Development of centrifugal chiller and heat pump using low GWP refrigerant

Transcription

1 Development of centrifugal chiller and heat pump using low GWP refrigerant Ryosuke Suemitsu 1*, Naoya Miyoshi 1, Yasushi Hasegawa 1, Kazuki Wajima 1, Yoshinori Shirakata 1, Kenji Ueda 1 1 Mitsubushi Heavy Industries Thermal Systems, Ltd

2 Today s Presentation 1. Introduction 2. Development of centrifugal chiller using low GWP refrigerant 3. Development of centrifugal heat pump using low GWP refrigerant 4. Conclusions 2

3 Cooling source Heating source 1. Introduction Paris Agreement (in December 2015, COP21) Every country shall update and submit the own country s reduction goal every 5 years. Montreal Protocol Kigali Revision (in October 2016) Mandatory of the HFC production and the step-by-step reduction HFCs (Ex. R-134a) GWP:100~4, s 2000s 2010s Transition of refrigerant The next-generation alternative refrigerant GWP: low Paris Agreement Montreal Protocol (2016) Centrifugal heat pump Centrifugal Chiller We use R-134a as the refrigerant of centrifugal chillers and heat pumps. (USRT) Capacity(kW) ,000 5, ,500 Clean room Building Shopping center/mall Tall building Capacity and temperature needs There is a need to transfer to low GWP refrigerants. 3

4 1. Introduction We need to take into consideration the following requirements to select alternative refrigerants; Environmental conditions: GWP 150, ODP 0.001, allowable concentration 800 ppm. Low toxicity and low flammability Physical properties: The design pressure must not be excessively high, because of the price of machines. Cycle efficiency is equivalent to that of R-134a. Cost Comparison of R-134a and olefins Refrigerant HFC Olefins 134a 1234yf 1234ze(E) 1233zd(E) Global Warming Potential (GWP) *5thIPCC 1300 <1 <1 1 Ozone Depletion Potential (ODP) Allowable concentration [ppm] Toxicity low low low low Flammability non low low non Safety class *ASHRAE34 A1 A2L A2L A1 Saturated pressure (@38 )[kpag] Theoretical COP *@ET=5,CT=38,η= Price / R-1233zd(E) rated value R-1234ze(E) and R-1233zd(E) meet our requirements. 4

5 Cooling source Heating source 1. Introduction We selected R-1234ze(E) and R-1233zd(E) for centrifugal chillers. A R-1234ze(E) type has been developed for the capacity from 300 to 5000 USRt. A R-1233zd(E) type has been developed for the capacity from 150 to 700 USRt. There are still some candidate refrigerants for centrifugal heat pumps. some candidate refrigerants Centrifugal heat pump 1233zd(E) 1234ze(E) Centrifugal Chiller Capacity (USRT) ,000 5,000 (kw) ,500 Clean room Building Shopping center/mall Tall building Capacity and temperature needs 5

6 2. Development of centrifugal chiller Refrigerant Comparison of R-134a and olefins for chiller Refrigerant HFC Olefins 134a 1234ze(E) 1233zd(E) Standard boiling point [ ] Saturated pressure (@6 )[kpag] Saturated pressure (@38 )[kpag] Saturated vapor specific volume (@6 )[m 3 /kg] Theoretical COP *@ET=5,CT=38,η= Price / R-1233zd(E) rated value R-1233zd(E) s cycle efficiency is better than R-134a, and the cost is better than R-1234ze(E). However, the specific gas volume is about five times larger than R-134a. R-1234ze(E) s physical properties are similar to R-134a. Advanced and compact design is made to replace with centrifugal chillers using R-1233zd(E). 6

7 2. Development of centrifugal chiller Compressor Refrigerant 134a 1233zd(E) Saturated vapor specific volume )[m 3 /kg] About five times larger Improvement of aerodynamic design CFD analysis was performed to optimize the impeller, the inlet guide vane, and the path form of refrigerant gas. Reduce to 140% compared with R-134a Ref. outlet Inlet guide vane Compared with R-134a, the volume of compressor reduces to 140%. the adiabatic efficiency is improved by 3% for the same capacity. Path of refrigerant gas Ref. inlet Impeller Outline drawing of centrifugal compressor 7

8 2. Development of centrifugal chiller Compressor Refrigerant 134a 1233zd(E) Saturated vapor sound speed )[m/s] Direct-connected motor For R-134a, the impeller is rotated by the motor via a step-up gear. Lower For R-1233zd(E), the impeller is directly mounted on the motor shaft, as the lower vapor sound speed can be achieved even if the capacity is same. A compact compressor unit with a motor Improved performance by reducing the losses as the result of eliminating the step-up gear and minimizing the number of compressor bearings 8

