EVALUATING THE EFFECTS OF COMMON FAULTS ON A RESIDENTIAL SPLIT SYSTEM

Transcription

1 Design & Engineering Services EVALUATING THE EFFECTS OF COMMON FAULTS ON A RESIDENTIAL SPLIT SYSTEM Report Prepared by: Design & Engineering Services Customer Service Business Unit Southern California Edison July 2012

2 Acknowledgements Southern California Edison s (SCE s) Design & Engineering Services (DES) group is responsible for this project. It was developed as part of Southern California Edison s HVAC Technologies and System Diagnostics Advocacy (HTSDA) program under internal project number. DES project manager Sean Gouw conducted this assessment with overall guidance and management from line manager Ramin Faramarzi, and HTSDA program manager Jerine Ahmed. For more information on this project, contact sean.gouw@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 ii

3 EXECUTIVE SUMMARY The goal of this project () is to quantify the impacts of common single or multiple faults on a typical residential split air conditioning system in a laboratory setting. Residential air conditioning maintenance is a commonly overlooked service. As a result, a variety of faults presents themselves in air conditioners throughout California homes. These faults pose considerable strain on the economics of Southern California Edison (SCE) customers, and add to the ever-increasing demands on the electrical grid. Residential Heating, Ventilating, and Air Conditioning (HVAC) equipment in California accounts for 9 billion kilowatt-hours (kwh): or roughly, 10 of the energy consumed by California homes. 1 Residential HVAC also accounts for approximately 24 of the peak demand in California. 2 For all central air conditioners used by homes in California, nearly half are over 10 years old. 1 At least 10 of energy consumed by HVAC equipment is expended from excessive run time, poorly maintained equipment, and controls problems. 3 Current residential HVAC maintenance practices face many challenges and opportunities for enhancement. Traditionally, these practices are open to varying interpretations and are reactive in nature. Homeowners typically do not have maintenance contracts established for regular servicing of their HVAC equipment. Homeowners usually call in for maintenance after their equipment fails. HVAC service contractors are then placed in reactionary situations, requiring them to assess and resolve issues chaotically and rapidly. Often, current repair and maintenance practices are not necessarily aimed at bringing HVAC equipment back up to optimum efficiency levels. In addition, variables influencing HVAC performance (equipment type, faults, indoor/outdoor conditions, etc.) are largely uncontrollable in the field and present their own unique challenges for accurately assessing and resolving maintenance issues. Given these challenges, a laboratory test environment offers a viable and controlled means for providing a better understanding of the impacts of various faults. Using the test method developed in a concurrent project (HT.11.SCE.003, Development of a Fault Detection and Diagnostics Laboratory Test Method for a Residential Split System ), a series of faults were imposed on a 3-ton residential split system air conditioner. Forty-nine single and multiple fault test scenarios were conducted. Test results revealed the following general trends: All faults under steady-state conditions demonstrated significant performance degradation o The following single-faults produced the highest measured steady-state impacts: Low charge Up to 61 efficiency degradation 1 EIA Residential Energy Consumption Survey (RECS) HVAC Energy Efficiency Maintenance Study 3 Advanced Automated HVAC Fault Detection and Diagnostics Commercialization Program. Southern California Edison Page iii

4 o Up to 65 gross cooling capacity degradation Condenser airflow reduction Up to 40 efficiency degradation Up to 21 gross cooling capacity degradation The following multiple-fault test scenarios produced the highest measured steady-state impacts: Low charge and non-condensables Up to 95 efficiency degradation Up to 96 gross cooling capacity degradation Low charge and condenser airflow reduction Up to 92 efficiency degradation Up to 89 gross cooling capacity degradation Extreme cooling capacity and efficiency degradations were realized in the most severe instance of the low charge and non-condensables multiple-fault test scenario, the most severe instance of the low charge and condenser airflow reduction multiple-fault test scenario, and the most severe instance of the low charge, evaporator and condenser airflow reduction multiple-fault test scenario. It may not be reasonable to assume these as realistic scenarios of maintenance mal-practice that would go unnoticed in the field. The findings from this project are expected to provide a better understanding of fault impact potential, in terms of steady-state HVAC performance, efficiency, and how and which key operating parameters shift in the wake of controlled, imposed faults. All faults in this scope demonstrated significant potential for inducing cooling performance and efficiency penalties, some with greater potential. However, this laboratory data cannot speak to transient impacts, or the prevalence and severity of faults actually experienced by HVAC equipment in the field. Additional laboratory testing is needed to understand the transient impacts of faults. These tests should analyze transient impacts and compare them to steady-state impacts. Any additional test burden associated with transient testing should be quantified and compared with that of steady state testing. All current and future laboratory efforts should be verified and calibrated with fault prevalence and severity data obtained from field studies. In addition, future laboratory investigation is needed to quantify any differences in fault impacts on different types of residential HVAC equipment. Because of the burden associated with testing all of the vast number of different HVAC makes/models available, field efforts are needed to prioritize equipment types of interest. Field investigation is also needed to determine what physical characteristics are prevalent and substantial enough to warrant additional laboratory testing (expansion device type, refrigerant type, etc.). Southern California Edison Page iv

5 ABBREVIATIONS AND ACRONYMS AFDD AHRI AMB ANSI ASHRAE BACnet Btu CASE CI COA CT CZ DB DES DP EE EER EI ET ETO Automated Fault Detection and Diagnostics The Air Conditioning, Heating and Refrigeration Institute Ambient American National Standards Institute The American Society of Heating, Refrigerating and Air Conditioning Engineers Building Automation and Control Networks (Communications Protocol) British Thermal Unit Codes and Standards Enhancement Capacity Index Condensing (temperature) Over Ambient Condensing Temperature Climate Zone Dry-Bulb Temperature Design and Engineering Services Dew Point Energy Efficiency Energy Efficiency Ratio Efficiency Index Evaporator Temperature (Saturated) Education, Training, and Outreach F Degrees Fahrenheit FDD Fault Detection and Diagnostics Southern California Edison Page v

