Optimum Refrigerant Charge Research Articles

Optimal Charge Amount for Different Refrigerants in Air-to-Water Heat Pumps

This paper describes an experimental study on the heat pump performance and compressor suction pressure, in order to find out the optimal refrigerant charge amount for different refrigerants. Independent of the choice of refrigerant, environmental and safety problems can be reduced by detecting the optimal amount of refrigerant charge in the heat pumps or refrigeration systems. In this investigation, a laboratory air-to-water heat pump was built to find out the charge effects on the coefficient of performance and heating capacity for three different gases including R22, R134a and R404a. Gas injection was done gradually into the system, and results were obtained and recorded at each stage. It was shown that refrigerant overcharge and undercharge decrease performance of the unit. Although heating capacity increases gradually, compressor work increases with additional charge and there must be an optimum charge amount to obtain the maximum coefficient of performance.

Experimental investigation on dynamic performance of air-source heat pump water heater using R134a

This paper describes the experiment carried out to analyse the effects of improper refrigerant charge and incorrect thermal expansion valve (TXV) opening on the ASHPWH using R134a. The performance of the system were measured in combinations of four refrigerant charges of 70%, 85%, 100% and 115% of the optimal value and three TXV opening of 30%, 45% and 60% of full opening at ambient temperature of 20°C D/15°C W (dry-bulb temperature/wet-bulb temperature). The results showed that the maximum coefficient of performances (COPs) were nearly 33%, 31.9% and 4.4% higher than that of 70%, 85% and 115% of the optimal refrigerant charge at 60% TXV opening, respectively. And it was found that the increase in TXV opening can enhance the COP when water temperature exceeded 30°C. Besides, an exergy analysis was conducted to evaluate the thermodynamic performance of the system and components in this study.

Partial load performance test of residential heat pump system with low-GWP refrigerants

This study investigated the partial load performance of an RAC unit using R-410A, R-32 and an HFO blend (R-446A). When compared to the optimal refrigerant charge of the R-410A system, that for the R-32 system was 20% lower and that for the R-446A system was 10% lower. The EER of the R-32 and R-446A systems at the same capacity under a full load were 104–110% and 97–98% that of the R-410A system, respectively. The compressor input powers in the SEER and SCOP conditions relative to those of the R-410A system were lower by a maximum of 9% and 7% for the R-32 system and higher by a maximum of 9% and 4% for the R-446A system. The overall SEER and SCOP values relative to those of the R-410A system were higher by 8% for the R-32 system and 1% for the R-446A system.

Experimental study of a miniature vapor compression refrigeration system with two heat sink evaporators connected in series or in parallel

A miniature vapor compression refrigeration system included two heat sinks connected in series (indicated as series system) or in parallel (indicated as parallel system) was built. The performance of the series system was studied and compared with that of the parallel system. The results indicate that the largest cooling capacity of the two systems is about 160 W and the optimal refrigerant charge is about 0.6 Mtotal in the miniature vapor compress refrigeration (VCR) system. There is no relation between the optimal refrigerant charge and the arrangement of the heat sinks. The coefficient of performance (COP) of the series system ranged from 1.81 to 3.22, while the COP of the parallel system was in the range of 1.51–2.92 under the cooling capacity of 100 W. The cooling of the heat sink 2 lag behind that of the heat sink 1 in the serial system, while the refrigerant is difficult to equally distribute in the parallel system.

Effects of refrigerant charge and structural parameters on the performance of a direct-expansion solar-assisted heat pump system

The direct-expansion solar-assisted heat pump (DX-SAHP) is widely studied as a refrigeration system, which can supply hot water for domestic use during the whole year. The system refrigerant charge and structure parameters are believed to have a great effect on the cycling thermal performance. The refrigerant mass charge including two-phase and single-phase in heat exchangers and pipes is calculated with distributed and lumped parameter approach mathematical models, respectively. Based on the system simulation program, the refrigerant distribution characteristics and system performance under varied structural parameters are obtained. The mathematical calculation results show that the 70%–80% refrigerant charge exists in the condenser and collector; the optimum refrigerant charge, solar collector area, condenser pipe length and condenser internal diameter for the system are 1.65–1.75 kg, 6.0 m2, 70 m and 9 mm, respectively. In the optimum parameters, the better system performance and feasible cost can be achieved.

