تجزیه و تحلیل عملکرد تجربی سیستم پمپ حرارتی بهبود یافته چندمنظوره

An improved multifunctional heat pump (MFHP) system that integrates an air-source evaporator and a water–water heat exchanger was developed. An experimental set-up and a mathematical model were constructed to evaluate the performance of the MFHP system. Some characteristics of the system, such as the effects of water–water heat exchanger, hot water outlet temperature, and cooling capacities of the air-source and water-source evaporators, were discussed based on experimental data. Experimental results show that the MFHP system could simultaneously supply hot water for bathing and cold air for air conditioning. In addition, the coefficient of heating performance (COPh) varied from 3.69 to 5.70. Analysis results show that the COPh and the hot water volumetric flow rate of the MFHP system were closely related to the inlet and outlet temperature of hot water and wastewater. Empirical models of COPh and hot-water flow rate were proposed to predict the heating performance of the MFHP system. The improved MFHP system is shown to have satisfactory energy saving performance.

Hot water is generally produced by various types of water heaters, such as gas, solar, and heat pump water heaters, to supply artificial springs, sauna rooms, and domestic and commercial facilities. However, the waste hot water generated from bath/shower is directly drained into the environment, thus resulting in thermal pollution and energy waste. Our experimental results show that the temperature of hot waste shower water is above 30 °C in hot climate areas such as Shenzhen, a city in Southern China. This hot waste shower/bath water is suitable as a heat source of heat pump water heaters in those areas. On the basis of the research published by Chen and Li [1], Ji et al. [2], and others [3], [4], [5] and [6], Wang developed a small-scale shower wastewater source heat pump (SWWHP) that utilizes bath/shower wastewater as heat source to save energy in hot climate areas [7]. An improved multifunctional heat pump (MFHP) system with an efficient redesigned air-source evaporator and an enhanced water–water heat exchanger was proposed based on the original SWWHP. The MFHP system can produce enough hot water for bathing, heating, or air conditioning by recovering heat from hot wastewater and air. Many researchers have studied the models of heat pump water heaters to predict the system performance of this technology. For instance, Meggers et al. used heat pump supply temperature Th, evaporator temperature Tc, and the temperature-lift (ΔT = Th − Tc) as variables to calculate the coefficient of heating performance (COPh) of the system [8]. They also proposed a model by using the Th, Tc, and heat transfer characteristics of the recovery tank to evaluate the average coefficient of performance (COPave) during a given period. Kim et al. investigated a residential air-to-air heat pump system and proposed the first-, second-, third- and fourth-order multivariable polynomial regression (MPR) reference models and an artificial neural network (ANN) reference model by using outdoor dry-bulb temperature TOD, indoor dry-bulb temperature TID, and indoor dew point temperature TIDP as independent variables [9]. These models [9] could be used in predicting the performance of air-to-air heat pumps if enough data were available. Greyvenstein developed a computer simulation model for water-to-air heat pumps on the basis of database parameters, such as characteristics of compressor and heat exchangers [10]. A detailed database should be prepared to calculate the refrigerant flow rate and the input power of the system to meet model requirements when using the Greyvenstein model. Stefanuk et al. modeled a superheat-controlled water–water heat pump on the basis of energy, mass, and momentum conservation laws, as well as heat transfer relations. However, the model required many available characteristic parameters of the components. For instance, the compressor characteristics were determined by using the curve-fitting method under different mass flow rates of the refrigerant, input power, evaporation temperature, and compressor discharging pressure [11]. On the basis of thermodynamic principles and heat transfer relations, Jin et al. developed the water–water heat pump model, which is a parameter estimation-based model [12]. Their model also depended on many parameters and characteristics of heat pump components. They selected eight parameters, namely, the compressor clearance factor, the constant part of the electromechanical power loses, the loss factor defining the electromechanical loss proportional to the theoretical power, superheat, heat transfer coefficients of condenser and evaporator, suction pressure drop, and discharge pressure drop, to solve the compressor model. In this paper, the authors investigated the experimental characteristics of the MFHP system and proposed novel empirical models to evaluate the performance of the MFHP system.

On the basis of the above analyses, the MFHP system provides a simple and efficient way of utilizing wastewater by recovering low-grade heat from wastewater. Experimental results show that the COPh varies from 3.69 to 5.70, thus denoting that the MFHP system has good energy saving performance. Moreover, the proposed empirical COPh and Vhw models under constant wastewater flow rate provide a new way for users or engineers to evaluate the performance of heat pump water heaters. Experimental and analysis results show that the water–water heat exchanger deteriorates the COPh of the MFHP system but could efficiently increase the hot-water flow rate. The water–water heat exchanger is necessary in providing adequate hot water when the temperature of the city water is low during winter. Compared with the original system, the COPh of the improved MFHP system increased by approximately 20% and the performance of the air-source evaporator improved. The improved system can meet the requirement of local or temporary (short time) air conditioning while supplying hot water. The MFHP system is designed for hot-climate areas such as Shenzhen, a city in Southern China, in which the temperature of city water (tap water) during winter is above 0 °C. All experiments were conducted under normal climate conditions of Shenzhen. Experiments under extreme climate conditions will be designed to investigate the performance of the MFHP system to develop a novel MFHP system that can meet the requirements of users in warm or cold climate areas. In addition, we will utilize environment-friendly refrigerants such as R410A or HC22 instead of R22 to investigate the performance of the MFHP system in the future.