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Humidity Effects in Mobile Air-Conditioning Systems

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Humidity Effects in Mobile Air-Conditioning Systems ,~-. Humidity Effects in Mobile Air-Conditioning Systems M. R. Whitchurch, W. E. Dunn, and N. R. Miller ACRC TR-126 August 1997 For additional information: Air Conditioning and Refrigeration Center University of Illinois Mechanical & Industrial Engineering Dept. 1206 West Green Street Prepared as part ofACRC Project 78 Urbana, IL 61801 Modeling, Diagnostics, and Control for Mobile Air-Conditioning Systems (217) 333-3115 w. E. Dunn and N. R. Miller, Principal Investigators .~. The Air Conditioning and Refrigeration Center was founded in 1988 with a grant from the estate of Richard W. Kritzer, the founder of Peerless of America Inc. A State of Illinois Technology Challenge Grant helped build the laboratory facilities. The ACRC receives continuing supportfrom the Richard W. Kritzer Endowment and the National Science Foundation. The following organizations have also become sponsors of the Center. Amana Refrigeration, Inc. Brazeway, Inc. Carrier Corporation Caterpillar, Inc. Copeland Corporation Dayton Thermal Products Delphi Harrison Thermal Systems Eaton Corporation Ford Motor Company Frigidaire Company General Electric Company Hydro Aluminum Adrian, Inc. Indiana Tube Corporation Lennox International, Inc. Modine Manufacturing Co. Peerless of America, Inc. Redwood Microsystems, Inc. The Trane Company Whirlpool Corporation York International, Inc. For additional information: Air Conditioning & Refrigeration Center Mechanical & Industrial Engineering Dept. University ofIllinois 1206 West Green Street Urbana IL 61801 2173333115 HUMIDITY EFFECI'S IN MOBILE AIR-CONDmONING SYSTEMS Michael Robert Whitchurch, M.S. Department of Mechanical and Industrial Engineering University of lllinois at Urbana-Champaign, 1997 W.E. Dunn and N.R. Miller, Advisors A humidity addition system was installed in the mobile air-conditioning test facility. The system is able to produce relative humidities at the evaporator inlet in excess of 95% RH. The system is able to control the humidity to with ± 2% RH of a setpoint. Regulation of the flow rate of water sprayed into the air provides the necessary humidity control. An analysis is developed to predict the ratio of latent heat transfer to total heat transfer from the air flowing over the evaporator. A large number of tests were conducted in the test facility to determine the actual latent heat transfer ratio. The latent heat transfer ratios predicted by the analysis are consistently lower than those measured in the test facility. A discussion of causes of the discrepancy is included in this paper. iii ~. TABLE OF CONTENTS Page LIST OF TABLES ................................................................................... viii LIST OF FIGURES ................................................................................. ix NOMENCLATURE ................................................................................. xi 1. INTRODUCTION............................................................................ 1 1.1 Objectives................................................................................ 1 1.2 Scope of Work.......................................................................... 1 1.3 Description of Existing Test Facility .............. .... ................. .............. 2 2. HUMIDITY ADDmON SySTEM......................................................... 5 2.1 System Requirements .................................................................. 5 2.2 System Construction ................................................................... 5 2.2.1 System Overview............................................................ 5 2.2.2 Humidity Chamber and Air Ducts ....................................... ,. 7 2.2.3 Water Circulation Subsystem .............................................. 9 2.3 System Control Scheme . 16 2.3.1 Control Scheme Overview ................................................. 16 2.3.2 Air Duct Heater ... ....... .... ... ......... ..... ............................... 16 2.3.3 Water Temperature.......................................................... 18 2.3.4 Water Flow Rate .... ................ ......................................... 19 3. SYSTEM TEST RESULTS. ......................... ... ................ .................. ... 21 3.1 Humidity Addition System Validation Tests ............................. ........... 21 3.1.1 Steady State Tests ........................................................... 21 3.1.1.1 General Test Description........................................ 21 3.1.1.2 Steady State Test Series 1 Results: Effects ofHCV Position and Water Temperature on Humidity Addition System Operation ................................................ 