Study of operational strategies for a hybrid solar-geothermal heat pump system

This research aims to improve the performance of an office building based on a new operation strategy for an evacuated tube solar collector-U-tube ground heat exchanger system. The main problem with the traditional operation strategy is the mismatch between the chiller capacity and the real cooling demand, which leads to operation of the air-conditioner units under low load rates and causes low system efficiency. In order to solve the above problem, we propose a new operation strategy, which controls the unit based on the load distribution of the building. Under this operation mode, the unit operates at full load rate during most operating times. Therefore, it can solve the mismatch between selection and operation and improve energy efficiency. We introduce the traditional operating strategy and design an experiment to evaluate the system performance for a solar thermal collector and geothermal heat exchanger system. We investigate the traditional operation strategy in detail, adopting the TRNSYS (Transient System Simulation) tool to develop a detailed simulation model that considers the seasonal system performance. The simulation results are validated by experiments. The simulation and experimental results show good agreement. Over 80% of the absolute relative errors have a magnitude falling within +/- 10%. As a result, compared with the traditional strategy, the proposed operation strategy can reduce the ground thermal imbalance in cold regions. The system coefficient of performance can be improved from 3.7 to 3.92, and the total electricity consumption is decreased by 6.4%.