuel s the total rate of nput of fuel energy to the CHP system. Ths s the most commonly used ndcator of CHP system effcency, although as we noted n the prevous report (Katpamula and Brambley), t fals to account for the qualty (exergy) of the dfferent energy streams. Equaton (1) s specalzed to a specfc generc CHP system confguraton later n ths report. To account for the qualty of the varous energy streams, we wll also use the value-weghted energy utlzaton factor (EUF VW ), whch s dscussed n more detal later n ths report and n Katpamula and Brambley (2006). The generc components of the CHP systems selected for development n ths project are: turbnes or recprocatng engnes as prme movers, heat recovery unts (whch are heat exchangers), absorpton chllers (whch covert waste heat from the prme mover to useful chlled water for coolng), supplemental vapor compresson chllers to help meet coolng loads durng tmes when the vapor compresson chller cannot or does not meet the entre load, 7 coolng towers, desccant systems for dehumdfyng ar, and pumps for movng lqud and fans for movng ar. Equatons for the effcency of these components (except pumps and fans) are provded n Katpamula and Brambley (2006) and summarzed n Table 1. These equatons wll be specalzed and expanded for each of the selected CHP confguratons later n ths report. Commssonng Verfcaton Commssonng verfcaton (CxV) s a process by whch the actual performance of the ndvdual components n a CHP system and the performance of the CHP system as a whole are verfed to comply wth the desgners and manufacturers recommended performance. Furthermore, for new systems, commssonng should nclude a systematc seres of actvtes, startng n the plannng phase and contnung through desgn, nstallaton, and start-up, amed at ensurng correct operaton of the CHP system. Before start-up, the process should nclude nspecton and testng of all components n the CHP system to ensure proper components are nstalled, they are nstalled correctly, and they perform properly. 7 Vapor compresson chllers used for ths purpose often are not consdered part of the CHP system, but because use of absorpton chllng must be optmzed as part of a larger system that ncludes vapor compresson chllng, they must be ncluded n decsons made by the supervsory controller regardng how much absorpton chllng and how much vapor compresson chllng to use to meet the total coolng load. 9

19 Table 1. Summary of expressons for CHP component effcences. Component Purpose Effcency/ Effectveness Relaton Small turbne generators Recprocatng Engnes Heat Recovery Unts (HRU) Absorpton Chllers Vapor- Compresson Chllers Prme mover to generate electrcty Prme mover to generate electrcty Heat exchange from hot exhaust gases from the prme mover to the heat recovery flud Generate chlled water usng heat to drve refrgerant from soluton n an absorpton refrgeraton cycle Generate chlled water usng electrc power to drve compressors n a vaporcompresson refrgeraton cycle W Elec EE η EE = QFuel, engne W Elec EE η EE = QFuel, engne ε HRU Q = Q HRU, actual HRU,max Q COP AbChller = Q Q evap gen Varables η = electrc generaton effcency W Elec = net electrcal power output Q Fuel.engne = total rate of nput of fuel energy to the prme mover η = electrc generaton effcency W Elec = net electrcal power output Q Fuel.engne = total rate of nput of fuel energy to the prme mover ε = heat recover unt HRU effectveness Q HRU,actual = rate of heat gan by the heat recovery flud Q HRU,max = maxmum possble rate of heat loss from the waste heat stream from the prme mover n the HRU COP AbChller = coeffcent of performance of the absorpton chller Q evap = rate of heat loss from coolng water passng through the evaporator Q gen = rate of heat loss from the heat source flud as t passes through the refrgerant generator evap COP Chller = COP Chller = coeffcent of WChllerElec performance of the chller Q evap = rate of heat loss from chlled water passng through the evaporator W ChllerElec = electrc power nput to the chller 10

20 Coolng Towers Desccant Systems Pumps Fans Cool chller condenser water va evaporaton and sensble heat transfer to ambent ar Remove mosture from ar wth the desccant regenerated usng waste heat Create a pressure dfference n lqud to nstgate flow usng an electrc motor as a source of mechancal rotatonal energy Create a pressure dfference n ar to support flow, usng an electrc motor as the source of mechancal rotatonal energy η CT η η = ( TCT, w, TCT, w, o ) ( T T ) CT, Elec = CT, w, Q W Q wb CT, th CT, elec d D η D = Qd, nput Pump η Fan W = W W = W Pump Pump, elec Fan Fan, elec η CT = coolng tower effcency (effectveness) η CT,Elec = coolng tower electrc utlzaton effcency T CT,w, = nlet temperature of condenser water to the tower T CT,w,o = outlet temperature of condenser water from the tower T wb = wet bulb temperature of the ambent ar Q CT, th = rate of heat loss by the coolng water as t passes through the coolng tower W CT, elec = electrc power use by the coolng tower fans and pumps η = desccant system effcency Q d = rate of mosture removal from the ar stream (dehumdfcaton load) Q d.nput = rate of heat nput for desccant generaton η Pump = pump effcency W Pump = mechancal power output from the pump to the lqud W Pump,elec = electrc power nput to the pump motor η Fan = overall effcency of the fan W Fan = useful power output from the fan W Fan, elec = electrc power nput to the fan motor A goal of ths project s to automate parts of the process for verfyng that commssonng has been done correctly and resulted n a CHP system that meets desgn and operaton expectatons. Although CxV can nclude actve testng of components and sub-systems, n ths project the ntent s to focus on verfyng performance to ensure that the system has been adequately 11

21 commssoned and to provde ndcators of commssonng stll needed when defcences are found. Ths process wll rely on the montorng algorthms descrbed n the precedng subsecton on performance montorng for nputs to CxV. The CxV algorthms wll provde the logc by whch measurements on performance are nterpreted relatve to performance expectatons to dentfy defcences n performance durng ntal operaton of the CHP system and the major ndvdual components. By verfyng the performance of the ndvdual components, defcences n overall system performance can be solated so that follow up efforts can be targeted at the offendng components. Some defcences may span multple components of the system. In these cases, controls or other ntegraton ssues wll be dentfed as needng recheckng and further commssonng. The outputs of the CxV algorthms wll be alarms, quanttatve ndcators of defcences, and supportng nformaton to help gude correctve actons. Detaled specfcatons are provded n the Commssonng Verfcaton secton later n ths report. 12

22 Component Montorng Ths secton specfes the equatons as well as an nput/output dagram for the algorthm module for performance montorng of each component of the generc CHP systems dentfed n Fgure 2 through Fgure 8. These components can be combned n the varous ways shown n these fgures to create CHP systems and, therefore, these algorthms can be used to montor the components n any of these systems. Prme Movers The prme mover converts chemcal energy n the fuel to rotatonal mechancal energy, whch then turns an electrc generator (see Fgure 9). Small turbnes and recprocatng engnes represent the most commonly used prme movers for CHP systems, especally those wth electrcal outputs of less than 1 MW. Both of these prme movers release waste heat n exhaust gases and through ther jackets. Jacket losses are not suffcently large for most small turbnes to warrant heat recovery, but for recprocatng engnes, water at approxmately 180 o F can be recovered by crculaton of coolng water through the engne jacket (Fgure 3, Fgure 4 and Fgure 8). For purposes of analyss, the prme mover and electrc generator wll be consdered as a sngle component. So the useful energy output s the electrc power (W Elec ), the rate of energy nput s the energy content (based on lower heatng value, LHV) of fuel flowng nto the prme mover (Q Fuel,engne ), and the unused power released from ths component s the sum of the heat losses n the exhaust gases and through the jacket. Fgure 9 Schematc dagram of prme mover and electrc generator. Effcency of Prme Movers The electrcal generaton effcency ( η EE ) for the prme mover/electrc generator combnaton s 13

23 = W Elec η EE. Eq. (2) QFuel, engne Ths s also the electrc generaton effcency of entre CHP systems for whch there s no addtonal electrcty producton (e.g., by a steam turbne) usng heat recovered from the exhaust gases of the prme mover and no addtonal fuel nput to other components for supplemental heatng. The rate of energy nput to the engne can be expressed as Q = m& LHV Fuel, engne Fuel Fuel Eq. (3) = ρ v& LHV, Fuel Fuel Fuel where m& Fuel s the mass flow rate of fuel nto the prme mover, v& Fuel s the volumetrc flow rate of the fuel, and LHV Fuel and ρfuel are the lower heatng value and densty of the fuel, respectvely, evaluated at the nput condtons. Combnng Eq. (2) and Eq. (3), the electrc generaton effcency can be expressed n terms of measurable varables as = W Elec η EE Eq. (4) m& FuelLHVFuel or W η = Elec EE ρfuelv& FuelLHV, Eq. (5) Fuel where Eq. (4) can be used when fuel consumpton s measured as a mass flow rate, and Eq. (5) can be used when fuel consumpton s measured as a volumetrc flow rate. The prme mover effcency (η engne ) s gven by the relaton W engne η engne =, Eq. (6) QFuel, engne where W engne s the rotatonal mechancal power output of the engne (small turbne or recprocatng engne). There are also losses from the electrc generator, whch ultmately dsspate as heat losses through the generator casng and can be accounted for wth the electrc generator effcency, = W Elec η generator, Eq. (7) Wengne 14

24 where W engne represents the mechancal shaft power output of the prme mover, whch equals the mechancal power nput to the electrc generator. When a gear box s used between the prme mover and the electrc generator, the electrc generator effcency can be expressed as = W Elec η generator, Eq. (8) Wgearbox where W gearbox s the mechancal shaft power output from the gearbox to the generator. In ths case, the gearbox effcency (η gearbox ) s the rato of the mechancal shaft output of the gearbox to the mechancal shaft output of the prme mover,.e., W = gearbox η gearbox. Eq. (9) Wengne The electrcal generaton effcency can be expressed as the product of these three component effcences,.e., η = η η η. Eq. (10) EE engne gearbox generator Eq. (10) shows, together wth Eq. (6) through Eq. (7), that more detaled measurements could be used to solate degradaton of electrcal generaton effcency to ether the engne (prme mover) or the electrc generator. If no gearbox s used n the system (e.g., n the case of mcro-turbne used as the prme mover), η gearbox s set to 1.0 n Eq. (10). Prme Mover Input/Output Dagram The nput/output dagram for montorng of prme mover-electrc generator performance s shown n Fgure 10. Arrows at the top of the dagram represent measured nputs, arrows on the left sde of the dagram represent fxed nputs, and arrows at the bottom of the dagram represent outputs. The algorthms (represented by the box) are based on Eq. (4) and Eq. (5). Heat Recovery Unt Heat recovery unts (HRU) are an essental part of a CHP system because they provde a means to recover heat from the exhaust gas of the prme mover (turbne or recprocatng engne). Although there are several types of HRUs used wth CHP systems, we wll lmt our development effort to those that use ndrect heatng methods: 1) ndrect heatng to provde hot water, 2) ndrect heatng to provde hot dry ar, and 3) ndrect heatng to provde process steam (descrbed n the next secton). Some CHP applcatons use auxlary frng (also called co-frng or supplemental frng n the lterature) to augment heat from the exhaust gases. Therefore, we wll develop HRU effectveness equatons assumng that there s auxlary frng. A schematc of an HRU s shown n Fgure 11, where a duct-burner s used for supplementng the heat from the exhaust gases. Although the fgure shows cold water enterng the HRU and hot water exstng t, ths confguraton can also be used wth cold ar enterng and hot ar extng the HRU. Furthermore, ths confguraton can also be used to generate steam from water (whch s covered n the next secton on heat recovery steam generators). 15