6 hr HTSDA HVAC ID ITD kw kwh lbs. ozs. LP LT N 2 OD PDA PIER Psi Hour HVAC Technologies and System Diagnostics Advocacy Heating, Ventilating, and Air Conditioning Indoor Indoor Temperature Drop Kilowatt Kilowatt-hour(s) Pounds Ounces Liquid Pressure Liquid Temperature Nitrogen Outdoor Personal Digital Assistant Public Interest Energy Research Pounds per square inch R Degrees Rankine RA RH RTU RWB SA SC SCE SCFM Return Air Relative Humidity Rooftop Unit (Packaged) Return Wet-Bulb Supply Air Sub-cooling Southern California Edison Standard Cubic Feet per Minute Southern California Edison Page vi

7 SH SME SP ST SWB TAG TR TTC TxV T/C W WB WHPA Superheat Subject Matter Expert Suction Pressure Suction Temperature Supply Wet-Bulb Technical Advisory Group Ton of Refrigeration Technology Test Center Thermostatic Expansion Valve Thermocouple Watt Wet-Bulb Temperature Western HVAC Performance Alliance Southern California Edison Page vii

8 CONTENTS EXECUTIVE SUMMARY III INTRODUCTION 1 The FDD Project Series... 1 Industry Input... 1 The Technical Advisory Group... 2 Problem Definition... 3 BACKGROUND 4 Fault Detection and Diagnostics... 4 anticipated barriers to adoption of FDD... 4 ASSESSMENT OBJECTIVES 6 TECHNOLOGY: THE HVAC TEST UNIT 7 TECHNICAL APPROACH/TEST METHODOLOGY 8 Calculations Test Scenarios RESULTS: THE IMPACTS OF IMPOSED FAULTS ON HVAC PERFORMANCE 19 Fault Impact Summary Baseline Performance Single Fault: Low Refrigerant Charge Single Fault: High Refrigerant Charge Single Fault: Liquid Line Restrictions Single Fault: Non-Condensables Single Fault: Evaporator Airflow Reduction Single Fault: Condenser Airflow Reduction Multiple Faults: Low Charge and Non-Condensables Multiple Faults: High Charge and Evaporator Airflow Reduction Multiple Faults: Evaporator and Condenser Heat Transfer Reductions Multiple Faults: Low Charge and Evaporator Airflow Reduction Multiple Faults: Low Charge and Condenser Airflow Reductions Southern California Edison Page viii

9 Multiple Faults: Low Charge, Evaporator and Condenser Airflow Reductions CONCLUSIONS AND RECOMMENDATIONS 50 APPENDIX A: ADDITIONAL PARAMETERS 51 Single Fault: Low Refrigerant Charge Single Fault: High Refrigerant Charge Single Fault: Refrigerant Line Restrictions Single Fault: Non-Condensables Single Fault: Evaporator Airflow Reduction Single Fault: Condenser Airflow Reduction Multiple Faults: Low Charge and Non-Condensables Multiple Faults: Evaporator and Condenser Airflow Reductions Multiple Faults: High Charge and Evaporator Airflow Reduction Multiple Faults: Low Charge and Evaporator Airflow Reduction Multiple Faults: Low Charge and Condenser Airflow Reductions Multiple Faults: Low Charge, Evaporator and Condenser Airflow Reductions APPENDIX B: PERFORMANCE AT VARYING INDOOR AND OUTDOOR TEST CHAMBER CONDITIONS 73 APPENDIX C: CALCULATION METHOD SUMMARY 77 REFERENCES 79 Southern California Edison Page ix

10 FIGURES Figure 1. Age of Central Air-Conditioners in California... 3 Figure 2. HVAC Test Unit - Indoor Unit (Left), Outdoor Condensing Unit (Right)... 7 Figure 3. Refrigerant-Side State Points... 8 Figure 4. Air-side State Points... 9 Figure 5. Low Charge Single-Fault Impacts Figure 6. High Charge Single-Fault Impacts Figure 7. Liquid Line Restriction Single-Fault Impacts Figure 8. Non-Condensables Single-Fault Impacts Figure 9. Evaporator Airflow Reduction Single-Fault Impacts Figure 10. Condenser Airflow Reduction Single-Fault Impacts Figure 11. Low Charge and Non-Condensables Multiple-Fault Impacts Figure 12. Evaporator and Condenser Airflow Reduction Multiple- Fault Impacts and High Charge and Evaporator Airflow Reduction Multiple-Fault Impacts Figure 13. Low Charge, Evaporator and Condenser Airflow Reduction Multiple-Fault Impact Figure 14. P-H Diagram: No-Fault Baselines Figure 15. P-H Diagram: High Refrigerant Charge Faults at AHRI Conditions Figure 16. High Refrigerant Charge Faults at two Non-AHRI Conditions Figure 17. Evaporator Airflow Reductions at AHRI Conditions Figure 18. Evaporator Airflow Reductions at two Non-AHRI Conditions Figure 19. Condenser Airflow Reductions at AHRI Conditions Figure 20. Condenser Airflow Reductions at two Non-AHRI Conditions Figure 21. Evaporator and Condenser Airflow Reductions at AHRI Conditions Figure 22. High Charge and Evaporator Airflow Reduction at AHRI Conditions Southern California Edison Page x

