Enhanced Operations & Maintenance Procedures for Small Packaged Rooftop HVAC Systems

Transcription

1 Enhanced Operations & Maintenance Procedures for Small Packaged Rooftop HVAC Systems Protocol Development, Field Review, and Measure Assessment Final Report April 2002 Prepared for: Eugene Water and Electric Board Eugene, OR Robert Davis Paul Francisco Mike Kennedy David Baylon Bruce Manclark, Delta-T i

2 TABLE OF CONTENTS Executive Summary... iv 1. Introduction Background Project Overview Field Measurement Overview Protocol Development Evaporator Airflow Refrigerant Charge Economizers Economizer Characterization Generalized Sequence of Operation Economizer Functional Testing Sensor Operation Minimum Outside Air Duct Losses Thermostats Results Evaporator Airflow Refrigerant Charge Coil Cleaning Economizers Field Results Duct Losses Energy Savings Impacts and Conservation Measures Coil Cleaning Airflow Improvement Refrigerant Charge Economizers Economizer Simulations Economizer Repair Measures Energy Savings and O&M Impacts Cost/Benefit Analysis Operations and Commissioning Packages Maintenance and Repair Enhanced Maintenance Procedures Contractor Relations Conclusions References Appendix A: Rooftop Packaged Unit Protocols... A-1 Appendix B: Duct Loss Discussion... B-1 i

3 TABLE OF TABLES Table 3-1. System Fan Flow Results Table 3-2. Refrigerant Test Results Table 3-3. Summary of Diagnosed Economizer Operational Issues Table 3-5. Outdoor Sensor Characterization Table 3-6. Economizer Airflow Results Table 4-1. Damper Adjustment Impacts Table 4-2. Ratio of Actual Economizer Savings to Ideal Economizer Table 4-3. Savings (Percent of Annual Cooling Energy) Table 4-4. Cost/Benefit Analysis (7-ton Prototype Unit) ii

4 TABLE OF FIGURES Figure 1-1. Economizers on Eugene Rooftop 3 Figure 2-1. TrueFlow Meters in Unit Slot. 8 Figure 2-2. TrueFlow Meters on Economizer 8 Figure 2-3. Fouled Evaporator Coil....9 Figure 2-4. Water Drainage from Cleaning Fouled Evaporator Coil.9 Figure 2-5. Fouled Condenser Coil.. 10 Figure 2-6. Cleaning Fouled Condenser Coil...10 Figure 2-7. Fouled Evaporator Coil..13 Figure 2-8. Water Drainage from Fouled Condenser Coil...13 Figure 2-9. Solid State Dry Bulb Sensor..13 Figure Electromagnetic Snap Disk..13 Figure 3-1. Outdoor Temperature vs. Compressor Amp Draw 26 Figure 3-2. Outdoor Air Fraction..34 iii

5 Executive Summary Introduction This report details the development of a field protocol used to evaluate the performance of packaged heating and cooling equipment installed on commercial buildings served by the Eugene Water and Electric Board (EWEB). The protocol is intended to identify energy savings opportunities and document changes in equipment operation with the potential to exploit such opportunities. Work was carried out during the summer and early fall of Rooftop packaged heat pumps and air conditioners are commonly used for space conditioning in light commercial buildings. This equipment is generally characterized by a constant-volume, single-speed fan with a gas-fired heating element or heat pump to provide heating; a cooling coil and compressor for air conditioning; and series of dampers and plenums to manage airflow and ventilation to the space served. The systems can be installed with economizers, which are meant to provide cooling to spaces using outdoor air when air temperature is appropriate. Since the use of the economizers in the Pacific Northwest should be able to offset half the electricity associated with cooling requirements, this technology has been mandated by energy codes in most units since the mid-1980s. Furthermore, the economizer has been a key factor in utility sponsored conservation programs for the commercial sector. By 1996, the economizer was mandated for all packaged rooftop systems with more than 5 tons of nominal cooling capacity (60,000 BTUh). As a result, an increasing number of these units are getting installed with economizers, which are meant to use outdoor air for cooling whenever possible. In most cases, HVAC companies do relatively non-invasive preventive maintenance on rooftop units, including changing system filters, performing routine checks on system operation, and occasionally performing more involved assessments of refrigerant charge. Little if any work is done to assure proper airflow or proper operation of economizers, or to assess and mitigate the possible impacts of duct losses. This level of maintenance is designed to provide an annual check of the equipment, but it seldom extends beyond a visual inspection and new air filters. This work is done under a maintenance contract that pays for a small amount of service and an on-call technician in the event of a unit failure. There are only limited studies showing the potential energy savings from more aggressive maintenance in packaged units. Hewett et al. (1992) found savings on the order of 1,900 kwh/yr for 17 Midwest rooftop sites that received refrigerant, airflow, and duct repairs. Vick et al. (1991) reported modest savings from tuning up the gas furnace portion of commercial package units; duct repairs were also undertaken but were not monitored, and economizer function was not evaluated (though it was identified as a potential source of substantial energy savings). Houghton (1997) reported savings of about 25% attributable to maintenance of air filters, coils, compressors and outdoor air dampers (economizers). iv

