Ground-coupled heat pump systems use the ground as a heat source and sink either with vertical or horizontal ground heat exchangers (GHXs) to supply heating in winter and cooling in summer. The ground heat source and sink has a near constant temperature, which is well suited to ground-coupled heat pumps, giving them consistent performance, regardless of the outdoor temperature. However, when the heat extracted from and rejected to the ground has great imbalance, the ground temperature will deviate from the original temperature with a long term operation. The deviation can reduce GHX performance greatly. As China has vast territory with variety climate, the annual cooling loads and heating loads are different at different places. And the imbalance between the extracted heat and the rejected heat also varies at different places. Therefore, it is necessary to analysis the regional suitability of the ground-coupled heat pump systems. The imbalance between the extracted heat and the rejected heat is analyzed by taking several typical cities in different climates. The new concepts of the Imbalance Ratio and the Extracted Heat to Rejected Heat Ratio are introduced as the weight factors to measure the imbalance in the ground. The values of the Imbalance Ratio and those of the Extracted Heat to the Rejected Heat Ratio are calculated. The optimum range of the Imbalance Ratio is recommended based on the vast investigation of the ground-coupled heat pumps. Some supplemental systems are put forward to supply heat in winter or to reject heat in summer at the places existing serious heat imbalance. The study is very meaningful to the scientific application of the ground-coupled heat pump systems in China.
Financial and economic analysis for ground-coupled heat pumps using shallow ground heat exchangers
