A Review of IES Energy Performance Analysis

Transcription

1 Proceedgs of IMECE2004: 2004 ASME International Mechanical Engeerg Congress and Exposition November 13-19, 2004, Anaheim, California IMECE EVALUATION OF DIFFERENT EFFICIENCY CONCEPTS OF AN INTEGRATED ENERGY SYSTEM (IES Andrei Yu. Petrov Abdolreza Zaltash Solomon D. Labov D. Tom Rizy Oak Ridge National Laboratory P. O. Box 2008,Oak Ridge, TN Xiaohong Liao Rehard Radermacher University of Maryland, 4164 Glenn L. Mart Hall, College Park, MD ABSTRACT The Integrated Energy System (IES market the United States (US and worldwide has been creasgly expandg over the last few years. But there is still a lot of disagreement terpretation of one of the most important IES performance ameters efficiency. Some organizations, for example, use higher heatg value (HHV of fu efficiency calculations while some use lower heatg value (LHV. Some accounts for auxiliary and asitic losses while others do not. Some adhere to the first-law of efficiency while some use other methods, i.e., calculations recommended by the Federal Energy Regulatory Commission or the US Combed Heat & Power Association. Different efficiency concepts based on actual performance testg from the IES Laboratory at Oak Ridge National Laboratory (ORNL are evaluated this paper. The equipment studied cluded: a 30-k microturbe, an air-towater heat recovery unit (, a 10-ton (35 k hot waterfired (direct-fired sgle-effect absorption chiller, and a direct-fired desiccant dehumidification unit. Efficiencies of different configurations of the above-mentioned equipment based on various approaches are comed. In addition, IES efficiency gas due to the replacement of a 1 st generation (effectiveness of approximaty 75% with a 2 nd generation (effectiveness of approximaty 92% for the same IES arrangement are discussed. The results showed that the difference HHV- and LHV-based efficiencies for different IES arrangements could reach 5-8%, and that the difference efficiency values calculated with different methods for the same arrangement could reach 27%. Therefore, it is very important to devop standard guides for efficiency calculations that would be acceptable and used by the majority of IES manufacturers and end-users. At the very least, every manufacturer or user should clearly dicate the basis for their efficiency calculations. INTRODUCTION The creased transmission le flow problems caused by deregulation of the ectric energy market the US and other devoped countries have created a key opportunity for the implementation and use of distributed energy resources (DER with and without waste heat recovery. A 2001 report preed by the National Energy Policy (NEP Devopment Group identified coolg, heatg, and power (CHP, or Integrated Energy Systems (IES, as a key strategy for addressg creased energy demands and peak power issues [1]. Also, it offers a means of creasg overall energy efficiency (by combg ectrical and thermal loads as wl as avoidg transmission and distribution le losses. Recent devopments DER technologies have created new opportunities for cost effective small-scale IES for use commercial buildgs. Prime movers, such as microturbes, reciprocatg enges, and fu cls, combation with thermally activated technologies (TAT, which use waste heat from these prime movers either for heatg or thermallydriven desiccant dehumidification (direct- or direct-fired and absorption coolg (direct- or direct-fired, are a major driver for makg IES viable and more cost effective. Facilities for devopg and testg IES under a variety of conditions have been devoped at a number of organizations. These facilities allow the teraction of the IES components to be optimized, so that their efficiency and 1 Copyright 2004 by ASME

2 commercial viability can be maximized. Two such facilities with complimentary programs are: the IES Laboratory at ORNL and the Integration Test Center at the University Of Maryland (UMD. The IES market the US and other devoped countries has been expandg over the last few years. But there is still a lot of disagreement the terpretation of efficiency and ratg conditions for IES products. Examples of standard ratg conditions for various components of IES products clude: Gas turbes and microturbes, ISO [2]: pressure of kpa or 1 atm, temperature of 15 C or 59 F, rative humidity of 60%. Reciprocatg enges, ISO [3]: pressure of 100 kpa or atm, temperature of 25 C or 77 F, rative humidity of 30%. Chillers, ARI 560 [4], ARI 210/240 [5], ANSI/CGA Z [6]: temperature