25 Fgure 10 Input/output dagram for prme mover-electrc generator montorng algorthms. Effectveness of Heat Recovery System The effectveness of the HRU s defned as the rato of the actual heat transfer rate to the maxmum possble heat transfer rate,.e., QHRU, actual ε HRU =, Eq. (11) Q HRU,max 16

26 Fgure 11 Schematc of heat recovery unt used to generate hot water. A smlar arrangement can be used to generate hot ar. where Q HRU,actual s the rate of thermal energy gan across the HRU by the heat recovery flud (e.g., heated water, heated ar or water converted to steam) and Q HRU,max s the maxmum possble rate of heat loss by the waste heat stream from the prme mover as t passes through the HRU. If the cold-sde materal does not change phase n the HRU, Q HRU,actual can be wrtten as: Q HRU, actual ( p HRU, w HRU, w, o HRU, w, = ρ vc & ) ( T T ). Eq. (12) Smlarly, Q HRU,max can be wrtten (for the non-phase-change case) as: where, ( ρv&c p ) HRU, mn ( vc ) ( T T ) Q HRU, max p HRU HRU, ex,,mn HRU, w, = ρ &, Eq. (13) s the mnmum of the two quanttes and ( vc & p ) HRU, ex ρ (for the exhaust gas flow) ( vc & p ) HRU, w ρ (for the heat recovery stream). Although the temperature of the exhaust gas may change sgnfcantly across the HRU, Eq. (13) v&c p ρvc & p because the mass flow rate of exhaust gas remans vald even when ( ρ ) = ( ) HRU, mn HRU, ex ( ρ&) v HRU, ex at the HRU nlet equals ts value at the outlet under steady-state condtons. Furthermore, the heat capacty of the exhaust gas vares by less than 10% between representatve HRU nlet and outlet condtons 8, further supportng the assumptons mplct n usng Eq. (13). 8 See, for example, Kovack

27 To reduce errors assocated wth usng a constant value for the heat capacty, c p,ex can be evaluated at the average of the HRU nlet and outlet temperatures. Usng Eq. (12) and Eq. (13), Eq. (11) can be re-wrtten as: p HRU,mn ( THRU, w, o THRU, w, ) ( T T ) ( ρvc & p ) HRU, w ε HRU =. Eq. (14) ( ρvc & ) HRU, ex, HRU, w, Smlarly, f hot ar s generated nstead of hot water, Eq. (14) can be re-wrtten as follows: p HRU,mn ( THRU, a, o THRU, a, ) ( T T ) ( ρvc & p ) HRU, a ε HRU =. Eq. (15) ( ρvc & ) HRU, ex, HRU, a, One of the flow rates appearng n Eq. (14) can be elmnated usng a heat balance on the HRU,.e., the heat loss by the exhaust gas as t passes through the HRU (Q HRU, ex ) s equal to the sum of the heat gan by the water as t passes through the HRU (Q HRU,w ) and heat losses through the walls of the HRU (L HRU ): Here, and Q Q Q HRU, ex = Q HRU,w + L HRU. Eq. (16) HRU, ex ( p HRU, ex HRU, ex, HRU, ex, o = ρ vc & ) ( T T ) Eq. (17) HRU, w ( p HRU, w HRU, w, o HRU, w, = ρ vc & ) ( T T ). Eq. (18) The rate of heat loss through the walls wll generally be very small compared to both Q HRU, ex and Q HRU,w (approxmately 1.5% of Q HRU, ex for an HRSG accordng to Kovack (1982), p. 213). Therefore, L HRU can be neglected wthout ntroducng sgnfcant errors, and & can be obtaned as a functon of & v HRU, w Substtutng ths expresson for from Eq. (16) as ( THRU, w, o THRU, w, ) vhru w ( T T ) p HRU, w v HRU, ex, ( c p ) HRU, ex HRU, ex, HRU, ex, o v HRU, ex ( ρc ) & =. Eq. (19) ρ HRU & v HRU, ex nto Eq. (14), we obtan ( THRU,, THRU, ex, o ) ( ex T T ), ε = Eq. (20) HRU, ex, HRU, w, 18

28 for an HRU that uses exhaust gases from a prme mover to produce hot water, when ρ v&c p = ( ρ v & c p,) HRU, ex, whch wll ordnarly be true. ( ) HRU, mn Followng smlar logc for an HRU that uses exhaust from a prme mover to heat ar, from Eq. (15), when ( ) HRU, mn HRU ρ v&c p = ( ρ v & c p ) HRU, ex. ( THRU,, THRU, ex, o ) ( ex T T ), ε = Eq. (21) HRU, ex, HRU, a, Also from Eq. (15), HRU ( THRU, a, o THRU, a, ) ( T T ) ε =, Eq. (22) HRU, ex, HRU, a, when ( v&c p ) HRU, mn ρ = ( ρ v & c p ) HRU, a. Determnaton of whch flud provdes ( ρv&c p ) HRU, mn and, therefore, whether to use Eq. (26) or Eq. (27), for an HRU heatng ar, can be accomplshed usng the followng relatons obtaned by rearrangng Eq. (19): ( v&c p ) HRU, mn ρ = ( v & c p ) HRU, ex ρ for ( T HRU, ex, THRU, ex, o ) > ( T HRU a, o T HRU, a, ), Eq. (23) and ( v&c p ) HRU, mn ρ = vc p ) HRU, a (ρ for ( T HRU, a, o T HRU, a, ) > ( T HRU ex, THRU, ex, o ),. Eq. (24) By usng Eq. (25) through Eq. (24), the effectveness of an HRU usng exhaust gases to produce hot ar or hot water can be determned from temperature measurements alone, wthout the need for any flow rate measurement. Of course, to determne the useful heat output of the HRU, one flow rate must be measured. Heat Recovery Unt Input/Output Dagram The nput and output dagram for the HRU s shown n Fgure 12 for water as the heat recovery flud. To estmate the HRU effectveness (one of the outputs shown), three temperature measurements are needed [see Eq. (20)]. Furthermore, to determne the rate of useful heat output (Q HRU,actual ) from the HRU the flow rate of the water and one addtonal temperature (T HRU,w,o ) must be measured [see Eq. (12)]. The measurement of auxlary nput flow s optonal and s not needed to estmate the effectveness or the rate of useful heat output. In addton to the fve measured nputs, the specfc heat and the densty of water are also needed. 19

29 Fgure 12 Input/output dagram for a heat recovery unt (HRU) wth water as a cold-sde flud. The nput/output dagram for montorng of an HRU producng hot ar from exhaust gases s shown n Fgure 13. Four temperature measurements are requred to determne whch flud establshes ( ρv&c p ) usng Eq. (23) and Eq. (24), and then three of those measurements are HRU, mn used to calculate the HRU effectveness from Eq. (21) or Eq. (22). No flow rate measurements are requred to determne the HRU effectveness; however, as wth the HRU that produces hot water, determnaton of the rate of useful heat output requres measurement of one flow rate, preferably the flow rate of ar, and values for the specfc heat and densty of the ar (only the specfc heat f the mass flow rate s measured drectly). The accuracy of results can be ncreased by evaluatng the specfc heat of gases at the average of nlet and outlet condtons. 20

30 Fgure 13. Input/output dagram for a heat recovery unt producng hot ar. Heat Recovery Steam Generator A heat recovery steam generator (HRSG) s a heat exchanger that recovers heat from a hot gas stream and produces steam that can be used n a process or used to drve a steam turbne. A common applcaton for a HRSG s n a combned cycle power plant, where hot exhaust from a gas turbne s fed to a HRSG to generate steam, whch n turn drves a steam turbne. In CHP applcatons, the HRSG s generally used to generate steam to fre an absorpton chller. HRSG s smlar to a HRU. The man dfference between the HRU and HRSG s that the HRSG generates steam nstead of hot water or hot ar. 21

31 Effectveness of Heat Recovery Steam Generator The effectveness of a heat recovery steam generator (ε HRSG ) also can be determned from the general equaton for ε HRU, Eq. (11). In ths case, the actual heat transfer ncludes the heat of vaporzaton of the water as well as the sensble heat used to ncrease ts temperature. Therefore, when expressed n terms of the change n the water sde, the rate of heat transfer s equal to the dfference n enthalpy between the water enterng the HRSG and the steam leavng the HRSG, both of the enthalpes beng functons of the flud temperatures and pressures,.e., Q = v& ρ) [ h( T, P ) h( T, P ) ], Eq. (25) HRSG, actual ( HRSG, w, o o HRSG, steam, o HRSG, w, under the assumpton that the mass flow rate of water nput to the HRSG s equal to the mass flow rate of steam output. Here, h HRSG,steam,,o s the specfc enthalpy of steam leavng the HRSG at temperature T o and pressure P o, and h HRSG,w, s the specfc enthalpy of the water enterng the HRSG at temperature T and pressure P. The volumetrc flow rate ( & ) and densty ( ρ HRSG, w, ) are for water at the nlet to the HRSG. v HRSG, w, Alternatvely, the rate of heat transfer could be determned for the rate of heat loss from the hot exhaust gas as t passes through the HRSG (assumng that jacket heat losses are neglgble). In ths case, the rate of heat transfer s gven by the relaton Q = v& ρc ) ( T T ), Eq. (26) HRSG, actual ( p HRSG, ex, HRSG, ex, HRSG, ex, o where v & HRSG, ex, and ρ HRSG,ex, are, respectvely the volumetrc flow rate and densty of exhaust gas comng nto the HRSG; c p,ex s the specfc heat of the exhaust gas mxture; and T HRSG,ex, and T HRSG,ex,o are the temperatures of the exhaust gas streams comng nto and leavng the HRSG, respectvely. The maxmum possble rate of heat transfer between the two fluds (Q HRSG, max ) s gven by Q = v& ρc ) ( T T ), Eq. (27) HRSG, max ( p HRSG, ex, HRSG, ex, HRSG, w, where T HRSG,w, s the temperature of the saturated lqud water comng nto the HRSG. Therefore, for an HRSG, the effectveness can be expressed as 9 ε HRSG ( v& ρ) = HRSG, w, ( v& ρc [ h( T, P ) p ) o HRSG, ex, o HRSG,steam, o ( T HRSG, ex, h( T, P ) T HRSG, w, HRSG,w, ) ], Eq. (28) or 9 Assumng that ( vρc p & ) ex, < ( vρc & p ) w,. 22