6 Delp et al. (1998) largely disproved the assumption that duct losses, because they were thought to be within the air and thermal barriers of the building, are not significant. Literature on economizers consists of the few studies in which economizer review was conducted. These studies have been based on a limited sample in a various localities. In general, reports of broken economizers range from about 50% to 80% of all units (e.g. Lunneberg, 1999; Davis Energy Group, 2001). Other efforts (e.g. Breuker et al. 2000; Pratt et al. 2000) have focused on monitoring and optimizing economizer function in the context of automated diagnostic systems. All these efforts are based on data collected in other parts of the country, generally using relatively older equipment. The relationship to the EWEB service territory or any other Pacific Northwest locality is very debatable. Furthermore, none of these papers distinguish between the various control options and configurations available for economizers and the distinct energy and maintenance issues raised by these strategies. Very little work has been done to develop and deliver hands-on protocols that can be used by HVAC technicians to characterize these systems and document energy efficiency improvements. It was hoped that, if a protocol was developed and tested in the field, technicians could incorporate it into a more comprehensive approach to troubleshooting and, in some cases, repairing rooftop units. Project Overview In early summer of 2001, a project to develop and deliver such a protocol for rooftop units in the Eugene Water and Electric Board (EWEB) service territory was undertaken by Ecotope, Inc., of Seattle. Technical and coordination support was provided by Delta T, Inc., and Eugene area HVAC contractors were hired to work on the systems and participate in learning the evaluation protocol. The primary goals of this project were to: 1. Develop a protocol that would allow contractors to evaluate the performance of the units, and to train contractors in using the protocol. The protocol included evaluation of refrigerant charge, airflow, economizer operation, and duct losses. 2. Develop an approach to the maintenance and repair of the units using information gathered during the evaluation to improve unit efficiency. 3. Use HVAC technicians to assist in the use of the protocol and to deliver this enhanced maintenance. 4. Evaluate the savings available from these systems and the costeffectiveness of measures that might be applied to these units. Because a comprehensive protocol did not exist prior to the project, this process required field testing and evaluation of the performance of a number of units, which has the added advantage of establishing a database of results found for tested systems. Refrigerant v

7 charge, airflow, and economizer operation were the primary focuses of the fieldwork, with duct losses of secondary interest. Also of interest was system scheduling (thermostat settings and air handler operation). Since evaluation of refrigerant charge was of primary interest, it was necessary to perform the fieldwork during the cooling season. Conditioning equipment tested in this project ranged in size from 2.5 to 15 nominal tons of cooling, with the average being about 7 tons. The units ranged in age from the mid- 1980s to very new (installed in the year 2001). All units but one were unitary packaged systems. One split-system unit was included as part of the study: a 5-ton unit that used R-410A as its refrigerant. Six of the units had dual compressors; the rest had single compressors. Some units used natural gas for heat, some were heat pumps, and others did not include heating. Most systems were constant volume; a few cases used variable-volume controls or zone dampers. In most cases, the evaporator fan was set to run on constant speed, though we did encounter some variable speed air handler systems. Testing was only done on units that could be maintained at a constant flow rate for the duration of the tests; if a system was constantly changing airflow and mixed air temperature (such as is often the case with VVT systems) most tests were not performed. Economizers were evaluated for a variety of issues. These included type of ambient sensor (dry-bulb vs. enthalpy), sensor setting, damper type, damper position controller, ability to move between positions, and airflow with the dampers in different positions. Economizers were also evaluated when possible on whether the dampers changed position at the sensor setpoint. Duct systems and thermostat type were also reviewed. Ducts were evaluated on whether they ran outside the thermal and air boundary envelopes of the building, ran completely inside, or ran in some sort of buffer space which might be influenced by both inside and outside conditions. Thermostats were inspected to determine settings during different periods, such as occupied vs. unoccupied periods and weekends vs. weekdays. They were also checked for constant fan operation. In a few cases it was determined whether they were single-stage or two-stage thermostats. Field Results and Energy Savings Estimates Various measurements of equipment performance were collected as part of the work. Of primary interest were refrigerant charge, evaporator airflow, economizer airflow (minimum/maximum air flow), and economizer function. Energy savings and measure economics are summarized in the table found near the end of this summary. Refrigerant charge evaluation was carried out with the CheckMe! program, developed by Proctor Engineering. This program uses the Carrier method (actual superheat or subcooling versus target superheat or subcooling). The CheckMe! procedure could be used on 14 units, with the following results: vi

