by D Springer · 2013 · Cited by 5 — pdf. Carrier (1995). “HVAC Servicing Procedures” Carrier catalog number 020-040. Carrier (2010). “Installation
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NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, subcontractors, or affiliated partners makes any warr anty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Re ference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831 -0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:reports@adonis.osti.gov Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: orders@ntis.fedworld.gov online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
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iii Measure Guideline: Air Conditioner Diagnostics, Maintenance, and Replacement Prepared for: The National Renewable Energy Laboratory On behalf of the U.S. Department of Energy™s Building America Program Office of Energy Efficiency and Renewable Energy 15013 Denver West Parkway Golden, CO 80401 NREL Contract No. DE -AC36 -08GO28308 Prepared by: David Springer and Bill Dakin, PE (Davis Energy Group) Alliance for Residential Building Innovation (ARBI) 123 C Street Davis, Cali fornia 95616 NREL Technical Monitor: Cheryn Metzger Prepared under Subcontract No. KNDJ -0-40340- 00 March 2013
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v Contents Contents . v List of Figures . vii List of Tables vii Definitions . viii Executive Summary x Acknowledgements x Introduction . 1 1 Section 1: Planning and Decision Making Criteria . 3 1.1 Defining the Problem ..3 1.2 Maintenance Approaches ..4 1.3 Energy Savings ..5 1.4 The Consequences of No Action ..5 1.5 Planning for Improvements and Risk Mitigation ..6 2 Section 2: Technical Description .. 7 2.1 General Performance Interactions .7 2.2 Airflow Impacts .7 Desired Airflow .7 What Affects Airflow? 7 Findings from the Field ..9 How Airflow Affec ts System Operation and Energy Use .11 Airflow Measurement Methods ..12 2.3 Refrigerant System Defects, Detection, and Correction .13 What Can Go Wrong 13 The Importance of Correct Refrigerant Charge ..13 The Effect of Non -Condensable Gases 14 Fault Detection and Diagnosis .15 Methods for Setting Refrigerant Charge .16 Diagnostic Methods for Assessing Refrigerant Charge ..16 Evaporator Coil Fouling and Damage to Distributor Tubes .17 2.4 Repair or Replace? .17 Condenser Replacement ..17 The Value of High Efficiency Systems ..19 Replacement of Other Components ..19 3 Section 3: Implementation .. 21 3.1 The Preliminary Diagnostic (PD) Method .21 Objectives and Scope 21 Skills and Tools Required ..22 Measuring Airflow .22 Before Starting Tests .23 Preliminary Diagnostic Steps 23 3.2 The Comprehensive Diagnostic (CD) Method 27 Objectives and Scope 27 Skills and Tools Requi red ..27 Refrigerant Charge Test Overview 28 Before Starting Tests .28 Test Procedures 28 Measurements (Enter all values into Table A -2) 29
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vi Cold and Hot Weather Testing 29 3.3 Calculations 30 Temperature Split 30 Condensing Temperature Over Ambient (COA) 30 Superheat .30 Subcooling .31 3.4 Diagnosis .31 Evaluating the Measurements ..31 Using Diagnostic Flow Charts .32 Removing and Replacing Refrigerant ..34 Equipment Replacement .35 References . 38 Appendix A: Test Forms and Checklists 41 Appendix B: Supporting Data and Calculations 43 B-1: Energy Savings for Replacement with High Efficiency Air Conditioners .43 B- 2: Replacement Blower Motor Energy Savings Estimates ..45 B- 3: Verification of Temperature Split Method for Checking Refrigerant Charge ..46 Appendix C: Detailed Methods and Procedures 48 C- 1: Air Conditioner Replacement Decision Tree .48 C- 2: Detailed Airflow Measurement Methods 49 General Instructions ..49 Powered Flow Hood (Fan Flowmeter) 49 Flow Grid 50 Flow Capture Hood 50 C-3: Detailed Condenser Coil Cleaning Instructions 51 C-4: Refrigerant Procedures to Prevent Non- Condensables and Restrictions .52 C-5: Vacuum Pump Maintenance ..52 C-6: Evacuation and Recovery Procedures 53 C-7: Charging Procedures .. 56 C- 8: Proper Refrigerant Procedures to Avoid Non-condensables and Restrictions .56 C-9: ASHRAE Recommendations for Proper Evacuation to Remove Non- condensable Air and Water Vapor .57 C-10: Method to Detect Blocked Distributor Tubes .57 Appendix D: Test Equipment Specifications and Calibration .. 58 D-1: Recommended Accuracy of Test Equipment 58 D- 2: Calibration Method for Digital Thermometer Sensors .58 D-3: Refrigerant Gauge Cal ibration Procedure ..58 D- 4: Other Devices 59
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viii Definitions ACCA Air Conditioning Contractors of America AHRI Air Conditioning, Heating, and Refrigeration Institute ANSI American National Standards Institute ARBI Alliance for Residential Buildin g Innovation ASHRAE American Society for Heating, Refrigeration, and Air Conditioning Engineers BPI Building Performance Institute CD Comprehensive Diagnostic (a procedure as defined in this document) CEC California Energy Commission CFC Chlorofluoro carbon CFM Cubic feet per minute COA Condensing Over Ambientfl, or the difference between the condensing temperature and the temperature of air entering the condensing coil DEG Davis Energy Group ECM Electronically commutated motor EER Energy Efficien cy Ratio, in Btuh per watt EPA Environmental Protection Agency EST Refrigerant evaporation saturation temperature Ft2 Square feet HERS Home Energy Rating System HFC Hydrofluorocarbon HVAC Heating, ventilation, and air conditioning kBtuh Thousand Br itish Thermal Units per hour kW Kilowatt kWh Kilowatt -hour MERV Minimum efficiency reporting value (for air filters) NSOP Normal system operating pressure (for airflow measurement corrections) PD Preliminary Diagnostic (a procedure as defined in this document) PG&E Pacific Gas and Electric Company PSC Permanent split capacitor (motor type) SCE Southern California Edison SEER Seasonal energy efficiency ratio