of 35 C or 95 F, rative humidity of 39%. Standardizg these conditions for CHP is currently under devopment and is beyond the scope of this work. This study will focus on IES efficiency only. Usually, efficiency is used to come how effectivy units utilize energy to provide similar output. One common characteristic of efficiency defitions is that they provide a ratio of energy output per unit of energy put, so that IES units of different capacities can be readily comed. The problem is that there are many ways to defe efficiency, especially when both ectric and thermal energy are volved. In this study, various efficiency defitions will be discussed and comed usg performance data gathered at the ORNL and UMD facilities. The position of this paper isn't to devop new calculation methods or dices for ratg IES performance metrics nor to revent or redefe thermodynamic processes. This is outside the scope of this study. The purpose of this paper is to show how different efficiency values rated to an tegrated ectrical and thermal system can be produced from the same test data dependg upon which calculation method is used. Although, we focus only on MTG prime movers for the IES system, the efficiency calculation can get even more complicated when different prime movers are comed. This is due to the different standard operatg conditions specified for these different prime movers. By far the worst culprit to differences efficiency values is whether LHV or HHV for the natural gas is used. NOMENCLATURE Acronyms: AC absorption chiller DFDD direct-fired desiccant dehumidifier DG distributed generation or generator DOE U.S. Detment of Energy HHV higher heatg value (i.e, of natural gas HPR heat-to-power ratio IES LHV MBtu MTG rb RTU TAT Variables: k heat recovery unit Integrated Energy System lower heatg value (i.e, of natural gas million Btu microturbe, or microturbo generator rouble roof top unit thermally-activated technology normalizg factor fu or energy put, TAT useful output ectric power output, asitics efficiency Subscripts c AC coolg econ economical ectrical power output fu-sav fu savgs fu-ut fu utilization put L latent coolg norm normalized ectrical asitics th thermal, heatg typ typical EXPERIMENTAL SETUP Two IES setups are discussed this paper. The first one, IES Laboratory, is based on a 30-k microturbe generator (MTG. The thermally-activated technologies (TAT consist of a 2 nd generation heat recovery unit (, an direct-fired (hot water-fired 10-ton (35 k sgle-effect absorption chiller (AC, and a direct-fired desiccant dehumidification unit (DFDD (Figure 1 [7]. A 1 st generation was previously tested and upgraded based tly on the results from testg at the IES Laboratory. The efficiency improvement achieved by the 2 nd generation will be discussed later this paper. There is an air duct network from the MTG exhaust to the and/or to the direct-fired desiccant dehumidifier. Also, there is a water loop network from the to the directfired desiccant dehumidifier and absorption chiller. Fally, there is an air mixg chamber leadg to the air duct network (for mixg outside air with exhaust air to lower its temperature and/or supplement its volume. The, which is designed to capture the waste heat from the MTG exhaust gas, is used to produce hot water for the absorption chiller. The sulated duct system along with outside air mixg is used to provide hot air for the direct-fired dehumidification unit. 2 Copyright 2004 by ASME

3 MTG ectrical efficiency: 1; thermal efficiency: th th (2a, or cludg ectrical asitics of the by addg them to the heat put (gross energy put: th th + (2b, Figure 1. IES Laboratory. The other IES setup, which is the Integration Test Center, consists of a 60-k MTG, an exhaust-fired AC and a solid DFDD [8]. The exhaust gas from the MTG is supplied series first to the AC and then to the DFDD. Chilled water produced the AC and dry air from the DFDD enters the roof top unit (RTU, and the supply air is used for the buildg conditiong purposes (Figure 2. or subtractg them from the useful thermal output (net energy output: th th AC coolg efficiency: c c AC (2c. (3a, or cludg ectrical asitics of the AC by addg them to the heat put: Exhaust Heat loss Chilled water Exhaust c c AC + (3b, ABSORPTION CHILLER Heat loss dry air RTU or subtractg them from the useful thermal output: Natural gas MICROTURBINE Power Parasitics SOLID DESICCANT Parasitics Air to Zone 2 c c AC DFDD latent efficiency: (3c. Figure 2. IES Facility at the Integration Test Center L L DFDD (4a, EFFICIENCY DEFINITIONS The various efficiency defitions considered this study are discussed bow. Seate component efficiency is the ratio of useful energy output to fu or thermal put of each specific IES unit. Examples for the current IES arrangements are: or cludg ectrical asitics of the DFDD by addg them to the heat put: L DFDD L + (4b, 3 Copyright 2004 by ASME

