PERFORMANCE OF GAS-ENGINE DRIVEN HEAT PUMP UNIT (GEDAC #23) FINAL SUMMARY TECHNICAL REPORT REPORT PERIOD: 10/01/2006 TO 12/31/2008

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1 PERFORMANCE OF GAS-ENGINE DRIVEN HEAT PUMP UNIT (GEDAC #23) FINAL SUMMARY TECHNICAL REPORT REPORT PERIOD: 10/01/2006 TO 12/31/2008 PRINCIPAL AUTHORS: ABDI ZALTASH, RANDY LINKOUS, RANDALL WETHERINGTON, PATRICK GEOGHEGAN AND ED VINEYARD OF ENGINEERING SCIENCE AND TECHNOLOGY DIVISION (ESTD) OAK RIDGE NATIONAL LABORATORY (ORNL) AND ISAAC MAHDEREKAL AND ROBERT GAYLORD OF TEAM CONSULTING, LLC REPORT ISSUED DATE: DECEMBER 2009 DOE AWARD: DE-FC26-06NT42816 SUBMITTED BY: BLUE MOUNTAIN ENERGY, INC WESTWOOD DRIVE LAS VEGAS, NV 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, makes any warranty, 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. Reference 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.

2 PERFORMANCE OF GAS-ENGINE DRIVEN HEAT PUMP UNIT (GEDAC #23) SUMMARY REPORT Abdi Zaltash, Randy Linkous, Randall Wetherington, Patrick Geoghegan, and Ed Vineyard Engineering Science and Technology Division (ESTD) Oak Ridge National Laboratory (ORNL) Isaac Mahderekal and Robert Gaylord Team Consulting, LLC INTRODUCTION Air-conditioning (cooling) for buildings is the single largest use of electricity in the United States (U.S.). This drives summer peak electric demand in much of the U.S. Improved air-conditioning technology thus has the greatest potential impact on the electric grid compared to other technologies that use electricity. Thermally-activated technologies (TAT), such as natural gas engine-driven heat pumps (GHP), can provide overall peak load reduction and electric grid relief for summer peak demand. GHP offers an attractive opportunity for commercial building owners to reduce electric demand charges and operating expenses. Engine-driven systems have several potential advantages over conventional single-speed or single-capacity electric motordriven units. Among them are variable speed operation, high part load efficiency, high temperature waste heat recovery from the engine, and reduced annual operating costs (SCGC 1998). Although gas engine-driven systems have been in use since the 1960s, current research is resulting in better performance, lower maintenance requirements, and longer operating lifetimes. Gas engine-driven systems are typically more expensive to purchase than comparable electric motor-driven systems, but they typically cost less to operate, especially for commercial building applications. Operating cost savings for commercial applications are primarily driven by electric demand charges. GHP operating costs are dominated by fuel costs, but also include maintenance costs. The reliability of gas cooling equipment has improved in the last few years and maintenance requirements have decreased (SCGC 1998, Yahagi et al. 2006). Another advantage of the GHP over electric motor-driven is the ability to use the heat rejected from the engine during heating operation. The recovered heat can be used to

3 supplement the vapor compression cycle during heating or to supply other process loads, such as water heating. The use of the engine waste heat results in greater operating efficiency compared to conventional electric motor-driven units (SCGC 1998). In Japan, many hundreds of thousands of natural gas-driven heat pumps have been sold (typically 40,000 systems annually) (Yahagi et al. 2006). The goal of this program is to develop dependable and energy efficient GHPs suitable for U.S. commercial rooftop applications (the single largest commercial product segment). This study describes the laboratory performance evaluation of an integrated 10-ton GHP rooftop unit (a 900cc Daihatsu-Aisin natural gas engine) which uses R410A as the refrigerant (GEDAC #23). ORNL Thermally-Activated Heat Pump (TAHP) Environmental Chambers were used to evaluate this unit in a controlled laboratory environment. EXPERIMENTAL Temperature conditioning for each TAHP chamber is provided by a dedicated glycol fluid loop which circulates glycol at he appropriate temperature through the fluid-to-air heat exchanger in the room. Additional temperature conditioning is provided by sheathed electric heaters located directly in the air stream. Each glycol loop includes a pump, fluid heater and (2) refrigerant-to-glycol heat exchangers. The rooms share a common refrigeration plant consisting of three 30- horsepower compound compressors which provide mechanical refrigeration for the room glycol circuits as well as for the Direct-Expansion (DX) dehumidification coils in each room and the DX precool and postcool coils in the Makeup Air System. The three compound compressors are water-cooled utilizing refrigerant R507 (AZ50). The design temperature range for each room is from -20ºF to +125ºF with a ±1ºF. The humidity range for the indoor chamber (small room) is 18 to 75% RH and the outdoor chamber (larger room) from 18 to 81% RH with humidity tolerances of ±1.5%. Humidity is provided from steam with a capacity of 75 lb/h at 30 psig supplied through a 1 NPT (National Pipe Thread Taper) pipe. Each room has 18 kilowatts of air heaters in addition to 18kW of glycol fluid heater. The test facility features a micro-processor-based control system designed around an Allen-Bradley PLC-5/20 Programmable Logic Controller (PLC). Multiple temperature and humidity control loops reside within the PLC, including several feed-forward and cascade control loops designed to optimize stability and maintain tight control tolerances even under rapidly-changing load conditions. Temperature sensors are 100 ohm Resistance Temperature Detectors (RTD s) with dedicated 4-20mA transmitters. Humidity is monitored with true dew-point sensors (capacitive humidity sensors), providing a reliable indication of actual moisture content unaffected by air temperature.