8 Four units were undercharged, with two showing significant undercharge (needing more than an 8 oz adjustment). Five units were overcharged; the average amount of overcharge was about 10% of the factory charge. In two cases, an apparent overcharge was due to a dirty condenser coil. When the coil was cleaned, the evaluation changed to correct charge. Depending on the size of the charge adjustment, annual cooling energy savings can be substantial. Evaporator airflow has significant bearing on system performance. Airflow was measured on 27 units with the new TrueFlow device, which enables direct assessment of airflow (unlike the indirect assessment offered by the Carrier method). Average evaporator airflow was 304 CFM/ton, with a range from CFM/ton. Manufacturers recommend evaporator airflow of 400 CFM/ton of nominal cooling; the measured lower average represents an energy savings potential of about 10%. Economizer airflow has direct bearing on indoor air quality and upon the amount of outside air available for free cooling (when outdoor air is used for cooling rather than the compressor). Minimum airflow averaged 20% of full system airflow. On average, this is close to the level of outside air recommended for ventilation by ASHRAE. The amount of minimum outdoor air fraction ranged from 0 to 92% of system airflow. Maximum outdoor airflow averaged 65% of full system airflow. This is an interesting finding, since it suggests that full system airflow cannot be supplied by outdoor air alone and therefore free cooling is less than supposed. A review of economizer function found a variety of problems with sensor operation, system changeover settings, damper operation, and related issues. Because the economizer section of the protocol was in continuous development during the project, it is difficult to generalize problems with economizers. However, the following tendencies are noted: Changeover settings are usually set to non-aggressive levels (55 F or cooler) and can be changed to more aggressive levels (60 F). This represents a potential savings of about 10% of cooling energy, based on DOE-2.1e simulations, and is estimated to occur in about 35% of EWEB s service territory. Where economizers are non-operational (estimated at 30% of all cases in the EWEB service territory) and are upgraded to a dry-bulb changeover setting of 60 F, simulated annual cooling energy savings are on the order of 25%. vii

9 In general, there are considerable opportunities for saving energy in the EWEB service territory from a combination of coil cleaning, air handler fan adjustment, and economizer adjustment. A systematic protocol will identify these opportunities and monitor progress in exploiting them. Cost/Benefit Analysis To evaluate the costs and benefits of an enhanced maintenance package for rooftop units, the individual measures had to be combined to reflect the manner in which these costs and benefits interact in specific cases. While the nature of these combinations is somewhat arbitrary, they do allow costs and benefits to be assigned to packages that are composites of enhanced maintenance and repair measures. This evaluation is based on an average unit observed in the EWEB service territory attached to a retail building characterized by the Bonneville Power Administration (BPA) small retail prototype. The average unit size that we observed in this sample was between 6.5 and 7 tons of cooling capacity, or approximately 80,000 BTU/hr of total cooling output. For purposes of this analysis, we have assumed that an individual packaged unit serves a retail zone of 2,700 square feet, with a median lighting power density that corresponds to an overall predicted cooling load of 11,000 kilowatt hours per year in the Eugene climate. A cost/benefit analysis is presented in Table 1. It has been derived from the combination of individual measures that were applied or were thought to be applicable to the rooftop units evaluated in Section 3 of this report. Table 1. Cost-Benefit Analysis (7-ton Prototype Unit) Cost Savings Payback ($) (kwh/year) ($/kwh) (Years) Commissioning Measures 1. Change-Over 275 1, Change-Over with T-Stat 675 2, Control Board 775 3, Control Board with T-Stat 1,125 4, New Economizer 1,600 4, Repair Measures 1. Refrigerant Charge* a. Damper Repair (Reset)* b. Damper Repair (Flow Adjustment) Gas Combustion Test* *Gas savings and/or heating impacts not calculated. For purposes of analysis, five separate retrofit packages were assessed, ranging in complexity and expense. These packages were designed to address the diagnosis and repair of economizers and airflow as a result of the direct review of the equipment using a viii

10 systematic protocol. In all cases, these repairs and procedures were designed to have a fairly long life and to correct difficulties that have resulted in deferred maintenance and related wear and tear, as well as design and installation that resulted in less-than-optimal operation of the equipment. Package 1: Coil Cleaning and recalibration of economizer sensors and minimum air setting: This package includes coil-cleaning of both the evaporator and condenser coils together with a review of the economizer sensors and economizer changeover settings, etc. This package of measures could be considered routine commissioning, in which a fairly straightforward diagnostic results in the technician understanding and repairing the economizer. Package 2: Reset change-over with addition of two-stage thermostat control : In approximately 25% of the units reviewed under this program, the control provided by the thermostat was a single-stage cooling set-point. In order for the economizer to function optimally, a two-stage cooling set-point was included. This package is essentially identical to Package 1, except that the thermostat would be placed in the zone and the system would be re-wired to accept two-stage control. Package 3: New economizer control board: This package would be based on an initial review of the economizer controls to determine the level of diagnostic effort required to repair or commission the economizer. In the event that these procedures did not yield sufficient information, a new control board would be installed. This control board would be assumed to handle two stages of cooling and provide integrated control for the economizer. This measure would allow the economizer to be optimized using a set of known controls and sensors, and a documented calibration to facilitate future maintenance. Package 4: Package 3 with additional two-stage thermostat: This option is included on the assumption that under some circumstances, a two stage thermostat would not be present and would have to be included in the economizer repair package in order to get both optimized control and effective temperature management in the zone. Package 5: New economizer: In spite of extensive diagnostics, there are some circumstances in which it may not be possible to even install a new control system. In these cases, the most obvious maintenance strategy would be to remove the existing economizer and install a modern model. In many cases (and especially in older equipment) this would obviate the need for detailed diagnostics. Work With Contractors The purpose of this effort was to try and establish the veracity of an enhanced HVAC contractor-based maintenance procedure in developing both energy savings and the services available to EWEB customers. Notwithstanding for a very limited sample, this effort showed the importance of enhanced maintenance in the overall functionality of rooftop units. ix