32 T T HRSG, ex, HRSG, ex,o ε HRSG =. Eq. (29) THRSG, ex, THRSG, w, HRSGs often have stages, whch produce steam at dfferent pressures (e.g., hgh-pressure steam, medum pressure steam, and low pressure steam). In these cases, the enthalpy dfference of each output stream must be consdered separately, so that Q = [ v& HRSG, s, o ρ HRSG, s, oh( To, Po ) HRSG,steam, o ] v& HRSG, w, ρ HRSG, w, h( T, P HRSG, w, HRSG, actual ) j j, Eq. (30) and ε HRSG = [( v& ρ) HRSG, s, o h( To, Po ) HRSG, steam, o ] j ( v& ρc p ) HRSG, ex, ( T j HRSG, ex, ( v& ρ) T HRSG, w, HRSG, w, h( T, P ) ) HRSG, w,. 10 Eq. (31) Here, the summaton n the numerator s over all HRSG stages of steam producton wth the flow rate, densty and enthalpy for each stage correspondng to the condtons (e.g., temperature and pressure) of the steam flow extng the jth stage of the HRSG. If energy losses from the HRSG are neglgble and essentally all of the energy transferred from the exhaust gas s used to produce steam, the effectveness of the HRSG can stll be determned from the relaton T T HRSG, ex, HRSG, ex,o ε HRSG =. Eq. (32) THRSG, ex, THRSG, w, Heat Recovery Steam Generator Input/Output Dagram The nput and output dagram for the HRSG s shown n Fgure 14. To estmate the HRSG effectveness (ε HRSG ), three temperature measurements are needed [see Eq. (32)]. To determne the rate of useful heat output [Q HRSG,actual ; see Eq. (30)] from the HRSG, addtonal measurements are needed. These nclude the flow rate of the water nput to the HRSG, the flow rate, temperature and pressure for each steam flow output from the HRSG, along wth the correspondng water and steam denstes. In addton, enthalpy tables are needed from whch to determne the specfc enthalpes of each steam flow and the water flow from ther correspondng measured temperatures and pressures. The measurement of auxlary nput flow s optonal and s not needed to estmate the effectveness or the rate of useful heat output; however, ts measurement wll provde nformaton useful to characterzng the fuel use and overall performance of the CHP system. Absorpton Chller Absorpton chllers are coolng machnes that operate just lke the mechancally/electrcally drven (vapor-compresson cycle based) chllers, except for the compresson process. Lke 10 Note that because water enterng the HRSG s n the lqud state, h w, s essentally a functon of temperature only, so that P HRSG, need not be measured. 23

33 Water Temperature In THRSG,w, ( o F) Water Flow Rate In vhrsg,w, (ft 3 /mn) Water Pressure In PHRSG,w, (psa) Steam Flow Rate j Out vhrsg,s,o,j (ft 3 /mn) Temperature of Steam Flow j Out THRSG,s,o,j ( o F) Pressure of Steam Flow j Out PHRSG,s,o,j ( o F) Exhaust Gas Temperature In THRSG,ex, ( o F) Exhaust Gas Temperature Out THRSG,ex,o ( o F) Auxlary Fuel Input Flow Rate vhru,aux,j (ft 3 /mn) Water Densty In ρ HRU,w, (lb/ft 3 ) Enthalpy Table for Steam/Water (Btu/lbm) Heat Recovery Steam Generator Algorthms Lower Heatng Value of Auxlary Fuel j, LHV Fuel,aux,j (Btu/ft 3 ) Heat Recovery Unt Effectveness εhru Useful Heat Output QHRU,actual (Btu/hr) Auxlary Fuel Input (Btu/hr) Fgure 14. Input/output dagram for a heat recovery steam generator. vapor-compresson cycle based chllers, absorpton chllers use a condenser, evaporator and expanson devce. The man dfference between the two types of chllers s how the low-pressure vapor extng the evaporator s converted to hgh-pressure vapor that enters the condenser (see Fgure 15). Instead of a mechancally-drven compressor, absorpton chllers use heat to drve the refrgeraton cycle. The heat needed to operate an absorpton chller can be delvered drectly or ndrectly. In a drect-fred absorpton system, heat s provded drectly by hot exhaust gases from the prme mover, whle ndrect-fred systems use ether steam or hot-water to power the refrgeraton cycle. If supplemental heat s needed, t can be provded by burnng auxlary fuel n a duct heater placed n the exhaust gas stream. 24

34 T AbChller,cw,o Q CT Condenser Thermal Compressor Generator Q gen Expanson Valve W n Absorber Q out. v AbChller,cw, T AbChller,cw, Evaporator. v evap,w, T evap,w, Q evap T evap,w,o Fgure 15 Schematc Dagram of a sngle-effect absorpton chller Effcency of Absorpton Chller The effcency of absorpton chllers s gven by the coeffcent of performance (COP AbChller ) defned as Q evap COP AbChller =, Eq. (33) Qgen where Q evap s the rate at whch water s cooled by the evaporator, Q gen s the rate of heat loss from the exhaust gas, steam or hot water as t passes through the absorpton unt s generator to desorb the refrgerant from soluton, and the pump energy, W n, s small compared to Q evap. 25

35 Here, Q evap = m& c ( T T o) evap, w, p, w evap, w, evap, w, = v& ρ c ( T T o), evap, w, evap, w, p, w evap, w, evap, w, Eq. (34) where m & evap, w, s the mass flow rate of chlled water nto the evaporator, v & evap, w, s the volumetrc flow of chlled water enterng the evaporator; ρ evap,w, and c p,w are the densty and specfc heat of chlled water enterng the evaporator, respectvely; and T evap,w, and T evap,w,o are the evaporator enterng and leavng chlled water temperatures. For drect-fred absorpton chllers: Q gen = v& ρ c ( T T o), Eq. (35) ex, ex, p, ex ex, ex, where ρ ex, s the densty of the exhaust gases enterng the absorpton chller, v & ex, s the volumetrc flow of exhaust gases enterng the chller, c p,ex s the specfc heat of the exhaust gases (evaluated at the average exhaust gas temperature n the chller), 11 and T ex, and T ex,o are the exhaust gas enterng and leavng temperatures. For absorpton chllers that use hot water from an HRU to generate the refrgerant: Q gen = v& ρ c ( T T o), Eq. (36) hotwater, hotwater, p, hotwater hotwater, hotwater, where ρ hotwater, and c p,hotwater are the densty and specfc heat of hot water enterng the absorpton chller, v & hotwater, s the volumetrc flow of hot water enterng the chller, and T hotwater, and T hotwater,o are the hot water enterng and leavng temperatures. For absorpton chllers that use steam to generate the refrgerant: Q gen = v& ρ h( T, P) h( T, P ) ), Eq. (37) steam, steam, ( steam, o o steam, o where ρ steam, s the densty of steam enterng the absorpton chller, v & steam, s the volumetrc flow of steam enterng the chller, h(t,p ) s the enthalpy of steam enterng the chller at temperature T and pressure P, and h(t o,p o ) s the enthalpy of steam leavng the chller at temperature T o and pressure P o. Absorpton Chller Input/Output Dagram Input/output dagrams for montorng of absorpton chller performance are shown n Fgure 16 for hot-water-fred chllers, Fgure 17 for steam-fred chllers and Fgure 18 for drect-fred chllers. Arrows at the top of the dagram represent measured nputs, arrows on the left sde of 11 The product of volumetrc flow rate of the exhaust gas and ts densty, whch s the mass flow rate, s constant through the chller durng steady operaton; therefore, v & ex, ρex, = v & ex, oρex, o, and ths quantty can be evaluated at ether the nlet or ext condtons. We recommend evaluatng c p, ex at the average of the nlet and outlet temperatures of the exhaust gas; however, the dfference n the value of c p, ex evaluated at the nlet condtons and the outlet condtons wll be less than about 8% for the exhaust gases n most practcal stuatons. 26

36 Chlled Water Supply Temperature T evap,w,o ( o F) Chlled Water Supply Flow v w,evap, (ft 3 /mn) Chlled Water Return Temperature T evap,w, ( o F) Water Temperature Out T hotwater,o ( o F) Water Temperature In T hotwater, ( o F) Water Flow In v hotwater, (ft 3 /mn) Chller Coeffcent of Performance COP AbChller Useful Coolng Energy (Btu/hr) Q evap Heat Input to Chller (Btu/hr) Q gen Fgure 16 Input/output dagram for montorng algorthms for an absorpton chller wth hot water as the source of heat for generatng refrgerant from soluton. 27

37 Chlled Water Supply Temperature T evap,w,o ( o F) Chlled Water Supply Flow v w,evap, (ft 3 /mn) Chlled Water Return Temperature T evap,w, ( o F) Steam Pressure Out P steam,o (psa) Steam Temperature Out T steam,o ( o F) Steam Pressure In P steam, (psa) Steam Temperature In T steam, ( o F) Steam Flow In v steam, (ft 3 /mn) Densty of Chlled Water ρw,evap, Specfc Heat of Water cp,w Absorpton Chller Algorthms Densty Functon for Steam ρsteam,(t,p) Enthalpy Table for Steam hsteam(t,p) Chller Coeffcent of Performance COP AbChller Useful Coolng Energy (Btu/hr) Q evap Heat Input to Chller (Btu/hr) Q gen Fgure 17 - Input/output dagram for montorng algorthms for an absorpton chller wth steam as the source of heat for refrgerant generaton. 28

38 Chlled Water Supply Temperature Tevap,w,o ( o F) Chlled Water Supply Flow vevap,w, (ft 3 /mn) Chlled Water Return Temperature Tevap,w, ( o F) Exhaust Gas Temperature Out Tex,o ( o F) Exhaust Gas Temperature In Tex, ( o F) Exhaust Gases Flow In vex, (ft 3 /mn) Auxlary Fuel Flow vfuel,aux (ft 3 /mn) Densty of Chlled Water ρ evap,w, Specfc Heat of Water c p,w Exhaust Gas Specfc Heat c p,ex (Btu/lb/ o F) Absorpton Chller Algorthms Exhaust Gas Densty In ρ ex, (lb/ft 3 ) Chller Coeffcent of Performance COPAbChller Useful Coolng Energy (Btu/hr) Qevap Heat Input to Chller (Btu/hr) Qgen Auxlary Fuel Use (Btu/hr) Fgure 18 Input/output dagram for drect-fred absorpton chller montorng algorthms. the dagram represent fxed nputs, and arrows at the bottom of the dagram represent outputs. For Fgure 16 and Fgure 17, the algorthms (represented by the box) are based on Eq. (33), Eq. (34), Eq. (36) and Eq. (37). For Fgure 18, the algorthms (represented by the box) are based on Eq. (33), Eq. (34), and Eq. (35). In the dagrams, the densty of lqud water or exhaust gases should be evaluated at the same condtons as the nlet flow rate s measured (the nlet as specfed n the dagrams). The specfc heat of water and exhaust gases s assumed constant across the chller, whch s a good assumpton for lqud water for the typcal range of temperatures across the chller, but t should be evaluated at the average of the nlet and outlet temperatures for exhaust gas. Although, the auxlary fuel flow rate s not ncluded n the equatons cted for drect-fred absorpton chllers, t s nput nto the algorthms and converted to an output as the auxlary rate of fuel use so that fuel used for supplemental frng can be tracked (t s not ncluded as an output for hot-water- and steam-fred chllers because t s an output for the HRU n those cases). 29

39 Coolng Tower Coolng towers (CTs) provde the rejecton of heat from the condenser and the absorber, whch s requred by the absorpton refrgeraton cycle. For a water-cooled condenser, heat s transferred from refrgerant to cool water, whch s pumped to the coolng tower. The coolng tower uses evaporatve coolng to reject heat from the hot water to the ambent envronment. The fans push (forced draft) or pull (nduced draft) ambent ar through the coolng tower. A schematc dagram of a coolng tower s shown n Fgure 19. Fgure 19 Schematc dagram of coolng tower used to reject heat from the condenser to the ambent envronment wth the fan shown n a locaton to provde nduced draft. Effcency of Coolng Towers The coolng tower effcency (η CT ) s defned as: = ( TCT, w. TCT, w, o ) ( T T ) η CT, Eq. (38) CT, w, wb 30

