FIELD SURVEY OF RTU FAN EFFICIENCY AND OPERATION PATTERNS

Transcription

1 Design & Engineering Services FIELD SURVEY OF RTU FAN EFFICIENCY AND OPERATION PATTERNS Report Prepared by: Design & Engineering Services Customer Service Business Unit Southern California Edison December 202

2 Acknowledgements Southern California Edison s Design & Engineering Services (DES) group is responsible for this project. It was developed as part of Southern California Edison s HVAC Technologies and Systems Diagnostics Advocacy Program (HTSDA) under internal project number. Jay Madden, P.E. conducted this technology evaluation with overall guidance and management from Jerine Ahmed. Western Cooling Efficiency Center (WCEC) and Davis Energy Group (DEG) designed and conducted the field surveys, tabulated the data, and prepared the report for this project. For more information on this project, contact jay.madden@sce.com. Disclaimer This report was prepared by Southern California Edison (SCE) and funded by California utility customers under the auspices of the California Public Utilities Commission. Reproduction or distribution of the whole or any part of the contents of this document without the express written permission of SCE is prohibited. This work was performed with reasonable care and in accordance with professional standards. However, neither SCE nor any entity performing the work pursuant to SCE s authority make any warranty or representation, expressed or implied, with regard to this report, the merchantability or fitness for a particular purpose of the results of the work, or any analyses, or conclusions contained in this report. The results reflected in the work are generally representative of operating conditions; however, the results in any other situation may vary depending upon particular operating conditions. Southern California Edison Page i

3 EXECUTIVE SUMMARY This study focuses on small commercial rooftop unit (RTU) supply air fans and how the thermostats controlling these supply fans are configured. According to the 2006 California Commercial End Use Survey, supply fans in the more than one million RTUs in California contribute.9% of total statewide commercial building electrical consumption. This compares to the cooling component (compressor and condenser fan) which represents 4.9% of total statewide electrical consumption. From this context, addressing supply fan energy efficiency is an important future research area. To evaluate the energy savings potential of any potential supply fan efficiency opportunity, the baseline operating characteristics need to be quantified based on actual field conditions. The goal of this project was to field survey small commercial building establishments to assess in-situ RTU supply fan electrical demand, and to record how the thermostat controlling the RTU is programmed, if at all. In addition to defining occupied and unoccupied periods of the day/week, a review of the thermostat configuration allows one to document whether the supply fans are operating continuously or cycling in response to a thermostat call for cooling or heating. Field surveys were completed during summer 202 at 26 RTUs in northern and southern California, with rooftop field measurements of supply fan power at a subset of 58 RTUs. Complete data sets were not obtained for every RTU surveyed as the access provided by each of the 98 surveyed commercial sites varied, resulting in different pieces of data recorded at each site. This is why many of the analyses have data set populations less than the full 26 records. The survey team gained access to commercial establishments by coordinating with HVAC contractor service calls, coordinating with building owners and municipal/public entities, and by cold-calling commercial establishments. Nameplate RTU data were collected at the 58 units, allowing RTU supply fan power characterization in terms of a kw/nominal ton metric. The survey results indicated that the supply fans ran continuously at about 40% of the surveyed RTUs serving commercial buildings. The other 60% cycled with calls for cooling or heating. In a third of the surveyed units, the supply fan operated continuously during unoccupied hours, with another 36% of the fans cycling during unoccupied hours. Table summarizes these results. While these proportions varied by building type, the sample sizes for each building type were not sufficiently large to make conclusions that are more detailed. Southern California Edison Page ii

4 TABLE : FAN OPERATION PATTERNS FOR OCCUPIED AND UNOCCUPIED STATES ROOFTOP UNITS (N=93) FAN OPERATION PATTERN OCCUPIED UNOCCUPIED Continuous 39.4% 32.% Cycles 58.5% 36.3% Off % Unknown 2.% 2.% Measured supply fan power in this survey as presented in Table 2 was slightly lower than results from the datasets in the Bonneville Power Administration RTU Pilot Servicing Program and the California Energy Commission (CEC) Small HVAC System Design Guide. Direct-drive supply fans were found to consume less energy per nominal ton of capacity relative to belt-drive fans. However, direct-drive fans were not observed in RTUs above 5 tons nominal capacity. TABLE 2: COMPARISON OF MONITORED SUPPLY FAN POWER DENSITY STUDY FAN POWER DENSITY (KW/NOMINAL TON) SCE Survey 0.5 Bonneville Power Administration RTU Pilot Servicing Program 0.8 CEC Small HVAC System Design Guide 0.8 Based upon the survey observations, RTU potential supply fan energy efficiency measures should not assume continuous supply fan operation during occupied hours. This assumption would result in calculated energy savings higher than actual results. It is also difficult to draw a conclusion regarding fan energy savings during unoccupied hours. One-third of the RTUs were observed to be operating continuously at night, some of which could possibly be due to thermostat programming errors. Theoretically, the programming errors should be corrected before fan energy measures are applied to these buildings. The survey found programmable thermostats or EMS at a majority of the RTUs, which provides the opportunity for features like programmed operation and night setback operation. However, lack of understanding of these controls resulted in bypassing these opportunities. Better awareness could result in better comfort levels in the conditioned spaces as well as lower energy consumption. Southern California Edison Page iii