4 Room enclosures are constructed of 24 gauge embossed galvanized steel walls with foamed-in-place internal insulation, and a 16 gauge galvanized floor. The indoor chamber is 14 8 x 11 4 x H and the outdoor chamber is 14 8 x 19 4 x H. GEDAC #23 heat pump was installed in the outdoor chamber with supply/return air from the indoor chamber. Both supply and return used 20 round flexible insulated duct. The supply consists of a single piece 15 feet in length while the return consists of two pieces 12 feet in length each totaling 24 feet. The flexible ducts are insulated with an R- value of 6. Figure 1 shows GEDAC #23 in the outdoor chamber of ORNL TAHP Environmental Chambers. The layout of GEDAC #23 shows the following spaces between the unit and the exterior walls of the outdoor chamber: Sides: 4.5 ft Front: 2.5 ft Rear: 2.0 ft Top: 5.0 ft Bottom: 32 inches The GEDAC unit was operated over a wide range of ambient conditions including the operating conditions for standard rating and performance tests (ANSI/ARI 340/360 Standard 2004, UL , ANSI/ASHRAE Standard , ANSI Z a Standard 1998). These operating conditions are shown in Tables 1 and 2 for both heating and cooling modes. It should be noted that the unit was charged with 25 lb of R410A. Evaluations were conducted at high ( rpm), intermediate ( rpm), low (1,650 rpm), and lowest (1,400 rpm) speeds of the engine.

5 2.0 ft 4.5 ft GEDAC # ft 2.5 ft Chamber Door Figure 1. GEDAC #23 in the outdoor chamber of ORNL TAHP Environmental Chambers

6 Table 1. Operating conditions for evaluation of GEDAC #23 In Cooling Mode Standard Rating Conditions Steady State* INDOOR UNIT Air Entering DB/WB/DP ( F) 80/67/60.2 OUTDOOR UNIT Air Entering DB/WB/DP ( F) Engine Speed (rpm) 95/75/66.5** 1,400 1,650 Part Load Ratio (PLR) 80/70/ /63/55.8 1,400 1,650 1,400 1,650 67/57/49.8 1,400 1,650 Cooling Steady State* 80/67/ /65/55** 1,400 1,650 Cooling Steady State Dry 80/57/36.8*** 80/65/55** 1,400 Coil* Low Temperature Operation Cooling* 67/57/ /57/49.8** 1,400 1,650 Maximum Operating Cooling Conditions* 75/63/ /67/ /67/60.2 1,400 1,650 1, /75/55** 1,400 1,650 2,200 75/63/55.8 1,400 2,200 High Ambient Temperature 80/67/ /75/58.2** 1,400 1,650 UL 1995 Condition 80/67/ /75/61.8 1,650 Higher Ambient 80/67/ /75/51.3** 1,400 Temperature 1,650 Highest Ambient 80/67/ /75/47.1** 1,400 Temperature 1,650 Ambient Temperature Cooling Cycling Testing 80/57/36.8*** 80/67/60.2** 0.25 (6.67 min on/20 min off) 0.50 (10 min on/10 min off) 0.75 (20 min on/6.67 min off) * Operating Conditions for Standard Raring and Performance Tests (ARI Standard 340/360, 2004). ** Wet bulb temperature condition is not required *** Wet bulb sufficiently low that no condensate forms on evaporator.

7 Table 2. Operating conditions for evaluation of GEDAC #23 In Heating Mode INDOOR UNIT Air Entering DB/WB/DP ( F) OUTDOOR UNIT Air Entering DB/WB/DP ( F) Engine Speed (rpm) Standard Rating Conditions High Temperature Heating Steady State* 70/60/53.5 (max) 47/43/38.7 1,650 Part Load Ratio (PLR) High Temperature Heating Steady State* 65/55.8/48.8 (max) 75/64.2/58.2 (max) 70/60/53.5 (max) 1,650 1,650 62/56.5/52.7 1,650 Low Temperature Heating Steady State* 75/64.2/58.2 (max) 70/60/53.5 (max) 1,650 17/15/9.4 1,650 Maximum Operating Conditions* Ambient Temperature Heating Cycling Test 65/55.8/48.8 (max) 1,650 80/68.5/62.8 (max) 75/65/59.5 1,650 70/60/53.5 (max) 47/43/ (6.67 min on/20 min off) 0.50 (10 min on/10 min off) 0.75 (20 min on/6.67 min off) Frost Accumulation 70/60/53.5 (max) 35/33/30.2 1,650 * Operating Conditions for Standard Raring and Performance Tests (ARI Standard 340/360, 2004). ** Wet bulb temperature condition is not required *** Wet bulb sufficiently low that no condensate forms on evaporator. The natural gas flow, refrigerant flow, and coolant flow rates were monitored by Coriolis mass flow sensors. The natural gas mass flow accuracy 0.06 lb/h. The mass flow accuracies for the refrigerant and water flow meters are ±0.10% and ±0.50%. Temperature probes, rotational speed measuring device, and pressure transducers along with the mass flow sensors were used to monitor GEDAC #23 via a password protected web control-based data acquisition system using Automated Logic Controller (ALC). Heat content (higher heating value) and the composition of the natural gas were obtained daily from the local gas company.

