1、640 2009 ASHRAEABSTRACT The COP of the latest fixed-speed centrifugal chiller is more than 6.4 and that of the latest variable-speed centrifugal chiller driven by an inverter reaches a 21.9 COP. This tremen-dous high performance is very effective for advanced heat source systems. Many energy conserv
2、ation studies have been conducted on industrial heat source systems in Japan. But there have been few reports on the heat source systems for busi-ness use. This paper suggests an operation method for the latest fixed-speed and variable-speed chillers based on those unique high-performance characteri
3、stics. The effects of new planning and operation method suited for the heat source system for business use. High-performance data based on actual measurements are used to evaluate the energy conservation. In addition, this paper provides a new planning and operating method for a whole heat source sy
4、stem, including a new estimation method of cooling tower performance, which is a very important element. INTRODUCTIONA high-performance centrifugal chiller, which uses ozone-safe hydrofluorocarbon (HFC) refrigerant and has a high COP greater than 6.0, has been available in Japan since 2000. Many hig
5、h-performance chillers have been installed in industrial heat source systems of semiconductor and flat-screen-display plants. In addition, the variable-speed centrifugal chiller, which is controlled by an inverter panel and has basic high performance, was developed in 2003. Design improvement and co
6、ntrol modifications have been implemented to correspond to actual operational trends, and the latest inverter chiller has high capability of following the cooling water temperature and cooling load today.The conventional centrifugal chiller has the highest performance at the maximum load point and t
7、ends to have low performance in the partial load range and different cooling water temperatures. Therefore, centrifugal chillers are oper-ated by the quantity control method, which maximizes the operation time at the maximum load point. The latest inverter centrifugal chiller has a load range with t
8、he highest COP at each cooling water temperature; thus, a new operation method that allows operation at the maximum chiller COP range is suggested. In Japan, about 60% to 70% of the centrifugal chill-ers are operated as the heat source equipment of industrial heat source systems. Many large-scale se
9、miconductor and flat-screen-display plants have been constructed in the past several years, and high-performance centrifugal chillers have been installed as energy-saving heat source facilities for the clean rooms of these plants. These industrial heat source systems have large cooling capacity and
10、energy consumption; therefore, it is very important to research and report the indus-trial heat source system in terms of high performance, energy conservation and high system COP. However, the research on high performance and energy conservation of the latest centrifugal chillers has been inadequat
11、e for commercial use heat source systems, which are primarily used for air-condi-tioning.Consequently, in this paper, the energy conservation of the air-conditioning load for commercial use is evaluated.Unlike the industrial heat source system, the cooling load of the air-conditioning heat source sy
12、stem is influenced heavily by climate conditions. A simulation is performed by using the measured air-conditioning load, meteorological data and by Energy Conservation Effects of Heat Source Systems for Business Use by Advanced Centrifugal ChillersKenji Ueda Yoshie Togano Yoshiyuki Shimoda, PhDKenji
13、 Ueda is a manager in the Air-Conditioning and Refrigeration System Headquarters, Mitsubishi Heavy Industries, Ltd., Takasago, Hyogo, Japan. Yoshie Togano and Kenji Ueda are graduate students and Yoshiyuki Shimoda is a professor in the Division of Sustainable Energy and Environment, Osaka University
14、, Suita, Osaka, Japan.LO-09-060 2009, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2009, vol. 115, part 2. For personal use only. Additional reproduction, distribution, or transmission in either print or digital fo
15、rm is not permitted without ASHRAEs prior written permission.ASHRAE Transactions 641establishing a performance evaluation method for the cooling towers. The actual measured data of the latest chiller as of 2007 is used to evaluate the performance of centrifugal chillers. To install all the needed va
16、riable-speed chillers costs much more than installation of the fixed-speed chillers. Therefore, operation with the appropriate combination of fixed-speed and variable-speed chillers and a control method are reported. An energy conservation is evaluated for the (1)latest fixed-speed chiller, (2) late
17、st variable-speed chiller, (3) combination of latest fixed-speed and variable-speed chillers. PERFORMANCE OF HIGH-PERFORMANCE CENTRIFUGAL CHILLERSThe centrifugal chiller is a large-capacity heat pump thatconsists of the main centrifugal compressor and shell and tube type of evaporator and condenser.