40 where, T CT,w, s the nlet temperature of the hot water to the tower, T CT,w,o s the outlet temperature of cooled water from the tower, and T wb s the wet-bulb temperature of the ambent ar to whch heat s rejected by the coolng tower. 12 The value of η CT only ndcates how well the coolng tower cools the condenser water n terms of how close the water temperature approaches the lmtng wet-bulb temperature of the ambent ar. It does not ndcate how the coolng was acheved or how much external electrcal energy nput was used to acheve ths reducton n temperature. For example, f the coolng tower medum becomes fouled, ncreasng resstance to ar flow and nhbtng heat transfer, the coolng tower fans mght run longer or at a hgher speed (for varable speed fans) to acheve the same temperature drop for the water that was accomplshed wth less fan energy when the medum was not fouled. In addton, electrc power s used to pump the condenser water to and from the coolng tower. To provde a metrc for how effcently electrcty s used n ths process, we defne a coolng-tower electrc utlzaton effcency (η CT,elec ) as Q CT, th η CT, Elec =, Eq. (39) WCT, elec where Q CT,th s the rate of heat loss by the condenser water n passng through the coolng tower and W CT,elec s the electrc power use by the coolng tower fans and pumps. The electrc power use s the sum of the electrc power used by all the ndvdual pumps and fans,.e., W CT, elec CT, elec, j, j = W Eq. (40) where W CT,elec,j s the electrc power use by the jth pump or fan and the summaton s over all pumps and fans. The rate of heat loss from the condenser water can be determned from measurements of the enterng water temperature (T CT,w, ), the extng water temperature (T CT,w,o ), and the volumetrc flow rate of water through the coolng tower ( & ) usng the relaton Q v CT, w CT, th w CT, w p, w ( CT, w, CT, w, o = ρ v& c T T ), Eq. (41) where ρ w and c p,w are the densty and specfc heat of lqud water, respectvely. Combnng Eq. (39) through Eq. (41), the coolng-tower electrc utlzaton effcency can be expressed as & ρw vct, wcp, w( TCT, w, TCT, w, o) η CT, Elec =. W j CT, elec, j Eq. (42) 12 If heat losses from ppng between the absorpton chller and coolng tower are small, then T CT,w, T AbChller,cw,o and T CT,w,o T AbChller,cw,. 31

41 Coolng Tower Input/Output Dagram The nput/output dagram for montorng of coolng tower performance s shown n Fgure 20. Arrows at the top of the dagram represent measured nputs, arrows on the left sde of the dagram represent fxed nputs, and arrows at the bottom of the dagram represent outputs. The algorthms (represented by the box) are based on Eq. (38) and Eq. (42). In ths dagram, the densty and specfc heat of lqud water are assumed to be constant across the coolng tower. They can be evaluated at the average of the water nlet and outlet temperatures. Water Temperature Out TCT,w,o Water Temperature In TCT,w, Ambent Ar Wet-Bulb Temperature Twb Water Flow Rate vct,w Fan Electrc Power WCT,elec,fans Pump Electrc Power WCT,elec,pumps Densty of Water ρ w Specfc Heat of Water c p,w Coolng Tower Montorng Algorthms Coolng Tower Effcency ηct Coolng Tower Electrc Utlzaton Effcency ηct,elec Coolng Tower Rate of Heat Rejecton QCT,th Fan Electrc Power WCT,elec,fans Pump Electrc Power WCT,elec,pumps Fgure 20 Input/output dagram for coolng tower montorng algorthms. 32

42 Pumps Pumps use rotatonal mechancal energy, usually provded by an electrc motor, to create the pressure dfferences that drve the flow of lquds. A schematc dagram of a smple pump s shown wth pertnent varables dentfed n Fgure 21. v Pump P dscharge Pump W pump,elec P sucton v Pump Effcency of Pumps Fgure 21 Schematc dagram of a pump. The effcency of a pump ( η Pump ) can be expressed as W Pump η Pump =, Eq. (43) WPump, elec where W Pump s the mechancal power output mparted by the pump to the lqud, and W Pump,elec s the electrc power nput to the pump motor. The mechancal power mparted by the pump to the lqud s equal to the product of the volumetrc flow rate through the pump and the pressure dfference across the pump,.e., W Pump = v& P P ), Eq. (44) Pump, w( dsch arg e sucton where Pump v& s the volumetrc flow rate through the pump, P represents pressure, and the subscrpts dscharge and sucton dentfy varables at the pump sucton port (nlet) and dscharge 33

43 port (outlet). The dfference between the dscharge and sucton pressures s sometmes called the statc head of the pump. Combnng Eq. (43) and Eq. (44), yelds the relaton for pump effcency vpump ( Pdsch arg e Psucton ) η Pump = &. Eq. (45) W Pump, elec Pump Input/Output Dagram The nput/output dagram for montorng of pump performance s shown n Fgure 22. Arrows at the top of the dagram represent measured nputs, and arrows at the bottom of the dagram represent outputs. The pump montorng algorthms (represented by the box) are based on Eq. (45). Fgure 22 Input/output dagram for pump montorng algorthms. 34

44 Fans Fans use rotatonal mechancal energy, usually provded by an electrc motor, to create the pressure dfferences that drve the flow of gases, often ar. A schematc dagram of a smple fan s shown wth pertnent varables dentfed n Fgure 23. v Fan P fan,o Fan W fan,elec P fan, v Fan Fgure 23 Schematc dagram of a fan. Effcency of Fans The effcency of a fan ( η Fan ) can be expressed as W Fan η Fan =, Eq. (46) WFan, elec where W Fan s the mechancal power output mparted by the fan to the gas, and W Fan,elec s the electrc power nput to the fan motor. The mechancal power mparted by the fan to the gas s equal to the product of the volumetrc flow rate 13 through the fan and the pressure dfference across the fan,.e., W Fan = v& P P ), Eq. (47) Fan ( Fan, o Fan, where v& Fan s the volumetrc flow rate through the fan, and P Fan, and P Fan,o represent the pressure mmedately upstream and downstream of the fan. 13 The work of compressng the ar s assumed neglgble, whch s reasonable for fans operatng at or below about 4 nches w.c. (= psg = 996 Pa). 35

45 Combnng Eq. (43) and Eq. (44), yelds the relaton for fan effcency vfan ( PFan, o PFan, ) η Fan = &. Eq. (48) W Fan, elec Eq. (48) provdes the effcency of the fan-motor combnaton rather than the fan alone. Fan Input/Output Dagram The nput/output dagram for montorng of pump performance s shown n Fgure 24. Arrows at the top of the dagram represent measured nputs, and arrows at the bottom of the dagram represent outputs. The fan montorng algorthms (represented by the box) are based on Eq. (45). Fgure 24 Input/output dagram for fan montorng algorthms. 36

46 Desccant System A desccant system s used n a CHP system for dehumdfcaton because t s capable of usng a low-grade thermal source to remove mosture from the ar, whch elmnates the overcoolng and reheatng step typcally employed n a conventonal coolng system for dehumdfcaton. The dry ar produced by the desccant system can be used for ndustral processes or space condtonng. A desccant system conssts of a desccant wheel, a supply (process) fan, an exhaust fan, and a heat source for regeneratng the desccant. In a CHP system, exhaust gases, ether drectly from the prme mover or ndrectly after passng through an HRU, are used for reactvaton of the desccant. In some cases, addtonal heatng s provded by a duct-burner, whch supplements the heat n the exhaust stream, as shown n Fgure 25. Fuel Input Duct Burner T a,o. v ex T ex, Q n Dry Ar W Elec T ex,o Exhaust. v a Most Ar T a, Regeneraton Supply DP a,o DP a, W Elec Fgure 25 Schematc of desccant system used to dehumdfy ar. Effcency of Desccant System The effcency of the desccant system ( η D ) s defned as the rato of dehumdfcaton load (rate of mosture removal) to the total electrc and thermal power nput for regeneratng the desccant: = Q d η D, Eq. (49) Qd, n + Wd, Elec where, Q d s the rate of dehumdfcaton, Q d,n s the rate at whch heat s used to regenerate the desccant and W d,elec s the total fan power nput (for both the process and the regeneraton streams). Q d can be calculated usng the followng equaton: Q d Qd, total Qd, sensble =, Eq. (50) where Q d,total s the rate of total heat transfer between the nlet and outlet on the supply (ar) sde, gven by Q = v& ρ) ( h( T, DP) h( T, DP) ), Eq. (51) d, total ( d, a d, a, d, a, o 37

47 h(t,dp) d,a, and h(t,dp) d,a,o are the specfc enthalpes of the enterng and leavng ar (process) streams at the correspondng dry-bulb and dew-pont temperatures (T and DP, respectvely). The mass flow measured ether at the nlet or outlet of the process stream s represented by the term ( v& ρ ) d,a. Q d,sensble s the rate of sensble heat transfer to the process ar stream between the nlet and outlet of the desccant system and can be calculated from: Q = v& ρc ) ( T T ), Eq. (52) d, sensble ( p d. a d. a, d, a, o where, T d,a, and T d,a,o are dry-bulb temperatures at the nlet and outlet of the ar sde of the desccant system. The term Q d,n represents the regeneraton energy nput: Q = v& ρc ) ( T T ), Eq. (53) d. n ( p d. ex d. ex, d, ex, o where T d,ex, and T d,ex,o are dry-bulb temperatures at the nlet and outlet of the regeneraton stream. The term W d,elec represents the sum of the fan power consumpton of the process (ar) and regeneraton (exhaust gas) fans. Desccant System Input/Output Dagram An nput/output dagram for montorng of desccant system performance s shown n Fgure 26. Arrows at the top of the dagram represent measured nputs, arrows on the left sde of the dagram represent fxed nputs, and arrows at the bottom of the dagram represent outputs. The outputs, wth excepton to the auxlary fuel nput, are all based on Eq. (49) through Eq. (53). In the dagram, the densty of supply ar and exhaust gases should be evaluated at the same condtons as the nlet flow rate s measured (the nlet as specfed n the dagrams). The specfc heat of supply ar and exhaust gases s assumed constant across the desccant system, whch s a good assumpton for both ar and exhaust gas because the varaton across the nlet and outlet s small. 38

48 Regeneraton Fan Power W d,r,elec (kw) Supply Fan Power W d,s,elec (kw) Regeneraton Fan Power W d,r,elec (kw) Supply Ar Flow v d,a, (ft 3 /mn) Dew Pont Temperature of Supply Ar at Outlet DP d,a,o ( o F) Temperature of Supply Ar at Outlet T d,a,o ( o F) Effcency of Desccant System η d Useful Latent Coolng Energy (Btu/hr) Q d Useful Sensble Coolng Energy (Btu/hr) Q d,sensble Dew Pont Temperature of Supply Ar at Inlet DP d,a, ( o F) Temperature of Supply Ar at Inlet T d,a, ( o F) Exhaust Gas Temperature Out T d,ex,o ( o F) Exhaust Gas Temperature In T d,ex, ( o F) Exhaust Gases Flow In v d,ex, (ft 3 /mn) Auxlary Fuel Flow v Fuel,aux (ft 3 /mn) Useful Total Coolng Energy (Btu/hr) Q d,total Heat Input for Regeneraton (Btu/hr) Q d,n Auxlary Fuel Use (Btu/hr) Fgure 26 - Input/output dagram for montorng algorthms for a desccant system. 39

