The thermodynamic aspect of a compression type heat pump （HP） is briefly described and special attention is given to investigation of condensing temperature influence on heat pump efficiency in heating mode, express...The thermodynamic aspect of a compression type heat pump （HP） is briefly described and special attention is given to investigation of condensing temperature influence on heat pump efficiency in heating mode, expressed by its coefficient of performance （COP）. Heat pumps are usually applied for the purposes of heating and cooling of energy efficient buildings where they have advantages in low-temperature systems, as it is well documented in the paper. The comparison of real thermodynamic processes with thermodynamically most favorable Camot＇s process is made. The results in the paper show that COP is diminishing with increasing of condensing temperature and also depends on real properties of working fluids. The impact of compressor efficiency for two real working media is also analyzed in the paper. There is significant diminishing of COP with diminishing of compressor efficiency. The intension of the paper is to help better understanding of this very effective and prosperous technology, and to encourage its development, production, and efficient application.展开更多
A series of experiments on the dynamic performance of the HPWH （heat pump water heater） unit with EXV （electronic expansion valve） under different environmental conditions were conducted. The dynamic heating capac...A series of experiments on the dynamic performance of the HPWH （heat pump water heater） unit with EXV （electronic expansion valve） under different environmental conditions were conducted. The dynamic heating capacity and COP （coefficient of performance） of the HPWH unit under different EXV openings were measured. The effects of the EXV opening on the performance of the HPWH unit were analyzed. Meanwhile, the dynamic performance of the HPWH with EXV was simulated and the results were compared with the experimental one. The experimental results indicate that during heating process, the COP increases firstly and then decreases for a fixed EXV opening, which is in good agreement with the numerical result. For different EXV openings, the COP and heating capacity of the system using larger EXV opening are superior to those using the smaller one in the initial heating stage. While in the late stage, the performance of system using smaller EXV opening is better. It is found that the system performance is improved significantly by changing the EXV opening in the different heating period and the average COP of the HPWH system is increased by 7.6%.展开更多
Heat pump cycles have been widely applied to dryers for their high efficiency. However, low–efficiency electrical heaters are often used during early drying stage for frozen foods or winter since a standard heat pump...Heat pump cycles have been widely applied to dryers for their high efficiency. However, low–efficiency electrical heaters are often used during early drying stage for frozen foods or winter since a standard heat pump cycle cannot operate at low temperature. This study introduced cascade heat pumps replacing electrical heaters to improve dryer performance at low temperatures. Experiments were performed to examine changes in performance of the cascade heat pump dryers in relation to ambient temperature, low-stage cycle mass flow rate, and high-stage cycle mass flow rate. The results showed a significant improvement in low-temperature dryer performance with the introduction of cascade heat pump cycles.展开更多
文摘The thermodynamic aspect of a compression type heat pump （HP） is briefly described and special attention is given to investigation of condensing temperature influence on heat pump efficiency in heating mode, expressed by its coefficient of performance （COP）. Heat pumps are usually applied for the purposes of heating and cooling of energy efficient buildings where they have advantages in low-temperature systems, as it is well documented in the paper. The comparison of real thermodynamic processes with thermodynamically most favorable Camot＇s process is made. The results in the paper show that COP is diminishing with increasing of condensing temperature and also depends on real properties of working fluids. The impact of compressor efficiency for two real working media is also analyzed in the paper. There is significant diminishing of COP with diminishing of compressor efficiency. The intension of the paper is to help better understanding of this very effective and prosperous technology, and to encourage its development, production, and efficient application.
文摘A series of experiments on the dynamic performance of the HPWH （heat pump water heater） unit with EXV （electronic expansion valve） under different environmental conditions were conducted. The dynamic heating capacity and COP （coefficient of performance） of the HPWH unit under different EXV openings were measured. The effects of the EXV opening on the performance of the HPWH unit were analyzed. Meanwhile, the dynamic performance of the HPWH with EXV was simulated and the results were compared with the experimental one. The experimental results indicate that during heating process, the COP increases firstly and then decreases for a fixed EXV opening, which is in good agreement with the numerical result. For different EXV openings, the COP and heating capacity of the system using larger EXV opening are superior to those using the smaller one in the initial heating stage. While in the late stage, the performance of system using smaller EXV opening is better. It is found that the system performance is improved significantly by changing the EXV opening in the different heating period and the average COP of the HPWH system is increased by 7.6%.
基金supported by Basic Science Research Program through the National Research Foundation of Korea
文摘Heat pump cycles have been widely applied to dryers for their high efficiency. However, low–efficiency electrical heaters are often used during early drying stage for frozen foods or winter since a standard heat pump cycle cannot operate at low temperature. This study introduced cascade heat pumps replacing electrical heaters to improve dryer performance at low temperatures. Experiments were performed to examine changes in performance of the cascade heat pump dryers in relation to ambient temperature, low-stage cycle mass flow rate, and high-stage cycle mass flow rate. The results showed a significant improvement in low-temperature dryer performance with the introduction of cascade heat pump cycles.