11 In this sense, the mere act of having a systematic protocol that requires certain things to be checked, and especially a protocol that requires a review of refrigerant charge and damper function, would harness a significant fraction of the savings and benefits that were identified in our review. The more sophisticated issues with economizer controls and complex issues with dampers would require a larger amount of effort. In many cases, this larger amount of effort would also yield noticeably greater savings, although in most cases these savings would also include functional compromising of the equipment to the point where a catastrophic failure might result in the absence of the measure. Contractors did express some hesitation to using the advanced diagnostic techniques in this project. Regarding airflow, there was some feeling that since nothing could be done to change the flow in many systems, one should not bother to measure it. For economizers, the process is seen as lengthy and nebulous, since it can be difficult to identify the source of a problem and since there are so many different types of economizers. It is quite apparent from the nature of the business we observed in this project and from the time allotted to this operation that the existing maintenance contracts are unlikely to result in any of the potential savings measures being identified, let alone attempted. Only if the contractors are able to sell an enhanced service, paid for either directly by the utility or by the customer, would any of these reviews even be possible. However, it must also be pointed out that, even in the presence of such a marketing effort, it is not entirely clear that the contractor services as currently observed would be able to deliver a sophisticated system review on any sort of regular basis. Conclusions This effort showed, albeit for a very limited sample, the importance of enhanced maintenance in the overall functionality of rooftop units. Even where enhanced controls would not be considered a viable measure, about 60% of the units reviewed required some maintenance that would result in improved function and efficiency. In about 20% of the cases, the review identified catastrophic or near-catastrophic failures that had not been recognized in previous maintenance visits. Contractors generally sell the routine maintenance check as a loss-leader. Seldom is the budget or time available to review even the refrigerant charge. Most technicians we spoke with believe this to be a waste of time and, in fact, in many cases it is of marginal significance. However, in a few cases (15% of those reviewed in our protocol), the result of applying the CheckMe! program led to the identification of serious failures or serious difficulties with the air coils that could not have been easily identified any other way. With economizers, there are really two layers of review, but at this stage the ability to understand a wide variety of economizers and the potential benefits from a detailed approach is limited. x

12 It is quite clear that even economizers that are set up properly and operate correctly may not be delivering a very high fraction of the potential economizer benefits because of non-aggressive changeover settings. Technicians often have neither the time nor the tools to address these issues. Only if the contractors are able to sell an enhanced service, paid for either directly by the utility or by the customer, would any of the reviews even be possible. It is quite likely that commissioning these small rooftop units so that the controls and dampers are properly set up at installation might achieve these performance benefits without enhanced maintenance services. In this scale of equipment, there is generally no quality control on the installation, let alone commissioning. It is obvious from the evaluation of the measure packages that a part of a cost-effective program would have to include a long term and extensive review of the operation, installation, and maintenance of the entire packaged unit. At the outset, this would be an extensive and expensive addition to the existing maintenance agreements offered by the service companies. If this program offered the opportunity to supply a diagnostic service and replace non-functional parts profitably, contractor resistance to this level of involvement would be reduced. An enhanced diagnostic procedure would include full operational review, repair, and replacement of economizer controls, reset of change-over controls, and evaluation and reset of airflow charge and damper settings in the initial year of operation. This would be followed by annual or semi-annual visits to ensure that the repairs continue to function and that any deficiencies in charge are quickly identified and repaired. This would also include periodic cleaning of coils and changing of air filters, thus replacing existing maintenance contracts. While we believe that this protocol remains somewhat incomplete and certainly has not addressed all the potential savings available from economizers, it is clearly evident that an enhanced service of this type can yield great benefits and energy savings to the utility and substantial benefits in reduced maintenance and energy costs to the building operators. As such, considerable effort should be expended to establish this protocol inside of the contractor community in Eugene, and to ensure that owners and operators of this type are aware of and demand the level of maintenance and review that this effort suggests. xi