8 The dry-bulb and dew-point temperatures of the return air were monitored by averaging thermistor (BAPI duct averaging thermistor) and chilled mirror (General Eastern Optica Hygrometer) respectively. The National Institute of Standards and Technology (NIST) traceable chilled mirror sensing technology of the Optica Hygrometer measures dew-point temperature by regulating the temperature of a polished metal mirror by the use of optical feedback such that a constant mass of dew or frost is maintained. The temperature of the mirror is measured with a precise PRTD and is, by definition, equal to the dew or frost point. The Optica chilled mirror sensors provide a measurement range from -112 F to 185 F dew-point with 0.4 F or better accuracy. The supply air dry-bulb and dew-point temperatures were monitored by averaging thermistor (BAPI duct averaging thermistor) and capacitive humidity sensor (Vaisala humidity sensor/transmitter) respectively. The Vaisala HMT337 warmed probe which provides NIST traceable measurement in near saturation environment. Fan evaluators (Air Monitor Corporation) were used to monitor the supply air and outdoor flow rates. The fan evaluator is a multi-point, self-averaging Pitot traverse station with integral air straightener-equalizer honeycomb cell, capable of continuously measuring fan discharges or ducted airflow. For the supply air, a 4.5 ft 2 (18 x 36 rectangular) the fan evaluator unit was used with 27 straight-run upstream and downstream of the unit. A differential pressure transducer (Veltron DPT2500-plus, accuracy 0.25% of natural span) calibrated for this evaluator was used to monitor the supply air flow. For the outdoor flow rates from the two fans, two 24 circular ducts (3.14 ft 2 ) Fan evaluator units were used with 24 straight-run upstream of each unit. Two differential pressure transducers (accuracy 0.25% of natural span) calibrated for these evaluators were used to monitor the outdoor air flow rates. Ohio Semitronics, Inc. (OSI) watt-transducer was used to monitor the total electric power consumption of the GEDAC unit. This included the power used by the indoor blower. The OSI unit is a self-powered 0-5 VDC output for 0-5 kw with accuracy of ±0.5% of full scale. Sensors used for these measurements and associated accuracies are shown in Table 2. The required accuracy of the test instrumentation is in accordance with ASHRAE and/or ASME documents (ANSI/ASHRAE , ASME PTC , ANSI/ASHRAE , ASME PTC , ASHRAE ). In addition, a web camera was used to observe the outdoor coil particularly during defrost cycle. The uncertainties for capacity and COP values are estimated to be approximately: 2.3 % for capacity (refrigerant side) 3.4 % for COP (refrigerant side) 4.1 % for capacity (air side) 4.8 % for COP (air side) The data acquisition system calculated and displayed important parameters such as the flow rates, capacities, and COP.

9 Table 3. Major test instrumentation and measurement accuracies Measurement Sensor Range Accuracy Temperature Strap-on thermistors -67 to 302 F Average Temperature Duct averaging thermistor -67 to 302 F Refrigerant pressures Transducer 0 to 750 psig 0.4 F (32 to 158 F) 0.4 F (32 to 158 F) 0.25% of full scale Coolant pressures Transducer 0 to 25 psig 0.25% of full scale Indoor Air flow Fan Evaluator* 0 to 4,400 cfm 2% Outdoor Air flow Fan Evaluators* 0 to 6,000 cfm 2% Coolant flow Natural Gas Flow Refrigerant flow Coriolis mass flow sensor Coriolis mass flow sensor Coriolis mass flow sensor 0 to 7,500 lb/h ±0.5% 0 to 20 lb/h ±0.06 lb/h 0 to lb/h ±0.1% Dew-Point Temperature Chilled mirror -40 to 140ºF ±0.2 F Humidity Transmitters (Dew-Point) Capacitive humidity sensor -40 to 212ºF ±0.4 F Rotational speed Portable tachometer 0 to 5000 rpm ±0.1% Electric power Watt transducer 0 to 5 kw ±0.5% of full scale * A multi-point, self-averaging Pitot traverse station with integral air straightener-equalizer honeycomb cell, capable of continuously measuring fan discharges or ducted airflow. RESULTS More than one hundred fifty cooling and heating tests were conducted on GEDAC #23 at various ambient conditions in a controlled environment (TAHP Environmental Chambers). These included cooling tests up to 125ºF and heating tests down to 17ºF. The data was available on the web via password protected Web Control and Automated Logic Controller (ALC). Figure 2 shows one of the Web Control graphics used for remote monitoring. In addition, a web camera was installed to monitor the frosting pattern on the outdoor coil of this unit. Both of these devices have been proven successful for remote monitoring.