11 TABLES Table 1. Calculation Methods Table 2. Baseline, No-Fault Test Scenarios Table 3. Single-Fault Test Scenarios Table 4. Multiple-Fault Test Scenarios Table 5. Table 6. Summary of Key Parameters Range of Percent Differences from Baseline, Tested at AHRI Conditions Summary of Key Parameters Range of Percent Differences from Baseline, Tested at non-ahri Conditions Table 7. Baseline Parameters Measurement Averages Table 8. Low Refrigerant Charge at AHRI Conditions Measurement Averages Table 9. Low Refrigerant Charge at Non-AHRI Conditions Measurement Averages Table 10. High Refrigerant Charge at AHRI Conditions Measurement Averages Table 11. High Refrigerant Charge at Non-AHRI Conditions Measurement Averages Table 12. Refrigerant Line Restrictions at AHRI Condition Measurement Averages Table 13. Refrigerant Line Restrictions at Non-AHRI Conditions Measurement Averages Table 14. Non-Condensables at AHRI Conditions Measurement Averages Table 15. Non-Condensables at Non-AHRI Conditions Measurement Averages Table 16. Evaporator Airflow Reductions at AHRI Conditions Measurement Averages Table 17. Evaporator Airflow Reductions at Non-AHRI Conditions Measurement Averages Table 18. Condenser Airflow Reductions at AHRI Conditions Measurement Averages Table 19. Condenser Airflow Reductions at Non-AHRI Conditions Measurement Averages Table 20. Table 21. Table 22. Evaporator and Condenser Airflow Reductions at AHRI Conditions Measurement Averages High Charge and Evaporator Airflow Reduction at AHRI Conditions Measurement Averages Evaporator and Condenser Airflow Reductions at AHRI Conditions Measurement Averages Southern California Edison Page xi

12 Table 23. Table 24. Table 25. Low Charge and Evaporator Airflow Reductions at AHRI Conditions Measurement Averages Low Charge and Condenser Airflow Reductions at AHRI Conditions Measurement Averages Low Charge, Evaporator and Airflow Reductions at AHRI Conditions Measurement Averages Table 26. Baseline Parameters Measurement Averages Table 27. Low Refrigerant Charge at AHRI Conditions Measurement Averages Table 28. Low Refrigerant Charge at Non-AHRI Conditions Measurement Averages Table 29. High Refrigerant Charge at AHRI Conditions Measurement Averages Table 30. High Refrigerant Charge at Non-AHRI Conditions Measurement Averages Table 31. Refrigerant Line Restrictions at AHRI Conditions Measurement Averages Table 32. Refrigerant Line Restrictions at Non-AHRI Conditions Measurement Averages Table 33. Non-Condensables at AHRI Condition Measurement Averages Table 34. Non-Condensables at Non-AHRI Conditions Measurement Averages Table 35. Evaporator Airflow Reductions at AHRI Conditions Measurement Averages Table 36. Evaporator Airflow Reductions at Non-AHRI Conditions Measurement Averages Table 37. Condenser Airflow Reductions at AHRI Conditions Measurement Averages Table 38. Condenser Airflow Reductions at Non-AHRI Conditions Measurement Averages Table 39. Table 40. Table 41. Table 42. Table 43. Table 44. Evaporator and Condenser Airflow Reductions at AHRI Conditions Measurement Averages Evaporator and Condenser Airflow Reductions at AHRI Condition Measurement Averages High Charge and Evaporator Airflow Reduction at AHRI Conditions Measurement Averages Low Charge and Evaporator Airflow Reductions at AHRI Conditions Measurement Averages Low Charge and Condenser Airflow Reductions at AHRI Conditions Measurement Averages Low Charge, Evaporator and Airflow Reductions at AHRI Conditions Measurement Averages Southern California Edison Page xii

13 Table 45. Table 46. Table 47. Table 48. Table 49. Performance at Varying Test Chamber Conditions Test 1-5 Measurement Averages Performance at Varying Test Chamber Conditions Test 6-9 Measurement Averages Performance at Varying Test Chamber Conditions Test 1-5 Measurement Averages of Additional Parameters Performance at Varying Test Chamber Conditions Test 6-9 Measurement Averages of Additional Parameters Cont d Summary: Applicable Calculation Methods Per Test Scenario EQUATIONS Equation 1. Energy Efficiency Ratio Equation 2. Refrigerant-Side Gross Cooling Capacity Equation 3. Refrigerant-Side Condenser Heat Rejection Equation 4. Refrigerant-Regression Condenser Heat Rejection Equation 5. Calculating Percent Variation Equation 6. Calculating Percent Difference Equation 7. Air-Side Gross Cooling Capacity Equation 8. Air-Side Gross Sensible Cooling Capacity Equation 9. Air-Side Gross Latent Cooling Capacity Equation 10. Air-Side Air Flow Rate Equation 11. Heat Rejection Southern California Edison Page xiii

14 INTRODUCTION THE FDD PROJECT SERIES Southern California Edison (SCE) initiated a series of six projects under the Heating, Ventilating, and Air Conditioning (HVAC) Technologies and System Diagnostics Advocacy (HTSDA) program. These projects explore many key efforts necessary to evaluate Fault Detection and Diagnostics (FDD) technologies as viable solutions for reducing energy and demand consumption in California homes. HT.11.SCE Development of a Fault Detection and Diagnostics Laboratory Test Method for a Commercial Packaged Unit HT.11.SCE Development of a Fault Detection and Diagnostics Laboratory Test Method for a Residential Split System HT.11.SCE Laboratory Assessment of Retrofit Fault Detection and Diagnostics Tools on a Packaged Unit HT.11.SCE Laboratory Assessment of Retrofit Fault Detection and Diagnostics Tools on a Residential Split System HT.11.SCE Evaluating the Effects of Common Faults on a Commercial Packaged Unit - Evaluating the Effects of Common Faults on a Residential Split System (this report) Projects HT.11.SCE.003, HT.11.SCE.005, and focus on a residential split system air conditioner application. Projects HT.11.SCE.002, HT.11.SCE.004, and HT.11.SCE.006 focus on a small commercial packaged rooftop unit (RTU) air conditioner application. For the specific application, the three projects work together cohesively to: Develop a working laboratory test method Apply the working test method in a laboratory assessment project Update the working test method, as concurrent with lessons learned in the laboratory assessment Use the data from the laboratory assessment to: o o Report on FDD performance Report on observed effects of faults INDUSTRY INPUT Industry input was important during development and scoping of the residential FDD project series. Channels such as the Western HVAC Performance Alliance (WHPA) provided the means to collect this input. In particular, the WHPA s Automated Fault Detection and Diagnostics (AFDD) subcommittee played an important role in the realization of the FDD project series. Southern California Edison Page 1