13 1. Introduction 1.1. Background Rooftop packaged heat pumps and air conditioners are commonly used for space conditioning in light commercial buildings. This equipment is generally characterized by a constant volume single speed fan with a gas fired heating element or heat pump to provide heating; a cooling coil and compressor for air conditioning; and series of dampers and plenums to manage air flow and ventilation to the space served. Several important variations were observed which include variable volume/temperature (VVT) systems designed to modulate air delivery based on zone temperature. We also observed several systems that were designed to provide cooling only. In those cases the heating was supplied by a secondary system in the space (usually electric zone heating). The systems can be installed with economizers, which are meant to provide cooling to spaces using outdoor air when air temperature is appropriate. Since the use of the economizers in the Pacific Northwest should be able to offset half the electricity associated with cooling requirements, this technology has been mandated by energy codes in most units since the mid 1980s. Furthermore, the economizer has been a key factor in utility sponsored conservation programs for the commercial sector. By 1996 the economizer was mandated for all packaged rooftop systems larger than 5 tons of nominal cooling capacity (65,000 BTUh) As a result an increasing number of these units are getting installed with economizers. While these code requirements have been part of the Oregon and Washington energy codes for over 20 years the nature of the economizer and economizer controls in these small package systems have evolved with increasingly complex and effective controls which operate the economizer and control the heating and cooling. The installation and maintenance of these economizers is critical to the overall efficiency of the system but the capacity and controls are designed to function without any of the energy savings features operating at all. As a result, the effectiveness of the unit at providing heating and cooling is very often maintained while the economizer and other control and operating features are compromised. In most cases, HVAC companies do relatively non-invasive preventive maintenance on rooftop units, including changing system filters, performing routine checks on system operation, and occasionally performing more involved assessments of refrigerant charge. Little if any work is done to assure proper airflow or proper operation of economizers, or to assess and mitigate the possible impacts of duct losses. This level of maintenance is designed to provide an annual check of the equipment but seldom extends beyond a visual inspection and new air filters. This work is done under a maintenance contract that pays for a small amount of service and an on-call technician in the event of a unit failure. There are only limited studies showing the potential energy savings from more aggressive maintenance in packaged units. Hewett et al. (1992) found savings on the order of 1900 kwh/yr for 17 Midwest rooftop sites that received refrigerant, airflow, and duct repairs. Vick et al. (1991) reported modest savings from tuning up the gas furnace portion of 1

14 commercial package units; duct repairs were also undertaken but not monitored, and economizer function was not evaluated (but was identified as a potential source of substantial energy savings). Houghton (1997) reported savings of about 25% attributable to maintenance of air filters, coils, compressors and outdoor air dampers (economizers). Delp et al. (1998) showed that, despite the assumption that duct losses are not important because the ducts are thought to be within the air and thermal barriers of the building, these assumptions are often incorrect. Literature on the economizer has focused on a few studies where economizer review was conducted. These studies have been based on a limited sample in a various localities. In general reports of broken economizers range from about 50% to about 80% of all units (e.g. Lunneberg, 1999; Davis Energy Group, 2001). Other efforts (e.g. Breuker et al. 2000; Pratt et al. 2000) have focused on monitoring and optimizing economizer function in the context of automated diagnostic systems. All these efforts are based on data collected in other parts of the country usually using equipment that is relatively older. The relationship to the EWEB service territory or any other Pacific Northwest locality is very debatable. Furthermore, none of these papers distinguish between the various control options and configurations available for economizers and the distinct energy and maintenance issues raised by these strategies. Very little work has been done to develop and deliver hands-on protocols that can be used by HVAC technicians to characterize these systems and document energy efficiency improvements. It is hoped that, if a protocol was developed, technicians could incorporate it into a more comprehensive approach to troubleshooting and, in some cases, repairing rooftop units Project Overview In early summer of 2001, a project to develop and deliver such a protocol for rooftop units in the Eugene Water and Electric Board (EWEB) service territory was undertaken by Ecotope, Inc., of Seattle. Technical and coordination support was provided by Delta T, Inc., and Eugene area HVAC contractors were hired to work on the systems and participate in learning the evaluation protocol. See Fig. 1-1 for an example of a typical rooftop. The primary goals of this project were to 5. Develop a protocol that would allow contractors to evaluate the performance of the units, and to train contractors in using the protocol. The protocol included evaluation of refrigerant charge, airflow, economizer operation, and duct losses. 6. Develop an approach to the maintenance and repair of the unit using information gathered during the evaluation to improve the efficiency of the unit. 7. Use HVAC technicians to assist in the use of the protocol and to deliver this enhanced maintenance. 8. Evaluate the savings available from these systems and assess the cost-effectiveness of various measure operations and maintenance packages. 2

