A method for sizing air source heat pump and electric boiler considering the peak and valley electricity prices

In a combined air source heat pump and electric boiler heating system, the capacity an oversized heat pump increases investment costs but decreases operation costs, and vice versa. Most current equipment selection methods are complex and ignore the impact of the peak valley price policy on system costs. This often leads to the selection of oversized equipment for the actual project, resulting in an increase in the total cost of the system. Therefore, we propose a new calculation method. The optimal number of non-guaranteed days for the air source heat pump (OGD) was used as the reference value for the calculation. A new optimization module was developed, and a system simulation model was built using Trnsys. The variation patterns of the OGD for 12 groups of buildings in Changchun, China, were analyzed. Finally, OGD recommendations were provided for 35 important cities in China. The results showed that OGD was not affected by changes in the building type or equipment installation costs. The average error of the annual cost calculation for different building types was 0.074%, and the maximum error was 1.7% when the equipment investment cost was changed. In addition, the OGD value was affected by a combination of outdoor temperature and local electricity prices. This value gradually decreased as the climate warmed. For regions with unfavorable price policies, such as Kashgar, China, the recommended local OGD value increased by 75.8%. The proposed method can be used as a methodological complement to the calculations of such systems during the design phase.