15 Involvement with the AFDD subcommittee included frequent updates of concurrent FDD-related efforts. One such effort was a Codes and Standards Enhancement (CASE) study AFDD proposal for Title-24. Part of this effort included listing of the highest priority faults for the CASE proposal to explore. This list, presented and vetted through the AFDD subcommittee, became the basis of the scope of faults the FDD project series would explore. The following scope of faults was established for the FDD project series: 1. Low Refrigerant Charge 2. High Refrigerant Charge 3. Refrigerant Liquid Line Restrictions 4. Refrigerant Non-condensables 5. Evaporator Airflow Reduction 6. Condenser Airflow Reduction THE TECHNICAL ADVISORY GROUP A technical advisory group (TAG) was established to provide support with specialized HVAC and FDD industry expertise. Specifically, feedback was sought regarding the test method and the scope of test scenarios to explore. When establishing the TAG, efforts were made to include as wide a range of participants as possible. This included outreach to industry members from California utilities, academia, and FDD and HVAC manufacturers: The Western Cooling Efficiency Center (WCEC), New Buildings Institute (NBI), Portland Energy Conservation Inc. (PECI), National Institute of Standards and Technology (NIST), Climacheck, Field Diagnostics, Pacific Gas and Electric Company (PG&E), Carrier, Purdue, Pacific Northwest National Laboratory (PNNL), Sempra, Taylor Engineering, and the University of Nebraska. Several TAG members were also active attendees and participants of the WHPA AFDD subcommittee meetings. TAG communication occurred through , phone calls, discussion in WHPA AFDD subcommittee meetings, and through a test-methodstrategy-focused webinar conducted on August 22, Through these means, solicited TAG feedback was obtained prior to conducting the laboratory assessment. Southern California Edison Page 2

16 Central Air Conditioners in California (Millions) Evaluating the Effects of Common Faults on a Residential Split System PROBLEM DEFINITION California homes consume approximately 85 billion kilowatt-hours (kwh) of electricity annually. 4 Of this, air conditioning equipment accounts for 9 billion kwh, or around At least 10 of energy consumed by HVAC is expended from excessive run time, poorly maintained equipment and controls problems. 5 Residential HVAC units also account for approximately 24 of the peak demand in California. 6 For all central air conditioners in California, nearly half are over 10 years old. 4 Figure 1 illustrates the age of residential central air conditioners in California ( < 2 Years ) ( 2-4 Years ) ( 5-9 Years ) ( Years ) ( 20 Years ) ( Don't Know ) FIGURE 1. AGE OF CENTRAL AIR-CONDITIONERS IN CALIFORNIA Current HVAC maintenance practices face many hurdles and opportunities for enhancement. Traditionally, these practices are open to varying interpretations and are reactive in nature. Homeowners typically do not have maintenance contracts established for regular servicing of their HVAC equipment. Homeowners typically call in for maintenance after their equipment fails. In this manner, repair and maintenance is not necessarily aimed at emphasizing optimization of equipment efficiency. 4 EIA Residential Energy Consumption Survey (RECS) c15.6.pdf 5 Advanced Automated HVAC Fault Detection and Diagnostics Commercialization Program. 6 HVAC Energy Efficiency Maintenance Study. Southern California Edison Page 3

17 BACKGROUND FAULT DETECTION AND DIAGNOSTICS FDD technologies interpret parameters to detect symptoms of a faulty operating state, and diagnose its root cause(s). FDD technologies may be classified as onboard (built-in or long-term retrofit), or in-field (used during equipment servicing) devices. FDD technologies have enormous potential to enhance the future of energy efficiency. FDD can provide the information necessary to accurately and reliably understand HVAC equipment performance, and improve HVAC maintenance through preventative strategies. Ideally, the FDD process would be implemented in an automated fashion: FDD technologies would be outfitted for long-term use with HVAC equipment, and have a means for remote connectivity. This would enable these technologies to actively inform building operators, homeowners, or service contractors, and solicit corrective actions before faults become severe or before critical failures occur. It is important to make a distinction between faults and failures. An HVAC unit may still operate under a fault condition, albeit with reduced efficiency and/or performance. Conversely, failure modes prohibit an HVAC unit from operating at all. It is anticipated that most benefits of FDD are realized through remediation of fault modes rather than failure modes. Failure modes are typically reacted to and resolved regardless of the presence of FDD technologies. ANTICIPATED BARRIERS TO ADOPTION OF FDD Cost Effectiveness Cost effectiveness depends upon the difference between the cost of the FDD technology, and the realized HVAC operating cost reductions. Realizing operating cost reductions is not as straightforward with FDD as it is with other widget-based technologies. Savings are dependent on: 1. Which faults occur in the HVAC system 2. Which faults are detected and diagnosed 3. Which faults are actively corrected 4. The financial impacts unique to the HVAC owner and application Product Availability and Performance - The range of commercially available onboard FDD products is very limited and only a handful of retrofit FDD products and in-field tools are available. Currently, industry lacks standardized methodologies for both evaluating FDD products and simulating common maintenance faults. As a result, there is a limited understanding regarding how well FDD devices perform. In addition, without a standardized method, it is challenging to make comparisons between existing studies exploring the impacts of common HVAC faults. As a result, the impacts of HVAC faults are not well understood, especially in scenarios that consist of multiple simultaneous faults. Southern California Edison Page 4

18 FDD and the Human Element One potential benefit of FDD technologies is the removal of uncertainties regarding varying human interpretation/diagnostics. However, one must consider that there potentially may not be suitable technological replacements for the creative/critical thinking abilities inherent with manual analysis of complex problems. The level of human involvement appropriate for HVAC FDD in a given application remains to be explored through continuing evaluations of FDD technologies and the impacts of common faults. Southern California Edison Page 5

19 ASSESSMENT OBJECTIVES The objective of this project is to use the data from the laboratory assessment conducted in project HT.11.SCE.005 (evaluation of the performance of a commercially available FDD technology for a residential split system air conditioner), to quantify the performance impacts of common HVAC faults on a typical split system air conditioner. This project seeks to inform Southern California Edison s (SCEs) Energy Efficiency Programs, as well as other developing FDD related efforts such as Codes and Standards Enhancement (CASE) studies for the California Code of Regulations, or the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). Southern California Edison Page 6