10 Performance Evaluation of GEDAC #23 The GEDAC #23 incorporates a Siemens Simatic S7-224XP programmable logic controller (PLC) for implementation of all controls and automation of the unit. Since previous GEDAC prototypes were based on discrete hardwired logic, one area of interest was to determine how well the GEDAC PLC would control the unit. Preliminary tests were conducted to evaluate the effectiveness of the coils (indoor and outdoor coils) and the Programmable Logic Controller (PLC). GEDAC PLC evaluation resulted in several modifications to the control logic to optimize the performance over a wide range of ambient conditions and engine speeds. This included changes to the logic that controls the air-fuel mixture, engine speed for higher heat loads, and logic to implement high pressure avoidance. After several weeks of operation, the GEDAC lost its ability to run above rpm. After in-depth troubleshooting, it was determined that the filter capacitor that is used to provide a stable voltage to the ignition module was faulty. This defect prevented the ignition module from receiving a stable source voltage for its operation. This capacitor failure was caused by excessive charge-discharge cycling of the capacitor through other devices in the same circuit. A replacement capacitor was installed along with a blocking diode that prevents the unnecessary discharge of the capacitor to the other circuit devices. The overall arrangement now produces a more stable DC source voltage for the ignition module. The PLC makes several temperature and pressure measurements using 0-10 VDC analog input channels. For cost saving considerations, thermistors are used for the temperature sensors. An analog output from the PLC is used as the excitation for these circuits. After numerous tests, it was determined there was an unacceptable degree of difference between chamber temperature measurements and those made by the PLC. Efforts to correct this with alternative methods of curve fitting the thermistor resulted in discrepancies of ±2ºF. It should be noted that the accuracy only needs to be as good as required for the intended control response.

11 Figure 2. Graphic Screens Used in Web Control for Remote Monitoring

12 Thermistor Measurement Implementation in the GEDAC PLC The GEDAC PLC must monitor several analog input signals in order to perform the intended control functions of the GEDAC. Among these input signals are two thermistorbased temperature measurements and two pressure measurements. Thermistors were selected due to their low cost, good overall accuracy, and the overall system s tolerance for extremely high and low temperatures. In addition, the GEDAC internal combustion engine is configured by the manufacturer with a thermistor for monitoring coolant temperature. Previous testing of the PLC using thermocouple inputs for monitoring temperature showed that approach would fail at extremely low temperatures due to sensitivities in the thermocouple module. The thermistor approach did not exhibit any low temperature problems and the overall connection circuit for thermistors is relatively simple to implement. To implement the temperature measurements with thermistors, the PLC uses a simple series circuit to derive the effective resistance in the thermistor as shown in Figure 3. Excitation voltage is provided by a PLC analog output which is configured to source +10 VDC continuously. An internal 250 ohm dropping resistor is used as the sensing impedance across the analog input channel set to a 0-5 VDC range. Figure 3. Schematic Circuit for Thermistor Temperature Sensing The original method of curve fitting developed by Team Consulting used a resistance mapping curve and a temperature conversion subroutine in the PLC logic. Experimental results indicated this method was acceptable for the coolant thermistor. However,

13 excessive error was observed for the ambient thermistor. This provided motivation to develop an alternative method for the PLC ambient temperature readings. The approach used by ORNL for the ambient sensor is similar to the method used by Team Consulting for the coolant thermistor. The same circuit was used. Since the thermistor type is a Precon Type II the appropriate resistance table was converted to a numeric table in Excel. An Excel spreadsheet was then used to calculate the effective ADC counts which PLC would use to calculate the temperature over the range of operating temperatures for the thermistor. This count-temperature curve was then analyzed with MATLAB to determine a simple curve fit algorithm that could be implemented in the PLC. The initial approach used a three segment fit with a first order polynomial. Experimental results for the ORNL algorithm showed excessive difference between the PLC measured temperature and two other measurements produced with the ALC system. Results also varied over time. In an effort to improve the PLC measurement, an external laboratory grade power supply was used to replace the PLC analog output as the excitation source of the thermistor. Experimental results showed some improvement but results still varied over time and the error was more than desired. As a result, a third and final implementation was developed. The final implementation replaced the 250 ohm drop resistor with one having a value of 1.78 k-ohms (1%). This value of resistance provides close to a 5-volt signal when the thermistor senses 160ºF which is the highest anticipated ambient temperature. The external laboratory power supply was removed from the circuit and the PLC analog output was again used as the excitation source for this implementation. A new curve fitting algorithm was designed. For this third approach a three-segment fit was chosen using second-order polynomial fit as calculated by MATLAB for the loglog ADC-count versus temperature plot. The segment transition points were selected to be 80 and 160ºF. Figure 4 shows the overall error over the temperature range of the thermistor. Since the expected range of ambient temperatures is not expected to exceed 160ºF, only the lower two segments were implemented in the PLC. The PLC implementation uses natural logs and exponents to implement this curve. The conversion equation is: 2 R LN adc _ counts R LN adc _ counts R offset tempk Exp Coefficients for the temperature conversion equation are show in Table 4. Initially, the offset term was set to zero. Table 4. Curve-Fit Coefficients Segment 1 Segment 2 R R R

14 Final Error final Error Temp F Figure 4. Curve-Fit Error Over the Temperature Range of Interest Experimental results have shown this third approach performs better than all previous approaches. Figure 5 shows a comparison between the PLC thermistor measurement and a reference reading take from the Automated Logic system. Additional experimentation indicated an offset was needed to correct for a negative bias in the excitation voltage source. An offset value of 3.778K, or 6.8ºF, was then added to correct for this bias. Excitation Accuracy An excitation source is required for the approach used for measuring temperatures with thermistors with the GEDAC PLC. For minimizing implementation cost, a spare analog output was chosen. This provides a relatively high-quality 10 VDC signal for exciting the thermistor circuit. The alternative would be to use an external power supply at additional cost and complexity. There are two important constraints one must consider when using a low-cost excitation source such as the PLC s analog output. First the specification on this module states there is a minimum resistance value the analog output can drive and still remain in specification. This minimum resistance value is 5 k-ohms for voltage source output 1. Another important specification for this module is output accuracy. Vendor documentation 1 indicates the analog output is accurate to ±0.5% of full-scale at 25 C (77 F), and ±2 % of full-scale over the wider range of 0-55 C. Analysis of the range of performance this analog output tolerance would produce is shown in Table 5. 1 Table A-18 Analog Expansion Modules Output Specifications, S7-200 Programmable Controller System Manual SIMATIC, S7-200 Programmable Controller System Manual