22 3.1.1.3 Steady State Test Series 2 Results: Effects of Ball Valve Positions on Humidity Addition System Operation .......... 28 3.1.1.4 Steady State Test Series 3 Results: Effects of HCV Position on Humidity Addition System Operation for Positions Between 0 and 35% Open ........................... 31 3.1.2 Transient Tests............................................................... 33 3.1.2.1 General Test Description ........................................ 33 3.1.2.2 Dynamic Response and Control Test Results.. .... ....... .... 34 v 3.1.2.3 Cabin Pulldown Test Results ................................... 37 3.1.2.4 Constant Relative Humidity Test Results .......... ........... 38 ,~'. 3.2 WetEvaporatorTests .................................................................. 40 3.2.1 Wet Evaporator Analysis ................................................... 40 3.2.2 Wet Evaporator Test Results............................................... 43 3.2.2.1 Comparison of Data to Analysis................................ 43 3.2.2.2 Experimental Errors .............................................. 47 4. CONCLUSIONS AND RECOMMENDATIONS ........................................ 49 4.1 Conclusions... .. ... .. .. .. ... .... .. ....... ... .. .. .. .. .. .. .. ... .. .. .... 49 4.2 Recommendations..... ...... ... .. .... ... ... .. .... ... .. ...... ..... ..... ...... 49 APPENDIX A ........................................................................................ 51 A.l Humidity Addition System Operation Procedures .................................. 52 A.l.l Preparing for Runs with the Humidity Addition System ............... 52 A.l.2 Setting Evaporator Air Inlet Relative Humidity During a Run ......... 52 A.1.3 Shutting Down Humidity System ......................................... 53 A.l.4 Shutting Down Test Facility After the Last Run of the Day ............ 53 A.l.5 Important Notes ............................................................. 53 APPENDIX B ........................................................................................ 54 B.l Humidity Sensor Calibration.......................................................... 55 APPENDIX C ........................................................................................ 61 C.l Wiring Diagrams. .. .......... ....... .. ............. ............. ... .... .. .. ......... 62 APPENDIX D ........................................................................................ 69 D.1 Converting Measured Voltages to Reduced Data ................................... 70 D .1.1 Temperature Instrumentation ............................................... 70 D.l.l.l Thermistor ........................................................ 70 D.l.l.2 Thermocouples ................................................... 70 D.1.1.3 Resistance Temperature Detectors (RIDs) .................... 72 D.1.2 Pressure Instrumentation ................................................... 73 D.l.2.1 Barometer ......................................................... 73 D.1.2.2 Pressure Transducers ............................................ 73 D.l.3 Other Instrumentation ....................................................... 74 D.1.3.1 MicroMotion® Mass Flow Sensor .............................. 74 D.1.3.2 Compressor Speed Sensor...................................... 75 D.1.3.3 Compressor Torque Sensor ..................................... 75 vi 0.1.3.4 Relative Humidity Sensors ...................................... 75 0.1.3.5 PID Controller Retransmission................................. 75 .i. 0.2 Calculating Refrigerant-Side Gauge Pressure Transducer Zero Offsets .... ..... 77 APPENDIX E ........................................................................................ 79 E.l EES Code to Implement Wet Evaporator Analysis With Constant dro/dh ....... 80 E.2 EES Code to Implement Wet Evaporator Analysis With Integration of dro/dh .. 83 REFERENCES ....................................................................................... 86 vii LIST OF TABLES Page Table 1.1 Mobile NC system test parameters. ........................................... 4 Table 2.1 HCV PID parameters. ........................................................... 20 Table 3.1 Steady-state test conditions, Series 1. ......................................... 22 Table 3.2 Constant system parameter values for steady-state humidity addition system tests. ...................................................................... 24 Table 3.3 Steady-state test conditions, Series 2. ......................................... 29 Table 3.4 Ball valve configurations. ....................................................... 30 Table 3.5 Steady-state test conditions, Series 3. ......................................... 32 Table 3.6 Dynamic characteristics of relative humidity responses. .................... 34
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