An Effect of Flow Non-Uniformity on Thermal Performance of Multi-Pipe Earth-To-Air Heat Ex-changers (str. 505 nr. 12/48/2017)
prof. dr hab. inż. Janusz Wojtkowiak
dr inż. Łukasz Amanowicz
  

Experimental investigations of multi-pipe earth-to-air heat exchangers (EAHEs) with short branches and small diameter of manifolds show a considerable non-uniformity in distribution of air between branches. In this paper an effect of this flow non-uniformity on the energy gains in the whole year EAHE operation is presented. In calculation, ground thermal resistance, water vapor condensation and changes of air flow rate were taken into consideration. The flow non-uniformity was described by means of experimentally obtained characteristics of Z-type and U-type EAHEs. The obtained results show that in Z-type heat exchangers with short branches (L/D = 75) and small collector diameters (d = dkol) the non-uniform division of air between parallel pipes has significant influence on the thermal performance of such exchangers. The thermal performance of Z-type structures was 3-14% lower compared to the structures of uniform airflow distribution. On the other hand, the thermal performance of the U-type heat exchangers was only 0-2% lower in comparison to exchangers of perfect airflow division. Thus, it was found that for heat exchangers with long branches (L/d>> 75) and/or adequately large collectors (dkol > d, dkol = f (L, n)), in which the unequal distribution of air is small, the effect of this inequality on the abstracted energy will be negligible.

 

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