5 ACRONYMS AC Air Conditioning Unit ACM Alternative Calculations Method ASHRAE American Society for Heating Refrigeration and Air Conditioning BPA Bonneville Power Administration CA California CEUS California Commercial End-Use Survey CFM Cubic Feet per Minute DEG Davis Energy Group DOE Department of Energy EMS Energy Management System HVAC Heating, Ventilation, and Air Conditioning IAQ Indoor Air Quality kw kilowatt PNW Pacific Northwest RTU Rooftop Unit RTUG Regional Rooftop Working Group SCE Southern California Edison UC University of California WCEC Western Cooling Efficiency Center Southern California Edison Page iv

6 CONTENTS EXECUTIVE SUMMARY II INTRODUCTION BACKGROUND 2 Ventilation Code Requirements... 2 Bonneville Power Administration RTU Pilot Servicing Program... 3 California Commercial End-Use Survey (CEUS)... 8 Small HVAC System Design Guide... 0 METHODOLOGY Survey Protocol... Survey Schedule... 2 RESULTS 3 DISCUSSION 28 CONCLUSIONS 30 REFERENCES 3 APPENDIX A: SURVEY DATA COLLECTION FORM 32 APPENDIX B: SURVEY DATA BY SITE 35 Southern California Edison Page v

7 FIGURES Figure : RTU evaporator fan kw per ton (BPA study)... 4 Figure 2: Capacity of Surveyed RTUs... 5 Figure 3: RTU Fan Hours per Day... 6 Figure 4: Compressor runtime vs. fan runtime... 8 Figure 5: Survey sites by county... 4 Figure 6: Survey sites by facility type and county... 5 Figure 7: Number of RTU in building surveys by facility type and region... 5 Figure 8: Number of RTUs per site by region (N or S) and facility type (individual site values shown in black)... 6 Figure 9: Observed RTU nameplate nominal capacity... 7 Figure 0: Thermostat manufacturers by facility type... 8 Figure : RTU manufacturers by facility type... 8 Figure 2: Fan operation characteristics during occupancy by region and facility type Figure 3: Fan operation characteristics during non-occupied periods by region and facility type Figure 4: Hours of continuous fan operation by facility type... 2 Figure 5: The average number of business hours per business day by facility type Figure 6: Ratio of average daily available cooling hours to business occupancy hours Figure 7: Measured supply fan kw/ton by site Figure 8: Fan power per ton by drive type versus RTU tonnage Figure 9: Measured supply fan kw/ton by region and facility type.. 26 Figure 20: Individual site occupied thermostat setpoints (by region-facility-schedule type) Figure 2: Individual site unoccupied thermostat setpoints in black (by region-facility-schedule type) Southern California Edison Page vi

8 TABLES Table : Fan operation patterns for occupied and unoccupied states... iii Table 2: Comparison of monitored supply fan power density... iii Table 3: RTU fan categorization sorting rules... 7 Table 4: Comparison of fan operation in multiple studies... 9 Table 5: Thermostat operation ( CEUS study)... 9 Table 6: Types of programmed RTU operation... 3 Table 7: Characterization of fan operations in terms of occupancy state, system setting, and fan setting... 9 Table 8: Fan operation patterns for occupied and unoccupied states... 9 Table 9: Average fan power per ton by drive type and RTU tonnage Table 0: Supply Fan Power Density Southern California Edison Page vii

9 INTRODUCTION This study focuses on small commercial rooftop unit (RTU) supply air fans and how the thermostats controlling these supply fans are configured. The information in this study assists in understanding the actual energy consumption and savings potential of conservation strategies that reduce supply fan energy and/or reduce fan operating hours. To evaluate the energy savings potential of any technology, the baseline operating characteristics of the device or system need to be quantified, documented, and based on actual performance. One often overlooked energy consuming component in commercial buildings is the supply air fan found in the ubiquitous commercial rooftop unit (RTU). From a statewide perspective, the operation of RTU supply air fans is of particular interest because the more than one million RTUs in California contribute to associated annual ventilation energy use totaling.9% of statewide commercial building electrical consumption. This compares to the cooling (compressor and condenser fan) annual energy end use estimate of 4.9% []. Supply fan annual energy use is dependent upon average operating hours, which varies widely depending on the facility type, space conditioning loads, comfort preferences, and how the RTU fan is controlled. Although both the RTU compressor(s) and supply fan are controlled by the same thermostat, the thermostat can operate the supply fan independently. The thermostat is set to one of the following settings: Auto where the supply fan cycles with the compressor operator On where the fan operates regardless of compressor operation Programmable thermostats and energy management systems (EMS) may be programmed to operate the fan on a schedule, such as during occupied hours only, to meet building ventilation needs. Therefore, surveying thermostat settings is required to gain understanding of typical operation patterns of RTU supply air fans. Southern California Edison Page

10 BACKGROUND By law, mechanical ventilation is required in all buildings, but a significant percentage of buildings that rely on RTU supply fans for ventilation do not program the fan to provide ventilation during all occupied hours. As a result, ventilation is only provided when the fan is running to satisfy a thermostat call for heating or cooling. Conversely, some fans operate continuously even in unoccupied buildings. Additionally, the average fan power consumed in RTUs is impacted by the fan design and the resistance of its ductwork. It is difficult for a utility program to estimate the energy savings for fan efficiency or fan controls when the baseline run-time and power consumption is unknown. Southern California Edison (SCE) and Western Cooling Efficiency Center (WCEC) searched for existing literature for commercial buildings with which to evaluate and compare supply fan operation, supply fan power consumption, or both. VENTILATION CODE REQUIREMENTS Ventilation design in commercial applications is code-driven and regulated to balance the competing goals of maintaining improved air quality with building energy consumption. California s most recent Building Energy Efficiency Standards (2008) states that occupied spaces in new buildings must be ventilated mechanically one hour before occupancy and during all periods in which the space is usually occupied, with the rate of ventilation varying by use and occupant density [2]. This requirement dates back to California s first version of the Building Energy Efficiency Standards published in 978 [3], which based requirements on the American Society for Heating Refrigeration and Air Conditioning (ASHRAE) standard Regulations in other states vary but most, if not all, are based on the International Code Council s International Mechanical Code, which is based on ASHRAE s current version of the ventilation standard 62., which requires mechanical ventilation in occupied commercial buildings. Southern California Edison Page 2

