An optimal control strategy for small-scale ASHP-integrated central air-conditioning systems: Coordinating indoor and outdoor temperatures

Abstract

Small-scale air source heat pump (ASHP)-integrated central air-conditioning system is widely used in residential buildings to provide both cooling and heating. Supply water temperature in this system is typically set to design values, which often leads to frequent oscillations in indoor temperature and substantial energy waste. This study proposes an optimal control strategy to regulate the supply water temperature in response to real-time load variations, based on the coordination of indoor and outdoor temperatures. The outdoor temperature serves as a primary input parameter for feedforward control, calculating the initial set-point of the supply water temperature to quickly respond to load changes. Meanwhile, the indoor temperature acts as an auxiliary input parameter for feedback control, modifying the calculated initial set-point. The control performance was validated using both a simulation platform and a real air-conditioning system. The results indicate that the proposed strategy can significantly improve the robustness and accuracy of indoor temperature control while also substantially reducing the system energy consumption. In experimental tests, the system energy consumption was reduced by 31.14% when the outdoor temperature varied between 27 °C and 36 °C during the summer. Furthermore, the results demonstrate that the proposed strategy can also significantly decrease the ON/OFF frequencies of fan coil water valves and ASHP under light load condition. Both were reduced from 58 times to just 3 times per day. This strategy is easy to implement in conventional temperature controllers and is particularly suitable for small-scale ASHP-integrated central air-conditioning systems with low thermal hysteresis and few uncertain interference factors.