4 or subtractg them from the useful thermal output: L L DFDD (4c. These methods of efficiency terpretation don t cover the IES as a whole, although it is useful for performance evaluation of dividual units. Heat-to-power ratio is the ratio of the useful thermal output to the net ectrical power output (Btu/kh or kj/kh [9, 10]: th HPR (5. This method can be useful evaluation of different IES operatg regimes. Overall efficiency is the most commonly used efficiency defition to date. It is the ratio of the sum of net ectrical power output and total useful heatg/coolg/latent output from TAT devices to the fu put [9, 10]: + overall (6a, or cludg ectrical asitics of all TAT devices of the current IES arrangement by addg them to the heat put: overall + + or subtractg them from the net ectrical output: ( overall + (6b, (6c. It should be noted that could be based on HHV or LHV of fu put such as natural gas. Therefore, care should be taken comg efficiency numbers from various sources because the difference could be as much as 10%. A better comison is to be consistent the use of LHV or HHV. Normalized overall efficiency accounts for the rative difficulty of producg ectric energy as comed to the total useful heatg/coolg/latent output [11, 12]: + ( k norm (7a, or cludg ectrical asitics of all TAT devices of the current IES arrangement by addg them to the heat put: + norm + ( k or subtractg them from the net ectrical output: norm ( + ( k (7b, (7c. The heat put used calculation of the norm could be based on the LHV or HHV of the fu. The normalizg factor k is used to show the rative value of thermal to ectrical products. FERC suggests usg a normalizg factor k of 0.5 and the LHV of the fu [12]. It should be noted that if ectrical asitics are accounted for the calculation of the norm, the TAT unit efficiency should also account for these asitics. Fu utilization efficiency is the ratio of the net ectrical power output to the net fu put [9]. The net fu put is obtaed by subtractg the fu put that is used to produce useful heatg/coolg/latent output(s, at a given TAT device efficiency(ies, from the total fu put: fu ut (8a, ( or cludg ectrical asitics of all TAT devices of the current IES arrangement by addg them to the heat put: fu ut (8b, + ( or subtractg them from the net ectrical output: ( fu ut (8c. ( Fu energy savgs efficiency reflects fu savgs associated with IES power generation as comed to the use of seate heatg/coolg/latent and ectric power sources [4], where typ- is the typical average ectric grid efficiency (i.e., 33% for the HHV of natural gas, and typ-th is the typical average TAT device efficiency (i.e., 80% [12, 13]: 4 Copyright 2004 by ASME

5 fu sav (1 (9a, + ( typ typ th or cludg ectrical asitics of all TAT devices of the current IES arrangement by addg them to the heat put: fu fu + sav (1 (9b, + ( typ typ th or subtractg them from the net ectrical output: sav (1 (9c. ( + ( typ typ th Economic efficiency is the modified version of the overall efficiency to account for economic values of fu put ($, net ectrical power output ($, and useful heatg/coolg/latent output ($ th [9]: econ $ + ( $ $ (10a, or cludg ectrical asitics of all TAT devices of the current IES arrangement by addg them to the heat put: econ $ + ( $ $ + ( $ or subtractg them from the net ectrical output: econ [( $ $ ] + (10b ( $ (10c. Each value coefficient is based on the cost to generate each energy stream (i.e., total cost of ectric ($ and total ectric consumption (k to generate $/k. CASE STUDIES There are three case studies considered this section. The first case presents the comison of various efficiency calculation methods for the IES consistg of a 30-k MTG and only. The comisons are for the 1 st and the 2 nd generation s, use of LHV or HHV of fu, and clusion or exclusion of ectrical asitics associated with the operation. The second case is the system efficiency calculation for the overall IES (30-k MTG, 2 nd generation, AC, and DFDD and different combations of these units. The third case deals with the combed performance of a buildg IES at full load, which tegrates a 60-k MTG, an exhaustfired AC, and a DFDD. The