20 TECHNOLOGY: THE HVAC TEST UNIT The HVAC test unit is a 3-ton (nominal) residential split system air conditioner, manufactured by Trane. This air conditioner setup consists of one indoor unit (cooling coil: 4TXC B042BC3HCAA, and furnace TUD1B080A9361A ), paired to an outdoor condensing unit (XR80, 4TTB3 036D1000AA). The indoor unit furnace was not used for the laboratory assessment. The test unit is a fixed capacity setup (fixed-speed fans and compressor) that uses R-410a refrigerant and features a thermostatic expansion valve (TxV). FIGURE 2. HVAC TEST UNIT - INDOOR UNIT (LEFT), OUTDOOR CONDENSING UNIT (RIGHT) Various residential HVAC units exist in the field, comprising a number of different possible physical configurations. This unit is just one possible configuration. It represents a standard efficiency unit, relevant to the current generation of products that will be aging. Other options to explore may include (but are not limited to) those which feature R-22 refrigerant, fixed orifice expansion devices, or higher efficiency units (larger heat exchangers, more efficient compressors, fans, etc.). Ultimately, field studies are needed to best characterize the various equipment types, and inform about what is most prevalent in the field. Southern California Edison Page 7

21 TECHNICAL APPROACH/TEST METHODOLOGY Figure 3 illustrates the refrigerant-side state points used in the laboratory tests. Refrigerant Mass Flow Meter R6 R5 Condenser Condensing Unit R4 Liquid Line Restriction Valve TxV R7 Evaporator Compressor R3 R2 (R8) R1 FIGURE 3. REFRIGERANT-SIDE STATE POINTS The following measurements are available at each refrigerant-side state point: R1, Evaporator Outlet Pressure, Temperature R2, Condensing Unit Inlet Pressure, Temperature R3, Compressor Inlet Temperature R4, Compressor Outlet Pressure, Temperature R5, Condenser Outlet Pressure, Temperature R6, Mass Flow Meter Inlet Pressure, Temperature R7, TxV Inlet Pressure, Temperature Enthalpies are calculated at R1, R3, R4, R5, and R7. No measurements exist at state point R8, but this state point is assumed to have the same enthalpy as state point R7. Refrigerant mass flow is measured near state point R6. Southern California Edison Page 8

22 Figure 4 illustrates the air-side state points used in the laboratory tests. Duct Inlet Fan ASHRAE Airflow Measurement Apparatus Return Duct A4 Supply Duct Evaporator Coil Furnace Evaporator Fan A1 A3 A2 Scale: None FIGURE 4. AIR-SIDE STATE POINTS The following measurements are available at each air-side state point: A1, Evaporator Fan Inlet Dry Bulb (DB) Temperatures (1-6), Wet Bulb/Relative Humidity (WB/RH) A2, Evaporator Coil Inlet DB Temperatures (1-4), Dew point (DP) A3, Evaporator Coil Outlet DB Temperatures (1-6), DP A4, Supply Duct DB and RH Enthalpies are calculated at all air-side state points for calculation and redundancy purposes. Air volumetric flow is measured using the ASHRAE airflow measurement apparatus, located upstream of the indoor unit. This device was built in accordance with ASHRAE Standard : Standard Methods for Laboratory Airflow Measurement. Airflow is measured in units of Standard Cubic Feet per Minute (SCFM). Additionally, condensate from the evaporator is plumbed to a separate tank outside of the test chamber. This tank is continuously weighed by a scale, and this data is logged to the data acquisition system. Southern California Edison Page 9

23 CALCULATIONS Various calculation methods are available for laboratory testing. Table 1 lists the calculation methods used in this project. TABLE 1. CALCULATION METHODS # Calculation Methods Calculated Parameters 1 Refrigerant-side measurements and calculations Gross cooling capacity, heat rejection 2 Refrigerant-side measurements and Gross cooling capacity, refrigerant mass flow, calculations -> compressor compressor power regression 3 Air-side measurements and calculations Gross cooling capacity, sensible cooling capacity, latent cooling capacity 4 Evaporator airflow equation: manufacturer literature of evaporator pressure drop versus Evaporator air mass flow rate airflow 5 Evaporator condensate scale Latent cooling capacity A comprehensive summary of calculation methods applicable to a given test scenario may be found in Appendix D, in Table 49. Energy efficiency ratio (EER) calculations are performed as follows: EQUATION 1. ENERGY EFFICIENCY RATIO Or Where = Energy efficiency ratio (refrigerant-side-gross-cooling-based), British thermal unit (Btu)/hr/Watt (W) = Energy efficiency ratio (air-side-gross-cooling-based), Btu/hr/W = Refrigerant-side gross cooling capacity, Btu/hr = Air-side gross cooling capacity, Btu/hr = Total power (compressor + fans + misc), W Refrigerant-side calculations for gross cooling capacity and heat rejection are performed as follows: Southern California Edison Page 10

24 EQUATION 2. REFRIGERANT-SIDE GROSS COOLING CAPACITY Where = Refrigerant-side gross cooling capacity, Btu/hr = Refrigerant mass flow rate, lb/hr = Enthalpy at refrigerant-side state point R1, Btu/lb = Enthalpy at refrigerant-side state point R8, Btu/lb EQUATION 3. REFRIGERANT-SIDE CONDENSER HEAT REJECTION Where = Refrigerant-side heat rejection, Btu/hr = Refrigerant mass flow rate, lb/hr = Enthalpy at refrigerant-side state point R4, Btu/lb = Enthalpy at refrigerant-side state point R5, Btu/lb In addition, the HVAC unit s manufacturer provided compressor regression curves for the HVAC test unit. The regressions provided a sanity check for the baseline scenarios to establish confidence in the test results. Given saturated condensing and evaporator temperatures, these curves are able to output cooling capacity, refrigerant mass flow rate, and compressor power. Heat rejection is not a direct output, but is estimated using cooling capacity and power (approximate heat of compression) outputs. Southern California Edison Page 11