49 System Level Montorng System level montorng s provded to ensure that the overall CHP system s performng up to specfcatons and that sgnfcant degradaton n performance has not occurred. If degradaton s detected and quantfed, montored component-level nformaton can be used to solate the cause of degradaton and correct t. Ths process s llustrated n the Applcaton Scenaro secton later n ths report. The system shown n Fgure 27 (created from Fgure 8 by makng the prme mover ether a recprocatng engne or small gas turbne) represents the most complete of the generc systems dentfed for treatment n ths project. All of the other CHP systems (Fgure 2 through Fgure 8) can be derved by specfyng the prme mover and elmnatng components from Fgure 27. As an example, consder the system shown n Fgure 5. By specfyng a turbne as the prme mover, elmnatng jacket heat recovery so that water from the absorpton cooler generator s pumped back to the heat recovery unt, and elmnatng the desccant system, the system n Fgure 5 s obtaned from the general dagram n Fgure 27. Auxlary Fuel Input Pump Exhaust Gases Water In Electrcty Output Duct Burner Recprocatng Engne or Small Turbne Hot Water Out Auxlary Fuel Input Heat Recovery Unt/Steam Generator Exhaust Desccant System Hot Water/ Steam Out Chlled Water Return Dry Ar Absorpton Chller Hot Coolng Water Cooled Coolng Water Chlled Water Supply Pump Most Ar Fuel Input Exhaust Fgure 27 Most complete of the CHP systems consdered n ths project. Coolng Tower System-Level Performance To montor the system-level performance of CHP systems, we propose to use two metrcs for effcency and several other metrcs calculated from sensed condtons or measured drectly. Based on the dscusson n the Scope Specfcaton (Katpamula and Brambley 2006), the two 40

50 selected effcency metrcs are the overall fuel utlzaton effcency ( η F ) and the valueweghted energy utlzaton factor (EUF VW ) 14, whch are defned as η F WElec + Qth, j j = Q Fuel Eq. (54) and EUF VW W Elec Elec th, j th, j j =. Eq. (55) Q j Y Fuel, j + Q Prce Y Fuel, j Here, W Elec s the net electrcal power output, Q th,j represents the net rate of useful thermal energy output from thermal recovery and/or converson process j (e.g., the coolng provded by an absorpton chller) wth the sum beng over all thermal recovery and converson processes n the system delverng energy for end use (e.g., an absorpton chller or a desccant unt), and Q Fuel s the total rate of nput of fuel energy to the CHP system. For systems wth fuel used for supplemental heatng (e.g., for a heat recovery unt, steam generator, or desccant regenerator), Q Fuel s the sum over all fuel nputs to the system,.e., Q Fuel = Q Fuel, j, j Eq. (56) where Q fuel,j s the rate of fuel energy nput at pont j n the system (e.g., to the prme mover or for supplemental heatng of exhaust gases before enterng the heat recovery unt) wth the sum beng over all fuel nputs to the CHP system. These fuel nputs may nclude the same fuel (e.g., natural gas) ntroduced at several dfferent ponts n the system or may be dfferent fuels (e.g., desel fuel for a recprocatng engne prme mover and natural gas for supplemental heat elsewhere n the system). The fuel energy may be based on the lower heatng value (LHV) or hgher heatng value (HHV) of the fuel. By conventon, the gas turbne ndustry uses the lower heatng value to characterze energy use and calculate effcences, whle the natural gas dstrbuton and electrc power generaton ndustres use the HHV for sales and to characterze natural-gas energy use (Energy Nexus Group 2002). Use of the LHV for determnng energy use or the effcency of small turbnes and recprocatng engnes n CHP systems seems reasonable because the products of combuston (exhaust) leave the turbne or engne at condtons at whch the water s n vapor phase. For montorng CHP system performance and detectng degradaton over tme, ether the LHV or the HHV can be used as long as the use s consstent. For comparsons to benchmarks such as data from manufacturers, care must be taken to ensure that the LHV or HHV s used consstently n determnaton of the benchmark and n calculatons of montored performance. Furthermore, f condensng HRUs are used n the system, the HHV should be used n calculatons of fuel energy nputs. 14 The EUF VW was ntroduced by Tmmermans (1978) and later elaborated upon by Horlock (1997). 41

51 Other varables appearng n Eq. (55) are defned as follows: Y Elec and Y th,j represent, respectvely, the value per unt of electrcty generated (e.g., n $/kwh) and the value per unt of useful heat (or coolng) provded (e.g., n $/mllon Btu) by the jth thermal applcaton technology (e.g., absorpton chller or desccant unt); and Prce Fuel,j s the prce of the fuel njected at pont j n the system, wth the dscusson of dfferent fuels versus a sngle fuel from the mmedately precedng paragraph applyng. By accountng for the value of products, ths metrc represents the value of products per unt of expendture on fuel and has unts of $ value of produced energy per $ of fuel consumed. In operatng a plant, EUF VW should be maxmzed to acheve the most economc operaton. Because generally Y elec > Y th,j for most thermal applcatons, a CHP plant should be operated to maxmze electrcty producton. If, however, the amount of electrcty above on-ste requrements cannot be sold to the grd, the electrcty producton should follow varatons n on-ste electrc load. Changes n the value of EUF VW caused by degradatons n CHP system performance would be weghted by ther effects on the value of the energy produced. As a result, faults and performance degradatons havng the greatest dollar mpacts would be recognzed by larger changes n the EUF VW. Other system-level varables that we propose to separately montor to provde nformaton useful for dagnosng changes n CHP system effcency and understandng operatng costs are: Current rate of useful heatng or coolng output, Q th (kw th or Btu/hr) Current electrc power output, W Elec (kw) Current total rate of fuel use, Q =, (kw Fuel, MJ Fuel /hr, or Btu Fuel /hr) Fuel Q Fuel j j Current rate of expendtures on fuel, Cost Fuel = QFuel, jprcefuel, j ($/hr) Average values of these metrcs over varous tme ntervals can also be constructed for each of them, e.g., average daly useful heat output, daly average hourly heat output, total daly heat output, and so forth for the other varables. These ndcators of overall system performance are supplemented wth the component performance ndcators to enable system-level and fner resoluton performance montorng and potentally fault detecton and dagnostcs n support of condton-based mantenance of CHP plants. CHP System-Level Input/Output Dagram The nput/output dagram for system-level performance montorng of a CHP system s shown n Fgure 28. Arrows at the top of the dagram represent measured nputs, arrows on the left sde of the dagram represent fxed nputs (relatve to the tme between samples of the measured nputs), and arrows at the bottom of the dagram represent outputs. The montorng algorthms (represented by the box) are based on Eq. (54), Eq. (55) and the expressons for other montored varables gven above. In ths dagram, the densty, specfc heat, and heatng value of each fuel stream (j) must be specfed. Although the densty and heatng value of the fuels are assumed to vary slowly compared to the tme between samples of the measured nputs and, therefore, are consdered fxed nputs, they could be vared by changng ther values perodcally based on measurement of them or nformaton from the fuel suppler. All ndvdual useful thermal outputs (j) must be specfed to ensure proper credtng of outputs and ther values (Y th,j ). j 42

52 System-level montorng provdes top-level ndcators of the performance of the CHP plant and s supplemented by component montorng, whch provdes greater detal and resoluton. Mass Flow Rate of Fuel j mfuel,j* Volumetrc Fuel Flow Rate j vfuel,j* Electrc Power Output Welec Net Rate of Useful Thermal Energy Output j Qth,j Densty of Fuel j ρ Fuel,j Lower Heatng Value of Fuel j Q Fuel,j Prce of Fuel j Prce Fuel,j System Level Montorng Algorthms Value per unt of Electrcty Generated Y elec Value per unt of Useful Thermal Energy Generated Y th,j * Measurement of ether m Fuel or v Fuel s requred, not both. When v Fuel s measured, ρfuel s also needed. Evaluated for each fuel flow j nto the CHP system. Input for each useful thermal output. Rate of Expendtures on Fuel CFuel QFuel Rate of Fuel Use Fgure 28 System level CHP montorng nput/output dagram Rate of Useful Heat Output Qth Welec EUFVW Electrc Power Output Value Weghted Energy Utlzaton Factor ηfuf Fuel Utlzaton Effcency 43

53 Commssonng and Performance Verfcaton Commssonng verfcaton (CxV) s a process by whch the actual performance of the ndvdual components n a CHP system and the performance of the CHP system as a whole are verfed to comply wth the desgners and manufacturers specfed and recommended performance. Furthermore, for new systems, commssonng should nclude a systematc seres of actvtes, startng n the plannng phase and contnung through desgn, nstallaton, and startup, amed at ensurng correct operaton of the CHP system. Before start-up, the process should nclude nspecton and testng of all components n the CHP system to ensure the correct components are nstalled, they are nstalled correctly, and they perform properly. A goal of ths project s to automate parts of the process of verfyng that commssonng has been done correctly and resulted n a CHP system that meets desgn and operaton expectatons. Although CxV can nclude actve testng of components and sub-systems, n ths project the ntent s to focus on verfyng performance to ensure that the system has been adequately commssoned and to dentfy components for whch further commssonng s stll needed when defcences are found. Performance verfcaton focuses on comparng the performance of the system and ts major components to ther orgnal (commssoned) performance durng routne operaton of the CHP system. The purpose of performance verfcaton s to ensure that peak performance s preserved durng operaton of the system and to provde a bass for condton-based mantenance and performance adjustments. When performance sgnfcantly devates from the expected level (baselne), alarms are automatcally trggered to alert operators to performance degradaton so that actons can be taken to mprove system performance and get t back to ts expected level. The CxV algorthms wll provde the logc by whch measurements of performance developed for performance montorng are nterpreted relatve to performance expectatons to dentfy any defcences n performance durng ntal operaton of the CHP system. By verfyng the performance of the ndvdual components, defcences n overall system performance can be solated so that follow up efforts can be targeted at the offendng components. Some defcences may span multple components of the system. In these cases, controls or other ntegraton ssues wll be dentfed as needng recheckng and further commssonng. The performance verfcaton algorthms satsfy a smlar functon durng routne operaton of the CHP system after start-up. The outputs of the CxV and performance verfcaton algorthms are alarms, quanttatve ndcators of defcences, and supportng nformaton to help gude correctve actons. The rest of ths secton provdes descrptons of the CxV processes and procedures, equatons upon whch the CxV and performance verfcaton algorthms wll be based, and nput/output dagrams dentfyng all nputs and outputs assocated wth the algorthms. CHP System Commssonng Procedures for characterzng the performance of CHP systems and acceptance testng of some generc components used n CHP systems can be found n the lterature (Southern Research Insttute 2000, 2002, 2004; Connected Energy Corporaton 2004). Standards for testng several CHP components are also avalable (ASME 1984, 1991, 1996, 1997; ANSI/ASME 1981; 44