11 BONNEVILLE POWER ADMINISTRATION RTU PILOT SERVICING PROGRAM The Bonneville Power Administration (BPA) is the federal marketing agent for power to all of the federally owned hydroelectric projects in the Pacific Northwest. The Pacific Northwest (PNW) Regional Technical Forum, through the Regional Rooftop Working Group (RTUG), surveyed and monitored approximately 50 RTUs in the greater Seattle area during the summers of 2009 and 200. Survey data compiled from this literature review included RTU cooling capacity (tons), evaporator fan kw, thermostat settings, and thermostat schedules. The RTUG measured and logged RTU power consumption for at least two weeks before intervention by a servicing program. Power data were reported as average power in hourly increments. A summary sheet and raw power data for each RTU are available on the Internet [4]. It is important to note that the BPA data comes from the greater Seattle area, where ventilation requirements are similar to California s Title 24 regulations for building standards. For example, in Seattle, ventilation is currently required for all occupied spaces, but only during the actual operating hours, not one hour proceeding occupancy, as in the California code. The BPA measured and analyzed evaporator fan power measured on 22 units, as reported on the summary sheet [4]. The service technician measured and reported the fan power when installing the monitoring equipment and again after performing the service on the unit. To be included in this data set, the fan power reading on the first visit had to match the fan power reading on the second visit to within 0% (three data points failed this criterion). The remaining 9 data points were binned by fan power per nominal ton (Figure ). The population mean is estimated as 0.85±0.0 kw/ton with 95% confidence. The following factors affect the fan power: Resistance of ductwork in the distribution system Resistance of air filters Fan and motor efficiency Supply air flow rates The Air-Conditioning, Heating, and Refrigeration Institute s Standard 340/ [5] specifies that, based on nominal tonnage, the calculated fan power should be 365 W per 000 CFM [226 W/m 3 /s] of indoor air circulated for both heating and cooling. At a typical supply fan flow rate of 400 cfm per nominal ton, this is equivalent to 0.5 kw/ton. On average, the surveyed RTU fan power (0.85 kw) consumption is 27% higher than the modeling assumption of 0.5 kw/ton at 400 cfm/ton. This is due to higher airflow rates, greater resistance, or reduced fan/motor efficiencies. Southern California Edison Page 3

12 Percent of Sample Field Survey of RTU Fan Efficiency and Operation Patterns 25% Population mean = 0.85 ± 0.0 kw/ton (95% Confidence) Sample size n=9 20% 5% 0% 5% 0% Measured Evaporator Fan kw per Ton of Rated Cooling FIGURE : RTU EVAPORATOR FAN KW PER TON (BPA STUDY) The most commonly surveyed unit in the BPA study are the 5-ton RTU, followed by 7.5 ton capacity RTUs, as shown in the 8 bin in Figure 2. Eighty percent of units surveyed were 0 ton capacity or less with no correlation between fan power per ton and unit size. Southern California Edison Page 4

13 Percent of Sample Field Survey of RTU Fan Efficiency and Operation Patterns 25% Population mean = 7.94 ± 0.82 tons (95% Confidence) Sample size n=9 20% 5% 0% 5% 0% Rated Tonnage for RTUs Surveyed FIGURE 2: CAPACITY OF SURVEYED RTUS An analysis of the BPA monitoring data from 36 RTUs determined the average number of fan run-hours per day, and whether the fan operated continuously, continuously during occupied hours only, or cycled with the compressor. The fan was considered on when the average power over a one hour monitoring logging interval was observed to be 20-20% of the technician measured fan power. The compressor was considered to be on when the total unit power rose above 20% of the fan only power. This approach will overestimate fan hours, since some short air conditioner cycling intervals will be included in the 20-20% category and be counted as the fan running for an entire hour. Since the service technician changed the operating pattern of the fan for approximately 0% of the units, only the data used before servicing is included in the results. Figure 3 shows that the fan operated continuously to provide ventilation approximately 40% of the time. An analysis of the power data estimated the fan and compressor run-times, and the average fan and compressor run-hours per day for each bin is shown above each bar in Figure 3. For fan run-hours of 20 hours per day or less, fan run-time increases as the average cooling run-time increases. Southern California Edison Page 5