18、 The latest high-perfor-mance centrifugal chiller has three characteristics: a high-effi-ciency compressor (aerodynamic performance is improved by the impellor and static channel), high-efficiency heat exchang-ers and high-level arithmetic control. The performance of the latest centrifugal chillers
19、is measured in a wide range of cooling water temperature and cooling load.Performance Test The performance test is conducted to understand how dependent the chiller performance is on cooling water temperature and cooling loads. The cooling capacity of the test chiller is 530 ton (1864kW). The specif
20、ications according to the JIS (Japanese Industry Standard) require 44.6F (7C) chilled water leaving temperature, 57.2F (14C) chilled water entering temperature, 89.6F (32C) cooling water entering temperature, and 98.6F (37C) cooling water leaving temperature.The testing facility is equipped with an
21、inverter power source, and tests of the variable-speed (to control rotation-speed of the compressor) and the fixed-speed chillers can be implemented. The COP at the rated point is 6.3 for the fixed-speed chiller and 6.13 for the variable-speed chiller. Theperformance test results are shown by the CO
22、P calculated from Equations (1) to (4).(1)(2)(3)(4)whereCOP =coefficient of performance of centrifugal chiller, Q = cooling capacity, kW= temperature of entering chilled water, F (C) = temperature of leaving chilled water, F (C)= specific weight of water, lb/ft3(kg/m3)= specific heat of water, kJ/lb
23、F (kJ/kgK)= flow rate of water, ft3/s (m3/s)= electric power consumption, kW= electric power consumption of inverter, kW= electric power consumption of main motor, kW= electric power consumption of control panel, kWThe cooling capacity is calculated from Equation (2) by using the specific heat and g
24、ravity value at the average temper-ature of the chilled water. The electric power consumption of the variable-speed chiller is the sum of the inverter input power (Einv) and control panel input power (Ectl). (See Equation (3).) Electric power consumption of the inverter panel consists of the input p
25、ower of the main motor, electric power loss of the inverter panel and electric consumption power of the inverter control panel and inverter cooling fan. The input power of the control panel includes the electric consumption power of the control motor for the inlet guide vane, hot gas bypass valve, e
26、xpansion valve, control board, relays, oil pump and oil heater.The electric power consumption of the fixed-speed chiller is the sum of the main motor input power and control panel input power (See Equation (4).)Accuracy of Performance TestThe uncertainty of the COP derived from actual measure-ments
27、is evaluated in accordance with ASME-applicable crite-ria. The uncertainty of COP comprises the accuracy of each measurement sensor and converter, and they are propagated independently. The COP calculated from Equation (1) relies on the relative accuracy of each measurement value of the chilled wate
28、r entering temperature, chilled water leaving temperature, chilled water flow rate, chilled water specific heat, chilled water density, and electric power consumption. The verification test is implemented if the chilled water flow rate is constant; therefore, care must be taken during the partial lo
29、ad operation because the uncertainty increases due to small temperature differences between the chilled water entering and leaving. The temperatures are measured by sensorsconnected to the converters and receivers in series. Therefore, the measurement sensors of the chilled water entering and leavin
30、g temperatures are put in the constant-temperature zone that is regulated to be 50.9F (10.5C) together with a refer-ence sensor, and each sensor is adjusted to indicate the same temperature after equilibrium is attained. The final displayed temperatures are measured. The water flow rate is measured
31、by the orifices for the measurement connected with differen-tial pressure transmitters and receivers. The orifice diameter and pipe internal diameter are measured and zero-point adjust-ment is implemented by the differential pressure gauge to minimize the relative tolerance of the flow rate. As a co
32、nse-quence of reducing the uncertainty in the measurement, the uncertainty can fall in the 2.64% at 100% cooling capacity range and 5.98% at 40% cooling capacity range. The uncer-COPQE-=Qtintout() Fl=EEinvEctl+=EEmtEctl+=tintoutFlEEinvEmtEctl642 ASHRAE Transactionstainty of the variable-speed chille
33、r is much higher than the fixed-speed chiller due to the relative accuracy of the inverter consumption power.Performance Test Result The performance test results shown in Tables 1 and 2 areplotted in Figures 1 and 2. The load is indicated by the smooth curve which is made by all connected points at
