Performance optimization of space heating using variable water flow air source heat pumps as heating source: Adopting new control methods for water pumps

In recent years, the application of air source heat pumps (ASHPs) in centralized heating has grown rapidly in North China. However, there is still lack of theoretical investigation on the control methods of water pump. To decrease the system power consumption, a mathematical model of variable-frequency ASHP used for supplying heating for ten users was established in this work. Meanwhile, three control methods of water pumps were proposed. The heating performance of ASHP system under the three control methods was investigated. Besides, the appropriate control methods of heating terminals under the three control methods were analyzed. Results showed that the minimum relative water flow rate is 30%. Among the three proposed control methods, the power input of water pump is the minimum in the pressure differential control method of the most unfavorable terminal, and its difference with the highest value is 0-31.84%. For the power input of ASHP system, it is always the maximum in constant flow control method, while the minimum in the pressure differential control method of the most unfavorable terminal. Compared with the values in the former control method, the power input of ASHP system in the latter control method decreases by an average of 13.40%.