25 EQUATION 4. REFRIGERANT-REGRESSION CONDENSER HEAT REJECTION Where = Refrigerant-side heat rejection (regression-based), Btu/hr = Refrigerant-side gross cooling capacity (regression output), Btu/hr = Compressor power (regression output), W = Conversion factor = , Btu/hr/W Percent variation is defined as the variation between two values, divided by the average of the data set. This data set may comprise the two values, or it may comprise several other values. For the purposes of this project, it is used when: a. Comparing different methods of calculations of a certain parameter b. Comparing values of a certain parameter from several repeat tests Percent variation is given by the following equation. EQUATION 5. CALCULATING PERCENT VARIATION Percent difference is defined as the relative shift in a parameter, or the difference of two values divided by one original value. Percent difference is used when comparing a parameter from one fault test scenario, to its baseline scenario (shift in a parameter due to a fault). Equation 6 gives the percent difference. EQUATION 6. CALCULATING PERCENT ERENCE It is important to note that refrigerant-side calculation issues exist for tests featuring non-condensables or mixed-phase refrigerant flow. Mixed-phase refrigerant flow occurred in the liquid line for all low charge tests (Tests 10-14, 47-55), and for all liquid line restriction tests (Tests 25-27). With mixed-phase refrigerant flow, refrigerant properties look-ups become inaccurate at state points R5 through R8. Without knowing refrigerant quality of the mixed-phase flow (percent vapor composition of total mass), state point properties such as enthalpy cannot be determined. Additionally, refrigerant mass flow meter measurements are Southern California Edison Page 12

26 compromised with mixed phase flow. As a result, refrigerant enthalpy method calculations become questionable with the presence of mixed-phase refrigerant flow. In addition, with mixed-phase refrigerant flow, while the regression model may still be suitable for predicting refrigerant mass flow and compressor power, any gross cooling capacity outputs are suspect. The model cannot account for any effects at the heat exchangers, and it is likely that heat transfer is compromised with mixed phase flow. Forced convection heat transfer coefficients for gases typically range from approximately 4.4 to 44 Btu/h-ft 2 - R; forced convection heat transfer coefficients for liquids typically range from approximately 8.8 to 3,500 Btu/h-ft 2 - R. 7 Furthermore, with a mixture of refrigerant and non-condensables (Tests 28-32), refrigerant mass flow measurements are compromised, and refrigerant properties look-ups for all refrigerant-side state points are no longer applicable. The regression model also becomes inaccurate: the relationships between system pressures and properties changes when pure R-410a is not present. For all tests featuring noncondensables or mixed phase refrigerant flow, refrigerant-side based calculations for gross cooling capacity (enthalpy method or regression method) are not used. The air-enthalpy method must be relied upon in these cases. Air-side calculations are performed using the equations that follow. EQUATION 7. AIR-SIDE GROSS COOLING CAPACITY Or Where = Air-side gross cooling capacity, Btu/hr = Air flow rate (measured or calculated), lb/hr = Enthalpy at air-side state point A2, Btu/lb = Enthalpy at air-side state point A3, Btu/lb = Air-side gross sensible cooling capacity, Btu/hr = Air-side gross latent cooling capacity, Btu/hr 7 Incropera, DeWitt, Bergman, Lavine, (2007), Introduction to Heat Transfer. 5 th Edition, John Wiley & Sons. Southern California Edison Page 13

27 EQUATION 8. AIR-SIDE GROSS SENSIBLE COOLING CAPACITY Where = Air-side gross sensible cooling capacity, Btu/hr = Air flow rate (measured or calculated), lb/hr = Specific heat of air (constant pressure), Btu/lb-F = DB at air-side state point A2, F = DB at air-side state point A3, F EQUATION 9. AIR-SIDE GROSS LATENT COOLING CAPACITY Or Where = Air-side gross latent cooling capacity, Btu/hr = Air flow rate (measured or calculated), lb/hr = Humidity ratio at air-side state point A2, lb moisture /lb dry air = Humidity ratio at air-side state point A3, lb moisture /lb dry air = Heat of vaporization of water (1 atm), Btu/lb = Condensate water flow rate (measured with scale), lb/hr Southern California Edison Page 14

28 EQUATION 10. AIR-SIDE AIR FLOW RATE Or Where = Air flow rate (measured or calculated), lb/hr = Volumetric air flow rate, air at standard conditions, ft 3 /min = Density of air at standard conditions = 0.075, lb/ft 3 = Volumetric air flow rate (equation output), ft 3 /min = Conversion factor = 60, min./hr Evaporator airflow was directly measured using calibrated instrumentation. In addition, pressure drop measurements were also measured, and used as a redundant means to verify measured airflow rates: A second order polynomial was fitted to eight manufacturer-published data points for evaporator SCFM versus pressure drop: Data points ranged from 0.05 in H 2 O to 0.4 in H 2 O. Once SCFM was calculated, it was compared to SCFM measurements. Airflow measurements are not done across the condenser, so a direct air-enthalpy calculation cannot be used for air-side-based heat rejection calculations. Instead, heat rejection is calculated through the sum of the air-side calculation for gross cooling capacity and compressor power measurements (approximate heat of compression). EQUATION 11. HEAT REJECTION Where = Heat rejection (air-side based), Btu/hr = Gross cooling capacity (air-side based), Btu/hr = Compressor power (electrical measurement), W = Conversion factor = , Btu/hr/W Southern California Edison Page 15