15 PLC Readings TE_138B TE_138A 100 Temperature ( F) /4/07 3:21 PM 12/4/07 3:36 PM 12/4/07 3:50 PM 12/4/07 4:04 PM 12/4/07 4:19 PM 12/4/07 4:33 PM Figure 5. Experimental Comparison of the Thermistor Implementation and a Reference Reading from the Automated Logic System Time Table 5. Worst Case Temperature Errors Caused By Analog Output Uncertainty PLC Analog Module Error Specification in Our Design Range of Readings for 85ºF (errors based on output only) Nominal Low High K Worst Case ± 2% ºC ºF K Nominal ± 0.5% ºC ºF Air-Fuel Mixture in the GEDAC PLC The GEDAC PLC controls both fuel-air mixture and throttle position for the engine by modulating two stepper motors. The implementation allows the PLC logic to determine the exact engine speed and fuel efficiency for any given operating condition. Initial testing of the GEDAC indicated some improvement could be made to how the fuel-air mixture and throttle controls were implemented. Over the course of 4 months, numerous tests were conducted at various operating conditions and for both cooling and heating modes. The interactive nature of the mixture and throttle controls with overall performance required a large number of tests to be conducted. In some cases simple trial and error experimentation was used to determine a set of operating constraints that provided acceptable overall operation of the GEDAC with the desired fuel efficiencies and engine speeds. It should be noted that at this time no experimentation has been conducted to optimize NO X and CO X emissions.

16 The implementation of mixture control was optimized around three distinct operating temperature ranges. A graphical representation of this is shown in Figure 6. Under normal conditions there are preset fuel-air mixture values that are used during GEDAC engine startup and initial engine warm-up. Once the engine temperature is within normal operating limits, the fuel-air mixture values are then set based on outdoor temperature and the differential pressure across the compressors. There are two nominal fuel-air mixture offset values that are selected based upon temperature. A simple multiplier is applied to the differential pressure value and added to the offset. This produces a richer value when the outdoor temperature is below 50 or above 100ºF. When the outdoor temperature is within this range, a leaner mixture is produced. This provides for better overall system efficiency and better engine speed stability. The logic to control engine speed is more complex than mixture control. Engine speed is determined by the mode of operation, the demand setting (i.e., stage), and the differential pressure across the compressors (i.e., for overpressure avoidance). The flexibility and power of the GEDAC PLC provides significant capabilities for controlling the engine and the overall GEDAC system. It allows radical changes to be easily implemented without impact to wiring or construction because the changes are made in software, not hardware. It also provides robust capabilities to accommodate sophisticated performance and exhaust emissions controls that may be implemented in the future.

17 Figure 6. Logic Flow Chart for the GEDAC Mixture Control Performance in Cooling Mode Following modifications to the PLC logic, performance evaluations of GEDAC #23 in Cooling Mode were initiated. Table 1 shows the evaluation plan which followed Air-

18 Conditioning & Refrigeration Institute (ARI) Standard 340/360 and Underwriters Laboratories Inc. (UL 1995). Evaluation of the gas engine-driven heat pump unit in cooling mode was completed over a wide range of conditions (engine speeds, outdoor and indoor temperatures, and humidity) including cycling tests at part load ratios (PLR) of 0.25, 0.5, and 0.75 (Table 1). Figure 7 shows the cooling performance of GEDAC #23 at high speed of rpm. It should be noted that at ambient temperatures above 112ºF the PLC would limit the high speed to 2,200 rpm instead of rpm. Gas cooling Coefficient of Performance (COP) goal of 1.2 at ARI steady-state rating condition of 95ºF outdoor (80ºF dry-bulb/60.2ºf dew-point temperatures for indoor) with capacity of 129,617 Btu/h (10.8 RT) was achieved at high engine speed of rpm. Figures 8-9 show the cooling performance at intermediate ( rpm) and lowest speed (1,400 rpm). Additional cooling test was also performed at engine speed of 1,650 rpm (Figure 10). Thermal images of the outdoor coils at 110ºF outdoor temperatures showed fairly uniform distribution over the face of the coils (Figure 11) confirming the results of the CFD model. Energy balance (Q input = Q output ) was also conducted using the following equations (assuming that the heat losses or heat gain caused by radiation and convection are negligible): Q input = Q NG + Q electric + Q IDC Q output = Q ODC + Q fans + Q radiator % Diff Where : Q input Q Q input output 100% Q input = Total energy entering the heat pump (Btu/h) Q output = Total energy leaving the heat pump (Btu/h) Q NG = Natural Gas input (Btu/h) Q electric = Electric power used (Btu/h) Q IDC = Cooling capacity or heat removed in the evaporator (Btu/h) Q ODC = Heat rejected through the outdoor coil (Btu/h) Q fans = Heat added by the fans (Btu/h) Q radiator = Heat rejected through the radiator (Btu/h) % Diff = Absolute percent difference (%) Measured values were used to determine the above-mentioned total energy input and output with the assumption that 80% of the total outdoor air flow goes through the outdoor coils. The largest absolute percent difference was approximately 10% and the lowest was approximately 1% with average value of 5%. It should be noted that the capacities were based on the refrigerant side (more accurate readings from the refrigerant mass flow meter than the indoor air flow and dew-point temperature readings).