15 Figure 1-1. Roof of pet store in Eugene with four package units with economizers visible. Economizers are the triangular hoods at the ends of the units Field Measurement Overview Because a comprehensive protocol did not exist prior to the project, this process required field testing and evaluation of the performance of a number of units, which has the added advantage of establishing a database of results found for tested systems. Refrigerant charge, airflow, and economizer operation were the primary focuses of the fieldwork, with duct losses of secondary interest. Also of interest was system scheduling (thermostat settings and air handler operation). Since evaluation of refrigerant charge was of primary interest, it was necessary to perform the fieldwork during the cooling season. As much of the work as possible would be carried out using standard service tools (refrigerant gauges, voltage test meters, hand tools, etc.). Refrigerant charge would be conclusively evaluated by the Carrier method, as run in semi-automated fashion by Proctor Engineering Group (PEG) in their CheckMe! Program, which allows contractors to call a toll free number, relay their measurements, and receive results and any recommendation for changing the charge. Airflow would be evaluated using the new TrueFlow Air Handler Flow Meters. Since evaluation of economizer operation is more a qualitative assessment of mechanical operation and controls than a quantitative measurement, this portion of the protocol would be essentially answering a set of questions and diagnosing any failures by whatever means necessary. 3

16 Some units would be monitored with data-logging equipment to assess changes in energy uses as a result of repairs. EWEB currently keeps track of energy usage on over 100 commercial buildings with the automated meter reading (AMR) process. It was hoped that this process could be utilized in assessing energy savings from units in buildings involved in the project. To further estimate the potential savings from performing additional maintenance and repairs on these types of units simulations were performed using DOE-2.1e. In developing the protocol, the intention was to test 30 buildings. The definition of building is somewhat fluid but, given the time required to complete the protocol, 1 to 2 units could be visited in an 8 hour period and so a total of 30 to 45 units were expected to be included in the project. Because of various factors, only 30 units were evaluated in a total of 19 separate businesses, including a small group of buildings in the Puget Sound area. Some units were in complexes serving a number of businesses, such as Willamette Square in Eugene and Kingsgate in the Puget Sound area. Not all parts of the final protocol were completed for each unit, since the protocol was under development throughout the project and because, in some cases, various problems prevented one or more major categories of the protocol from being completed. Also, toward the end of the field testing, it was felt that time was best spent getting the best understanding possible on economizers, so the flow and charge protocols, which were both well in hand, were sacrificed. Conditioning equipment tested in this project ranged in size from 2.5 to 15 nominal tons of cooling with the average being about 7 tons. The units ranged in age from the mid- 1980s to very recent (i.e., installed in the year 2001). All units but one were unitary packaged systems. One split-system unit was included as part of the study: a 5-ton unit that used R-410A as its refrigerant. Six of the units had dual compressors; the rest had single compressors. Some units used natural gas for heat, some were heat pumps, and others did not include heating. Most systems were constant volume single zone; a few cases used variable volume controls or zone dampers. In most cases, the evaporator fan was set to run on constant speed, though we did encounter some variable speed air handler systems. Testing was only done on units that could be maintained at a constant flow rate for the duration of the tests; if a system was constantly changing airflow and mixed air temperature, such as is often the case with VVT systems, most tests were not performed. Economizers were evaluated on a variety of issues. These included type of ambient sensor (dry-bulb vs. enthalpy); control logic; orientation of dampers; style of dampers; damper position controller; ability to move between positions accurately; and airflow with the dampers in different positions. Economizers were also functionally tested, when possible, to determine that the unit responded correctly to ambient conditions. To understand the impact of various economizer operation strategies and control approaches, we developed several detailed DOE-2.1e simulations. This process used the prototype commercial buildings used to evaluate regional conservation programs. The 4

17 effect of these runs was to provide guidance as to the control algorithms and other operational approaches to diagnosing the economizers. Duct systems were reviewed qualitatively in this project, primarily by characterizing the type of air space in which the majority of the ducts run. The goal was to judge whether the ducts were running outside the thermal and air boundary envelopes of the building, running completely inside, or running in some sort of buffer space which may be influenced by both inside and outside conditions. The effect of duct losses depends greatly on the location of the ducts. Thermostats were inspected to determine settings during different periods, such as occupied vs. unoccupied periods and weekends vs. weekdays. They were also checked for constant fan operation. In a few cases it was determined whether they were singlestage or two-stage thermostats. In addition to the collection of technical information and the development of the protocol, it was also of great interest to work with HVAC technicians in the field and try to facilitate independent contractor utilization of this protocol. In part because of scheduling difficulties and contractor availability, this part of the project was not successful; that is, contractors did not get to a point where they could use the procedure on their own. It is hoped that follow-up work will achieve this goal, since even the best protocol will be of no use to the utility if it is never used. The following section, section 2, of the report discusses protocol development. Section 3 includes the results from the field tests, which is broken down into sections on evaporator/economizer airflow; refrigerant charge; economizer function; and ducts. Section 4 discusses estimates of energy savings from improvements, including data from tested units as well as simulation results. Section 5 discusses contractor participation and the possibility of developing a utility-based program for this sector. Section 6 includes the conclusions and recommendations that result from this study. The final protocol is included as Appendix A. This Appendix includes a protocol checklist, as well as detailed descriptions of how to perform various tests. 2. Protocol Development It was understood from the beginning of the project that the field protocol would be under constant development. The elements of the protocol would be: measuring evaporator airflow, measuring system refrigerant charge, assessing the type and function of the economizer, and reviewing the performance of the duct system. During the project, several items were added to the protocol (including more specific information on compressor and economizer function) Evaporator Airflow One of the main points of concentration in this study was the direct measurement of airflow across the system evaporator. Several researchers (e.g. Parker et al. 1997; Proctor et al. 1997; Proctor 1991) have described the heat delivery efficiency of heating and 5

