Research and Development of Residential Heat Pump Midterm Report: Performance Analysis and Design Crosby Laboratory Department of Mechanical Engineering University of Maine Orono, Maine Team Members: Donald S. Jarvi Adam Koppel Kyle Knowlton Eric Bragdon Advisor: Jim LaBrecque
Abstract: The following will include detailed information relating to the progress of development on the residential heat pump unit. Information will include performance test data of the fans, compressors, and heat exchangers as well as public relations progress and goals to be accomplished the following semester. Objective: The heat pump unit was assembled and partially designed by a previous team of mechanical engineering technology students. The unit was in operating condition and took little preparation in getting the unit to operate. Our main goal for this semester was to improve, enhance, and optimize the features of the heat pump making the unit have higher performance and operate more efficiently. Just by inspection, without the unit running, we noticed several areas improvement such as fan positioning, aesthetics, and controls. Currently, the controls system is in crude shape and takes up an unnecessary volume. The aesthetics of the unit resemble a prototype, which is in fact what the unit is, and also has loose structure. By the end of this project, we hope to have a unit that will closely resemble that of one that would be sold by retailers. Performance: Upper Heat Exchanger Fan: After the unit was up and operating, performance data was taken on the compressor, fans, and heat exchangers. Using the fans performance data provided by the manufacturer, we immediately saw that the upper coil fan (condenser in the winter evaporator in the summer) was oversized. But due to the complex positioning of the upper heat exchanger, various pressure drops would cause this data to be different than the actual capacity of the fan in our setting. So, an air velocity meter was used to gather a velocity profile of both upper and lower fans.
Figure 1: A velocity profile as a function of height on upper heat exchanger. Integrating the velocity profile gives an average velocity of 926.75 ft/min. Using the exposed heat exchanger area of 1.02 ft 2, the air volumetric flow can be computed using Q=VA, giving an air flow of 810 CFM. From the manufacturer s fan curve, we should be achieving about 1200 CFM. This makes the fan less efficient than if a properly sized fan was used due to unnecessary pressure drops across the awkwardly positioned heat exchanger. Lower Heat Exchanger Fan: For the lower heat exchanger, a radial orientation was used to gather the velocity profile. Figure 2: A velocity profile as a function of radius for the lower heat exchanger.
Integrating the velocity profile gave an average velocity of 857 ft/min. For the lower heat exchanger, an area of 1.396 ft 2 was used giving a flow rate of 1196.6 CFM. However, this fan is not oversized where the desired capacity is higher than that of the upper fan. Compressor: Compressor performance data was computed after collecting air temperatures off of the heat exchangers, subcooling temperatures, and subcooling pressures. Temperatures were collected using a handheld air temperature gage thermocouples attached to subcooling pipes. Pressure readings were taken using a Texas Instruments pressure transducer. Heat Energy and Electrical Input vs. Outside Temperature 2.50 8800 7800 2.00 6800 5800 Heat Energy (tons) 1.50 1.00 4800 3800 Electrical Input (watts) Heat Energy (tons) Electrical Energy (watts) 2800 0.50 1800 800 0.00-200 -40-20 0 20 40 60 80 Outside Temperature (F) Figure 3: Graphical display of heat energy received and electrical energy put in as a function of outdoor air temperature.
Figure 4: Plot of coefficient of performance represented in terms of Carnot and refrigerant performance as a function of outdoor air temperature. As seen in figures 3 and 4, the compressor delivers a reasonable amount of thermal energy while reaching COP s in the range of 3.5 on mild days. NOTE: much of the
thermodynamic analysis of the compressor depends on the isentropic efficiency of the comressor which we assumed to be n =.9. Upper Heat Exchanger: During test analysis, quick temperature readings were taken at various points on both heat exchangers using an infrared temperature gage. With the compressor running at about 60%, the temperatures on the upper heat exchanger were 110 F where the desired temperature is about 95 F. The group concluded that this is a poor configuration of fan size and heat exchanger size combination. Lower Heat Exchanger: The lower heat exchanger configuration with its fan seems to be performing to our desired standards. The group decided to keep this configuration. Design: After test analysis was completed, areas for improvement were exposed mainly in the upper heat exchanger. A new fan was sized based on air flow capacity, sound pressure level, and positioning. The group decided on the EBM Papst R4E310-AR06-01. This fan is different than the axial fan currently installed on the unit. It features a motorized impeller design that delivers the same capacity, but with lower sound pressure level and more capable of overcoming such static pressure over the upper heat exchanger. The new fan was sized for the following specifications provided to us by the manufacturer. Figure 5: Fan performance curves provided by the manufacturer. Curve numbers represent model numbers provided in Figure 6. Source: EBM Papst.