54 Coolng Tower Insttute 2000), and manufacturers provde gudance for ntal testng and startup of the components they manufacture, but the authors found no nformaton publshed n the open lterature on the overall commssonng process for CHP systems. Despte the lack of publshed nformaton, CHP systems should be checked before and durng ntal operaton; the plannng and performance of these checkng/verfcaton actvtes n a systematc manner s the process of commssonng. Commssonng of a new CHP system should nclude the followng major actvtes: 15 Develop commssonng plan Develop commssonng specfcatons Perform commssonng-focused desgn revew Develop nstallaton check lsts Develop start-up and verfcaton checks Develop functonal tests Observe constructon Perform checks of nstalled systems and equpment Wtness start-up Perform functonal tests Verfy complance wth specfcatons and dentfy defcences Correct defcences Perform pertnent functonal tests Verfy performance Approve and report Contnued commssonng over the lfe of the system. When exstng systems are commssoned, the steps assocated wth desgn are generally not possble, and the process must focus on evaluatng the condton, performance and operaton of the CHP plant. Usng termnology parallel to that used by the buldng commssonng ndustry, ths process for exstng systems s called retro-commssonng and would have the followng major actvtes: 16 Develop project objectves Revew avalable documentaton on the CHP system and hstorcal fuel use and energy producton data Develop a retro-commssonng plan Perform system assessment Develop dagnostc montorng and test plans Execute dagnostc montorng and tests Analyze results and dentfy defcences and potental mprovements Implement repars and mprovements Retest and re-montor to verfy performance mprovements Prepare report Resume or contnue operaton Re-commsson as needed over lfe of the system. 15 Adapted wth changes from a descrpton of the buldng commssonng process n PECI (2006). 16 Adapted wth changes from Haasl and Sharp (1999). 45

55 The algorthms for performance montorng and CxV developed n ths project wll make performance assessment, testng, and verfcaton of performance mprovements easer both durng ntal system start-up and later durng operaton of the system. Furthermore, the algorthms wll provde a bass for automatng these processes so they can be done contnuously and correctve actons (mantenance) can be mplemented when performance degradatons necesstate. Ths wll help keep CHP system performance at peak levels and enable contnuous CHP system commssonng whle the plant operates. Approach to Commssonng and Performance Verfcaton The fuel utlzaton effcency and electrc power producton wll be used to montor overall CHP system performance. The effcency or effectveness (as approprate to the component) and other selected crtcal parameters wll be used to montor the performance of each of the major components of the CHP system (heat recovery unts, chllers, coolng towers, desccant systems, pumps and fans). Durng system start-up, the performance of the overall system and ndvdual components can be compared to manufacturer performance benchmarks to verfy that the system and components are nstalled and operatng properly. After the system s operatng, a baselne can be emprcally developed for each performance ndcator from data collected over a tranng perod. The performance ndcators can then be compared to these baselnes to determne when performance has degraded sgnfcantly. A computer system mplementng the algorthms should provde alarms when suffcently large and statstcally sgnfcant decreases from baselne performance values are detected, partcularly when they persst over tme. The performance ndcators would always be avalable to operators to vew, trends would be recorded, and alarms would prompt operatons staff to nvestgate and assess whether degradatons n performance warrant adjustments to operatons or mantenance actons. Ths nformaton should be presented to the operatons staff contnually to enable them to make tmely decsons, preventng further system performance degradaton and potental damage to equpment. Detecton of performance degradaton s not as smple as comparng the actual current value of the performance ndcator (e.g., fuel utlzaton effcency) calculated from the latest values of the measured varables to a sngle fxed alarm threshold for that performance ndcator. Because many of the performance ndcators depend on the value of exogenous varables, ther benchmarks wll vary as the values of the ndependent exogenous varables change. For example, the fuel utlzaton effcency of a turbne vares wth ambent temperature. As a result, even when n perfect condton and fully commssoned, ts fuel utlzaton effcency wll vary when the ambent temperature changes. As a result, the baselne for fuel utlzaton effcency must be a functon of ambent temperature (.e., a lne rather than a pont). The bass for a generc process for verfyng proper performance or detectng performance degradaton s shown n Fgure 29. The performance ndcator (effcency or effectveness) s some functon of one or more ndependent explanatory varables (V), such as outdoor-ar temperature. Gven that ths functon can be determned for the ntal, as properly commssoned, performance of the system or component, the current level of degradaton s 46

56 Performance Indcator (Effcency or Effectveness) η b η a Degradaton Baselne Independent Varable (e.g., Outdoor-Ar Temperature) Fgure 29 Bass for generc performance verfcaton and degradaton detecton process. determned as the dfference between the actual measured value of the performance ndcator (η a ) and the baselne value (η b ) correspondng to the value on the baselne for the current value(s) of the explanatory varable(s) (V 1 n Fgure 29). The degree of degradaton s the dfference between these two values of the performance ndcator,.e., Degradaton b V 1 = η η. Eq. (57) a The baselne s determned emprcally from actual performance data collected whle the system s operatng properly (presumably, early n ts lfe after commssonng). In practce, however, ths lne s lkely not well defned by two emprcal measurements. Instead, measurements are lkely to defne a thck lne or cloud of ponts. Ths s caused by three factors: 1) random error n emprcal measurements, 2) the nfluence of other varables not explctly accounted for n establshng the baselne, and 3) measurements made durng transent operaton of the system. Random measurement error s found n all measured quanttes, the degree dependng on the characterstcs of the measurng system (e.g., a sensor and assocated electroncs). The second factor results when varatons n the performance ndcator occur from other physcal condtons not explctly ncluded n the baselne functon. Ths wll result, for example, f the nfluence of an exogenous varable s unknown or deemed nsuffcent to warrant measurng and ncludng n the baselne. An example of the latter may be the nfluence of ambent humdty on the combuston temperature of the fuel n a turbne. The effect of humdty varatons on the actual fuel utlzaton effcency may be very small compared to other factors, and, therefore, these varatons mght be neglected n establshng a baselne. The humdty varatons wll potentally cause several slghtly dfferent values of measured effcency at each specfc outdoor-ar temperature. As a result, the data ponts form a thck lne or cloud around an average lne representng fuel utlzaton effcency versus outdoor-ar temperature (see Fgure 30). 47

57 (a) (b) (c) Ideal Baselne Effcency Effcency Effcency Outdoor-Ar Temperature Fgure 30 Effect of non-explct varables and measurement uncertanty on an emprcally determned baselne: a) deal baselne for effcency a functon of only outdoor-ar temperature wth perfect measurements, b) baselne developed from a relatvely small number of measured ponts, and c) emprcal baselne from a large number of ponts wth sgnfcant measurement uncertanty and dependence on other varables. When two varables have sgnfcant mpacts on the performance ndcator, both should be used to explan varatons n the ndcator, n whch case the lne becomes a surface. When more than two varables must be used to establsh the baselne, they defne a surface n mult-dmensonal space. The amount of data requred to establsh the baselne ncreases rapdly as the number of varables used to explan varatons ncreases, and a purely emprcal method requres more data than can be collected over a reasonable perod of tme ( tranng perod ). Therefore, for more than about two varables, ths purely emprcal method becomes mpractcal, and another method s requred. For the components n the CHP systems consdered n ths project, we expect two or fewer explct explanatory varables for each of our performance ndcators to be suffcent and, as a result, a purely emprcal method for establshng performance baselnes wll be used. A threshold for the devaton of actual performance from the baselne performance can be used to decde when an alarm should be ssued. An alarm s ssued when η η AlarmTheshold. Eq. (58) b a > Two prmary factors should drve selecton of the alarm threshold: 1) ensurng that the probablty that Eq. (58) s satsfed s suffcently large, gven uncertanty n the underlyng measured data; and 2) ensurng that other factors such as the energy and cost mpacts of the devaton observed are suffcent to warrant an alarm to operators. The frst s accomplshed by statstcally accountng for the uncertanty n the baselne and the uncertanty n the measurements of current condtons. By ensurng statstcal sgnfcance, false alarms are largely prevented. 17 Once uncertanty s adequately consdered, the second s largely based on estmaton of mpacts and judgment of the sgnfcance of those mpacts. In settng thresholds, t s mportant to avod alarms becomng a nusance by alertng operators to condtons they 17 Even under the most strngent sgnfcance crtera, some false alarms may occur. The probablty of a false alarm wll approach but not reach zero. 48

58 consder nsgnfcant, even when they are statstcally sgnfcant devatons from the baselne. Ths s especally mportant for new technologes, where f they become a nusance, they wll lkely be gnored by users. So, for example, a cost threshold for mportance of a problem (.e., performance degradaton) mght be set and the correspondng devaton beyond statstcal sgnfcance determned to establsh the alarm threshold. In automatng ths approach n software, thresholds can be made adjustable so users can loosen or tghten them relatve to ntal default settngs to customze the montorng system s behavor. A Bn-Based Method for Baselne Performance We have found the modelng methodology presented n ths secton useful n establshng performance baselnes for detectng anomales n energy consumpton by buldngs (Katpamula et al. 2003) and plan to apply t n ths project to CHP performance montorng. It has the advantage that t can capture both lnear and non-lnear behavor. The method s based on the concept of data bns borrowed from the feld of buldng energy data analyss. A bn s an nterval (bn) of values of an ndependent varable wth whch a value of another (dependent) varable s assocated. For example, the weather at a locaton can be characterzed by the number of hours per year on average that the outdoor-ar temperature falls nto 5 F bns between some mnmum temperature and some maxmum temperature, as shown n Fgure 31. Smlarly, bns can be defned for energy uses that are correlated wth outdoor-ar temperature (e.g., energy use for coolng a buldng; see Fgure 32). Temperature (F) Temperature Bn SomeTown, USA Hours per Year Table of Temperature Bns for SomeTown, USA Bn ( F) Hours per Year Fgure 31 Temperature bns are shown for a fcttous locaton n the U.S. Temperature Bn Buldng A Coolng Energy Use (kwh/hr) Coolng Energy Bns for Buldng A Bn ( F) kwh/hr Fgure 32 - Example of bns for coolng energy use by a buldng. 49

59 When multple varables are used to explan the varatons n energy use mult-dmensonal bns can be used, where a mult-dmensonal bn s defned as the ntersecton of one-dmensonal bns based on each of the varables. Ths s shown n Fgure 33 for three-dmensonal bns that characterze a varable such as energy use n terms of three explanatory varables. A representatve value of the dependent varable s assgned to each bn defned by the ranges of values of the ndependent varables. For an energy use model, the dependent varable s energy consumpton. For an energy producton model, for example a turbne, the dependent varable s the amount of energy produced. Δ(OAT) Δ(ORH) Δ(TOW) Fgure 33. An example three-dmensonal bnnng scheme wth bns defned by three explanatory varables: outdoor-ar temperature, outdoor-ar humdty, and tme of week. The model s traned by collectng data emprcally and assgnng t to bns. Gven a sample of emprcal data wth each set of the sample consstng of a values for a complete set of N ndependent explanatory varables (x 1, x 2, x 3,, x N ) and the correspondng measured value of the dependent varable, an N-dmensonal model s created by assgnng each set of data n the sample to the bn n whch the pont defned by the values of ts ndependent varables les. An example bn s shown n Fgure 34. When a suffcent number of ponts have been assgned to each bn, the model s consdered fully traned. A representatve value of the dependent varable s then assgned to each bn, completng the model. The medan of the values of the dependent varable n the bn makes a good representatve value for both large and small numbers of ponts per bn. Once the model s traned, t s used to estmate baselne values of the dependent varable [e.g., the CHP system effcency or the effcency or effectveness of an ndvdual CHP component, η b n Eq. (57) and Eq. (58)] gven a set of measured values for the ndependent varables. The bn model represents the baselne behavor of the system or component durng the tranng perod. 50