detailed description of the test procedures and strumentation volved is given other publications [7, 8]. The basic test and price ameters used calculation of the efficiencies for the first case are shown Tables 1 and 2. The tests were performed at similar ambient temperature, MTG power output, flowrate and thermal load. The resultg efficiency calculations are given Table 3. These data clearly dicate that the replacement lead to an crease overall IES efficiencies. These data also show the large difference efficiency values that were calculated with different methods. If fu savgs and economic efficiencies are excluded from consideration, this difference could reach 26.6%. Use of the LHV of natural gas stead of HHV calculations creases the efficiency most cases by %. This depends on the method of calculation used. Regardg the ectrical asitics, the use of normalized, fu utilization and fu savgs efficiencies mitigates or offsets the effect of these asitics, if they are added to the heat put. Exclusion of the ectrical asitics from consideration other methods of efficiency calculation (except for the economic efficiency creases the efficiency by %. But subtraction of ectrical asitics from the net ectrical power output almost always decreases the efficiencies. In some cases this may result negative efficiency values: for example, calculation of fu savgs efficiency with ectrical asitics added to the heat put may show some benefits (2.3%, but when these asitics are subtracted from the net ectrical power output, the efficiency becomes negative (-1.2%, Table 3. Therefore, both manufacturers and end-users of the IES equipment should dicate clearly what efficiency defition they usg to calculate their system performance to ensure proper terpretation of technical data and comison of data with others. Analysis of the economic efficiency produced some terestg results. The comison was made for three different locations: Tennessee (USA, New York State (USA, and Moscow Region (Russia. The 2003 commercial gas and ectric prices for the US locations are taken from [15], and the similar 2004 data plus price for the thermal energy Moscow Region - from [16] (Table 2. 5 Copyright 2004 by ASME

6 Table 1. Basic Test Parameters Used Calculation of Efficiencies Test Case No. 1 Parameters Unit IES with 1 st generation IES with 2 nd generation Ambient o F ( o C 90.8 ( (32.2 temperature Heat put with natural gas HHV Btu/h (k ( (116.9 Heat put with natural gas LHV Btu/h (k ( (105.2 MTG ectric k power output (Btu/h ( ( Heat supplied to Btu/h Heat recovered by (k Btu/h (k ( (42.4 ( (48.2 Table 2. Gas, Electric, and Thermal Prices for Different Locations Parameters Tennessee, USA 2003 New York, USA 2003 Moscow, Russia 2004 Gas price 8.63 $/1000 ft $/1000 ft rb/1000 m 3 [10, 11] Gas price, $/MBtu* 8.11 (HHV 9.01 (LHV 8.25 (HHV 9.17 (LHV 0.85 (HHV 0.94 (LHV Electric price 6.55 c/kh c/kh 1.34 rb/kh [10, 11] Electric price, $/MBtu** Thermal price rb/gcal [11] Thermal price, $/MBtu Notes: *the HHV of natural gas is Btu/ft 3, the LHV of natural gas is Btu/ft 3. **exchange rate 1 $ 28.5 rb: From the data it is evident that the economic efficiency strongly depends on the price ratio between fal products and raw materials. For example, Moscow Region, Russia, this ratio is 6.8 times higher than Tennessee, USA. Therefore, assumg all other conditions beg the same, and if the HHV of natural gas is used calculations, the economic efficiency (ectrical of this IES Moscow Region would be 6.8 times higher than Tennessee. It should be noted that the economic efficiency is site specific and depends on the energy prices at the site. This is confirmed by the drastic reduction overall economic efficiency with addition of the useful thermal output with a rativy low market price Moscow Region. This difference prices also contributes to creased efficiency when ectrical asitics are subtracted from the net ectrical power output as comed to the case when they are added to the heat put. This is different from all other efficiency methods. Also, sce natural gas price is given on volumetric basis, there is no difference economic efficiency calculated with HHV or LHV of natural gas. The second case cludes more IES units but excludes analysis of some efficiency defitions, for example, overall economic efficiency, due to unavailability of prices for coolg or latent coolg output. Table 4 presents the test ameters used calculation of the efficiencies; the efficiencies of dividual components of the IES, as wl