34、the same cool-ing water leaving temperature. Both the fixed-speed and vari-able-speed chillers tested by the same machine are plotted in the same graph. The differences are described below:Evaluation of the COP of the Latest Fixed-speed Chiller. The latest fixed-speed chiller is operated in a coolin
35、g water temperature range from 55.4F (13C) to 98.6F (37C).The latest fixed-speed chiller shows the highest COP at the maximum load point. The COP is lower as the load becomes lower due to the characteristic of the inlet guide vanes which control the load by controlling the refrigerant gas flow at th
36、e suction of the centrifugal compressor. It is reported that the aerodynamic loss of the centrifugal compressor is higher as the inlet guide vanes opening is lower. The COP is higher as the cooling water temperature becomes lower due to the lower head by smaller temperature difference between chille
37、d water and cooling water temperature. The maximum chiller COP exceeds 11 and the maximum chiller COP is 80 % higher than the COP at rated point, which is a 100% loading and 98.6F (37C) cooling water leaving temperature. Evaluation of the COP of the Latest Variable-speed Chiller. The latest variable
38、-speed chiller is operated at a cool-ing water temperature from 55.4F (13C) to 98.6F (37C)and shows a very high COP. It has the load, not maximum load,of the highest COP at each temperature of cooling water leav-ing. The maximum chiller COP exceeds 20.0.The COP curves of 60.8F(16C) and 68F(20C) in F
39、igure 2 show the charac-teristic obviously. The peak COP of 60.8F(16C) cooling water temperature is about 18 around 50% cooling load and that of 68F(20C) cooling water temperature is over 13 around 60% cooling load. These COP curves of the latest vari-able-speed chiller are obtained only by the rota
40、tion-speed control, which does not have any loss, over 60% load range and by vane control, which has loss, together with the rotation-speed control under 60% load range. The unique characteristic of the latest variable-speed chiller is confirmed through the comparison between Figures 1 and 2.The COP
41、 of the variable-speed chiller is less than that of the fixed-speed machine at the rated point, which is a 100% loading and 98.6F (37C) cooling water leaving temperaturedue to the inverter loss. The COP at 98.6F (37C) cooling water leaving temperature except around 100% load is almost the same as th
42、at of the latest fixed-speed chiller. Because the compressor rotation-speed of the latest fixed-speed chiller is optimally designed on the condition of 98.6F (37C) cooling water leaving temperature. And this rotation-speed shall be Table 1. COP of Fixed-Speed Centrifugal Chiller (Latest)Type of Chil
43、ler Temperature of Leaving Cooling WaterCooling Load Uncertainty98.7F,(37C)95F,(35C)86F,(30C)77F,(25C)68F,(20C)60.8F,(16C)55.4F,(13C)Fixed Speed (Latest)100% 2.62% 6.32 6.62 7.39 8.40 9.85 11.680% 3.17% 5.99 6.27 7.08 8.04 9.24 10.860% 4.09% 5.61 5.81 6.44 7.36 8.43 9.6940% 5.97% 4.69 4.87 5.34 5.96
44、 6.85 8.11 9.6720% 11.7% 2.95 3.05 3.29 3.64 4.31 5.24 6.76Table 2. COP of Variable-Speed Centrifugal Chiller (Latest)Type of Chiller Temperature of Leaving Cooling WaterCooling Load Uncertainty98.7F,(37C)95F,(35C)86F,(30C)77F,(25C)68F,(20C)60.8F,(16C)55.4F,(13C)Variable Speed (Latest)100% 2.64% 6.1
45、3 6.56 7.95 9.62 11.9 14.080% 3.18% 6.13 6.59 8.13 10.2 13.4 16.560% 4.10% 5.67 6.16 7.62 9.93 13.6 17.840% 5.98% 4.43 5.02 6.58 8.90 12.7 17.4 22.420% 11.7% 2.96 3.27 4.05 5.94 9.09 12.9 20.7ASHRAE Transactions 643applied to the latest variable-speed chiller as well at 98.6F (37C) cooling water lea
46、ving temperature. The compressor rotation-speed of the variable-speed chiller is controlled lower as the cooling water leaving temperature is lower from 98.6F (37C). Therefore, the COP difference between Figures 1 and 2 increases as cooling water temperature becomes lower.ESTIMATION MODEL OF COOLING
47、 TOWER PERFORMANCEOne of the features of both types of the latest centrifugal chiller is the capability of following the cooling water temper-ature for performance improvement. It is very important to calculate the cooling water temperature accurately to evaluate Figure 1 COP curves of fixed-speed c
48、hiller. Figure 2 COP curves of variable-speed chiller.644 ASHRAE Transactionsthe energy consumption of the heat source system; therefore, the calculation method of the cooling tower performance is included in the simulation.In this paper, the heat source system comprises of chillers, chilled water p
49、umps, cooling water pumps, cooling towers and system controllers. The heat source system is evaluated by calculation results of the energy consumptions of chillers, pump motors, and cooling tower fans.Performance-Estimation ModelFigure 3 shows the performance calculation procedure of the open-circulating cooling tower. In the estimation model, the performance of filler is dealt with a heat transfer unit, NTU_F-, and is shown by the standard equation, Ka, of the thermal voltage, which uses t