14 Percent of Sample Field Survey of RTU Fan Efficiency and Operation Patterns 45% 40% 35% Sample size n=36 Avg. fan hrs/day=22.7 Avg. comp hrs/day=2.3 30% 25% 20% Avg. fan hrs/day=0. Avg. comp hrs/day=7.0 Avg. fan hrs/day=3.8 Avg. comp hrs/day=7.3 Avg. fan hrs/day=7.9 Avg. comp hrs/day=.3 5% 0% Avg. fan hrs/day=6.2 Avg. comp hrs/day=4.0 5% 0% Fan Run Hours Per Day FIGURE 3: RTU FAN HOURS PER DAY The type of controller for the RTU was recorded for 07 of the RTUs surveyed. The thermostat was a programmable thermostat 73% of the time and an energy management system (EMS) 27% of the time. The study reported no manual thermostats. Setbacks of cooling and heating setpoints were generally reported during unoccupied hours. An initial method was developed to categorize RTU fan operation as shown below: The fan is continuous if it runs 24 hours a day. The fan is occupied if it runs during occupied hours only. The fan is cycling if the fan only runs when there is a call for heating or cooling. The RTUs are categorized by evaluating the power draw of the RTU over the course of a week. This method was subjective, error-prone, and time consuming, so the following rules were developed to sort each RTU into the appropriate category as shown in Table 3: The fan is continuous if the fan is running 90% of the time. The fan is occupied if the compressor run time percentage divided by the fan time percentage is less than 0.75 and the fan runs less than 90% of the time. The fan is cycling if the compressor run time percentage divided by the fan time is at least 0.75 and the fan runs less than 90% of the time. Southern California Edison Page 6

15 While 0.75 may be lower than expected, it is required to account for the difficultly in determining the difference between fan and compressor operation in hourly averaged data. For example, extra fan only hours are in many cases full RTU operation for a partial hour. Selecting 0.75 as the cutoff between cycling and occupied-only use resulted in the closest match to a subjective graphical analysis done previously. Applying these parameters, 40% of the RTU fans surveyed ran continuously, 27% operated only with the compressor when providing cooling, and 33% ran during occupied hours regardless of the cooling state (Figure 4). TABLE 3: RTU FAN CATEGORIZATION SORTING RULES FAN OPERATION CATEGORY EQUATION Continuous: Occupied: Cycling: Southern California Edison Page 7

16 Compressor runtime [%] Field Survey of RTU Fan Efficiency and Operation Patterns 00% 90% 80% 70% cut-off Continuous Occupied Cyclic 60% 50% 40% 30% 20% 0% 0% 0% 0% 20% 30% 40% 50% 60% 70% 80% 90% 00% Fan Runtime [%] FIGURE 4: COMPRESSOR RUNTIME VS. FAN RUNTIME CALIFORNIA COMMERCIAL END-USE SURVEY (CEUS) The California Commercial End-Use Survey of 2003 estimates the magnitude of electricity end-usages in commercial buildings [7]. The survey included a sample of 2,790 commercial facilities from the service areas of Pacific Gas and Electric (PG&E), San Diego Gas & Electric (SDG&E), Southern California Edison (SCE), Southern California Gas Company (SCG), and the Sacramento Municipal Utility District (SMUD). The objective of the study is not specific to RTUs, but several details about RTUs were gathered as part of the survey. Because of privacy concerns, this report is not publicly available, so SCE provided an analysis of the survey data for their service territory only. The CEUS had significantly more classifications for the fan operation than did the BPA study, and classified the fan operation during both occupied and unoccupied hours. Table 4 shows that the sample of 568 RTUs and associated thermostats indicate continuous operation of fans in 9.3% of units and continuous operation during occupied hours in 44.9% of the units. The measured fan hours in the 2003 CEUS study is significantly less than measured during the 2009 BPA Rooftop Unit Servicing Program, with the fan operating less during both occupied and unoccupied Southern California Edison Page 8

17 hours. The CEUS data also shows that programmable thermostats and EMS were significantly less prevalent in 2003 as shown in Table 5. TABLE 4: COMPARISON OF FAN OPERATION IN MULTIPLE STUDIES BPA ROOFTOP UNIT SERVICING (N=33) CEUS 2003 (N=568) Fan Operation Pattern Occupied Hours Unoccupied Hours Occupied Hours Unoccupied Hours Continuous 73% 40% 44.9% 9.3% Cycles 27% 60% 5.5% 3.9% Manual %.6% Off % Night Cycles % Unknown % 5.% TABLE 5: THERMOSTAT OPERATION ( CEUS STUDY) CONTROL TYPE PERCENT OF SAMPLE (N=568) Unknown 9.4 Always On 3.6 EMS 6. Manual 4.4 Programmable 3.3 Time Clock 8. Southern California Edison Page 9

18 SMALL HVAC SYSTEM DESIGN GUIDE The Small HVAC System Design Guide, published by the CEC, evaluated several parameters that effect RTU efficiency, including fan energy consumption [7]. The 2003 report presented average airflow and power measurements for evaporator fans in 79 RTUs in California, a subset of the 25 total units monitored for the study. The average measured airflow was 325 cfm/ton and the average measured fan power was 0.8 kw/ton. This is in agreement with the BPA study from 2009, which suggests that fan power averages are not specific to geography and did not change between 2003 and Southern California Edison Page 0