29 TEST SCENARIOS Table 2, Table 3, and Table 4 present the scope of test scenarios performed in the laboratory assessment. The standard AHRI test chamber conditions are 80 F/67 F/51 (DB/WB/RH) for the indoor chamber, and 95 F DB for the outdoor test chamber. TABLE 2. LINE, NO-FAULT TEST SCENARIOS Test # Description Indoor Chamber Air Condition Outdoor Chamber Air Condition 1 80 F/ F DB F/ F DB (DB/WB/RH) 3 80 F DB 4 75 F/ F DB F/52 5 No Faults 95 F DB (DB/WB/RH) 6 75 F DB 7 70 F/ F DB F/ F DB (DB/WB/RH) 9 75 F DB TABLE 3. SINGLE-FAULT TEST SCENARIOS Test # Description 10 Low Refrigerant Charge Low Refrigerant Charge Low Refrigerant Charge Low Refrigerant Charge Low Refrigerant Charge High Refrigerant Charge High Refrigerant Charge High Refrigerant Charge High Refrigerant Charge High Refrigerant Charge High Refrigerant Charge High Refrigerant Charge High Refrigerant Charge Refrigerant Line Restrictions - 32 psi drop 24 Refrigerant Line Restrictions - 66 psi drop 25 Refrigerant Line Restrictions - 98 psi drop Indoor Chamber Air Condition 80 F/67 F /51 (DB/WB/RH) 75 F /63 F /52 (DB/WB/RH) 70 F /59 F /52 (DB/WB/RH) 80 F /67 F /51 (DB/WB/RH) 75 F /63 F /52 (DB/WB/RH) 70 F /59 F /52 (DB/WB/RH) 70 F /63.3 F /70 (DB/WB/RH) 75 F /67.9 F /70 (DB/WB/RH) 75 F /67.9 F /70 (DB/WB/RH) 80 F /67 F /51 (DB/WB/RH) Outdoor Chamber Air Condition 95 F DB 115 F DB 75 F DB 95 F DB 115 F DB 75 F DB 85 F DB 85 F DB 95 F DB 95 F DB 26* Refrigerant Line Restrictions 88 psi drop 75 F /63 F / F DB Southern California Edison Page 16

30 Test # Description 27* Refrigerant Line Restrictions 96 psi drop 28 (see multiple faults) 29 Non-Condensables 0.3 ozs. N 2 30 Non-Condensables 0.8 ozs. N 2 30a (see multiple faults) 31 Non-Condensables 0.8 ozs. N 2 32 Non-Condensables 0.8 ozs. N 2 33 Evaporator Airflow Reduction Evaporator Airflow Reduction Evaporator Airflow Reduction Evaporator Airflow Reduction Evaporator Airflow Reduction Condenser Airflow Reduction 467 psig Compressor Discharge Pressure Condenser Airflow Reduction 575 psig Compressor Discharge Pressure Condenser Airflow Reduction 613 psig Compressor Discharge Pressure Condenser Airflow Reduction 622 psig Compressor Discharge Pressure Condenser Airflow Reduction 612 psig Compressor Discharge Pressure Indoor Chamber Air Condition (DB/WB/RH) 70 F /59 F /52 (DB/WB/RH) 80 F /67 F /51 (DB/WB/RH) 75 F /63 F /52 (DB/WB/RH) 70 F / 59 F /52 (DB/WB/RH) 80 F /67 F /51 (DB/WB/RH) 75 F /63 F /52 (DB/WB/RH) 70 F /59 F /52 (DB/WB/RH) 80 F /67 F /51 (DB/WB/RH) 75 F /63 F /52 (DB/WB/RH) 70 F /59 F /52 (DB/WB/RH) Outdoor Chamber Air Condition 75 F DB 95 F DB 115 F DB 75 F DB 95 F DB 115 F DB 75 F DB 95 F DB 115 F DB 75 F DB *The restriction imposed in Test 25 is the same restriction imposed in Tests 26 and 27. However, return and outdoor chamber air condition variations cause fluctuations in the measured pressure drop. Southern California Edison Page 17

31 TABLE 4. MULTIPLE-FAULT TEST SCENARIOS Test # 28 30a 43* 44* 45* Description Indoor Chamber Air Condition Fault 1: Low Charge 32 Fault 2: Non-Condensables 0.3 ozs. N 2 80 F /67 F /51 Fault 1: Low Charge 76 (DB/WB/RH) Fault 2: Non-Condensables 0.8 ozs. N 2 Fault 1: Evaporator Airflow Reduction 33 Fault 2: Condenser Airflow Reduction 438 (467) psig Compressor Discharge Pressure Fault 1: Evaporator Airflow Reduction F /67 F /51 Fault 2: Condenser Airflow Reduction 489 (575) psig (DB/WB/RH) Compressor Discharge Pressure Fault 1: Evaporator Airflow Reduction 57 Fault 2: Condenser Airflow Reduction 575 (613) psig Compressor Discharge Pressure Fault 1: High Refrigerant Charge F /72.4 F /70 Fault 2: Evaporator Airflow Reduction 56 (DB/WB/RH) Fault 1: Low Refg Charge - 13 Fault 2: Evaporator Airflow Reduction 32 Fault 1: Low Refg Charge - 13 Fault 2: Condenser Airflow Reduction 624 psig Compressor Discharge Pressure Fault 1: Low Refg Charge - 13 Fault 2: Evaporator Airflow Reduction 32 Fault 3: Condenser Airflow Reduction 607 (624) psig Compressor Discharge Pressure Fault 1: Low Refg Charge 27 Fault 2: Evaporator Airflow Reduction 49 Fault 1: Low Refg Charge 27 Fault 2: Condenser Airflow Reduction 618 psig Compressor Discharge Pressure Fault 1: Low Refg Charge 27 Fault 2: Evaporator Airflow Reduction 43 Fault 3: Condenser Airflow Reduction 601 (618) psig Compressor Discharge Pressure Fault 1: Low Refg Charge 40 Fault 2: Evaporator Airflow Reduction 53 Fault 1: Low Refg Charge 40 Fault 2: Condenser Airflow Reduction 615 psig Compressor Discharge Pressure 80 F /67 F /51 (DB/WB/RH) 80 F /67 F /51 (DB/WB/RH) 80 F /67 F /51 (DB/WB/RH) Fault 1: Low Refg Charge 40 Fault 2: Evaporator Airflow Reduction 56 Fault 3: Condenser Airflow Reduction 601 (615) psig Compressor Discharge Pressure *Note: Compressor discharge pressure is presented in the form, P (P) Outdoor Chamber Air Condition 95 F DB 95 F DB 95 F DB 95 F DB 95 F DB 95 F DB Where P = resultant compressor discharge pressure, after evaporator airflow reduction is imposed P = the originally imposed pressure, prior to evaporator airflow reduction Southern California Edison Page 18

