Testing and analysis of corrected specific frictional resistance in the ground heat exchanger with water as heat-transfer fluid

Abstract

As the scale of a ground-coupled heat pump system increases, the proportion of energy consumed by the conveying system increases. It is crucial to obtain an accurate specific frictional resistance in the ground heat exchanger (GHE) to facilitate a more accurate design; this has the potential to reduce the energy consumption on the source side and improve the efficiency of the ground-coupled heat pump system. This study investigates the relationship between velocity, temperature, and pressure drop in a double U-shaped GHE with water as the heat-transfer fluid to obtain the corrected specific frictional resistance (CSFR). The test results showed that the ratio of standard specific frictional resistance (SSFR) to measured specific frictional resistance (MSFR) was greater than 1.2. The MSFR was used to fit and validate the CSFR formula, so as to determine the relationship between the CSFR and the four variables, which were density, dynamic viscosity, velocity, and inner diameter. The design based on the CSFR improved the system coefficient of performance by 7.61% compared to the SSFR design option. Therefore, use of the CSFR formula to calculate the pressure drop in the GHE groups facilitates more accurate and refined design of ground-coupled heat pump systems.