Optimum Refrigerant Charge of Refrigerator Working with Alternative Refrigerants for R12 (R134a, R600a and R290)

This study presents the impacts of suitable refrigerant charge to test the performance of laboratory refrigerator rig for using three refrigerants of (R134a, R600a and R290) instead of R12 .The coefficient of performance and maximum consumption amperes are taken as function to evaluate the optimum charge of these refrigerants. The results imply that the over refrigerant charge will reduce the system performance. Compared the optimum refrigerant charge of R600a is (45g), R290 is (70 g) and R134a is (60g), instead of R12. The results show that the refrigerator with R134a gives lowest capacity reduction with same performance to R12 from other alternative refrigerant, and can be taken as the best alternative refrigerant.

Experimental Assessment of residential split type air-conditioning systems using alternative refrigerants to R-22 at high ambient temperatures

Steady state performance of residential air conditioning systems using R22 and alternatives R290, R407C, R410A, at high ambient temperatures, have been investigated experimentally. System performance parameters such as optimum refrigerant charge, coefficient of performance, cooling capacity, power consumption, pressure ratio, power per ton of refrigeration and TEWI environmental factor have been determined. All refrigerants were tested in the cooling mode operation under high ambient air temperatures, up to 55°C, to determine their suitability. Two split type air conditioner of 1 and 2 TR capacities were used. A psychrometric test facility was constructed consisting of a conditioned cool compartment and an environmental duct serving the condenser. Air inside the conditioned compartment was maintained at 25°C dry bulb and 19°C wet bulb for all tests. In the environmental duct, the ambient air temperature was varied from 35°C to 55°C in 5°C increments. The study showed that R290 is the better candidate to replace R22 under high ambient air temperatures. It has lower TEWI values and a better coefficient of performance than the other refrigerants tested. It is suitable as a drop-in refrigerant. R407C has the closest performance to R22, followed by R410A.

Performance test of residential heat pump after partial optimization using low GWP refrigerants

The present study aimed to improve the performance of the residential heat pump using R-32 and L-41b as a HFO blend after partial optimization by modifying heat exchanger and compressor discharge volume as well as providing the drop-in test data using low GWP refrigerants. Cooling and heating capacities, COP, discharge temperature, pressure drop of evaporator and condenser of the residential heat pump system were measured in case of drop-in test and test after partial optimization. Optimal refrigerant charge for R-32 and L-41b systems was less by 18–25% than that of R-410A system. Capacities of R-32 and L-41b systems through the drop-in test showed 105% and 89–94% of those of R-410A system respectively, while the COP of R-32 and L-41b systems showed 99–101% and 104–105% of those of R-410A systems, respectively. Discharge temperatures of R-32 system showed up to 94.7 °C, while those of L-41b system showed up to 86.4 °C through the drop-in test. Cooling and heating capacities of R-32 and L-41b systems after partial optimization showed 99% and 101% of those of the R-410A system. Discharge temperatures of R-32 and L-41b systems after partial optimization were 81.8 °C and 85.2 °C under cooling standard mode, while they were 81.7 °C and 80.2 °C under heating standard mode. Pressure drops of heat exchanger by using L-41b after partial optimization were lower by 8% under cooling mode and 11% under heating mode for condenser and by 21% under cooling standard mode and 7% under heating standard mode for evaporator than those in case of drop-in test.