Figure 6: Fan performance data provided by manufacturer. Selected fan is highlighted in yellow. Source: EBM Papst. New Features: Several new features that the group plans to add to the unit include air filters, sterile UV lighting, humidification nozzles, and domestic hot water heat exchanger. Air Filters: The group decided to use the AspenAire FG241414 which measures 14 x14 and has a power usage of less than 2 W at 24 VAC. Domestic Hot Water Heat Exchanger: The group chose the Turbotec Turbo-Flow BTSSN-12 air to water heat exchanger. This new technology features an inner coil that creates turbulance in the fluid being heated/cooled. This drastically increases the COP of the unit in the summer where the unit is being an as an air conditioner as well as a water heater simultaneously. All other new features have not been precisely sized and have not yet decided on a manufacturer at this time. Conclusion: Our team has learned a lot this semester about heat pump technology and the refrigeration cycle. Our advisor Jim LaBrecque has been a great help with teaching us how to solve real-world issues associated with refrigeration equipment, and has helped us to get funding for next semester. Another part of our project has been raising awareness about heat pump technology and the energy savings associated with it. Our public relation work included attending a climate change expo, a winter energy and heating expo, and a news interview with channel 2 WLBZ, all of which showcased our senior project. Our milestones changed from our initial list to incorporate our PR work. Our design also changed to allow for a new top fan on the unit. Our milestone list for next semester includes rebuilding the unit and changing the layout, using most of the parts we already have. Once our new parts are ordered and arrive, we will use our SolidWorks drawings to help fabricate a new case and we will begin construction.
Parts List: Compressor Panasonic Rotary model 5KD240XAC21 Spec. No. SC- 52173009 -A Capacity: 2 Ton Electronic Expansion Valve Parker Electronically Controlled type with 650 steps of resolution Inlet: 1/4" Outlet: 3/8" Coils AlumiCool Micro-channel Top coil dimensions: 15.55" x 10.2" Bottom coil dimensions: 15.55" x 30.2" Filter Dryer Parker Size: 4.5" long x 3" diameter Top Fan EBM Papst EC centrifugal fan model R3G 310-AP52-01, motor M3G074-CF Inlet ring: model 31051-2-4013 Size: 310mm diameter Blade style: backward-curved Bottom Fan EBM Papst EC Axial fan model A3G300- AB56-02 Size: 300mm Blade style: sickled Ventilation Fan EBM Papst VarioPro model 6248N12P Desuperheater Coil For DHW Production TurboTec model BTSSN-12