19 COP Capacity 140 Cooling Gas COP Cooling Capacity (kbtu/h) Outdoor T ( F) Figure 7. GEDAC #23 cooling performance at high engine speed ( rpm) COP Capacity Cooling Gas COP Cooling Capacity (kbtu/h) Outdoor T ( F) Figure 8. GEDAC #23 cooling performance at intermediate engine speed ( rpm)

20 COP Capacity Cooling Gas COP Cooling Capacity (kbtu/h) Outdoor T ( F) Figure 9. GEDAC #23 cooling performance at lowest engine speed (1,400 rpm) COP Capacity 140 Cooling Gas COP Cooling Capacity (kbtu/h) Outdoor T ( F) Figure 10. GEDAC #23 cooling performance at low engine speed (1,650 rpm)

21 COIL A COIL B Figure 11. Thermal images of the outdoor coils (A and B) at 110ºF outdoor condition

22 Performance in Heating Mode Evaluation plan in heating mode followed ARI Standard 340/360 (Table 2). Evaluation of the gas engine-driven heat pump unit in heating mode was completed over a wide range of conditions (engine speeds, outdoor and indoor temperatures, and humidity) including cycling tests at part load ratios (PLR) of 0.25, 0.5, and 0.75 (Table 2). Figure 12 shows the performance of GEDAC #23 at high speed of rpm. Gas heating COP of 1.4 with capacity of 129,394 Btu/h at ARI steady-state rating condition of 47ºF outdoor was achieved at high engine speed of rpm. Gas COP (Heating) COP Capacity Capacity (kbtu/h) Outdoor Temperature ( F) Figure 12. GEDAC #23 heating performance at high engine speed ( rpm) Figures show the performance at intermediate ( rpm) and low speed (1,650 rpm). Results showed gas heating COP of approximately 1.4 and capacity of approximately with capacity of approximately 11 Btu/h at ARI rating condition of 47ºF outdoor at intermediate engine speed of rpm (Figure 13). Energy balance around the heat pump unit in heating mode is represented by the following equations: Q input = Q NG + Q electric + Q ODC Q output = Q IDC + Q fans + Q radiator

23 % Diff Where : Q input Q Q input output 100% Q input = Total energy entering the heat pump (Btu/h) Q output = Total energy leaving the heat pump (Btu/h) Q NG = Natural Gas input (Btu/h) Q electric = Electric power used (Btu/h) Q IDC = Heating capacity (Btu/h) Q ODC = Heat recovered from the outdoor coil (Btu/h) Q fans = Heat added by the fans (Btu/h) Q radiator = Heat rejected through the radiator (Btu/h) % Diff = Absolute percent difference (%) The heat rejected through the radiator is represented by: Q radiator = Q total coolant Q recovered Where: Q total coolant = Total heat available for recovery (Btu/h) Q recovered = Internal heat recovery from the coolant to the refrigerant in the refrigerant-coolant heat exchanger (Btu/h) Q recovered is calculated from the refrigerant side by the following equations:. Q IDC mrefrig ΔH Q recovered refrig. m refrig C prefrig T refrig Where: C p refrig = Heat capacity of refrigerant at the average temperature entering and leaving the refrigerant-coolant heat exchanger (Btu/lb.ºF). m refrig = Refrigerant flow (lb/h) ΔH refrig = Refrigerant enthalpy change across the refrigerant-coolant heat exchanger (Btu/lb) ΔT refrig = Refrigerant temperature change across the refrigerant-coolant heat exchanger (ºF) The largest absolute percent difference between Q input and Q output was approximately 15% and the lowest was approximately 1% with average value of 7%. As expected, the percent differences in the heating case are larger than the cooling case due to all the additional calculations discussed above. It should be noted that the capacities were based on the air side (no refrigerant flow measurements were obtained at all engine speeds due to the presence of two-phase flow).

24 Gas COP (Heating) COP Capacity Capacity (kbtu/h) Outdoor Temperature ( F) Figure 13. GEDAC #23 heating performance at intermediate engine speed ( rpm) 20 Gas COP (Heating) COP Capacity Capacity (kbtu/h) Outdoor Temperature ( F) Figure 14. GEDAC #23 heating performance at low engine speed (1,650 rpm)

25 Evaluation of the Defrost Cycle Defrost cycle was also evaluated at 35ºF outdoor dry-bulb (DB) temperatures (Table 1) at high speed of 2400 rpm. GEDAC #23 is currently using a demand defrost method integrated into the PLC logic to avoid unnecessary defrost cycles. GEDAC #23 uses the hot gas bypass defrosting system (heat of the pressurized refrigerant is used for defrosting via a bypass loop around the indoor coil) (Byczynski and Reed 1991). The bypass loop is activated via a solenoid valve that opens when the pressure drop across the outdoor coil goes beyond 0.20 WC (initially this was set for 0.31 WC) with hot refrigerant being injected before the TXVs. To measure the pressure differential, caused by the frosting, two identical open ended copper tubes were placed as close as possible to the location of the pressure readings for GEDAC pressure switch. These tubes were connected with equal length of plastic tubing to an Omega Differential Pressure Transmitter Model PX653 scaled at 0-2 WC. The transmitter was factory calibrated and NIST traceable at 25, 50, 75 and 100% Full scale (FS) with accuracy of 0.25% FS. The initial design of the defrost cycle (injecting the bypassed refrigerant before the TXVs) did not provide adequate heat to defrost the coils. This bypass was modified to inject the refrigerant after the TXVs via two capillary tubes x 10. This system provided enough heat to keep the coils free of visible frost and maintaining the pressure drop around 0.2 WC. Figure 15 shows a slight decrease (approximately 3ºF) in the supply temperature during the defrost cycle (from approximately 97ºF to 94ºF). Figure 16 shows a decrease in COP of approximately 7% (from approximately 1.27 to 1.18) with approximately 9% drop in capacity (from approximately 114,993 to 104,732 Btu/h). 110 T Supply T Return T ( F) /10/07 9:36 AM 12/10/07 12:00 PM 12/10/07 2:24 PM 12/10/07 4:48 PM Time Figure 15. GEDAC #23 air supply and return temperatures during defrost cycle