An experimental study on charge optimization of a trans-critical CO2 cycle

The phasing out of hydrochlorofluorocarbon and chlorofluorocarbon fluids and further environmental problems arising from new, synthetic working fluids stimulate a continuously rising interest on natural candidates. The nontoxic and nonflammable CO2 impacts neither on ozone depletion nor on global warming if leaked to the atmosphere. The critical temperature of CO2 (31.1 °C) is almost ambient and, therefore, it undergoes a trans-critical refrigeration cycle. In cooling mode operation, a trans-critical CO2 system, as compared to conventional air-conditioners, has a lower performance which, contrary to conventional systems, strongly depends on the refrigerant charge. In this paper, the performance of the trans-critical system was evaluated experimentally under different refrigerant charge amounts. The influence of charge on coefficient of performance (COP), cooling capacity, compression ratio, suction line superheat was analyzed in detail. The experimental results indicate that the COP of the trans-critical cycle attains a maximum at optimal refrigerant charge. By varying the charge the cooling capacity attains a maximum, as well, that corresponds to the optimal charge. In order to understand the effect of refrigerant charge on the performance of each device of the plant, an exergetic analysis based on the experimental data was carried out. The analysis shows that the exergy flow destroyed in the compressor is one of the major causes of overall exergy destruction. At the optimal refrigerant charge, the compression losses attain a minimum.

나선형 핀-튜브 증발기를 적용한 냉장고의 성능 특성에 관한 연구

본 연구는 평판 핀-튜브 증발기와 나선형 핀-튜브 증발기를 적용한 가정용 냉장고의 성능특성 비교를 통하여 기존에 사용하고 있는 핀-튜브 증발기를 나선형 핀-튜브 증발기로 대체할 수 있는 가능성을 고찰하는데 그 목적이 있다. 실험은 2 단 15 열의 평판 핀-튜브 증발기와 2 단 15 열에서 2 단 11 열까지 열 수를 단계적으로 감소시킨 3 종류의 나선형 핀-튜브 증발기를 실제 냉장고에 적용하여 수행하였다. 핀-튜브 증발기의 열 수가 감소할수록 냉동시스템의 최적 냉매 충전량은 감소하였으며, 2 단 13 열과 2 단 11 열의 나선형 핀-튜브 증발기를 장착한 냉장고의 소비전력은 기존 2 단 15 열의 평판핀-튜브 증발기를 적용한 냉장고 대비 각각 1.5%와 2.8% 감소하였다. 또한 내착상 실험결과 나선형 핀-튜브 증발기가 기존 평판 핀-튜브 증발기와 비교하여 같은 착상조건에서 3~7% 향상된 냉각능력을 보였다. 냉각속도 실험에서는 모든 증발기는 동등수준의 성능을 나타내었다.

PERFORMANCE OF R-1234YF IN MOBILE AIR CONDITIONING SYSTEM UNDER DIFFERENT HEAT LOAD CONDITIONS

"Drop-in" tests of R-1234yf in a mobile air conditioning (MAC) system were conducted, and the system performance results were compared with those of the same system using R-134a. The performance tests were performed in a psychrometric calorimeter test facility based on enthalpy-difference method. The system performance was investigated under low-, middle- and high-load conditions. The results showed that the optimum refrigerant charge of R-1234yf was approximately 90% compared with that of R-134a under the same MAC system. When operated under optimum refrigerant charge, the system cooling capacity and COP of R-1234yf was 11% and 8.3% lower than that of the R-134a system, respectively. When wind tunnel test was conducted on a practical vehicle, the result showed that the carriage temperature in the vehicle with the R-1234yf system dropped slower. The average carriage temperature and blower outlet temperature were 2°C higher than those of the R-134a system during the test.

Experimental analysis of the low-GWP refrigerant R1234yf as a drop-in replacement for R134a in a typical mobile air conditioning system

This study investigated the performance of a typical mobile air conditioning system using R134a and R1234yf as the working fluids under different working conditions. The system is composed of a microchannel parallel flow condenser, a laminated plate evaporator, a variable displacement compressor, and a thermal expansion valve. The different working cycles of each refrigerant were comprehensively compared. The optimum refrigerant charge amount of the R1234yf system was approximately 95% of the R134a system during drop-in tests. The performance of the R134a system was a little higher than that of the R1234yf system. The cooling capacity and system coefficient of performance of the R134a system were 12.4% and 9% larger, respectively. This result is mainly because of the thermophysical property differences between the two refrigerants and the improper expansion valve opening of R1234yf. Analysis on the whole cycle revealed that the R1234yf system could obtain a higher evaporating pressure and a larger superheat and subcooling. Redesigning the expansion valve for R1234yf could improve performance of the system.