19 METHODOLOGY The goal of this survey was to collect data relevant to supply fan operation from over 200 thermostats, with a target subset of over 50 on-roof data points. On-roof data includes RTU nameplate information and fan power measurements. Various strategies were developed to gain access to commercial buildings and their roofs. Rooftop data were more difficult to obtain. Permission from the tenant or building owner to access the roof was required. To disaggregate the data collection sample, the team collected data from different types of commercial buildings in northern and southern California, including restaurants, retail stores, small offices, medical facilities, warehouses, and schools. A two-fold approach was undertaken to collect survey sites for the in-building thermostat portion of the project. In southern California, the project team connected with several commercial HVAC contractors that operate in the greater Los Angeles area. The team briefed the contractors on the nature of the work and coordinated the site visits. One of the HVAC contractors cooperated fully and scheduled site visits directly through the dispatch coordinator. Each day, the dispatcher informed the field survey team about the next day s schedule of site visits, which allowed the field survey staff to gain access to the building or rooftop. A key advantage in this strategy was that the field survey staff could gain access to the building and often to the rooftop in coordination with the HVAC service technician. The field survey team also tried this approach with a HVAC contractor in the Sacramento area, but the level of coordination and the availability of appropriate sites resulted in limited opportunities. The Davis Energy Group (DEG) and the Western Cooling Efficiency Center (WCEC) used local contacts in Davis, CA to arrange some on-roof surveys at a commercial office park, City of Davis public buildings, and a city public school. SURVEY PROTOCOL DEG worked with WCEC and SCE to develop a Field Survey Recording form to help the team gather the appropriate data. A copy of this form is in Appendix A. The first page of the form provides space to enter in building characteristics and the second page provides space to enter on-roof data. The in building section of the survey focused on the following: Characterizing the facility by commercial building type Defining the normal occupancy period for the building for each day of the week Documenting thermostat type and model Reviewing thermostat programming (occupied and unoccupied schedule of temperatures, fan scheduling) Assessing any comfort or Indoor Air Quality (IAQ) issues with the building contact (anecdotal information) Southern California Edison Page

20 The on-roof section of the survey focused on the following: Documenting the RTU manufacturer and model number (model number includes nominal cooling capacity information) Documenting the RTU physical characteristics (condenser configuration, number of compressors, presence of economizer, refrigerant type) Documenting supply fan data (nominal horsepower, belt or direct-drive, and measured supply fan kw) Manufacturer model numbers were used to research and document nominal equipment capacities, and then added to the online survey form. Whenever possible, photos were taken to document the building exterior, thermostat, and RTU physical characteristics. Electrical measurements were completed using a Fluke 735 threephase power logger, which is commonly used in conducting energy studies and basic power quality logging. The accuracy of power measurement of the Fluke 735 is specified as.5% of the measured value, not including errors from the current transducers. The current transducers were I5A/50A Clamp PQ4, for which the accuracy varies by the measured current, with the range being 2.5% of measured value below 2.5 amps and 0.5% of the measured value above 25 amps. The completed surveys were uploaded to a GoogleDocs site to allow the project team to access them. SURVEY SCHEDULE Field activities began in late June 202 and continued until late September 202. DEG hired an engineering intern to complete most of the in building survey work and some of the on-roof data. After an initial training period in northern California, the intern completed site surveys in Los Angeles on July 8-3, 202 and on September 4-2, 202. DEG engineering technicians also gathered on-roof data, and then completed all on-roof power measurements. The intern and engineering technicians worked closely with the southern California mechanical contractor to facilitate access to the chosen sites. Southern California Edison Page 2

21 RESULTS To assess the differences between RTU and fan behaviors, the team completed surveys at 98 different sites in different climate zones and sampled 26 RTUs. Not all of RTUs were independently controlled with their own thermostats. Some of the thermostats only displayed the current temperature and the temperature setpoints were programmed in a building management system. In this survey study, there were four different types of programmed RTU operation, and the types and percentages in the sample are summarized in Table 6. TABLE 6: TYPES OF PROGRAMMED RTU OPERATION PROGRAMMED RTU OPERATION TYPE PERCENT OF SAMPLE (N=22) Programmable Thermostat 83.0% Building Management System 9.9% Manual 0.9% Time-Clock 6.% Surveys were also completed in multiple climate zones to provide a preliminary assessment of potential differences between RTU and fan behaviors throughout California. At a subset of the survey sites where occupancy and thermostat data were collected, rooftop access was also provided, allowing for collection of RTU physical data (manufacturer, model number, number of compressors, condenser coil configuration, etc.) and measurement of the supply fan power during operation. This section of the report summarizes the results. Full site tabulations of the data can be found in Appendix B. The team completed site surveys in Los Angeles, Orange, and Riverside in southern California, and Yolo and Solano in northern California. The graphs in this section provide basic descriptive information about the survey sites. Figure 5 shows the total number of sites surveyed in each county. Southern California Edison Page 3

22 Number of Sites Field Survey of RTU Fan Efficiency and Operation Patterns Yolo Los Angeles Orange Riverside Solano County FIGURE 5: SURVEY SITES BY COUNTY Approximately two-thirds of the total sites in northern California are in or around Davis, CA. Within each of these counties, seven main types of commercial buildings are used in this study, including food/liquor, health care, office, restaurant, retail, and school. Miscellaneous commercial sites, such as theaters and automotive repair shops, are included in the study. Figure 6 shows 83% of the survey buildings were retail, restaurant, and office sites. Figure 7 presents the number of in building surveys by building type and location. Fast food restaurants represent close to half of the in building surveys; office and retail sites represent one-third of the building types. Southern California Edison Page 4

23 Number of RTUs County Field Survey of RTU Fan Efficiency and Operation Patterns Yolo Solano 2 Riverside 5 Orange 2 Los Angeles 6 9 Facility Type FIGURE 6: SURVEY SITES BY FACILITY TYPE AND COUNTY Restaurant Office Retail Store Misc School Food/Liquor Health Care Northern CA Southern CA FIGURE 7: NUMBER OF RTU IN BUILDING SURVEYS BY FACILITY TYPE AND REGION Southern California Edison Page 5

