2B.1 Chilled-Water Return (and Supply) Temperature B.3 Cooling-Water Supply Temperature / Flow

Transcription

1 Appendix 2B: Chiller Test Results B.1 Chilled-Water Return (and Supply) Temperature B.2 Chilled-Water Flow B.3 Cooling-Water Supply Temperature / Flow B.4 Pressure/Temperature Figure 2B - 1: COP variation with change of chilled-water temperature Figure 2B - 2: Cooling load variation with change of chilled-water temperature Figure 2B - 3: COP variation with change of chilled-water Figure 2B - 4: Cooling load variation with change of chilled-water Figure 2B - 5: COP variation with change of cooling-water temperature Figure 2B - 6: Cooling load variation with change of cooling-water temperature Figure 2B - 7: COP variation with change of cooling-water Figure 2B - 8: Cooling load variation with change of cooling-water Figure 2B - 9: COP variation with change of steam pressure Figure 2B - 10: Cooling load variation with change of steam pressure Table 2B - 1: Primary inputs of the test program Table 2B - 2: Primary inputs and outputs of tests varying chilled-water temperature Table 2B - 3: Primary inputs and outputs of the tests by varying chilled-water Table 2B - 4: Primary inputs and outputs of the tests by varying cooling-water temperature Table 2B - 5: Primary inputs and outputs of the tests by varying cooling-water Table 2B - 6: Primary inputs and outputs of the tests by varying steam pressure

2 Appendix 2B: Chiller Test Results The effects of cooling load variations on the chiller performance (chilled-water temperature) have been summarized in sunsections and In the testing program, the effects of the following five operating conditions on chiller performance were tested using the same test approach: chilled-water (and ) temperature chilled-water cooling-water temperature / steam pressure Each of the five operating conditions identified above was varied one at a time over a range of their design values, as indicated in Table 2B-1. Table 2B-1 listed the variable adjusting ranges for each of the five operating parameters. Within its range each operating condition was tested at six to twelve values, and each test obtained 30 to 300 data sets at 2-minute intervals during steady-state operation of the chiller. A total of 51 tests were conducted over an estimated 220 hours of chiller operation. Table 2B - 1: Primary inputs of the test program Chilled-water Chilled - water m 3 /h Primary operation parameters Cooling-water Cooling-water pressure kg/s kpa Chilled water Design Design Design Design Chilled water Design Design Design Design Cooling water T Design Design Design Design Cooling water Design Design Design Design pressure Design Design Design Design Number of tests The results of these tests in terms of the chiller load and the coefficient of performance are reported and discussed in subsection 2B.1 to 2B.4. 2B.1 Chilled-Water Return (and Supply) Temperature There were a total of 11 individual tests of different chilled-water temperatures. The primary inputs and outputs of the chiller are listed in Table 2B-2. In these tests, the chilled-water temperature was set at 7, but when the chilled-water temperature was varied from 10.9 to 22, the chilled- 119

3 water temperature increased from 5.1 to The chiller coefficient of performance and the cooling load are plotted in Figure 2B-1 and 2B-2, respectively. In Figure 2B-1, as the chilled-water temperature increases gradually from 5.14 to 13.53, the COP increases from 1.0 to In Figure 2B-2, the solid curve represents the measured cooling load, and the dashed curve represents the cooling load provided by the manufacturer for a natural-gas-driven chiller with the same cooling capacity and similar structure. The two curves check closely. The primary reason for the cooling load and the COP increase with the increase of chilled-water and temperature is that the heat transfer in the evaporator is facilitated by increasing the chilledwater and temperature. The heat transfer capacity is a function of chilled-water and temperature, and rate. The component and comprehensive computational models will be used in chapter 3 to analyze the quantity effects of the chilled-water and temperature. In the operation of this absorption chiller, increasing the chilled-water and temperatures is one of the effective strategies to save thermal energy consumption. Both the COP and the cooling load are increased by increasing the chilled-water and temperatures. Table 2B - 2: Primary inputs and outputs of tests varying chilled-water temperature Measurement values for chiller inputs Coolingwater Chilled Cooling- water water Measurement values for chiller outputs Condensate Cooling load Test F1 F6 T20 T32 T22 T23 F2 T21 Q cooling COP No. m 3 /h kg/s kg/h kw 120

