Characteristics And Performance Of A Co2 Heat Pump At 50% Overcharged Conditions (original) (raw)
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Characteristics and performance of a CO2 .pdf.pdf
A CO2 water to water heat pump system was used to investigate the effects of throttle valve opening and water flow rates at higher charge capacity (149% of the full charge). It was observed that the throttle opening affects the gas cooler pressure (and inlet temperature) where the less the opening the higher the pressure. Although the increase in gas cooler pressure was improving the gas cooler heat output and therefore the system efficiencies, there is an optimum pressure which when exceeded, the system performance deteriorates. This optimum pressure also is related to a certain throttle opening which is approximately at 20% in this study. Similarly, as the throttle valve is reduced, the overall system becomes more ideal as indicated by Lorentz efficiency. On the other hand, the higher the flow rates the higher the performance although it’s better to keep the chilling water (evaporator) flow rate low and cooling water (gas cooler) flow rates high than vice versa for the best heat pump performance. However, if the main intention is to idealize the system, then it’s better to keep the chilling water flow rates high and the cooling water flow rates low as stipulated by the Lorentz efficiency. Many systems tend to be overcharged while the refrigerant is being refilled and therefore will behave as observed in this study, thus its importance
Performance optimization of CO2 heat pump water heater
International Journal of Refrigeration, 2018
, 865-241-0972) Highlights A HPWH model has been developed and calibrated using previous experimental data. The impact of ambient temperature and water supply temperature has been reported. The performance has been compared to an R134a based system. The impact of wrap configuration vs. gas cooler configuration has been investigated. The impact of water circulation rate has been reported.
Effects of various parameters on the efficiency of a CO2 heat pump: a statistical approach
Journal of Thermal Engineering, 2015
The influence of variables such as; refrigerant amount, chilling and cooling water temperature, throttle valve opening, cooling and chilling water flow rates, on the efficiency (coefficient of performance -COP) of a water to water carbon dioxide heat pump was investigated. Design of experiments was done using design-expert® 6 software for regression analysis. A response surface method known as central cubic design was used to provide optimum results with minimum experiments. Through multiple regression analysis, an empirical equation relating the COP to the variables was derived. Analysis of variance revealed that these regressions are statistically significant at 95% confidence level compounded with a very low standard deviation and a high adequate precision. The close relationship between the predicted COP values and the actual values further proves the worthiness of the empirical equation. It was observed that cooling water temperature had the highest influence followed by the chilling water temperature. Surprisingly, the amount of the refrigerant was third followed by the throttle valve opening. Understandably, chilling water flow rate had the least effect on the COP. Through response surface diagrams, the interactive influence of the variables were also observed. The COP values arrived at varied from 1.545 to 6.914 although if the variables were optimized fully within the scope of this study, a value of up to 11.8 could be achieved. Still, if the variables range is increased further, higher COP could be achieved. Finally, a discussion was done in a bid to explain these results.
A simplified method to evaluate the energy performance of CO2 heat pump units
International Journal of Thermal Sciences, 2011
The prediction of the performances of CO 2 transcritical heat pumps demands accurate calculation methods, where a particular effort is devoted to the gas cooler modelling, as the correlation between high pressure and gas cooler outlet temperature strongly affects the cycle performance. The above-mentioned methods require a large amount of input data and calculation power. As a consequence they are often useless for the full characterisation of heat pumps which are sold on the market.
Experimental investigation of transcritical CO2 heat pump for simultaneous water cooling and heating
2010
This pa per pres ents the ex per i men tal per for mances of a transcritical CO 2 heat pump pro to type for si mul ta neous wa ter cool ing and heat ing ap pli ca tions. Sys tem be hav ior and per for mances such as cool ing ca pac ity, heat ing ca pac ity, and sys tem co ef fi cient of per for mance (COP) have been stud ied ex per i men tally for var i ous oper at ing pa ram e ters such as wa ter mass flow rate, wa ter in let tem per a ture for both evap o ra tor and gas cooler, and ex pan sion valve open ing. Per for mance is also compared with pre vi ous test data. Test in di cates that the ex pan sion valve open ing has a sig nif i cant ef fect as well near the full valve clos ing con di tion (up to 20°). Study shows that both the wa ter mass flow rate and in let tem per a ture have sig nif i cant effect on sys tem per for mances. Test re sults show that, at gas cooler pres sure of 90 bar, the ef fect of evap o ra tor wa ter mass flow rate on the sys tem per for mances is more pro nounced (COP in creases 0.6 for 1 kg/min.) com pared to the gas cooler wa ter mass flow rate (COP in creases 0.4 for 1 kg/min.) and the ef fect of gas cooler wa ter in let tem per a ture is more sig nif i cant (COP de creases 0.48 for given ranges) com pared to the evap o ra tor wa ter in let tem per a ture (COP in creases 0.43 for given ranges).
Effects of refrigerant charge amount on the performance of a transcritical CO2 heat pump
International Journal of Refrigeration, 2005
A typical transcritical CO 2 system shows lower performance than conventional air conditioners in cooling mode operation. In addition, the CO 2 system shows a large variation of the performance according to refrigerant charge whereas the conventional systems do not show large variation. In this study, the performance of the CO 2 heat pump was measured and analyzed by varying the refrigerant charge amount at standard cooling condition. In addition, the performance sensitivity of the CO 2 system as a function of refrigerant charge was compared to those for the R22, R410A, and R407C systems. The cooling COP of the CO 2 system was reduced more significantly at undercharged conditions than at overcharged conditions as the deviation from the optimal charge increased. The expansion loss was the dominant factor affecting system performance at undercharged conditions, while the gascooler loss became the major parameter at overcharged conditions. Among the systems investigated and compared in this study, the CO 2 system showed the most reduction in performance at undercharged conditions.
Typical Initial Output of a Co 2 Heat Pump
2012
Many of the refrigerants currently being used in heating, ventilation, air conditioning and refrigeration systems have high global warming potential. One potential, environmentally friendly replacement refrigerant is carbon dioxide (CO2). In this study, a CO2 trans-critical water to water test bed was used to study the output of a typical heat pump. Initial experimental results and thermo-physical properties were analyzed by NIST REFROP and plotted in a temperature-entropy (T-S). The energy output in the gas cooler were compared to the energy input in the compressor and the efficiency of the system in terms of coefficient of performance (COP) was observed to vary from 3.7 to 3.9. It was observed that there was a wide difference between the theoretical and experimental results when the same state conditions are considered. This was related to change on theoretical processes due to efficiency consideration of the equipment involved and flow process variables like friction which affect...
For clarify main affecting factors on air-source transcritical CO 2 heat pump water heaters, and the influence extent of these main affecting factors, at fixed water inlet temperature of 12 C, an experimental research was conducted on a prototype in a range of ambient temperatures (À15 Ce35 C) and water outlet temperatures (55 Ce80 C). Based on the experimental results, effect of water outlet temperatures and ambient temperatures on the optimal discharge pressure and system COP was illustrated, and with change of water outlet temperatures and ambient temperatures, variation of CO 2 gas cooler outlet temperatures, evaporating temperatures and other cycle variables was presented and interpreted. According established simulation model, we conducted simulation for the prototype and the cycle respectively adopted another two gas coolers with difference heat transfer surface. As one conclusion, for an established plant, correlation for the optimal discharge pressure as the function of ambient temperatures and water outlet temperatures can be achieved by fitting numerous simulation or experimental results.