24 RTUs/Site Field Survey of RTU Fan Efficiency and Operation Patterns Figure 8 plots the number of RTUs per site surveyed on-roof, by location (N=northern CA, S=southern CA) and building type. Each black dot represents an individual data point; the red dot and line represents the mean value and the standard error of the mean. Interestingly, for each of the facility types, southern California sites always had more RTUs per site than northern California. This could be an artifact of the small dataset. Nameplate data (make and model number) collected during the on-roof survey were researched on the Web to derive nominal equipment capacity (in tons) N = northern California S = southern California Data Point Avg. for Facility Type Error Bars Denote One Standard Error of the Mean FIGURE 8: NUMBER OF RTUS PER SITE BY REGION (N OR S) AND FACILITY TYPE (INDIVIDUAL SITE VALUES SHOWN IN BLACK) Figure 9 provides a breakdown of observed RTU capacities. The majority of the RTUs surveyed were found to be between four and ten tons per RTU, with capacity ranging from 3 to 25 tons. Average capacity for the 5 RTUs was 6.50 tons, with a standard deviation of 3.33 tons. Southern California Edison Page 6

25 Percent of Sample Field Survey of RTU Fan Efficiency and Operation Patterns 40% 35% 30% 25% 20% 5% 0% 5% 0% Rated Tonnage for RTUs Surveyed FIGURE 9: OBSERVED RTU NAMEPLATE NOMINAL CAPACITY Figure 0 and Figure characterize the distribution of thermostats and RTU manufacturers surveyed in the sample. Although Honeywell thermostats were by far the most common (63 observations), the total number of different thermostat manufacturers (22) was greater than anticipated. In terms of RTU manufacturers, Lennox, Trane, and Carrier were the most commonly observed (representing two-thirds of the units), with the remaining one-third comprised of six other manufacturers. Southern California Edison Page 7

26 RTU Manufacturer Thermostat Manufacturer Field Survey of RTU Fan Efficiency and Operation Patterns York White-Rodgers Venstar Totaline TCS Basys Controls Robert Shaw Ritetemp Proliphix Novar Nest Maple Chase LuxPro Lux500 Lux Lennox Johnson Controls Invensys Honeywell Emerson Carrier Braeburn Source Food/Liquor Health Care Misc. Office Restaurant Retail School Total Facility Type FIGURE 0: THERMOSTAT MANUFACTURERS BY FACILITY TYPE York Trane Rheem Lennox Goodman Carrier Bryant BDP 2 2 American Standard Food/Liquor Health Care Misc. Office Restaurant Retail School Total Facility Type FIGURE : RTU MANUFACTURERS BY FACILITY TYPE Southern California Edison Page 8

27 The descriptive data presented up to this point characterizes the sites, building types, RTU characteristics, and thermostat manufacturer. To investigate the energy implications of the supply fan and thermostat control, the data need to be evaluated from a quantitative perspective by defining operational characteristics of the RTU supply fan based on field-observed thermostat programming. Table 7 defines potential fan operation states based upon whether the building is occupied or not, the thermostat is programmed or operated manually, and whether the fan setting is auto or off. For example, continuous fan operation can occur in either occupied or unoccupied conditions, but the thermostat must be scheduled for operation, with the fan set in the on mode. TABLE 7: CHARACTERIZATION OF FAN OPERATIONS IN TERMS OF OCCUPANCY STATE, SYSTEM SETTING, AND FAN SETTING OCCUPANCY STATE SYSTEM SETTING FAN SETTING FAN OPERATION OCCUPIED UNOCCUPIED SCHEDULE MANUAL AUTO ON Continuous Cycles Manual Auto Manual On Off Unknown Similar to the results shown in Table 4: Comparison of fan operation in multiple studies Table 4, Table 8 presents the results, for the six categories, found from the RTU survey data. Figure 2 and Figure 3 summarize the data based on this classification for both occupied periods of the day and unoccupied. The data are categorized by region and facility type with the x-axis label including the total number of sites per category, and the columns denoting the number of sites within each category. Overall, 76 out of 93 sites were found to operate the supply fans continuously during occupancy. During non-occupied periods, 32 of 93 sites were found to have the supply fan cycling in response to cooling operation, with none of the supply fans operating continuously. TABLE 8: FAN OPERATION PATTERNS FOR OCCUPIED AND UNOCCUPIED STATES ROOFTOP UNITS (N=93) FAN OPERATION PATTERN OCCUPIED UNOCCUPIED Continuous 39.4% 32.% Cycles 58.5% 36.3% Off % Unknown 2.% 2.% Southern California Edison Page 9

28 Percent of Sample Percent of Sample Field Survey of RTU Fan Efficiency and Operation Patterns 00% 90% 80% 70% 60% 50% 40% 30% 20% 0% 0% Unknown Manual - On Manual - Auto Cycles Continuous N = northern California S = southern California FIGURE 2: FAN OPERATION CHARACTERISTICS DURING OCCUPANCY BY REGION AND FACILITY TYPE 00% 90% 80% 70% 60% 50% 40% 30% 20% 0% 0% Unknown Cycles Continuous Off N = northern California S = southern California FIGURE 3: FAN OPERATION CHARACTERISTICS DURING NON-OCCUPIED PERIODS BY REGION AND FACILITY TYPE Figure 4 summarizes the hours of fan operation by facility type for the 76 RTUs that operated the supply fans continuously, either with manual or scheduled thermostat control. For manually control thermostat, the number of daily fan operating hours was determined to be equal to the occupancy period of the day; for scheduled RTUs, the fans were assumed to operate 24 hours per day. Southern California Edison Page 20