4 Figure 2B - 1: COP variation with change of chilled-water temperature 1.4 Coefficient of Performance (COP) Thermal COP Overall COP Chilled Water Supply Thermal COP Overall COP Temperature, T32 ( ) Figure 2B - 2: Cooling load variation with change of chilled-water temperature 24 Actual cooling load (kw) Measured data Manufacturer's rated performance data Cooling load Rated performance data Chilled water temperature ( ) 121

5 2B.2 Chilled-Water Flow To investigate how the chilled-water affects the chiller performance and other internal properties of the chiller, the chilled-water was varied from 1.2 m 3 /h to 3.6 m 3 /h in a series of 10 tests. The chilledwater temperature is maintained at 7 by decreasing and varying the chilled water temperature from 17 to The cooling-water temperature is set at 30, but the chiller actually maintains the cooling-water around 31 for all tests. The steam pressure is fixed at 620 kpa, the steam changed on the basis of the cooling loads. The test conditions and primary results are summarized in Table 2B-3. The bold line in the table refers to the design condition. Figure 2B-1 shows that the thermal COP increased from 0.96 to 1.06 as the chilled-water was increased from 1.2 m 3 /h to 3.6 m 3 /h. Figure 2B-2 shows the cooling load changes with the variations of chilled-water for the ten tests. The test results indicate that the chiller can be operated within a broad range of chilled-water from 2 m 3 /h to 3.3 m 3 /h without degrading chiller performance. The cooling load is affected slightly by the chilled-water because of its effect on the heat transfer in the evaporator, but the does not affect the COP and cooling load as much as the chilled-water and temperature. The quantitative analysis of chilled-water on the chiller performance will be discussed on the basis of chiller model in chapter 3. These data show that the best operational, most efficient strategy for chiller operation is to satisfy the cooling load to the extent possible with high chilled-water s and with high (and ) temperature. Table 2B - 3: Primary inputs and outputs of the tests by varying chilled-water Measurement values for chiller inputs Coolingwatewater Chilled- Cooling- water Measurement values for chiller outputs Condensate Cooling load Test F1 F6 T20 T32 T22 T23 F2 T21 Q cooling COP No. m 3 /h kg/s kg/h kw 122

6 Figure 2B - 3: COP variation with change of chilled-water 1.30 Coefficient of Performance (COP) Overall COP Thermal COP Thermal COP Overall COP Chilled Water Supply Flow Rate (kg/s) Figure 2B - 4: Cooling load variation with change of chilled-water 20 Measured cooling load (kw) Cooling load Chilled Water Supply Cooling load Flow Rate (kg/s) 123

7 2B.3 Cooling-Water Supply Temperature / Flow Cooling-water removes heat from the absorber and the condenser. The heat transfer in these two components is a function of cooling-water and temperature. These conditions directly affect both the sorbent and the refrigerant temperature. Lower cooling-water temperature and higher rate effectively remove the heat generated in the absorber and the condenser, so the COP and cooling capacity are high, but if the cooling-water temperature is too low, the chiller is in danger of freezing the evaporator tubes and crystallizing the sorbent in the LTHX. Both situations are harmful to the chiller. The purpose of these tests is to investigate the effects of the cooling water temperature and rate on the chiller performance and other internal properties of the chiller. In these tests, the cooling-water temperature is decreased from to in a total of 12 steady state tests. The test results are plotted in Table 2B-4, Figures 2B-5, and 2B-6. Table 2B - 4: Primary inputs and outputs of the tests by varying cooling-water temperature Measurement values for chiller inputs Cooling- Chilled- Coolingwater water water Measurement values for chiller outputs Condensate Chilled- Cooling water load Test F1 F6 T20 T32 T22 T23 F2 T21 Q cooling COP No. m 3 /h kg/s The cooling-water rate was decreased from 1.55 kg/s to 0.78 kg/s in a total of six steady-state tests. The cooling load for this experiment is lower than the design capacity because the cooling-water temperature is set at 32 instead of 30. The test results are summarized in Table 2B-5, Figures 2B-7 and 2B-8. In the experiments, the chilled-water temperature was set at 14 ; the chilled-water temperature set point was 7, and the steam pressure was fixed at 640 kpa. kg/h kw 124