18 cooling systems as a function of the airflow across the evaporator. The mass flow of air across the heat exchanger will have a direct bearing on the ability of the system to meet the cooling or heating load. Air conditioning systems depend on a certain amount of air moving across the evaporator at any given time to effectively transfer heat from the conditioned space to the refrigerant, after which the refrigerant being circulated by the compressor gives up the heat at the condenser. Manufacturers of air conditioning equipment have typically suggested that an airflow rate of 400 ft 3 /min (CFM) per nominal ton of cooling is the desired airflow. Although manufacturers vary somewhat about this number, 400 CFM/ton is the generally agreedupon benchmark for assessing whether airflow is adequate. Various laboratory and field researchers have found that airflows of 350 and even 325 CFM/ton do not significantly degrade either system capacity or efficiency, though reduction of the flow rate does cause a greater portion of the capacity to be directed toward latent cooling (moisture removal is largely irrelevant in the Pacific Northwest cooling climates). Low airflow is often due to inadequately-sized ducts or dirty filters or coils. Other causes can be inappropriate selection of fan speed on a multi-speed fan. High airflow is usually due to an incorrect fan speed setting. There are various methods that have been used in the past to measure system airflow. The industry standard method is that described by Carrier Corporation in their refrigerant-charging/airflow measurement procedures. In these procedures, the cooling load on the air conditioner is used along with the sensible temperature split across the evaporator (the temperature difference between air upstream and air downstream of the evaporator coil) to impute whether the airflow is adequate, too low, or too high. The cooling load is determined using the condensing air entering temperature (usually fairly close to the ambient i.e., outdoor air temperature) and the wet bulb temperature of the air stream entering the evaporator. The condenser air entering temperature describes the heat sink to which heat gathered by the evaporator is rejected. The entering air wet bulb temperature describes the amount of moisture that must be removed as part of the cooling. If air is very moist then more of the capacity will be used to condense moisture out of the air, and less will be available for sensible cooling, which will result in a lower expected temperature split. Carrier suggests that, if the sensible temperature split is within three degrees of the target level, the airflow is about of 400 CFM/ton and adequate. In practice this is untrue. Consider that a common temperature split is about 20 F. A three degree discrepancy is 15%, which translates directly into a 15% difference in flow. This shows that, rather than being on the order of 400 CFM/ton, a split that is 3 F high would translate to a flow of 340 CFM/ton, assuming that the charge was correct and that the coils were clean. The temperature split method also has the problem that it is not directly measuring flow. Rather, it is using temperature measurements in conjunction with charts to impute airflow. The temperature split is essentially the result of three things: the amount of refrigerant in the evaporator coil, the airflow across the coil, and the ability of the coil to transfer heat. 6

19 The charts do also evaluate charge, but the results are not used in assessing airflow. Instead, if the unit is either over- or undercharged, but the airflow is said to be adequate, it is likely that correcting the charge will result in the estimated airflow no longer being adequate. In effect, the airflow assessment is relative to the charge. The charts also assume a clean evaporator,, which is often a poor assumption in these units since coil cleaning is not part of routine maintenance in the EWEB service territory. Dirt reduces the ability of the coil to transfer heat, resulting in a temperature split that is smaller than it should be for the given charge and airflow. Clearly, since the temperature split method relies on assumptions that may easily be incorrect, it cannot be depended on to provide a good quantitative assessment of airflow. This also means that no quantitative estimate of potential savings due to flow changes can be made using this method. This method can be useful at a qualitative level, however, as it will typically catch the large problems. A further problem with simply using the temperature split to evaluate airflow is that we also want to know how much air is coming in through the economizer under various situations. The temperature split does not evaluate this flow, and even if it did, the magnitude of the uncertainty in the result is such that nothing could be inferred as to the fraction of the air that was from outdoors. For this project, Ecotope utilized a new airflow measurement device, the TrueFlow Air Handler Flow Meter. This device was developed by Ecotope in concert with The Energy Conservatory. This device is a calibrated perforated plate that correlates a measured pressure drop across the plate with an airflow, and has been shown to be a very accurate means of directly measuring airflow (Palmiter and Francisco 2000). This device was designed for residential-size filter slots. For the larger filter slots of commercial units, several plates were often required. In these cases, the airflow through each plate is measured and the results are added together. The TrueFlow meter is currently being absorbed into the HVAC community and should become a relatively common piece of technology within the next several years since it substantially reduces the uncertainty of the temperature split methods and is fast and simple to use. At this point, the use of the device represents a significant addition to the testing usually done by contractors, but the reliability of the estimates warrant its use in this type of program. The protocol involves measuring both the economizer flow and air handler fan flow simultaneously (see Figs. 2-1 and 2-2 for examples of TrueFlow installation), to get an estimate of the percentage of outdoor air under various economizer positions. Flow meters are inserted in place of the system filters and at the inlet of the economizer. The protocol sheets provide places to indicate which readings are for economizer flows and which are for system flows, as well as what position the economizer is in. The supply and return pressures are also measured and entered, both with the flow meters installed 7

