Types Of Ground Heat Exchangers Research Articles

Performance analysis of short helical borehole heat exchangers via integrated modelling of a borefield and a heat pump: A case study

This paper presents a new simulation tool package that calculates the energy efficiency of an entire Ground Source Heat Pump (GSHP) system. The package consists of two detailed models of borehole heat exchangers and heat pump equipment coupled in a single well-integrated calculation tool.It was used to analyze two types of ground heat exchangers in the same operating conditions for two Italian climates. Research focused on comparing a short helical-shaped pipe configuration with the more widespread and longer double U-tube. Analysis was carried out at the same energy exchange rate with the ground and addressed the difference in total borehole depth. The package also took into account the effects of the weather on the heat transfer between the heat exchanger and the surrounding ground.Analysis found that a much shorter total borehole depth was needed for the helical-shaped pipe, which consequently reduces installation costs. Therefore, this configuration may be a suitable alternative to conventional U-shaped tubes, especially for new residential housing with low energy loads and where deep probe drilling is not possible. Finally, this paper also investigates the influence of the axial effects in the ground on the seasonal energy efficiency of the whole system.

Evaluation of Heat Exchange Rate of Different Types of Ground Heat Exchangers

This research presents an experimental study of heat exchange rate of U, W, 2U and coil type ground heat exchangers (GHEs) measured by thermal performance tests (TPTs). The four types of GHEs were installed in a partially saturated dredged soil deposit of Incheon International Airport area. Thermal response tests (TRTs) were conducted for U, W and 2U type GHEs to deduce the ground thermal conductivity. Besides, TPTs were also conducted for U, W, 2U and coil type GHEs to evaluate heat exchanger rates under 100-hr continuous and 8-hr intermittent operation conditions for five days. Coil shaped GHE showed about twice higher thermal performance than the others GHEs. Furthermore, intermittent operation condition showed 30~40% higher heat exchange rates than continuous operation condition.

Characteristics of an analytical solution for a spiral coil type ground heat exchanger

This paper presents an efficient spiral coil source model and its analytical solution, developed to consider 3-dimensional shape effects and radial dimension effects of a spiral coil type ground heat exchanger (GHE) using Green’s function method. To avoid singular integrals, the solution is expressed using an error function by which the computational limitation is avoided. To analyze the characteristics of the analytical model, predicted results of the model were compared with test measurements by a thermal response test conducted in a model chamber, and numerical analysis results implemented in ABAQUS/Standard.

Performance evaluation under the actual operating condition of a vertical ground source heat pump system in a school building

This study is to evaluate the performance of a ground source heat pump (GSHP) system installed in the Pusan National University, Korea. The GSHP system consists of ground heat exchanger (GHE), measuring devices and heat pumps which have 2 compressors (inverter type and fixed type). The closed vertical type GHE is constructed with 24 boreholes of 175m in depth. The outdoor temperature, the indoor temperature and relative humidity, the inlet and outlet temperature of circulating water are obtained. Also, the electricity consumption of compressor and cooling (heating) load are measured in order to analyze the COP of heat pump. From the measuring data, the variation of ground temperature at 2.5m, 5.0m in depth are affected by outdoor air temperature. But it is proved that the ground temperature is almost constant below 10m in depth. In cooling period, the COP of the heat pump is 6.0–10.9 at partial load condition, while the overall system COP is 4.3–7.4. In heating period, the COP of the heat pump is 4.3–8.3 at partial load condition, while the overall system COP is 3.0–6.2.

Foundation heat exchangers for residential ground source heat pump systems—Numerical modeling and experimental validation

A new type of ground heat exchanger that utilizes the excavation often made for basements or foundations has been proposed as an alternative to conventional ground heat exchangers. This article describes a numerical model that can be used to size these foundation heat exchanger (FHX) systems. The numerical model is a two-dimensional finite-volume model that considers a wide variety of factors, such as soil freezing and evapotranspiration. The FHX numerical model is validated with one year of experimental data collected at an experimental house located near Oak Ridge, Tennessee. The model shows good agreement with the experimental data—heat pump entering fluid temperatures typically within 1°C (1.8°F)—with minor discrepancies due to approximations, such as constant moisture content throughout the year, uniform evapotranspiration over the seasons, and lack of ground shading in the model.

Experimental study of several types of ground heat exchanger using a steel pile foundation

An experimental study of several types of ground heat exchangers (GHEs) installed in a steel pile foundation, including double-tube, U-tube, and multi-tube GHEs, was carried out at Saga University. Water flows through the heat exchangers and exchanges heat to or from the ground. The performance of GHEs was investigated under actual operation in the cooling mode with flow rates of 2, 4, and 8 l/min. Temperatures of the ground and GHE tube wall were measured to find the temperature distributions according to the depth of the ground and depth of the GHE tube wall. The temperatures of the inlet and outlet of circulated water were also measured to calculate the heat exchange rate. The double-tube had the highest heat exchange rate, followed by the multi-tube and U-tube GHEs. For example, the average heat exchange rate of GHEs over 24 h of continuous operation with a flow rate of 4 l/min was 49.6 W/m for the double-tube, 34.8 W/m for the multi-tube, and 30.4 W/m for the U-tube. An increasing flow rate increased the heat exchange rate of the GHEs. The heat exchange rates increased significantly for flow rate increases from 2 to 4 l/min, but only slightly changed from 4 to 8 l/min.

Heat and mass transfer model of a Ground Heat Exchanger: theoretical development

A new approach to the simulation of a horizontal type Ground Heat Exchanger is proposed resulting in a better accuracy and at the same time a reduced computational effort. These results come from the concentration of the computational effort at the locations with the largest temperature and moisture gradients, i.e. the pipe–soil interface. The model takes into account heat and moisture transfer in the soil allowing for more accurate predictions of the soil thermal response to the heat fluxes induced by the GHE operation. This in turn allows for a more accurate prediction of the soil temperature field and the circulating fluid temperature profile. A comparison of the results obtained by using the implicit and explicit methods of solving the set of governing equations is discussed. The implicit method requires partial linearization of the heat and mass transfer equations but results in a considerably shorter simulation time. The explicit formulation allows for the solution of the fully nonlinear set of heat and mass transfer equations at the expense of increased simulation time. The following analysis shows that the difference between the solutions obtained using these two methods is minimal, thus favouring the implicit formulation. Copyright © 1999 John Wiley & Sons, Ltd.