26 COP /10/07 9:36 AM 12/10/07 12:00 PM 12/10/07 2:24 PM 12/10/07 4:48 PM Time Figure 16. GEDAC #23 COP during defrost cycle EnergyPlus Modeling The test plan included conditions required to obtain appropriate correlations for gas engine-driven heat pump model in the EnergyPlus. EnergyPlus is a building energy simulation program for modeling heating, cooling, and other energy use in buildings. Parametric requirements for gas engine-driven heat pump model in EnergyPlus are: Cooling performance curve for each stage (engine speed) o Cooling capacity (Cap) modifier curve as a function of temperature (biquadratic curve) Cap = a cc + b cc *WB + c cc *WB 2 + d cc *EDB + e cc *EDB 2 + f cc *WB*EDB o Energy input ratio (EIR) modifier curve as a function of temperature EIR = a ec + b ec *WB + c ec *WB 2 + d ec *EDB + e ec *EDB 2 + f ec *WB*EDB o Part load fraction (PLF) correlation as a function of part load ratio PLF = a pc + b pc *PLR + c pc *PLR 2 + d pc *PLR 3 o Available waste heat (WH) modifier curve as a function of temperature (bi-quadratic curve) WH = a wh + b wh *EDB + c wh *EDB 2 + d wh *DB + e wh *DB 2 + f wh *DB*EDB

27 Heating performance curve for each stage (engine speed) o Heating capacity (Cap) modifier curve as a function of temperature (biquadratic curve) Cap = a ch + b ch *DB + c ch *DB 2 + d ch *EDB + e ch *EDB 2 + f ch *DB*EDB o EIR modifier curve as a function of temperature EIR = a eh + b eh *DB + c eh *DB 2 + d eh *EDB + e eh *EDB 2 + f eh *DB*EDB o PLF correlation as a function of part load ratio PLF = a ph + b ph *PLR + c ph *PLR 2 + d ph *PLR 3 o Available waste heat (WH) modifier curve as a function of temperature (bi-quadratic curve) WH = a wh + b wh *DB + c wh *DB 2 + d wh *EDB + e wh *EDB 2 + f wh *DB*EDB a, b, c, d, e, and f = Fitted constants DB = Indoor coil entering air dry bulb temperature (ºC) EDB = Outdoor dry bulb temperature (ºC) WB = Indoor coil entering air wet bulb temperature (ºC) Defrost cycle behavior The cycling tests were performed for both heating and cooling (Tables 1 and 2). Tables 4-6 show the fitted constants for Cap, EIR, and available waste heat at different engine speeds. Table 7 shows the PLF at intermediate engine speed (2000 rpm). The R- Square (R 2 ) values are indicators of how well the model fits the data. An R-Square value of 1.0 indicates that the model perfectly fits the data. Engine Speed (rpm) Table 4. Fitted constants for capacity (Cap) modifier curves a b c d e f R-Square (R 2 ) Cooling Mode 1, , E E Heating Mode 1, E

28 Engine Speed (rpm) Table 5. Fitted constants for energy input ratio (EIR) modifier curves a b c d e f R-Square (R 2 ) Cooling Mode 1, , Heating Mode 1, E E Engine Speed (rpm) Table 6. Fitted constants for available waste heat modifier curves a b c d e f R-Square (R 2 ) Cooling Mode 1, , E Heating Mode 1, E E Table 7. Fitted constants for part load fraction (PLF) correlations at intermediate engine speed (2000 rpm) a b c d R Square (R 2 ) Cooling Mode Heating Mode The experimental data used for the above-mentioned capacity, EIR, and available waste heat modifier models are shown in Tables 8-14 (it should be noted that the temperatures were converted from ºF to ºC for the models). The indoor blower power consumptions at low- and high-speeds were measured to be approximately 0.3 kw (approximately scfm) and 1.5 kw (approximately 4,000 scfm), respectively.

