Balance Point Choosing And Thermo Economic Optimization Of Air-source Heat Pump

Air-source heat pump is wider and wider used in our country. How to design an air-source heat pump system can achieve well economic interests is worth researching. This paper analyses the effecting factors in air-source heat pump design, putting forward a concept of economic balance point, i.e. based on this point the LCC of the air-source heat pump system will be minimized. Author developed mathematic equation of LCC, and provided values or calculations for each parameter in the LCC equation. By analyzing, author achieved a conclusion: balance point is a function of heat pump equipment and energy price. Later, author uses LccWare3.0 to calculate the balance point temperature of several cities in China,and analyzes effect of each parameter on the annual cost of air-source heat pump. The application of the thermo economic optimization design in an air-source heat pump system is important in achieving economical life cycle cost. Previous works on thermo economic optimization mainly focus on directly calculating exergy input into the system. However, it is usually difficult to do so because of the uncertainty of input power of fan on the air side of the heat-exchanger and that of pump in the system. This paper introduces a new concept that exergy input into the system can be substituted for the sum of exergy destruction and exergy output from the system according to conservation of exergy. In order to perform thermo economic optimization, a program is firstly developed to evaluate the thermodynamic property of R22 on the basis of Martin-Hou state equation. From the thermodynamic relations and equations derived from the energy balance and heat ex-changer characteristics, an objective function and constraining equations are obtained. Optimum values of the operating variables are identified at thermodynamic and thermo economic optimum conditions. Results show that the total irreversibility produced in the system and the cost of energy consumption are minimum at thermodynamic optimum conditions, but the annual cost of owning and operating the system is minimum at the thermo economic optimum condition. So, under thermo economic optimization condition, the air-source heat pump can achieve the most economical interest.