Abstract
The paper discusses two mathematical models for the air flow through a plate heat exchanger with parallel plates. The first exhausts the used air and then supplies the fresh air. The second exhausts the used air above the plate and simultaneously supplies fresh air under it (counter-flow exchanger). In both cases, the exhaust air heat is used to heat the supply air. The purpose of the research is to verify which exchanger uses the exhaust air heat more efficiently. The method of the Trefftz function was used to determine approximate solutions of the analysed problems. The results obtained for 1.2 mm thick steel, aluminium, and copper plates and for external winter, summer, and spring–autumn temperatures are discussed. The results indicate that steel is the best material for a plate heat exchanger, and the counter-flow exchanger is more efficient of the two. Thanks to the use of thin steel plates and the reduction of the air exchange time to a few minutes, cheap and efficient counter-flow exchangers can be obtained.
Highlights
A recuperator is a device used, among others, for supplying and extracting air from rooms as part of ventilation systems with heat recovery
There are many recuperator types, including those discussed in monographs [1,2] and presented on numerous websites, e.g., [3]
The exhaust air flows in the heat exchanger without mixing with the supply air
Summary
A recuperator is a device used, among others, for supplying and extracting air from rooms as part of ventilation systems with heat recovery (recuperation systems). Connected to a properly executed ventilation system, it recovers heat (energy) from air, reducing the building’s energy demand. The most important part of any recuperator, which determines heat recovery parameters, is the heat exchanger located centrally in the recuperator. There are many recuperator types, including those discussed in monographs [1,2] and presented on numerous websites, e.g., [3]. The exhaust air flows in the heat exchanger without mixing with the supply air. Energy is exchanged between the air fluxes. It enables the recovery of heat or cold (depending on the season). Numerous publications discussing heat exchanger types are known
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