60 Δ Δ Δ Fgure 34 An example three-dmensonal energy bn s shown for outdoor-ar temperature (OAT), tme of week (TOW) and outdoor relatve humdty (ORH) as the ndependent varables. Ponts correspondng to sets of ndependent varable values and ther correspondng energy values, E, that fall n the ranges defned by ths bn are shown as ponts nsde the bn. To maxmze use of tranng data and potentally mnmze the length of the tranng perod requred to obtan adequate data, we ntroduce the concept of dynamc bns to ths approach to modelng. In ths approach, the bns are not defned a pror wth data assgned to them. Instead, bns are defned as needed around a center pont defned by the current values of the ndependent varables (thus the term dynamc bns ). Only one bn s defned at a tme, as needed. For example, for the ndependent varables used n Fgure 33 and Fgure 34, the pont mght be defned, for example, as 9:30 am on Tuesday (TOW = 57.5), outdoor-ar temperature (OAT) of 82.5 F and outdoor-ar relatve humdty (ORH) of 72.5%. The coordnates of ths bn would then cover the ndependent varable ntervals TOW = 57.5 ± ΔTOW/2, OAT = 82.5 ± ΔOAT/2 and ORH = 72.5% ± ΔORH/2. For ΔTOW=1 hour, ΔOAT=5 F and ΔORH=5%, the bn s defned as shown n Fgure 34. All values for the ndependent energy varable for ponts n the tranng data set wthn the lmts of ths bn are then assgned to the bn. An example applcaton of ths model to energy use by a chller s shown n Fgure 35 and Fgure 36. In Fgure 35, plots of actual measured energy consumpton and correspondng values of the expected energy consumpton of a chller are shown for a 3-month perod n Values of expected energy consumpton were generated usng a bn-based model and correspondng values for the ndependent varables durng ths tme perod. The top plot n Fgure 36 shows the same data wth expected energy consumpton plotted on top of actual energy consumpton, clearly revealng the dfferences. The bottom plot shows an energy consumpton ndex for the same data defned as the rato of actual to expected energy consumptons. Ths plot shows that the chller s consumng more energy than t would have f mantaned n ts baselne (tranng-perod) state. Small crcles have been added n the bottom plot of Fgure 36 to hghlght ponts at whch a dagnostc algorthm assgned alarms to these devatons. These alarms would ndcate to system operators that the devaton represents suffcent performance degradaton to deserve further assessment. The bn-based model possesses several characterstcs that contrbute to ts strength for use n establshng performance montorng baselnes. It s conceptually smple and as a result, 51

61 Fgure 35 The actual measured energy consumpton (top) and expected energy consumpton (bottom) from a bn-based model for a chller are shown. Fgure 36 Actual measured and expected energy consumpton (top) and an Energy Consumpton Index (bottom) are shown for the chller n Fgure

62 potentally appealng to users n the feld. Operatons staff abhor black boxes that they smply do not understand. A smple model facltates understandng and provdes an ntal bass for establshng user trust n the method. Furthermore, ths model has proven effectve n establshng baselnes for other dagnostc problems,.e., trackng the performance of energy usng systems and equpment n buldngs. The method s flexble, accommodatng whatever ndependent explanatory varables are approprate to the system or component, and can be customzed to an applcaton s unque characterstcs. Bn wdths can be adjusted to tune the model to capture features of most mportance. Applcaton to buldng energy trackng has shown that for applcatons wth slowly changng drvng condtons (values of ndependent varables), the model can even be appled usefully whle t s stll undergong tranng. Moreover, the model can capture both lnear and non-lnear relatonshps between the dependent and ndependent varables and transtons from regons of lnear behavor to regons of non-lnear behavor smoothly. The model also possesses a few weaknesses that must be noted and assessed durng applcaton. When used to establsh a performance baselne wth whch to compare future performance as a means to detect performance degradaton, the model wll absorb any degradaton occurrng durng the tranng perod. If the degradaton s only apparent (.e., assocated wth spurous measurements), t wll not affect the resultng model, but f the degradaton s real, persstent, or part of a trend, t wll affect the model, and the model wll represent behavor wth some degradaton present. Therefore, the best tranng data are measurements made durng system/component operaton for whch performance s known to be good or proper. Accordngly, we recommend that tranng data be acqured over a tme perod mmedately followng verfcaton of system commssonng or re-tunng of system operatons, when performance s known (or more lkely) to be at ts peak. The bn-based modelng approach s only practcal for a small number of varables because the amount of data requred for tranng grows rapdly wth the number of ndependent explanatory varables. We generally use a rough gude of no more than three ndependent varables and even ths depends on the range of each of the varables, the bn dmenson for each varable, the frequency of data collecton, and the range of operatng condtons. Fnally, no physcs are captured n the structure of the model. The model has essentally no structure, whch makes t flexble, but as a result t has no underlyng functonal form from whch physcal relatonshps are easly derved. Therefore, t has lttle value to provdng underlyng knowledge of how and why a system or devce behaves the way t does, but ths s not the ntent of the proposed applcaton, whch s merely to establsh a baselne for comparson of values of performance ndcators n the future to those captured by the baselne. Input/Output Dagrams Ths secton provdes the nput/output dagrams for the CxV and performance verfcaton algorthms. 53

63 Commssonng Verfcaton Input/Output Dagrams A generc nput/output dagram for CxV s shown n Fgure 37. Arrows at the top of the dagram represent nputs based on values calculated n the performance montorng algorthms for the CHP system or a component. The nputs are the actual values of the performance ndcator and the uncertanty of the value. The arrow on the left s a commssonng benchmark (η Cxb ) based on the manufacturer s clamed or warranted performance, whch may be for a sngle operatng pont (set of condtons) or several ponts for whch the operatng condtons are specfed. The actual value must be taken at condtons correspondng to the benchmark condtons, or the CxV algorthm must adjust the value based on measured condtons to the condtons correspondng to the benchmark. The commssonng verfcaton alarm threshold s also a fxed nput that establshes the devaton of actual performance from the baselne performance to decde when an alarm should be ssued. The arrows at the bottom of the dagram represent the outputs of the CxV algorthm. The comparson provded by the CxV algorthm s based on Eq. (58). The generc algorthm apples to all CHP components as well as the overall system. Fgure 37 Input/output dagram for the CxV algorthms. When a component or the overall CHP system does not conform to expectatons as ndcated by the verfcaton of performance varable, the offendng component should be re-commssoned to mprove ts performance. Proper performance can then be verfed usng the correspondng CxV algorthm. When the overall CHP system does not satsfy CxV, ndvdual components mght be the cause, n whch case they ndvdually would not pass verfcaton, or the ntegraton of the components, for example by the control system, may be faulty. After examnaton and correcton, the system should pass CxV. 54

64 Performance Verfcaton Input/Output Dagrams A generc nput/output dagram for performance verfcaton durng routne operaton of the CHP system s shown n Fgure 38. Measured nput varables are shown at the top of the dagram. These nclude the actual value of the performance ndcator based on measured condtons, the values of the measured drvng condtons used n the baselne model, and the uncertantes assocated wth all measured varables. The model tself s part of the performance verfcaton algorthm. Fgure 38 Generc nput/output dagram for performance verfcaton. 55

65 Fxed nputs are shown on the left sde of the dagram and are nput by the user. The outputs are shown at the bottom of the dagram and nclude the performance verfcaton varable, whch ndcates whether the measured value of the performance ndcator s suffcently close to the baselne value for the current condtons, the actual value of the performance ndcator, the baselne value for the performance ndcator, the devaton of the actual measured value of the performance ndcator from ts baselne value, an alarm f the devaton exceeds the alarm threshold, and the current values of the drvng condtons (ndependent varables n the baselne model). The bns used for modelng are created on an as-needed bass as part of the performance verfcaton algorthms (the box n Fgure 38) Performance verfcaton could be done on a contnuous bass wth the varables aggregated (e.g., summed or averaged) over approprate tme ntervals. The output wll enable system operators to detect unusual degradatons n performance, whch could ndcate mmedate operaton problems, or gradual degradaton over tme, whch could ndcate a need for mantenance, repar, or an adjustment to operatons. Alarms are provded to drect operator attenton to sgnfcant devatons from expected performance. 56

66 CHP Performance Montorng (PM) and Commssonng Verfcaton (CxV): Algorthm Deployment Scenaro Ths secton addresses how the algorthms developed n ths project could be used n start-up and operaton of a CHP system. The algorthms could be deployed n a number of dfferent ways, ncludng embeddng them n controllers used to control the CHP components or developng a software applcaton that runs on an ndependent plant computer platform. In ths secton, we descrbe a hypothetcal deployment scenaro n whch the algorthms under development n ths project for CHP system montorng and CxV are deployed to montor and perform verfcaton of start-up operatons of a CHP plant on an ndependent computer platform. The major elements of the CHP software applcaton as shown n Fgure 39 are: 1) a process to record sensor and control data from the CHP system, 2) a database to store the nformaton, 3) a set of processes to pre-process the raw data (e.g., perform qualty control, conversons of unts, aggregate data over tme, etc.) and post the data back nto the database, 4) a set of algorthms that are used to process the raw data to generate useful results, 5) a process that allows users to confgure the CHP applcaton and vew confguraton settngs usng a web browser and 6) a process that enables users to vew the results n a web browser. Many of the mplementaton detals are not dscussed here because the scope of the current project s to develop the algorthms, not a tool for deployment. Stll we provde ths example to llustrate for the reader how these algorthms could be deployed n practce. The algorthms provde the bass for tools that could be developed n a follow-on project or by manufacturers and thrd-party servce provders. We antcpate that most tools developed n the future wll be web-based, so users of the tools wll not need to nstall any specal software on ther computers to ether confgure the CHP applcaton or revew results. We antcpate that the raw data from varous sensors and control ponts n a CHP plant are recorded n a database perodcally (for example, at 1 mnute to 15 mnute ntervals); these data are then perodcally pre-processed to generate addtonal (derved) data. The pre-processed data, for example, can be smple aggregatons of sub-hourly data nto hourly values or calculatons of derved engneerng quanttes (for example, the COP, whch s calculated usng data from a number of prmary sensors). It can also nvolve calculaton of movng averages for certan measured quanttes. The results of pre-processng are wrtten back nto the database. A set of algorthms, ether contnuously or perodcally, analyzes both the raw and pre-processed data to generate useful nformaton and post t back to the database. Users can then revew the results or the system can provde alarms and suggestons to users through the web browser. 57

67 Workstaton Raw Data from CHP System CHP System Raw Sensor and Control Data Raw and Pre- Processed Data Database Pre-Processed Data Pre- Processng Algorthms Processed Data Internet Confguraton Data Results Web Browser User Interface Fgure 39 A potental system archtecture for a CHP montorng and commssonng-verfcaton software system usng the algorthms developed n ths project. 58

