Proposition of Design Capacity of Borehole Heat Exchangers for Use in the Schematic-Design Stage

Seung-Min Lee,Yong-Sung Jang,Eui-Jong Kim,Seung-Hoon Park

doi:10.3390/en14040822

Abstract

This study proposes a simple ground heat exchanger design capacity that is applicable in the schematic-design stage for several configurations used for borehole heat exchangers (BHEs). Three configurations—single, compact, and irregular types—were selected, and the heat transfer rate per unit BHE was calculated considering heat interference. In a case study with a typical configuration and general range of ground thermal conductivity, the BHE heat transfer rate of the compact configuration decreased owing to heat interference as the number of BHEs increased. However, with respect to the irregular configuration, the heat transfer rate increased as the same number increased. This was attributed to the relatively large increment rate of the distance between the boreholes in the irregular configurations, making the heat recovery factor more dominant than the heat interference. The results show that the average heat transfer rate values per BHE applicable to each configuration type in the schematic-design stage were 12.1 kW for the single configuration, 5.8 kW for the compact type, and 10.3 kW for the irregular configuration. However, owing to the large range of results for each case study, the error needs to be reduced by maximally utilizing the information available at the schematic-design stage.

Highlights

The design capacity of a ground-coupled heat pump system (GCHP) during the early design stage of a construction project is determined through the application of a set capacity per unit of equipment
The x-axis of each graph represents the number of borehole heat exchangers (BHEs), and the y-axis represents Qbhe, the heat transfer rate per borehole for each case
The heat transfer rate according to the BHE configuration type was analyzed for each configuration

Summary

Introduction

The design capacity of a ground-coupled heat pump system (GCHP) during the early design stage of a construction project is determined through the application of a set capacity per unit of equipment. The ground-coupled heat pump system is distinct such that the capacity and efficiency of the system are largely dependent on the design of the ground heat exchanger constituting the heat source loop, which may cause problems such as increased costs following an inaccurate early design stage. The detailed estimation of an equipment system’s capacity is determined upon the completion of the building design by selecting the appropriate equipment factors to counter the acquired loads [1]. Before the design development stage, the estimation of the approximate capacity and cost via a simple method in order to factor in the size and limitations of the entire construction project is common.

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