29 Hours of Fan Operaton Field Survey of RTU Fan Efficiency and Operation Patterns N = northern California S = southern California Data Point Avg. of Facility Type Error Bars Denote One Standard Error of the Mean FIGURE 4: HOURS OF CONTINUOUS FAN OPERATION BY FACILITY TYPE For RTUs that do not operate the supply fans continuously, both the length of the business day and control of the thermostat (manual control vs. programmed cooling setpoints) dictate the number of supply fan operating hours. Figure 5 plots the average number of business hours per business day for each of the facility types in both northern and southern California. Many commercial buildings operate their systems both before and after normal building occupancy times to accommodate unusual schedules, as well as to ensure that the building is conditioned prior to occupancy. Southern California Edison Page 2

30 Hours/Day Field Survey of RTU Fan Efficiency and Operation Patterns N = northern California S = southern California Data Point Avg. for Facility Type Error Bars Denote One Standard Error of the Mean FIGURE 5: THE AVERAGE NUMBER OF BUSINESS HOURS PER BUSINESS DAY BY FACILITY TYPE The following series of graphs explore the thermostat programming in terms of variations in cooling setpoints during occupied and unoccupied periods by facility type and location. There are three different kinds of temperature and occupancy schedules as follows: Manual (M): A manual cooling schedule is the result of the varying comfort level of the business or the limitations of the thermostat, i.e. non-programmable. When a thermostat is turned on, set, and adjusted while the business is occupied, it is assumed that cooling is on during normal business hours only. This assumption is made because there is no way to determine whether business operators, with manually operated cooling, habitually turn off or increase the temperature set-point to prevent unnecessary cooling during unoccupied hours. Daily (D): A daily cooling schedule is programmed in the thermostat and can vary on an hourly basis throughout the day. Weekly (W): A weekly cooling schedule is programmed in the thermostat and can vary on an hourly and daily basis. It was important to note that thermostat and cooling programs could be overridden by the end user at any point in time, which introduced error into the analysis. Figure 6 plots the ratio of actual conditioned hours divided by occupied hours for each of the building types. A value of.0 would suggest space conditioning only occurring during occupied periods. Values less than.0 represent facilities where the cooling system is only enabled (by schedule or manually) for a fraction of the full day. Values greater than.0 indicate extended conditioning hours. Southern California Edison Page 22

31 Ratio Field Survey of RTU Fan Efficiency and Operation Patterns D = Daily, M = Manual, W = Weekly N = northern CA, S = southern CA Data Point Avg. Ratio Error Bars Denote One Standard Error of the Mean FIGURE 6: RATIO OF AVERAGE DAILY AVAILABLE COOLING HOURS TO BUSINESS OCCUPANCY HOURS Supply fan power readings allowed the characterization of fan energy use according to a kw/nominal ton metric, based on the RTU nameplate data. Supply fans are either belt-drive or direct-drive, so additional disaggregation was warranted. Figure 7 shows the range of measured fan power per nominal ton, depending on the drive method. On average, the beltdrive supply fans draw 0.54 kw/ton (standard error of the mean of kw/ton) and the direct-drive supply fans drew 0.39 kw/ton (standard error of the mean of kw/ton). Although the minimum power per ton measurements are close for the two drive methods, the maximum measurements differ significantly. This difference could be due to properties other than the motor, such as a high resistance distribution system, dirty air filters, etc. Figure 8 plots belt-drive and direct-drive fan kw/ton, as a function of RTU capacity (tons) and Table 9 provides similar data in a tabular form. For the sample of units surveyed, the direct-drive fans are limited to RTUs of 5 tons or less, representing 58% of the surveyed RTUs in the <= 5 ton size range. For both drive types, Table 9 shows almost no trend. It appears that the fan kw/ton remains constant except for the 8.5 tonnage data. However, given there are only two 8.5 ton belt-drive datapoints, there is no statistical basis to indicate a trend without further data. The limited sample of larger RTUs (0 tons and greater) also does not suggest a clear trend in the larger sized units. Due to the limited numbers of RTU data points that have both tonnage and fan power readings, it is difficult to determine with adequate certainty if there is a valid correlation between average fan power per ton and RTU tonnage. Further study in this area is warranted to determine if units in the 5 to 0 size range might be preferred candidates for potential fan efficiency measure strategies. Southern California Edison Page 23

32 kw/ton kw/ton Field Survey of RTU Fan Efficiency and Operation Patterns Belt Direct Data Point Avg. for Drive Type Error Bars Denote One Standard Error of the Mean FIGURE 7: MEASURED SUPPLY FAN KW/TON BY SITE Belt Direct Tonnage FIGURE 8: FAN POWER PER TON BY DRIVE TYPE VERSUS RTU TONNAGE Southern California Edison Page 24

33 TABLE 9: AVERAGE FAN POWER PER TON BY DRIVE TYPE AND RTU TONNAGE BELT DIRECT CAPACITY (TONS) COUNT AVERAGE [KW/TON] COUNT AVERAGE [KW/TON] Another investigation examined the variation in fan power measurements at different facilities and regions. The fan power per ton was categorized into the seven facility types and then further filtered for northern and southern California. In Figure 9, individual data points are plotted as open circles, the mean is shown with a solid red circle, and the error bars represent the standard error of the mean. For this limited dataset, surveyed southern California restaurant sites demonstrated a higher kw/ton than other facility types. This observation, although anecdotal at best, is indicative for the need for further study. Southern California Edison Page 25

