DIRA S.L. (Desenvolupament, Investigació i Recerca Aplicada S.L.)

Transcription

1 : new refrigerant replacement for R-22 with low Global Warming Potential (GWP). Performance comparison with six existing refrigerants. CARRIED OUT BY DIRA S.L. (Desenvolupament, Investigació i Recerca Aplicada S.L.) Summary The cooling performance results of refrigerant, tested in a calorimeter designed to emulate the cooling conditions, demonstrate that the refrigerant has good energy efficiency, provides high cooling performances with reduced power consumption, and can be conveniently used, therefore, as a suitable replacement for R-22. Index 1. Objective 2. Refrigerants 3. Calorimeter circuit 3.1. Measuring instruments 4. Methods 4.1. Introduction 4.2. Dynamic tests 4.3. Stable state tests 4.4. Suction superheat 5. Results and conclusions 5.1. Cooling capacity, power input and COP 5.2. Suction pressure, discharge pressure and compression ratio 5.3. Discharge temperature 1

2 1. Objective GRIT S. L. (Gases: Research, Innovation & Technology SL), based in Barcelona, asked DIRA SL (Desenvolupament, Investigació i Recerca Aplicada SL) to test and compare the performance of seven refrigerants with regard to energy efficiency and other properties that can be used to obtain a deeper understanding of their behaviour. These tests were performed in DIRA SL (Carretera del Mig, 92, L'Hospitalet de Llobregat), by means of a suitable calorimeter to that effect. Specifically, two types of tests were performed: Dynamic tests Stable state tests 2. Refrigerants GRIT S. L. supplied to DIRA S. L. seven refrigerants, six of which were identified only as numbered samples, so that those in charge of conducting the tests were unaware of their identity. Thus, the set of tests consisted of blind tests. Only the R-22 sample was identified for commissioning the calorimeter, get a reference for determining the evaporation temperature of the different refrigerants and calibrate the sensors installed to monitor the system. The samples were supplied in conventional gas cylinders between 4 and 7 litres. The following designations indicate the different refrigerants: Sample 1 - Sample 2 R-22 Sample 3 MO99 (R438A) Sample 4 MO29 (R422D) Sample 5 MO59 (R417A) Sample 6 RS44 (R424A) Sample 7 RS-45 (R434A) These codes are also used in the graphs and the tables below. 3. Calorimeter circuit The circuit of the calorimeter used in the tests was specifically designed to estimate the performance characteristics of new refrigerants. Compressor Model 1,5 HP K7.2X from GELPHA Equipment designed for R-404A y R-507 Capable of operating in a wide range of temperatures Condenser Air-cooled Model Type HRT/ PN 2

3 Expansion device Danfoss valve TES2 designed for R404A o R507 external balance; then a 3-output capillary distributor was mounted. Evaporator and inertia thermal load The load consisted of a mixture of 25 litres of propylene-glycol and 25 litres of water, contained in a 50 litres cylinder. This load was stirred magnetically in order to achieve good heat transfer and quick thermal equilibrium inside. The evaporator is composed of three copper coils, each one of 15 m of length, wrapped around the container of the thermal load and contained in an outer cylinder. The narrow space between the inner and outer cylinders was filled with a mixture of ethylene glycol and water. 5 litres of each element was introduced to achieve a good heat transfer between the heat load and the evaporator coils Measuring instruments All tests were performed with the same cooling circuit, in the same conditions and with the same tracking equipment. Pressures were measured with a Testo recorder, while temperatures were stored by means of three recorders equipped with four temperature probes each: Testo 177-T4 (1 unit) and Testo 176- T4 (2 units). To these temperature recorders, it must be added a Testo 925, with which the temperature of the mixture of water and propylene glycol was measured. Finally, the power consumption was recorded by electricity meters Landis Gyr. With all this equipment it is possible to measure and record the following variables: Condensing and evaporating pressure. Temperature at the end of condenser. Temperature at the middle of condenser. Compressor discharge temperature. Output liquid temperature from condenser. Surface temperature of the outer cylinder at the top. Surface temperature of the outer cylinder at the middle. Surface temperature of the outer cylinder at the bottom. Evaporator outlet temperature. Inlet liquid temperature into expansion valve. Temperature of the blend propylene glycol-water. Power consumption of the compressor. 4. Methods 4.1. Introduction To cover the full range of required conditions it was necessary to combine dynamic tests with stable-state tests Dynamic tests All refrigerants have been tested using the method described below: First, the mixture of water and propylene glycol is heated using resistors to +50 C in order to provide a heat source to the evaporator. After reaching this temperature, the compressor starts to operate the refrigeration circuit. Heating the mixture to 50 C ensures that the temperature of the evaporator starts at least at +7 C, the maximum temperature required by the evaporator. 3

4 Condensing temperature is kept constant throughout the process at +45 C. This temperature is obtained by controlling the air flow to the condenser. The test ends when the mixture of water and propylene glycol reaches +32 C or reaches stability state conditions. The collected data were recorded and analyzed using Excel software, calculating following key parameters to characterize system performance: The electric power of the compressor (Pot Abs) was obtained by measuring the wattmeter. The cooling capacity of the refrigerant (Pot Frig) was obtained by the sum of the power of the heat load and the contribution of the environment.. Thus, the cooling power is obtained as follows: The COP of the system was obtained from the ratio of Pot Pot Frig and Abs Stable state tests All refrigerants have also been tested in stable conditions to achieve a low evaporating temperature, heating the mixture of water and propylene glycol with thermal loads of 2000, 1500, 1000W, 500W and 0W, maintaining at all times the condenser at +45 C. The Thermal gain obtained from the environment load was calculated using the following expressions: 4.4. Suction superheat Due to the fact that the identity of refrigerants was unknown (except R22) during the tests, it was not possible to calculate the suction superheat using thermodynamic tables. That is why several thermal probes placed around the evaporator were used. 4

5 It is estimated the average evaporation temperature of each refrigerant from data obtained with R22. The final temperature of evaporation can be obtained by adding half the glide to this temperature. From this temperature, it has been tried to have at all times an average of 5 C superheat at the evaporator outlet, since this temperature varies due to the expansion valve. 5. Results and conclusions 5.1. Cooling capacity, power input and COP 5

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7 As seen both in the tables and graphs above, the COP of the (sample 1) is of the same magnitude as that of R-22 (sample 2), achieving high cooling capacities with low consumption Suction pressure, discharge pressure and compression ratio The pressures shown in the following table are obtained from the experimental measurements. These pressures do not precisely coincide with the pressure that would correspond to the different condensing and evaporating temperatures. The values of the power shown in the preceding paragraph have been corrected taking into account the above. 7

8 In the graph it can be observed how the suction pressure of the is a bit lower than that of R-22 in all operating ranges, being very similar to the suction pressure of sample 3. 8

9 5.3. Discharge temperature 9