In order to make ground-coupled heat pump system operate efficiently in long term

soil needs to be maintained heat balance in an annual cycle. Auxiliary cold source or heat source is needed if necessary. An evaluation method of soil heat balance was proposed

heat balance equation was given

and annual heat balance rate of soil was also defined. Soil heat balance point Δg0 and floating range 80%Δg0~120%Δg0 were derived

where the upper and lower limit correspond to the cold critical region and hot critical region

respectively. According to field data of heat storage

heating and cooling experiments based on the demonstration project

heat balance point was 80% and floating range was 65%~95%

which can be used as indices to measure soil heat balance. Based on the indices

it is evaluated that the ground-coupled heat pump with solar seasonal heat storage (GCHPSSHS) system could be applied to severe cold zone and a part of cold zone A of China. The evaluation method of soil heat balance based on annual heat balance rate can be used to analyze soil heat balance problem of ground-coupled heat pump system with auxiliary cold source or heat source

evaluate the regional applicability of the system

and design an efficient system which can keep soil heat balance.