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x Executive Summary Heating and cooling energy use represents about 54% of all energy consumed in existing residential buildi ngs. Field studies have shown that more than half of installed air conditioning (AC) systems have significant defects, and that proper maintenance of cooling systems can reduce their energy use by as much as 50%. Since the 1990s, an immense body of knowledge on the importance of proper maintenance of heating, ventilation, and air conditioning (HVAC) systems and the impact of defects has been accumulated, and research in this area is continuing. Though some of this information has found its way into standards and utility programs, general maintenance practices continue to miss details that could realize significant energy savings at minimal cost. This guideline targets home performance contractors who are relatively inexperienced with HVAC systems, HVAC technicians who can benefit from recent research on AC system faults and diagnostic methods, and program managers who may apply this information in structuring successful HVAC tune -up programs. Home performance contractors who are not attentive to air conditioner performance are missing the opportunity to deliver optimal energy savings to their customers. Systems that are not in obvious need of replacement may still perform far below their rated conditions. Alt hough these systems are complicated, many faults that substantially degrade performance can be easily identified and in some cases corrected by the home performance contractor during the normal course of completing home inspections and duct testing. Little information is available on methods to diagnose systems and particularly to detect and discriminate between multiple faults such as inadequate airflow, incorrect charge, liquid line restrictions, evaporator and condenser coil fouling, and the presence of non- condensable refrigerant contaminants. While there has been some progress with development of computer diagnostic tools for use in utility programs, a systematic method is needed to detect and identify major system faults by field technicians who do not have access to these tools. This guideline provides information on the impact of various defects and the potential energy savings that can result from proper maintenance, and describes a two -step process for diagnosing and correcting faults. The first step involves a fundamental inspection and tests that can be completed by home performance contractors with BPI or similar training to identify or diagnose, and in some cases remediate, relatively non -technical problems such as low airflow and fouled condenser coils. The second step is designed to be implemented by experienced HVAC technicians and provides a systematic approach that can be used to identify system faults. Acknowledgements Davis Energy Group (DEG) would like to acknowledge the U.S. Department of Energy Building America program and thei r funding and support of development of this g uideline as well as research that informed it. The detailed diagnostic method described in this g uideline was adapted from Appendix RA3 of the California Title 24 Residential Energy Efficiency Standards (CEC 2008). Substantial guidance with the development of diagnostic methods was provided by Jim Phillips of The Energy Savers. Also, DEG would like to acknowledge Marshall Hunt of Pacific Gas & Electric Company for the direction he provided in developing the two- step approach.
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1 Introduction Space cooling and heating constitutes 54% of residential energy use nationwide (DOE 2010), and HVAC tune -ups are a potentially very cost -effective component of residential retrofits. Laboratory testing suggests that service an d replacement can produce HVAC energy savings on the order of 30% to 50% (Messenger 2008). A recent sampling of more than 1,300 air conditioning (A/C) units from the Arkansas CoolSaver Program revealed that corrections in charge and airflow netted an average increase in delivered Btu/h of 38% and a peak kW demand reduction of 0.5 kW per tune-up (Kuonen 2011). However, as expressed in Kuonen™s Home Energy article, fiSimply put, the service practices we performed in the past to get the job done are not getting the job done today. Past practice and best practice no longer belong in the same sentence.fl Other programs have verified the need for air conditioner maintenance. Downey (2002) reported that of 8,873 systems tested, 65% required repairs. Mowris (2004) reported field measurements of 4,168 air conditioners where 72% of systems had improper refrigerant charge and 44% had improper airflow. These faults are widespread due to a lack of standards, training, information, and other market barriers regarding prop er evacuation and maintenance procedures. Mowris (2011a) surmises that many systems are undercharged due to long line sets where no additi onal refrigerant is added or where systems have leaking refrigerant over time. However, there is the possibility that low charge diagnoses may be caused by a false diagnosis of undercharge due to refrigerant restrictions, lower ambient temperatures, inaccurate analog pressure sensors, or inaccurate refrigerant line temperature sensors. For example, a system with the corre ct charge when loaded at high ambient temperatures (i.e., 95 F or higher) may produce a false undercharge indication when checked at lower ambient temperatures, or a false undercharge indication can be caused by inaccurate temperature sensors producing hig her suction line or lower liquid line temperatures. Superheat tables available from manufacturers (Carrier 1995) or the California Energy Commission (2008) account for changes in outdoor temperature, but these tables may not predict the proper required sup erheat for all systems without thermostatic expansion valves (TXV) at low ambient temperatures. False diagnosis of undercharge will cause a decrease in system efficiency if refrigerant is unnecessarily added. The lack of information and training on correct procedures can result in an unintentional degradation of system performance. Incorrect charge procedures and inaccurate or badly maintained service equipment can turn a mediocre system into a poorly performing system. This measure guideline attempts to b ridge the gap between potential and realized whole house energy savings by developing field guidelines for HVAC diagnosis, repair, and equipment replacement. The intent of this document is to provide easy- to-implement, cost- effective, and reliable methods for home performance contractors and technicians to follow for the diagnosis and correction of AC system problems, particular ly during the course of the energy upgrade process. It expands on ACCA Standard 4 (Maintenance of HVAC Systems) and Standard 5 (HVA C Quality Installation Specification) as they pertain to residential AC and heat pump systems, and offers a way to capture a source of energy savings that is frequently ignored in the course of completing retrofits.
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