Thermo-economic analysis of four different types of ground heat exchangers in energy piles

Abstract In this paper, thermal efficiency of four different types of ground heat exchangers in energy piles is investigated (type: double-U, triple-U, double-W and spiral). Five thermal performance tests are conducted to analyze ground heat exchangers operation under an intermittent condition (7 days on for cooling, 26 days off, 7 days on for heating). Results show that double-U type is with worst heating and cooling performance, accounting for 67–69% thermal efficiency than spiral and double-W types which are with similar thermal outputs. For technical problems, only heating performance of triple-U type is examined experimentally but the cooling performance is studied numerically. The findings show that tripe-U type performs highest thermal efficiency among all types. By examination of different pipe dimensions heat transfer rate of spiral type with 32 mm diameter is increased by 32% than that of 25 mm diameter. In addition, cost-benefits evaluation shows that triple-U shaped ground heat exchanger has highest economic performance, followed by double-U, spiral and double-W type. However, pipe material is only a small consists of the total installation costs. Hence, thermal efficiency is a more important factor to consider than pipe costs in practical application.

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