Operation Of Ground Source Heat Pump System Research Articles

Dynamically coupled modelling of ground source heat pump systems considering groundwater flow and unbalanced seasonal building thermal loads

The ground source heat pump (GSHP) system is a promising technology to exploit shallow geothermal energy via ground heat exchangers, GHEs (e.g., deep boreholes or piles) for space heating or cooling. Although GSHP systems have been widely used in temperate regions owing to their environmentally clean characteristics and excellent energy-saving performance, their use in cooling-dominated areas, such as subtropical or tropical regions (e.g., Hong Kong or Singapore), remains limited. The operation of GSHP systems in these regions may be subjected to unbalanced seasonal thermal loads on buildings and induce heat accumulation in soils surrounding GHEs, leading to potential deterioration in the long-term performance (e.g., coefficient of performance, COP) of GSHP systems. To properly evaluate the long-term COP of GSHP systems in cooling-dominated areas, a dynamically coupled simulation approach is proposed in this study. The proposed method integrates building thermal loads with ground heat transfer under groundwater seepage flow, within a unified framework. The effectiveness of this approach is demonstrated through a case study where, in the absence of groundwater seepage flow, the soil temperature increased by 17.2 °C. In contrast, when groundwater seepage flow was considered, the GSHP system not only maintained a high long-term cooling COP but also achieved up to 30 % electricity savings. These findings demonstrate the feasibility and sustainability of applying GSHP systems in cooling-dominated areas with the aid of groundwater seepage flow.

Experimental comparison of First-law analysis of peak hour operation of GSHP system under optimized conditions

The present study presents a novel procedure to study energy – efficient performance of a Ground − Source Heat Pump (GSHP) system during peak hour space cooling and heating operations by integrating an experimental study with First law analysis and optimization techniques. The main objective of the study is to identify how closely the results of First law analysis agree with the actual experimental results when operated under optimized conditions. The experimental data obtained during peak hour operation of a 17.58 kW GSHP system for each three days of operation in summer and winter seasons are considered for the analysis. The Coefficient of Performance (COP) and Power Consumption (W) of the GSHP system are computed using an energy balance based on First law using the experimentally measured heat rejection by the Borehole Heat Exchangers (BHEs) and the cooling effect. For optimization using the Taguchi method, six distinct measured parameters, each at three different levels, are selected as variables. Analysis of Variance (ANOVA) was carried out on COP and W to ascertain the parameters that exert the most significant influence on the performance of the GSHP system. During peak hour operation, the temperature difference between the inlet and outlet water in the BHE was found to be 10–11 °C in cooling mode and 3 °C to 4 °C in heating mode operations. Temperatures of water in the BHEs and air at the heat pump, which contribute to the heat interaction, are found to be the most influential parameters for cooling and heating mode operations. The COP for cooling mode computed by the optimization technique, 3.59, closely agrees with the experimental COP of 3.73. Similarly, the optimized COP for heating mode, 3.84 is found to be closer to the experimental COP of 4.32. The optimized power consumption deviates by 14.21 % and 11.94 % from the experimental results for cooling and heating modes, respectively.

Operation performance test and energy efficiency analysis of ground-source heat pump systems

The improper operation of a ground source heat pump (GSHP) system is a significant cause of poor energy efficiency. Despite the increasing popularity of GSHP systems in China, few field test has been conducted on the operation of GSHP systems in the southwest and western regions of the country, and there is a lack of comprehensive comparative study. This study tested the operation performance of 26 GSHP systems in Sichuan, Chongqing, and Shaanxi under typical operation conditions. The performances indexes of the systems were calculated and investigated, including the coefficients of performance of the heat pump and system, water transfer factor of the water pump, and energy efficiency ratio of the system. These parameters were then compared and analyzed based on existing literature and relevant domestic standards concerning energy efficiency. Accordingly, suggestions were proposed for improving the operation performance of GSHP systems from the aspects of system design, construction, and operation. Results show that the average coefficient of performance (COP) of the tested systems was less than 3.0 under heating conditions, which did not meet the requirements for energy-saving operation stipulated by the national standard and fail to achieve the initial intention of saving energy in buildings by using GSHP systems. Based on the analysis, typical problems were diagnosed in GSHP systems. Specifically, the heat pumps usually operate in part-load conditions and at low efficiency for a long time; the transfer and distribution systems operate with small temperature differences and large flows; and the settings of room temperatures tend to be unreasonable. In view of the operation performance, ground-coupled heat pump (GCHP) systems are recommended for use in the western regions of China.

Heating and cooling performance of a minitype ground source heat pump system

A minitype ground source heat pump (GSHP) system was designed and installed in the green energy building of Shanghai Jiao Tong University for the purpose of satisfying the thermal environment of a meeting room with the covered area of 180m2. The rated cooling capacity of the heat pump is 22.3kW with the electricity consumption of 5.3kW. Correspondingly, the rated heating capacity and electricity consumption in heating mode is 29.5kW and 6.9kW, respectively. The ground heat exchanger consists of 9 vertical boreholes. There is a single U-tube with the diameter of 32mm in each borehole. The whole length of the U-tube is 580m. The experimental investigation was carried out in both cooling mode and heating mode. After one year, the average temperature of soil was about 18°C, which is nearly the same as the original soil temperature. The experimental results are instructive to the design and operation of GSHP systems in Shanghai and other cities with similar climatic feature.

The Coupled Heat Conduction & Advection Model for Ground Heat Exchanger and its Application for Utilizable Resource Amount Calculation in Soil

Following the wide application of ground source heat pump (GSHP) system, especially for large area ground heat exchanger (GHE), it is really necessary to have a standard calculation or assessment method to estimate the utilizable resource amount in soil around GHE. As for the GHE area, the soil works as a thermal storage actually which means it is heat gain in summer to meet the heat demands in the coming winter, and the cool energy gain in winter to be used for next summer air-conditioning. So it is really necessary to know the utilizable resource amount for better design of GSHP system and then the highly efficient operation of the system too. Hereby, a coupled heat conduction and heat advection model is introduced to simulate the performance of ground heat exchanger. Thus we can see the importance of utilizable resource amount estimation method. The reasonable resource amount estimate method is good for the scientific design, normal utilization, and high-efficient operation of GSHP system.