as Heat to Power Ratio (HPR, are given Table 5. Table 6 shows the efficiencies of different IES arrangements. The data produced suggests that it might be beneficial to perform analysis of IES operation based on different efficiency defitions. For example, addition of a hot waterfired AC reduces fu-ut by 3.2% (with the clusion of all the ectrical asitics added to the heat put, decreases the overall efficiency by 13.8%, and changes the fu savgs efficiency from positive 2.9% to negative 18.1%. But addition of DFDD usg the MTG exhaust gas after as the energy put significantly creases the IES efficiency. Thus as expected, it confirms that more extensive use of exhaust heat results more efficient IES. If IES units are arranged series (with termediate heat recovery, then the resultg efficiency should account for all ectrical asitics, cludg those of termediate units that provide energy puts to the IES units downstream. The results also show that the number of units cluded IES and the associated value of ectrical asitics can result significant difference between the efficiencies calculated with the two methods of either addg the ectrical asitics to the heat put or subtractg these asitics from the net ectrical output. The difference the overall efficiency calculation creases from 0.7% for the IES consistg of MTG and only to 5.2% for the IES consistg of four units: MTG,, AC, and DFDD. In the case of fu savgs efficiency it is much more drastic; creasg from 3.3% (MTG + to 34.5% (total IES MTG + + AC + DFDD. The third case that volves 60-M MTG considers the same efficiency defitions as the previous one. The test ameters are listed Table 7, and the efficiencies of dividual IES components and different IES arrangements Tables 8 and 9. It should be noted that MTG+AC+DFDD arrangement this case is similar to MTG++DFDD arrangement from the second case, usg exhaust-fired AC stead of (termediate heat recovery. The basic trends the behavior of different efficiencies are the same as the case with 30-k MTG, but due to higher dividual efficiencies of IES units, the absolute efficiency values are higher. 6 Copyright 2004 by ASME

7 Table 3. Calculated Efficiencies Test Case No. 1. IES with 1 st generation IES with 2 nd generation Efficiency HHV LHV HHV LHV No No No No th HPR, Btu/kh (kj/kh ( ( overall norm (FERC* fu-ut fu-sav econ- (TN econ- (NY econ- (Mos econ (Mos Note: efficiency marked with * is based on the LHV of natural gas; the remag ones on the HHV of natural gas. The upper values the columns account for ectrical asitics by their addition to the heat put and the bottom values account for ectrical asitics by their subtraction from the net ectrical output. Table 4. Basic Test Parameters Used Calculation of Efficiencies Test Case No. 2 Parameters Unit IES with 2 nd generation Ambient temperature o F ( o C 76.9 (24.9 Heat put with natural gas HHV Btu/h (k (113.2 MTG ectric power output k (Btu/h 22.8 ( Heat supplied to Btu/h (k (49.4 Thermal output of Btu/h (k (45.9 Electrical asitics of k (Btu/h 2.0 ( Heat supplied to AC Btu/h (k (43.2 Coolg output of AC Btu/h (k (30.4 Electrical asitics of AC k (Btu/h 3.6 ( Heat supplied to DFDD Btu/h (k (12.8 Latent output of DFDD Btu/h (k (8.3 Electrical asitics of DFDD k (Btu/h 6.0 ( Table 5. Calculated Efficiencies of Individual IES Components and HPR Test Case No. 2. Efficiency MTG AC DFDD No No No 18.9 th c HPR, Btu/kh (kj/kh ( Copyright 2004 by ASME

8 Table 6. Calculated IES Efficiencies Test Case No. 2. Efficiency MTG+ MTG++AC MTG++DFDD Total IES No No No No overall norm (FERC * fu-ut fu-sav Note: efficiency marked with * is based on the LHV of natural gas; the remag ones on the HHV of natural gas. The upper values the columns account for ectrical asitics by their addition to the heat put and the bottom values account for ectrical asitics by their subtraction from the net ectrical output. Table 7. Basic Test Parameters Used Calculation of Efficiencies Test Case No. 3 Parameters Unit IES with 60k microturbe Ambient temperature o F ( o C 73.0 (22.8 Heat put with natural Btu/h (k (210.7 gas HHV MTG ectric power k (Btu/h 52.1 ( output Exhaust heat consumed Btu/h (k (79.6 by AC Coolg output of AC Btu/h (k (60.5 Electrical asitics of k (Btu/h 6.4 (21838 AC Exhaust heat supplied to Btu/h (k (36.4 DFDD Latent output of DFDD Btu/h (k (26.0 Electrical asitics of DFDD k (Btu/h 8.1 (27638 Table 8. Calculated Efficiencies of Individual IES Components Test Case No. 3. Efficiency MTG AC DFDD No No c Table 9. Calculated Efficiencies