32 RESULTS: THE IMPACTS OF IMPOSED FAULTS ON HVAC PERFORMANCE FAULT IMPACT SUMMARY Table 5 details the percent differences of three key parameters (total power, EER, and gross cooling capacity), for fault categories tested at AHRI conditions. Extreme values for percent differences are highlighted in red. Additional notable parameters are presented in the proceeding sections, as well as in Appendix A. Southern California Edison Page 19

33 TABLE 5. SUMMARY OF KEY PARAMETERS RANGE OF PERCENT ERENCES FROM LINE, TESTED AT AHRI CONDITIONS Type Fault Category Range of Differences from Baseline GROSS TOTAL POWER EER COOLING CAPACITY Low Charge (13 to 40) 0 to to to -65 Single (1-fault) Multiple (2-fault) Multiple (3-fault) High Charge (10 to 30) 2 to 13-1 to -8 1 to 3 Liquid Line Restriction (32 psi to 98 psi) 1 to -2 1 to to -34 Non-Condensables (0.3 ozs. N 2 to 0.8 ozs. N 2) 5 to 11-1 to to -2 Evaporator Airflow Reduction (33 to 57) -5 to to to -20 Condenser Airflow Reduction (467 psig to 613 psig compressor discharge pressure) 12 to to to -21 Low Charge (32) and Non- Condensables (0.3 ozs. N 2) to -3 to to to -96 Low Charge (76) and Non- Condensables (0.8 ozs. N 2) Evaporator Airflow Reduction (33) and Condenser Airflow Reduction (438 psig compressor discharge pressure) to Evaporator Airflow Reduction (57) and Condenser Airflow Reduction (575 psig compressor discharge pressure) High Charge (30) and Evaporator Airflow Reduction (56) Low Charge (13) and Evaporator Airflow Reduction (32) to Low Charge (40) and Evaporator Airflow Reduction (53) Low Charge (13) and Condenser Airflow Reduction (624 psig compressor discharge pressure) to Low Charge (40) and Condenser Airflow Reduction (615 compressor discharge pressure) Low Charge (13), Evaporator Airflow Reduction (32) and Condenser Airflow Reduction (607 psig compressor discharge pressure) to Low Charge (40), Evaporator Airflow Reduction (56) and Condenser Airflow Reduction (601 psig compressor discharge pressure) 2 to to to to to to to to to to to to -73 Southern California Edison Page 20

34 Table 6 details the percent differences of three key parameters (total power, EER, and gross cooling capacity), for fault categories tested at non-ahri conditions. Extreme values for percent differences are highlighted in red. Additional notable parameters are presented in the proceeding sections, as well as in Appendix A. TABLE 6. SUMMARY OF KEY PARAMETERS RANGE OF PERCENT ERENCES FROM LINE, TESTED AT NON-AHRI CONDITIONS ERENCES FROM LINE GROSS TOTAL EER COOLING POWER TYPE FAULT CATEGORY CAPACITY 40 Low Charge at Test 4 ID/OD Conditions High Charge at Test 4 ID/OD Conditions psi Liquid Line Restriction at Test 4 ID/OD Conditions ozs. N 2 Non-Condensables at Test 4 ID/OD Conditions Evaporator Airflow Reduction at Test 4 ID/OD Conditions Condenser Airflow Reduction (622 psig compressor discharge pressure) Single at Test 4 ID/OD Conditions (1-fault) 40 Low Charge at Test 9 ID/OD Conditions High Charge at Test 9 ID/OD Conditions psi Liquid Line Restriction at Test 9 ID/OD Conditions* -11* -18* -27* 0.8 ozs. N 2 Non-Condensables at Test 9 ID/OD Conditions Evaporator Airflow Reduction at Test 9 ID/OD Conditions Condenser Airflow Reduction (612 psig compressor discharge pressure) at Test 9 ID/OD Conditions *Note: 96 psi liquid line restriction at Test 9 ID/OD conditions resulted in a frosted evaporator coil Southern California Edison Page 21

35 LINE PERFORMANCE Test 2, 4, and 9 serve as the baselines for all fault test scenarios conducted. Measurement averages of various baseline parameters are detailed in Table 7. TABLE 7. LINE PARAMETERS MEASUREMENT AVERAGES # PARAMETER (UNITS) TEST 2 TEST 4 TEST 9 Indoor Chamber Air Condition DB ( F) Indoor Chamber Air Condition WB ( F) Outdoor Test Chamber DB ( F) Compressor Power (W) 2,649 3,089 2,095 2 Evaporator Fan Power (W) Condenser Fan Power (W) Total Power: Compressor, Fans & Misc. (W) 3,325 3,769 2,774 5 EER - Refg-side (Btu/hr/W) EER - Air-side (Btu/hr/W) Refrigerant-side Gross Cooling Capacity 35,187 28,548 34,929 8 Air-side Gross Cooling 33,319 26,613 33,104 9 Refrigerant-side Heat Rejection 42,966 37,252 41, Heat Rejection: Air-side Gross Cooling Capacity + Compressor Power 42,358 37,155 40, Evaporator Air Flow Rate (SCFM) 1,147 1,165 1,190 SINGLE FAULT: LOW REFRIGERANT CHARGE Table 8 details the measurement averages of key operating parameters for the 13 (Test 10), 27 (Test 11), and 40 (Test 12), low refrigerant charge faults, tested at AHRI ID/OD test chamber conditions. Additionally, the percent differences from Test 2 s values are presented. Table 9 details the measurement averages of key operating parameters for the 40 low refrigerant charge fault level, tested at non-ahri test chamber conditions. Additionally, the percent differences from their appropriate baseline values are presented. Figure 5 depicts gross cooling capacity, total power, and EER for all low charge single-fault tests. Generally, performance is not impacted significantly at 13 low charge, but drops off considerably at 27 and 40. Comparing 40 low charge at varying ID/OD test chamber conditions (Tests 12-14), cooling capacity and EER are impacted most at Test 13. Southern California Edison Page 22