20 and with the filters installed, which allows for a simple correction to be made to account for any change in flow caused by the flow meters. This adjustment is typically small. Once the data has been collected, the total flow is calculated for both the economizer and the system fan, and the adjustment is applied to each to get the corrected flow. There are also spaces on the data sheets to enter the percent of outdoor air and the CFM/ton of cooling. A separate sheet is used for each economizer position tested. Figure 2-1. TrueFlow Air Handler Flow Meters installed in a rooftop unit filter slot. Figure 2-2. TrueFlow Air Handler Flow Meters installed on an economizer Refrigerant Charge Refrigerant charge is a major focus of any work with air conditioning systems. The amount of refrigerant in the system being circulated by the compressor has a direct bearing on capacity and efficiency of air conditioning. Many reports have been written on the effects of too much or too little refrigerant charge on the cooling capacity and efficiency of these systems. The refrigerant charge portion of the protocol required the least development, because standard methods for checking charge are essentially the best available methods. The primary change over what contractors currently do is the use of the CheckMe! standardized form that requires certain information, which is called in to a toll free number. In order for contractors to use the CheckMe! program, which has its foundation in the Carrier method, they must go through a one-day certification class. An additional feature of this program is that it not only provides the results but also gives recommendations for how much refrigerant to add or remove, if appropriate. For refrigerant charge, this approach uses the outdoor dry bulb temperature and the return air wet bulb temperature to evaluate the sensible/latent cooling split. The results can be used with lookup tables to determine the expected increase in temperature in the refrigerant vapor line (the superheat ) or decrease in temperature in the refrigerant liquid line (the subcooling, only used for systems with thermostatic expansion valves (TXVs)). The target can be compared to measured superheat or subcooling, based on pressure and temperature measurements from the refrigerant lines. A deviation from the target indicates that there is either too little or too much refrigerant. 8

21 There are several important qualifications for using this protocol. Major system faults (e.g., bad electrical components, very dirty indoor/outdoor coils) can invalidate the charge assessment. These qualifications were not fully understood when this project began, primarily regarding coil cleanliness. In fact, after observing the results on a few sites with fouled coils, we consulted Proctor Engineering and realized that we should have been more careful in ensuring that coils were clean before proceeding with the CheckMe! process. However, once this was cleared up, some confusing results started to make more sense. For example, dirty coils are less effective heat exchangers and therefore, CheckMe! might identify an apparent overcharge where one does not exist. In package units, unless there is an initial mistake to factory charging, there are leaky components, or the system has been "adjusted" at some time in the past, the system should be fairly close to the factory charge. The corollary of this fact is that, in our observation, technicians are very reluctant to make refrigerant charge changes to commercial rooftop units unless the change is large. During this project, in fact, even when CheckMe! suggested that adjustments should be made, the recommended adjustments were usually small and technicians typically did not change the charge in the system. Proctor Engineering has made improvements to CheckMe! since this project that incorporate the factory charge and unit size and type (commercial/residential) into the CheckMe! database. This information will eventually be used to refine recommended charge adjustments for packaged commercial units. An important addition to the refrigeration protocol has to do with ensuring the cleanliness of refrigeration coils before performing refrigeration charge assessment, as the Carrier method assumes clean coils. If one plunges ahead in evaluating refrigerant charge and evaporator airflow without ensuring that both the condenser and evaporator coils are relatively clean, the conclusions reached can be faulty. This is because dirty coils compromise the ability of the coils to transfer heat, which can show up as a superheat that is too low, implying too high of a charge. Especially where condenser coils are very dirty and discharge pressures are very high (over 300 lbs. psig), the compressor works much harder than needed to deliver a given amount of cooling. See Figs. 2-3 through 2-8 for examples of dirty coils and coil cleaning. Figure 2-3. Fouled evaporator coil at bakery. Figure 2-4. Water drainage from cleaning fouled evaporator coil at bakery. 9