68 CHP Performance Montorng and Commssonng Verfcaton: Applcaton Scenaros In ths secton, we descrbe two hypothetcal scenaros n whch the algorthms under development n ths project for CHP system montorng and CxV are used n the start-up and operaton of a CHP plant. The plant n ths scenaro uses a small natural-gas-fred turbne as the prme mover wth heat recovered from the exhaust to produce hot water. The hot water s used to fre an absorpton chller to provde coolng to a commercal buldng (see Fgure 40). A duct burner fred wth natural gas s used to provde supplemental heat to the absorpton chller to meet buldng needs when coolng demand exceeds the capacty provded by the exhaust alone. Pump Auxlary Fuel Input Water In Duct Burner Exhaust Gases Heat Recovery Unt Exhaust Hot Water Chlled Water Return Coolng Water Out Absorpton Chller Coolng Water In Chlled Water Supply Fuel Input Small Turbne Electrcty Output Coolng Tower Pump Fgure 40 CHP system used n applcaton scenaro. The CHP system s rated at 1 MW e and produces about 1.7 MW th of useful heat, whch s avalable to the absorpton chller n the form of hot water at 257 F ( 125 C). Chlled water s suppled by the chller at approxmately 45 F ( 7 C) for use n coolng a commercal buldng. The COP of the absorpton chller s about The local prce of natural gas to fuel the turbne and auxlary duct burner s currently about $1.00/therm ( $9.50/GJ), and the prce of electrcty s $0.10/kWh. The value of the coolng provded (based on comparson to coolng from a vaporcompresson ar condtoner and electrcty at the prce ndcated) s approxmately $0.035/kWh th ($10.25/mllon Btu) of coolng. A scenaro descrbng the use of montorng s presented frst and s followed by a scenaro llustratng the use of the commssonng verfcaton process. 59

69 The montorng system provdes contnuous streams of data for the followng effcency and effectveness metrcs: Value-weghted energy utlzaton factor, EUF VW System fuel utlzaton effcency, η F Electrc generaton effcency, η EE Heat recovery unt effectveness, ε HRU Absorpton chller coeffcent of performance, COP AbChller Coolng-tower effcency, η CT Coolng-tower electrc utlzaton effcency, η CT, Elec Coolng-tower pump effcency, η Pump. In addton, the system provdes real-tme montorng for the followng condtons: Fuel nput rate to the turbne, ρ Fuel & Auxlary fuel nput to duct burner, & v Fuel, Turbne LHV Fuel v Fuel, Aux Exhaust-gas temperature, T Turbne, ex Rate of useful heat output, Q th Chlled-water supply temperature, T evap,w,o Chlled-water return temperature, T evap,w, Temperature of water enterng the HRU, T HRU,w, Temperature of water leavng the HRU, T HRU,w,o Exhaust-gas temperature leavng the HRU, T HRU,ex,o Current electrc power output, W Elec (kw) Average daly electrc energy output, 24hours 0 W Elec dt Average electrc power output over the last n hours, (kwh/day) t WElec dt / t n Daly average hourly electrc power output, W / 24 (kw) Coolng-tower water nlet temperature, T CT,w, Coolng-tower outlet temperature, T CT,w,o Coolng-tower approach, T CT,w,o - T wb Coolng-tower range, T CT,w, T CT,w,o 24hours 0 Elec dt n (kw) The system montors these performance parameters and condtons and provdes alarms to the operators when condtons devate sgnfcantly from baselne values. A hypothetcal sequence of values s shown n Table 2 to llustrate a scenaro where montorng of these parameters asssts operators n detectng and correctng a system performance problem much qucker than would be possble wthout such a montorng system. Montorng of an actual system would lkely be done usng a much shorter tme nterval than the 30-mnute nterval used n the table. Thrty mnutes has been used for llustratve purposed. 60

70 Condtons at 13:00 are consstent wth those for several mmedately precedng tme steps (values not shown n the table), and the system s runnng properly. At 13:30, devatons for a few performance varables (COP AbChller, η CT, Q th, and T CT,w,o ) from the values at 13:00 can be seen, but ther magntudes are so small that no problems are apparent. In fact, these devatons are all wthn the range of normal varatons lkely to be observed durng normal, fault-free, operaton. Table 2. Sequence of montored values for performance parameters and physcal condtons. Tme 13:00 13:30 14:00 14:30 15:00 EUF VW η F η EE ε HRU COP AbChller η CT η CT, Elec η Pump Q Fuel,turbne = ρ Fuel v& Fuel,Turbne LHV Fuel (kw) Q Fuel,aux = ρ Fuel v& Fuel,AuxlaryHeat LHV Fuel (kw) W Elec (kw) Q th (kw th ) T Turbne, ex ( F) T evap,w,o ( F) T evap,w, ( F) T HRU,w, ( F) T HRU,w,o ( F) T CT,w, ( F) T CT,w,o ( F) T wb ( F) T CT,w,o - T wb ( F) T CT,w, - T CT,w,o ( F)

71 At 14:00, some substantal changes n performance varables are evdent. The value-weghted energy utlzaton factor has decreased by about 4.5% (from 1.12 to 1.07), not enough to be alarmng by tself, but f ths perssts over the long run, fuel cost ncreases wll be substantal. The fuel utlzaton effcency has also decreased from 59% to 54%, and the effectveness of the heat recovery unt has decreased from 63% to 54% (.e., by 14%), tendng to ndcate that somethng s wrong wth the heat recovery. The electrc generaton effcency has not decreased, but the COP of the chller has dpped from 68% to 60%, and most alarmngly, the overall coolng tower effcency and electrc-utlzaton effcency of the coolng tower have decreased by 26% (from 70% to 52%) and 50% (from 7.0 to 3.5), respectvely. The output of the chller has also decreased from 1180 kw th to 1000 kw th. These observatons drect operator attenton mmedately to the coolng tower, whch clearly has some sort of problem. Lookng at some of the measured varables for the coolng tower reveals that the temperatures of the water enterng and leavng the coolng tower have ncreased by 6 F and 7 F, respectvely, further supportng the operator s concluson that the coolng tower has developed a problem, s not rejectng heat effectvely from the condenser water, and s usng more electrcty to run ts fans (known because the condenser pump effcency has not degraded, leavng only the fans to have caused ths ncrease). In response to these observatons, the operator sends two techncans to nspect the coolng tower. Upon nspecton, the techncans fnd a large pece of cardboard from some sort of contaner for shppng a large applance or machne lodged aganst the ar nlet openngs to the coolng tower. The cardboard appears to be blockng the flow of ar nduced by the fans. The techncans surmse that shortly after noon, when a volent wnd storm blew through the area, cardboard debrs from nearby trash contaners must have blown up aganst the coolng tower and became lodged. To compensate for reduced flow area, the coolng-tower controller began runnng addtonal fans, ncreasng the electrc power consumpton of the coolng tower and causng the observed substantal decrease n coolng-tower electrc effcency, η CT, Elec, but wth lttle affect on coolng of the coolng water. As a result, the coolng-tower performance decreased sgnfcantly. The techncans remove the cardboard and dspose of t properly. They return to the control room. The entre nspecton and repar took about 15 mnutes. Ffteen mnutes later at 14:30, the effect of removng the cardboard s clearly apparent n the montored data. The fuel utlzaton effcency has ncreased back to 59%. The heat recovery effectveness s nearly up to ts pre-ncdent level at 62%, and the coolng-tower effcency and electrc utlzaton effcency have both nearly fully recovered to pre-event levels, now beng 68% and 6.5, respectvely. The chller output s also close to fully recovered at 1185 kw coolng. The coolng-tower nlet and outlet water also has nearly returned to pre-event temperatures. By 15:00, all parameters ndcate full recovery, concludng our performance montorng scenaro. Wthout the level of montorng provded by ths project, the coolng-tower problem would lkely have perssted for some tme, possbly a day, a week, or even longer. Fuel use and costs would have ncreased, coolng-output would have remaned low, and equpment would have run longer and harder. Detecton of many dfferent operaton faults and causes of degradaton are possble wth close montorng. The key s to provde nformaton n real tme or short tme ntervals to enable plant operators to contnually know the state of the CHP plant, ts major systems and components. 62

72 To llustrate applcaton of the capabltes provded by the CxV algorthms, we provde the scenaro that follows for the system shown n Fgure 40. In ths case, the scenaro focuses on the performance of the prme mover, a small turbne, and the electrc generator to produce electrcty and waste heat n the exhaust gases as a by-product. The system manufacturer has rated the turbne at 1 MW e at whch t wll produce 1.7 MW th of heat captured n hot water at 257 F (125 C). The hot water s produced by a matched heat recovery unt. When fred at 80% of capacty, the manufacturer specfcaton ndcates that at an outdoor-ar temperature of 60 F (~15.6 C), the turbne-generator wll produce 800 kw e and 1.36 MW th of heat n hot water at 257 F (125 C). Upon ntal start-up of the system, after allowng tme for the system to reach steady operaton at 80% of full frng rate, the CxV system reports the followng: Electrcal output, W Elec, s 800 kw e, whch s wthn the expected range of levels for the current outdoor temperature and fuel frng rate Thermal output s 1100 kw th, whch s below the expected range. Usng ts dagnostc capabltes, the CxV system also reports that: Turbne exhaust-gas temperature, T Turbne, ex, s 670 F (354 C), hgher than expected (whch s 620 F or 327 C) Hot water temperature leavng the HRU, T HRU,w,o, s 302 F (150 C), hgher than expected (whch s 257 F or 125 C) and recommends checkng control of the varable-speed water crculaton pump, whch appears to be pumpng at a lower rate than necessary. A techncan checks the pump controller and fnds that the operatng range and calbraton are not correct. He replaces the table for these varables n the control code wth a table from the manufacturer based on testng the pump n the system (before ntal frng). Upon replacng the table and watng for the system to reach steady operaton, the CxV system reports that operaton s as expected. Ths aspect of operaton of the CHP plant has now been corrected and verfed by the CxV system. 63

73 Summary Ths document provdes detaled functonal specfcatons for the algorthms for CHP system performance montorng and commssonng verfcaton, scheduled for development under FY2006 fundng. The report dentfes 7 generc CHP system confguratons for whch algorthms wll be developed from a total of 10 orgnally dentfed n the Scope Specfcaton (Katpamula and Brambley 2006). The report then provdes specfcatons for montorng ndvdual components present n the seven selected CHP confguratons. Each specfcaton ncludes equatons for calculatng performance metrcs and a dagram showng all fxed nputs, measured nputs, and outputs for the algorthms. An analogous specfcaton s also provded for performance montorng at the system level. Commssonng and performance verfcaton are then dscussed n some detal that are applcable to both exstng and new CHP systems. A method to model system performance and detect degradatons s presented along wth equatons and an nput/output dagram. Verfcaton of commssonng s accomplshed essentally by comparng actual measured performance to benchmarks for performance provded by the system ntegrator and/or component manufacturers. The results of these comparsons are then automatcally nterpreted to provde a concluson regardng whether the CHP system and ts components have been properly commssoned and where problems are found, gudance s provded for correctons. The report then presents an example of how the montorng algorthms could be deployed as a stand-alone software package. Scenaros are also provded that llustrate how the algorthms could be used for performance montorng durng operaton of a CHP system and as a means for verfyng proper commssonng of a CHP system durng ntal start-up or restart. The report concludes by dentfyng the next steps n the project. 64

74 Next Steps The next step n the project s to develop and document algorthms satsfyng the specfcatons n ths document. The algorthms wll be documented n the form of pseudo-computer code and flow charts n a report. A plan wll also be prepared for testng these algorthms, whch wll be executed n FY2007. Testng wll nvolve mplementng the algorthms n computer code, runnng that code aganst exstng data sets, and comparng the results wth known or ndependently determned performance ndcators. The computer code wll be research grade, wll lack an nterface for easy use n the feld by plant staff, and wll not be sutable for delvery as a tool wthout sgnfcant addtonal development. Its purpose wll be to verfy proper performance of the algorthms. 65

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