Approximated flow characteristics of multi-pipe earth-to-air heat exchangers for thermal analysis under variable airflow conditions

摘要

The design process of multi-pipe earth-to-air heat exchangers requires mainly two considerations: the calculations of (i) thermal and (ii) flow performance. The influence of non-uniform airflow distribution among branch-pipes on the thermal performance is usually neglected, although it does occur in multipipe structures. In order to bridge this knowledge gap, in this paper, the formulas which enable calculation of an exchanger's total pressure losses and individual branch-pipe airflows as a function of total airflow are presented. The results show that pressure losses for 45 degrees structures can be up to 30% lower than those for 90 degrees structures, and the maximum airflow in a single branch-pipe can be more than 10 times higher than the minimum airflow measured in another branch-pipe. To demonstrate the influence of the non-uniform airflow distribution between parallel branch-pipes on the heat exchanger's thermal performance, an example analysis was carried out. The results show that heat and cool gains calculated over one year for real airflows (derived from the approximated flow characteristics of the exchangers presented in this paper) can be up to 20% lower than the maximum possible gains calculated assuming ideally uniform airflow distribution between parallel branch-pipes. (C) 2020 The Authors. Published by Elsevier Ltd.