Appendix A: Test data collected for compressor performance analysis. Done by Adam Koppel 12/14/2008 Fixed Indoor Condensing 95 290 psia Comp. Displacement 24 cm^3 / rev. Supply Temp. 80 0.000847521 ft^3 / rev Sub-cool 5 Superheat 10 n compressor 0.9 changable BTU / lbm BTU / lbm-r Ft^3 / lbm Changeable lbm / hr Enthalpy Entering Entropy Entering Outside Temp. Evaporator Temp. ρ Vapor Entering rpm Compressor Mass flow rate Compreesor Compressor 65 45 0.4321 2010 236.545 124.625 0.2524 60 40 0.4848 2240 234.956 124.500 0.2548 55 35 0.5438 2490 232.864 124.100 0.2557 50 30 0.5722 2600 231.061 123.700 0.2569 45 25 0.6295 2830 228.609 123.250 0.2583 40 20 0.6788 3030 226.988 122.700 0.2590 35 15 0.7357 3260 225.330 122.200 0.2599 30 10 0.7760 3410 223.457 121.500 0.2601 25 5 0.8895 3880 221.826 121.250 0.2627 20 0 0.9519 4100 219.025 120.600 0.2631 15-5 1.0250 4360 216.304 119.950 0.2636 10-10 1.2368 4400 180.907 119.900 0.2680
5-15 1.3349 4400 167.612 119.200 0.2686 0-20 1.4915 4400 150.014 118.700 0.2703-5 -25 1.6425 4400 136.223 118.050 0.2716-10 -30 1.8932 4400 118.184 117.600 0.2742-15 -35 2.0730 4400 107.933 116.900 0.2752-20 -40 2.3937 4400 93.473 116.400 0.2779-30 -50 2.9445 4400 75.988 115.100 0.2806 fixed Assuming Coil can handle load Isentropic Isentropic Enthalpy taking Temp. Exiting Enthalpy Exiting isentropic n into Actual Comp. Enthalpy Exiting Compressor Compressor Account Exiting Temp. Condenser 120.0 132.70 147.44 173.0 46.00 122.5 133.48 148.31 176.3 46.00 125.0 134.25 149.17 179.5 46.00 127.5 135.03 150.03 182.7 46.00 130.0 135.80 150.89 185.9 46.00 132.5 136.55 151.72 189.0 46.00 135.0 137.30 152.56 192.1 46.00 137.5 138.05 153.39 195.2 46.00 140.0 138.80 154.22 198.3 46.00 144.0 139.94 155.49 203.1 46.00 148.0 141.08 156.76 207.8 46.00 152.0 142.22 158.02 212.5 46.00 156.0 143.36 159.29 217.2 46.00 160.0 144.50 160.56 222.0 46.00 165.0 145.90 162.11 227.8 46.00 170.0 147.30 163.67 233.6 46.00 175.0 148.65 165.17 239.2 46.00
180.0 150.00 166.67 244.8 46.00 185.0 151.35 168.17 250.3 46.00 TU/ hr Tons BTU / lbm BTU/ hr BTU / lbm BTU/ hr Watts dot high Tons of Heating Q low Q dot low W Compressor W dot Compresser W dot Compresser 23996 2.00-78.625-18598 22.82 5398 1583 24037 2.00-78.500-18444 23.81 5593 1640 24024 2.00-78.100-18187 25.07 5837 1712 24038 2.00-77.700-17953 26.33 6085 1784 23978 2.00-77.250-17660 27.64 6318 1853 23998 2.00-76.700-17410 29.02 6588 1932 24010 2.00-76.200-17170 30.36 6840 2006 23997 2.00-75.500-16871 31.89 7126 2090 24006 2.00-75.250-16692 32.97 7314 2145 23981 2.00-74.600-16339 34.89 7642 2241 23957 2.00-73.950-15996 36.81 7961 2335 20266 1.69-73.900-13369 38.12 6897 2022 18989 1.58-73.200-12269 40.09 6719 1970 17185 1.43-72.700-10906 41.86 6279 1841 15817 1.32-72.050-9815 44.06 6002 1760 13906 1.16-71.600-8462 46.07 5444 1597 12862 1.07-70.900-7652 48.27 5210 1528 11279 0.94-70.400-6580 50.27 4699 1378 9283 0.77-69.100-5251 53.07 4032 1183 COP Carnot 9.25 COP Refirgerant 4.12 11.10 8.54 3.95 4.45 10.09 7.93 3.79 4.30
7.40 3.64 6.94 3.51 6.53 3.37 6.17 3.28 5.84 3.14 5.55 3.01 5.29 2.94 5.05 2.83 4.83 2.74 4.63 2.64 4.44 2.55 4.27 2.47 4.11 2.40 3.83 2.30