9 2. Development of centrifugal chiller Evaporator and condenser The shell & tube type heat exchanger, and flooded type evaporator Since the specific gas volume is larger, and the differential pressure between the condenser and evaporator is smaller than R-134a, pressure drop should be carefully considered. We analyzed the actual chiller and measured the verification test Ref. outlet Chilled water Ref. inlet Evaporator Outlet Inlet Ref. inlet Ref. outlet Condenser Cooling water Outlet Inlet 9

10 2. Development of centrifugal chiller Evaporator and condenser Test results of evaporator Test result of condenser Compared with R-134a, The volume of the evaporator and condenser reduce to 120%. The outside heat-transfer coefficient of evaporator registers no more than 10% decrease, and the coefficient of condenser registers no more than 20% decrease at the rated condition. 10

11 2. Development of centrifugal chiller Model machine verification Comparison of specification Model Existing Developed Rated capacity 200 USRt (703 kw) Refrigerant R-134a R-1233zd(E) Chilled water temp C 7.0 C Chilled water flow rate m 3 /h Cooling water temp C 37.0 C Cooling water flow rate m 3 /h m 3 /h Power consumption kw kw COP Dimensions L W H m m Installation area 5.55 m m 2 Shipping weight 3.9 ton 4.3 ton The COP is improved by 3% compared with an existing type that had the same capacity, under the rated capacity conditions. The installation area reduces about 105% that of the existing type for the capacity from 150 to 700 USRt. *machine rated value = 200 USRt Performance Result Test machine appearance 11

12 3. Development of centrifugal heat pump Industrial customers have required us heat pumps to use high temperature heat. Refrigerant We have been developing a high temperature heat pump heating pressurized water to the temperature from 160 C to 200 C The target COP is 3.5 with the aim of boiler replacement. The operational temperature must be considered. This requires the following; Stability at high temperature: Prevention of isomerization and decomposition. Standard boiling point: The size of compressor should not be too small for the adiabatic efficiency. The design pressure should not be too high for the manufacturing. Critical point: The critical temperature should be higher than the operating temperature to improve the efficiency of the cycle. Lubricant oil The lubricant oil must maintain the stability at high temperature, requiring the temperature-dependent viscosity and solubility in the refrigerant. 12

13 3. Development of centrifugal heat pump Refrigerant and lubricant oil First step; We investigated the replacement with a low GWP refrigerant in a 90 C application. Comparison of R-134a and olefins for 90 C applications Refrigerant HFC Olefins 134a 1234ze(E) 1233zd(E) Standard boiling point [ C] Critical temperature [ C] Saturated pressure (@90 C)[MPaA] Saturated vapor specific volume (@30 C)[m 3 /kg] Theoretical COP *@ET=25,CT=91,η= R-1233zd(E) meets our requirements Stability: at up to 150 C but, poor at 200 C We still have some candidate refrigerants. Accelerated thermal stability testing for 90 C applications R-1233zd(E) : Mineral oil Temperature [ C] Test condition Duration [h] Air/moisture [ppm] Result Acid Value [koh/g] 50: /100 < : /100 < : / : / : / Mineral oil was selected Stability of R-1233zd(E): Thermal stability for 90 C applications Enough solubility and viscosity: Kinetic viscosity and solubility are 125% and 112%, compared with requirements for the bearings of up to 160 C applications. 13

14 3. Development of centrifugal heat pump Equipment design Heat pump cycle We adopted the compression bleeding cycle for the temperature from 160 C applications. The bleeding cycle is highly efficient by using some of the refrigerant gas to discharge from the low stage compressor for intermediate heating. The compressors have two-stages compression. Two-stage compression bleeding cycle Aerodynamic shape of compressor The compressor was designed for a high head and large volume flow rate to reduce the number and the capacity. The compression ratio is larger by 40%, compared with a chiller. The flow rate is larger by 39%, and the adiabatic efficiency is improved by 3.5%, compared with an existing type. 14

15 3. Development of centrifugal heat pump Application Heat pumps heating water to the temperature from 160 C to 200 C are suitable for industrial applications, for example, chemical reaction and dried processes. We have been investigating the details to propose a heat system for industrial processes. ex) heat and energy balance operating time temporal axis of thermal demand and heat source Future work The heat pumps operating at high temperature using low GWP refrigerants are going to be developed through the stages, 90 C, 160 C, 200 C. The development of refrigerants and lubricant oil are being conducted in parallel with that of the heat pump. We focus to introduce a model to heat pressurized water to 200 C in practical applications by

16 4. Conclusions and Acknowledgements A centrifugal chiller using low GWP refrigerant have been developed. A R-1234ze(E) type have been developed for the capacity from 300 to 5000 USRt. A R-1233zd(E) type have been developed for the capacity from 150 to 700 USRt. A centrifugal heat pump using a low GWP refrigerant is being developed. In the experiments, R-1233zd(E) was selected for a heat pump heating water to 90 C. The design have been completed and we are preparing for drop-in testing. The developments of heat pumps heating water to 90 C, and higher temperatures are going to be carried out, with a final goal of operation at 200 C. This work is supported by New Energy and Industrial Technology Development Organization(NEDO). 16

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