8 The test results indicate that decreasing the cooling-water temperature is one of the most effective ways for improving the total performance of the absorption chiller. The increase of cooling-water rate can improve the COP and the cooling load of the chiller; but the improvement is less effective than the decrease of cooling-water temperature. Figure 2B - 5: COP variation with change of cooling-water temperature 1.3 Coefficient of Performance (COP) Overall COP Thermal COP (model) Thermal COP Thermal COP Overall COP Cooling Water Supply Temperature ( ) Figure 2B - 6: Cooling load variation with change of cooling-water temperature Measured cooling load (kw) Cooling load Cooling Water Supply Cooling load Temperature ( ) 125

9 Table 2B - 5: Primary inputs and outputs of the tests by varying cooling-water Measurement values for chiller inputs Coolingwater Coolingwater Measurement values for chiller outputs Chilled- Condensate water Cooling load Test F1 F6 T20 T32 T22 T23 F2 T21 Q cooling COP No. m 3 /h kg/s kg/h kw Figure 2B - 7: COP variation with change of cooling-water 1.2 Coefficient of Performance (COP) Thermal COP Overall COP Thermal COP Overall COP Cooling Water Flow (kg/s) 126

10 Figure 2B - 8: Cooling load variation with change of cooling-water 18 Measured cooling load (kw) Cooling load Cooling load Cooling Water Flow (kg/s) 2B.4 Pressure/Temperature The chiller requires steam input to the HTRG to heat the sorbent solution and produce the refrigerant at a pressure/temperature that allows for additional heat transfer to the sorbent and refrigerant production in the LTRG. The pressure of the steam should be appropriate to optimize the chiller performance in terms of the COP and cooling load. If the steam pressure/temperature to the HTRG is too low, it cannot transfer sufficient heat to the sorbent solution, and produce sufficient refrigerant; therefore, both the cooling load and COP are decreased. If the steam pressure is too high, too much refrigerant is generated, consequently the evaporation pressure/temperature may be too low and ice may formed in the evaporator. Excess refrigerant may spill from the refrigerant tray into the sorbent pool in the absorber, loosing its evaporation cooling capacity. If the steam pressure and the solution temperature are too high, corrosion will occur more rapidly in the HTRG and the noncondensable gases will degrade chiller performance. In practice, the sorbent solution temperature should not exceed 160. The chiller control system automatically adjusts the steam valve to avoid excess steam pressure/temperature. Figure 2B-9 shows that a COP increase from 0.61 to 0.99 results from increasing steam temperature from 176 kpa to 644 kpa. It is notable that a steam higher than 300 kpa or 145, changes the COP very little. Figure 2B-10 shows that the cooling loads increase almost linearly with the improvement of steam pressure. The effect of steam pressure/ temperature on chiller 127

11 performance will be further investigated on the basis of a computational performance model developed in chapter 3. Table 2B - 6: Primary inputs and outputs of the tests by varying steam pressure Measurement values for chiller inputs Coolingwater Coolingwater Measurement values for chiller outputs Chilled- Condensate water Cooling load Test F1 F6 T20 T32 T22 T23 F2 T21 Q cooling COP No. m 3 /h kg/s kg/h kw Figure 2B - 9: COP variation with change of steam pressure 1.2 Coefficient of Performance (COP) Thermal COP Overall COP Supply Thermal COP Overall COP Temperature ( ) 128

12 Figure 2B - 10: Cooling load variation with change of steam pressure 20 Measured cooling load (kw) Cooling load Supply Cooling load Temperature ( ) 129