29 Table 8. Experimental data used for the model in cooling mode, at lowest engine speed (1,400 rpm) Air Entering T Outdoor Return Air Return Return Natural gas Capacity Power Use Speed Indoor Heat Available Outdoor Coil DP DB Air Air Energy (excluding indoor Blower for Recovery TE138 Average TE137 DP WB Input blower) Air Flow (Coolant) ( F) ( F) ( F) ( F) ( F) (Btu/h) (Btu/h) (kw) (rpm) (scfm) (Btu/h) , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , * , , , ,102.5 * Rated condition used to normalize capacity, EIR, and waste heat curves. Table 9. Experimental data used for the model in cooling mode, at low engine speed (1,650 rpm) Air Entering T Outdoor Return Air Return Return Natural gas Capacity Power Use Speed Indoor Heat Available Outdoor Coil DP DB Air Air Energy (excluding indoor Blower for Recovery TE138 Average TE137 DP WB Input blower) Air Flow (Coolant) ( F) ( F) ( F) ( F) ( F) (Btu/h) (Btu/h) (kw) (rpm) (scfm) (Btu/h) , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , * , , , , , , , , , , , , , , , , , , , , , , , , ,527.2 * Rated condition used to normalize capacity, EIR, and waste heat curves. Table 10. Experimental data used for the model in cooling mode, at intermediate engine speed ( rpm) Air Entering T Outdoor Return Air Return Return Natural gas Capacity Power Use Speed Indoor Heat Available Outdoor Coil DP DB Air Air Energy (excluding indoor Blower for Recovery TE138 Average TE137 DP WB Input blower) Air Flow (Coolant) ( F) ( F) ( F) ( F) ( F) (Btu/h) (Btu/h) (kw) (rpm) (scfm) (Btu/h) , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , * , , , , ,151.0 * Rated condition used to normalize capacity, EIR, and waste heat curves.

30 Table 11. Experimental data used for the model in cooling mode, at high engine speed ( rpm) Air Entering T Outdoor Return Air Return Return Natural gas Capacity Power Use Speed Indoor Heat Available Outdoor Coil DP DB Air Air Energy (excluding indoor Blower for Recovery TE138 Average TE137 DP WB Input blower) Air Flow (Coolant) ( F) ( F) ( F) ( F) ( F) (Btu/h) (Btu/h) (kw) (rpm) (scfm) (Btu/h) , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , * , , , , ,130.2 * Rated condition used to normalize capacity, EIR, and waste heat curves. Table 12. Experimental data used for the model in heating mode, at low engine speed (1,650 rpm) Air Entering T Outdoor Return Air Return Natural gas Capacity Power Use Speed Indoor Heat Available Outdoor Coil DP DB Air Energy (excluding indoor Blower for Recovery TE138 Average TE137 DP Input blower) Air Flow (Coolant) ( F) ( F) ( F) ( F) (Btu/h) (Btu/h) (kw) (rpm) (scfm) (Btu/h) , , , , , , , , , , * , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,061.6 * Rated condition used to normalize capacity, EIR, and waste heat curves. Table 13. Experimental data used for the model in heating mode, at intermediate engine speed ( rpm) Air Entering T Outdoor Return Air Return Natural gas Capacity Power Use Speed Indoor Heat Available Outdoor Coil DP DB Air Energy (excluding indoor Blower for Recovery TE138 Average TE137 DP Input blower) Air Flow (Coolant) ( F) ( F) ( F) ( F) (Btu/h) (Btu/h) (kw) (rpm) (scfm) (Btu/h) , , , , , , , , , , , , , , , , , , , , * , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,553.8 * Rated condition used to normalize capacity, EIR, and waste heat curves.

31 Table 14. Experimental data used for the model in heating mode, at high engine speed ( rpm) Air Entering T Outdoor Return Air Return Natural gas Capacity Power Use Speed Indoor Heat Available Outdoor Coil DP DB Air Energy (excluding indoor Blower for Recovery TE138 Average TE137 DP Input blower) Air Flow (Coolant) ( F) ( F) ( F) ( F) (Btu/h) (Btu/h) (kw) (rpm) (scfm) (Btu/h) , , , , , , , , , * , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,884.9 * Rated condition used to normalize capacity, EIR, and waste heat curves. CONCLUSIONS AND RECOMMENDATIONS Overall, GEDAC #23 unit achieved the performance goals in both heating and cooling modes of operation. Gas COP in cooling mode was found to be approximately 1.2 with capacity of 129,617 Btu/h (10.8 RT) at 95ºF ARI steady-state rating condition. Thermal images of the outdoor coils showed fairly uniform distribution over the face of the coils confirming the results of the CFD modeling. Gas heating COP was found to be approximately 1.4 with capacity of 129,394 Btu/h at 47ºF ARI steady-state rating condition at high engine speed of rpm. The results of this performance evaluation were used to develop a gas engine-driven heat pump model for the EnergyPlus (building energy simulation program). This model will be incorporated in the next official release of EnergyPlus in April The hot gas bypass defrosting circuit provided adequate heat to defrost the coils. This defrost cycle was initiated when the pressure drop across the outdoor coil went beyond 0.2 WC (demand defrost coded into the PLC). Recommendations on future work to improve the next-generation GEDAC units include: Addition of an oxygen sensor on the engine exhaust that could be used by PLC to adjust the air/fuel mixture to achieve the desire oxygen content in the flue. Evaluate a single outdoor coil instead of current two coil system of GEDAC #23 to make the configuration less complex and eliminate at least one TXV. In addition, this would allow the outdoor fans to be used for keeping the engine compartment temperature <150ºF. Provide additional louvers on the engine compartment for air circulation to keep the engine compartment and the coolant pump temperatures <150ºF. Moving the solenoid valves for the oil return (potentially a high maintenance item) closer to the access panel. Evaluate the potential benefits of variable speed blower for better control of the air delivery temperature to the conditioned space. Once the defrost cycle is activated, recommend to keep the solenoid on the bypass loop activated for a minimal period of 10 minutes for more complete defrost.