Analysis of Short Time Period of Operation of Horizontal Ground Heat Exchangers

Abstract

Ground source heat pump (GSHP) systems have been proven to have higher efficiency compared to conventional air source heat pump systems for space heating and cooling applications. While vertical ground heat exchangers (GHE) are favorable in GSHP installation, this type of configuration requires higher capital costs as opposed to horizontal configuration. Numerical simulation has been used to accurately predict the thermal performance of GHE. In this paper, numerical analysis of thermal performance for slinky horizontal GHE loops in different orientations and operation modes is discussed. It was found that the loop orientation is not so important due to the little effect it has on thermal performance. While the mean heat exchange rate of copper loop increases 48% compared to HDPE loop, the analysis supports the common claim that heat exchange rate is predominantly limited by the thermal conductivity of the ground. With the same amount of circulation work, the mean heat exchange rate increases by 83%-162% when operated in parallel loops operations. The performance in these operations can be further optimized to 10%-14% increase when spacing between adjacent loops was provided. The spacing helps to minimize interference of heat flow that would penalize the overall thermal performance. OPEN ACCESSResources 2015, 4 508 Keywords: ground source heat pump; ground heat exchangers; numerical simulation; horizontal; slinky IntroductionGround source heat pump (GSHP) systems have been proven to have higher efficiency compared to conventional air source heat pump (ASHP) systems for space heating and cooling applications. This is due to the relatively stable subterranean temperature in which GSHP systems exploit to extract and reject heat, whereas ASHP systems are exposed to large fluctuation in ambient temperature and climate conditions. GSHP installations do not require large cooling towers, or can be coupled with one for greater efficiency. Hence, their running costs are lower than ASHP systems. Garber et al. [1] suggest that potential savings from a GSHP system largely depend on projected HVAC system efficiencies and gas and electricity prices. The risk analysis performed shows that a full-size GSHP with auxiliary back up is potentially the most economical system configuration.The thermal performance of GSHP depends on many parameters such as short-term weather variations, seasonal variations, moisture content of soil, and thermal conductivity of soil among others that would affect the temperature of ground [2]. GSHP systems extract and reject heat by means of ground heat exchangers (GHE). GHE can be generally classified into two widely installed closed-loop types, which are vertical and horizontal configurations. Vertical GHE are pipes installed vertically in boreholes typically 15-120 m deep. Meanwhile, pipes are laid and buried in trenches 1-2 m deep in horizontal ground heat exchangers (HGHE) installations. Vertical GHE, commonly installed where availability of land area is scarce, provides high and steady thermal perfo...

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Hourly Simulation of an Earth-to-Air Heat Exchanger in a Low-Energy Residential Building

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