of Individual IES Components Test Case No. 3. Efficiency MTG+AC Total IES (MTG+AC+DFDD No No overall norm (FERC * fu-ut fu-sav Note: efficiency marked with * is based on the LHV of natural gas; the remag ones on the HHV of natural gas. The upper values the columns account for ectrical asitics by their addition to the heat put and the bottom values account for ectrical asitics by their subtraction from the net ectrical output. CONCLUSIONS This study shows that the defition of efficiency can make quite a difference its value. The results showed that the difference HHV- and LHV-based efficiencies for different IES arrangement could reach %, and that the difference efficiency values calculated with different methods for the same arrangement could reach 26.6%. The use of lower heatg value provides an optimistic view of performance. HHV should be adopted these calculations as the price of the natural gas is based on HHV. For the short-term, both IES equipment manufacturers and end-users should be clearly aware of the efficiency defition used. In the long-term, it is very important to devop standard guides for efficiency calculations that would be acceptable and used by the majority of IES manufacturers and end-users. These guides are currently under devopment and are based on HHV of fu. 8 Copyright 2004 by ASME

9 ACKNOLEDGMENTS The authors would like to thank the Office of Energy Efficiency and Renewable Energy, U.S. Detment of Energy DOE, for supportg this work. This research was also supported t by an appotment to the Oak Ridge National Laboratory (ORNL Postdoctoral Research Associates Program admistered jotly by the Oak Ridge Institute for Science and Education and ORNL. This work was conducted by ORNL under DOE contract DE-AC05-00OR22725 with UT-Battle, LLC. REFERENCES [1] Report of the National Energy Policy Devopment Group, 2001, Riable, Affordable, and Environmentally Sound Energy for America s Future, U.S. Government Prtg Office, ashgton, DC. [2] ISO, 1997, Gas Turbes Procurement Part 2: Standard Reference Conditions and Ratgs, Standard , International Organization for Standardization, Geneva, Switzerland. [3] ISO, 2002, Internal Combustion Enges Determation and Method for the Measurement of Enge Power General Requirements, Standard 15550, International Organization for Standardization, Geneva, Switzerland. [4] ARI, 2000, Absorption ater Chillg and ater Heatg Packages, Standard 560, Air-Conditiong & Refrigeration Institute, Arlgton, VA. [5] ARI, 2003, Unitary Air-Conditiong and Air- Source Heat Pump Equipment, Standard 210/240, Air-Conditiong & Refrigeration Institute, Arlgton, VA. [6] ANSI/CGA, 1996, Performance Testg and Ratg of Gas-Fired, Air Conditiong and Heat Pump Appliances, Standard ANSI Z / CGA M96, CSA America, Inc., Clevand, OH. [7] Zaltash, A., Petrov, A. Yu., Rizy, D. T., Labov, S. D., Veyard, E.A., and Lkous, R. L., 2003, Laboratory Research on Integrated Energy Systems (IES, ICR0203, Proc., 21 st International Congress of Refrigeration, International Institute of Refrigeration, Paris, France, pp [8] Popovic, P., Marantan, A., Radermacher, R., and Garland, P., 2002, Integration of Microturbe with Sgle-Effect Exhaust-Driven Absorption Chiller and Solid he Desiccant System, HI , ASHRAE Transactions, Vol. 108, pp [9] Ptier, R. V., 2001, Cogeneration: How Efficient is Efficiency? Power, No. 3-4, pp [10] Petchers, N., 2003, Combed Heatg, Coolg & Power Handbook: Technologies and Applications: An Integrated Approach to Energy Conservation / Resource Optimization, The Fairmont Press, Lilburn, GA. [11] Sokolov, E. Ya. and Martynov, V. A., 1997, Methods for Calculation of Basic Performance Parameters of Steam-Turbe, Gas-Turbe, and Steam-Gas Cogeneration Units, MEI Publishg House, Moscow, Russia. [12] ASHRAE, 2000, Heatg, Ventilatg, and Air- Conditiong Systems and Equipment, Handbook, American Society of Heatg, Refrigeratg, and Air- Conditiong Engeers, Atlanta, GA. [13] Smith,. P., 2001, Cogeneration Overview, Proc. Cogeneration Technology orkshop, University of iscons, Madison, I, Book 2, pp [14] EPA Report, 2002, Technology Characterization: Reciprocatg Enges, Energy Nexus Group, Arlgton, VA. [15] EIA, 2004, Official Energy Statistics from U.S. Government, Energy Information Admistration, Detment of Energy, ashgton, DC. Available from [16] Price List, 2003, Tariffs for Electrical and Thermal Energy for Users Moscow Region, Introduced on January 01, 2004, /MO, Power Committee of Moscow Region, Moscow, Russia. 9 Copyright 2004 by ASME