Performance Experiment of Natural Refrigerant Cascaded Refrigeration System

In this paper, the performances of natural refrigerant R290/CO2 cascaded refrigeration system using R290 as high temperature cycle refrigerant and CO2 as low temperature cycle refrigerant were investigated experimentally. The test results show that both CO2 compressor and R290 compressor start up stably and present good running performance. The start-up power and start-up electric current of CO2 compressor are higher than that of R290 compressor. The COP (Coefficient of performance) of R290/CO2 cascaded system enhances with the increase of cooling water mass flow rate and the decrease of cooling water inlet temperature. The effect of CO2 refrigerant charge on the COP of cascaded system is obvious; however, the effect of R290 refrigerant charge on the COP of cascaded system is not obvious. Hence, the hermetic scroll type compressor is urgent to be developed and used in CO2 cycle for ensuring run safely and reliably, the value of cooling water mass flow rate and the cooling water inlet temperature must be selected reasonability for saving water resource and energy, as well as the charge amount must be determined by experiment for obtaining the optimum refrigerant charge.

Performances of a split-type air conditioner employing a condenser with liquid–vapor separation baffles

In this paper, a kind of heat exchanger with liquid–vapor separation baffles used as condenser was proposed for enhancing its thermal performance. Two HCFC22 air-conditioning units using the new heat exchanger and the traditional fin-and-tube heat exchanger respectively were constructed. The optimal system refrigerant charge amount and capillary tube length for both systems were experimentally investigated. The results showed that the enhanced condenser unit could supply the equivalent cooling capacity and energy efficiency ratio (EER) as those of the baseline one at the standard cooling condition when it had only 63.1% condenser heat transfer area and 80.3% charge amount of the baseline unit. Compared with the baseline unit, the cooling capacity and EER of the new unit were reduced more significantly at undercharge conditions, but their degradations were limited at overcharged conditions. Discharge and suction pressure, mass flow rate, subcooling and superheating degree were also investigated and discussed.

지열 히트펌프에서 운전변수가 냉난방 성능에 미치는 영향에 대한 실험연구

In this research, an experimental study is performed to investigate the effects of system operating variables on the cooling and heating characteristics of heat pump system using geothermal heat source and carbon dioxide as a refrigerant. System variables analyzed include compressor frequency, electronic expansion valve opening, refrigerant charge, secondary fluid temperature and flow rate. Results show that optimum refrigerant charge and electronic expansion valve opening position exist at the maximum point of COP curve, and both cooling and heating capacity increase but COPs decrease with the increase of compressor frequency. The change of a secondary fluid temperature leads to variation of overheat area and enthalpy difference in the evaporator and gas cooler. which again results in considerable variations of cooling and heating capacity and COP. In the case of effects of secondary water fluid flow rate, both cooling capacity and COP increase with the increase of secondary flow in evaporator or gas cooler, whereas heating capacity and COP decrease with the increase of flow rate in gas cooler.

단일유로 멀티사이클 및 바이패스유로 멀티사이클 적용 냉동시스템의 성능특성에 관한 실험적 연구

The object of this study is to investigate the performance characteristics of refrigerators using a single-circuit multi cycle and a bypass two-circuit multi cycle. Each refrigeration cycle was tested by varying secondary fluid mass flow rate and temperature. Based on the experimental data, the optimum refrigerant charge was 48 g and the COP at the optimum secondary fluid mass flow rate was 1.53 for the single-circuit multi cycle. For freezer(F)-only mode, both the single-circuit multi cycle and the bypass two-circuit multi cycle were operated at overcharge conditions, resulting in an increase of the secondary fluid mass flow rate. The maximum COPs of the single-circuit multi cycle and the bypass two-circuit multi cycle were 1.22 and 1.35, respectively. The COP increased by 10.7% with the application of the bypass two-circuit multi cycle.

