Restoration performance and operation characteristics of a vertical U-tube ground source heat pump system with phase change grouts under different running modes

Abstract

This work investigates the effects of different operation modes on the restoration performance and operation characteristics of a ground source heat pump (GSHP) system backfilled with phase change materials (PCM). A numerical GSHP system model considering site conditions and dynamic loads was developed and validated. The effects of daily working schedules, load features and operation schedules of short time period operation modes, and phase-transition temperature of PCM grout were explored. The results show that PCM grout is more suitable for buildings with less-persistent thermal demand considering the importance of restorability. Operating the GSHP with cooling & heating alternate load is the most effective way to improve the overall performance of the system, but a suitable operation schedule should be used. Decreasing the cycle ratio is the best method to promote the system performance under the same hourly load intensity, while for the operation schedules with higher hourly load intensity, a shorter cycle period is recommended. The phase-transition temperature of PCM grout influences the system stability and sustainability greatly as it controls when the melting occurs. The grout with the phase-transition temperature of 20.4 °C is demonstrated to be the most suitable one under our conditions as it provides relatively stable and effective performance over the entire summer and has a higher utilization ratio of the latent heat.