34 kw/ton Field Survey of RTU Fan Efficiency and Operation Patterns N = northern California S = southern California Data Point Avg. for Facility Type Error Bars Denote One Standard Error of the Mean FIGURE 9: MEASURED SUPPLY FAN KW/TON BY REGION AND FACILITY TYPE The thermostat setpoints during the occupied and unoccupied periods for each facility type, location, and thermostat type (M, D, or W) are shown in Figure 20 and Figure 2, respectively. As seen in Figure 20, some of the designated daily and weekly schedules appear to be inaccurate. Because these survey data were collected throughout the summer, it is reasonable to expect that very few commercial businesses would be maintaining setpoints during occupied periods at temperatures above 78 F, let alone 80 F. It was observed that of the 36 thermostat schedules, 25 may well have been programmed incorrectly. Incorrect was defined as irregular temperature setpoints and schedules or abnormally high temperature setpoints, such as a thermostat programmed with lower cooling setpoints in the middle of the night, and higher setpoints during normal mid-day occupancy periods. Many of these thermostats were operated manually, apparently indicating that the building occupants were not able to correctly program the thermostat. For example, if a cooling setpoint steadily decreases to 72 F, jumps to a setpoint of 80 F for fifty minutes, and then returns to 72 F, the schedule is not programmed properly. Conversely, in Figure 2, it is not practical for some of the businesses to cool the conditioned space during unoccupied hours. For instance, some of the restaurants, offices, and schools were operating their air conditioning systems to maintain temperature setpoints below 75 F during unoccupied periods. The extreme case of cooling during unoccupied period was one of the northern California offices that had a daily unoccupied setpoint of One particular bar/restaurant establishment did have a corroborated mid-day setpoint of 80 F. They operated numerous ceiling fans in lieu of lower cooling setpoints for much of the day. Later at night when occupancy increased, the setpoints were lowered. Southern California Edison Page 26

35 Temperature [F] Temperature [F] Field Survey of RTU Fan Efficiency and Operation Patterns 62 F. This facility can save energy by reprogramming the thermostat or at least turning it off while the facility is unoccupied. This may also work for other sites D = Daily, M = Manual, W = Weekly N = northern CA, S = southern CA Data Point Avg. Setpoint Error Bars Denote One Standard Error of the Mean FIGURE 20: INDIVIDUAL SITE OCCUPIED THERMOSTAT SETPOINTS (BY REGION-FACILITY-SCHEDULE TYPE) D=Daily, M=Manual, W=Weekly N = northern CA, S = southern CA Data Point Avg. Setpoint Error Bars Denote One Standard Error of the Mean FIGURE 2: INDIVIDUAL SITE UNOCCUPIED THERMOSTAT SETPOINTS IN BLACK (BY REGION-FACILITY-SCHEDULE TYPE) Southern California Edison Page 27

36 DISCUSSION The survey results indicated that the supply fans ran continuously of 40% of packaged RTUs serving commercial buildings. The other 60% cycled with calls for cooling or heating. In one-third of the surveyed units, the supply fan operated continuously during unoccupied hours, another 36% of the fans cycled during unoccupied hours, and the remainder of the fans were set to off. While these proportions varied by building type, the sample sizes for each building type were not sufficiently large to make more detailed conclusions. Measured supply fan power in this survey was slightly lower than results from previous studies. Table 0 compares the results of this study with those of previous works. Directdrive supply fans were found to have a lower demand per nominal ton than belt-drive supply fans. However, direct-drive fans were not observed in RTUs above 5 tons nominal capacity. TABLE 0: SUPPLY FAN POWER DENSITY STUDY FAN POWER DENSITY (KW/NOMINAL TON) SCE Survey 0.5 Bonneville Power Administration RTU Pilot Servicing Program 0.8 CEC Small HVAC System Design Guide 0.8 Observations from the field survey team provide additional insights into how commercial building owners and occupants interact with their RTU. The surveyed sites include a range of building occupants including restaurant franchises, owner-occupied commercial sites, tenant-occupied sites, and public buildings. The best-maintained and operated RTUs tended to be those owned by a city, public entity, or larger organizations that have an institutional focus on maintenance, as well as the financial allocation in the budget for regular upkeep. Typically, the larger commercial sites need to manage and regularly schedule RTU maintenance because of the sheer number of the systems and all the potential issues that can arise. These larger operations also tended to control and monitor unit operation remotely through building management systems and are therefore were better equipped to quickly identify and fix performance problems. Among owner-occupied establishments, there was a perceived wide range of understanding about how the RTU is controlled and maintained. Some people were very much in tune with both the RTU and control settings, while others were not. For the tenant-occupied establishments, the landlord or property management company generally handles maintenance issues and the tenants often have little knowledge about the process. The feedback from the field suggests that some landlords seem to monitor and maintain RTUs regularly, while others only fix issues when there are significant complaints from the employees or clientele. In the latter category, some of the RTUs on older buildings had been repaired repeatedly to the point of being barely serviceable. Southern California Edison Page 28

37 A fair number of people interviewed on-site were not aware how the thermostats in their establishment were set up. This was most true for tenant-occupied buildings. Examples included verbal reporting of fan settings or cooling setpoints that didn t match reality, e.g. employees stating the fan is set to Auto not On, and the fan setting (on the thermostat) was found to be set to On. Another example was one employee would state that the system is not programmed, while a second employee stated that the system does have a program. Despite seeing a large number of newer, programmable thermostats, most were not programmed at all or were programmed incorrectly. In many of these cases it looked as though someone had tried programming the thermostat but either gave up or decided to run the system manually. Among the smaller business establishments surveyed, the majority used their thermostats as on/off switches, turning them to Auto when they started to feel warm (often around 2- PM) and then switching them to Off at the end of the business day. Southern California Edison Page 29