이산화탄소 급탕 열펌프의 운전조건에 따른 성능 특성에 관한 실험적 연구

In this study, the steady state performance of a <TEX>$CO_2$</TEX> heat pump water heater was measured with a variation of operating conditions such as refrigerant charge amount, compressor frequency, EEV opening, and water mass flow rate. Transient state performance tests were also conducted to investigate major system effects associated with the interaction between the <TEX>$CO_2$</TEX> heat pump water heater and the water tank. Optimum refrigerant charge amount for the system was 1600 g. At compressor frequencies of 50 Hz and 60 Hz, water mass flow rates of 95 kg/h and 105 kg/h, and EEV opening of 8% and 16%, the water heating temperatures were <TEX>$65^{\circ}C$</TEX> and <TEX>$68^{\circ}C$</TEX> and COPs were 3.0 and 2.8, respectively. In the transient condition, the instantaneous COP decreased with an increase in the inlet water temperature.

Influence of the source and sink temperatures on the optimal refrigerant charge of a water-to-water heat pump

This paper presents the results of a study carried out to elucidate the influence of the source and sink temperatures on the optimal charge of a propane water-to-water 16 kW heat pump which does not incorporate any liquid receiver. The unit had been fully tested along a previous experimental study, at various refrigerant charges and different condensing temperatures. A detailed mathematical model was then employed to simulate the unit performance. The predicted results were in very good agreement with the experiments, and furthermore, showed the same trends found in a similar unit tested at the KTH (Sweden) when the evaporation temperature was progressively decreased. Then, the model was employed to study the influence of the source and sink temperatures on the optimal charge of the unit. The simulation showed that the great variation of the optimal charge with the variation of the evaporation temperature is mainly due to the variation of the amount of refrigerant in the compressor oil.

Performance enhancement study of mobile air conditioning system using microchannel heat exchangers

In the present paper, two retrofitted compact and high efficient microchannel heat exchangers were proposed. The new microchannel heat exchangers have advantages in compactness (17.2% and 15.1% volume reduction for evaporator and condenser, respectively), weight (2.8% and 14.9% lighter for evaporator and condenser, respectively), heat transfer characteristics compared with the currently used heat exchangers in mobile air conditioning (MAC) industry. One enhanced and one baseline R134a MAC systems were established including the new microchannel heat exchangers and the traditional MAC heat exchangers, respectively. The system performances have been experimentally carried out under variable ambient conditions in psychrometric calorimeter test bench. The optimal system refrigerant charge amounts for both systems were tested and the results showed that the enhanced system with more compact heat exchangers could reduce system charge amount and the minimum effective charge amount was less than that of the baseline system. The enhanced system could supply more cooling capacity to car compartment under all test conditions because of higher performance heat exchangers. The coefficient of performance ( COP) of the enhanced system was slightly lower than that of the baseline system under idle conditions but higher under all the other test conditions. Cooling capacity and COP of the enhanced system was increased by about 5% and 8% under high vehicle speed condition.

Performance optimization of a hybrid cooler combining vapor compression and natural circulation cycles

A hybrid cooler combining vapor compression and natural circulation cycles was developed for the cooling of telecommunication equipment in the cabinet-type base station of mobile communication. This hybrid cooler normally operates in the vapor compression mode at high ambient temperatures, but works in the natural circulation mode at low ambient temperatures by the thermosiphon principle. The performance of the hybrid cooler was measured according to the refrigerant charge, outdoor temperature, heat exchanger geometry, and the vertical distance between the condenser and the evaporator. The optimum design conditions for these variables are discussed with respect to the performance of the hybrid cooler in both operating modes. The difference in the optimum refrigerant charge between the two operating modes was solved by installing a liquid receiver. The temperature difference between the indoor and ambient air was introduced as a control parameter for use when changing the operating mode.