Analysis and design of an air to air heat exchanger used in energy recovery systems

With the continuous worldwide energy use increase, energy efficiency is gaining high importance. Consequently, many methods have been investigated for potential energy savings. One of these methods is the use of heat recovery systems. These systems basically re-use waste heat and reduce energy consumption. Also, they are increasingly used to reduce heating and cooling demands of buildings. Their main feature is to provide fresh air to the place which is heated by the exhaust air with the help of a heat exchanger (HEX) working between two different temperature sources. The most commonly used types of heat exchangers in ventilation systems are cross-flow and counter-flow heat exchangers. Cross-flow heat exchangers have a thermal efficiency in the range of 50-75% while counter-flow heat exchangers have 75-95%. Many studies have been carried out to increase the efficiency of this type of heat exchangers. In this study, different designs of cross-flow and counter-flow exchangers are compared using ANSYS Fluent software. The aim is to determine how the plate surface geometry affects heat transfer and pressure drop. It is aimed to find the optimum design with maximum efficiency, high heat transfer and low pressure drop for heat exchangers. As a result, it has been observed that thermal efficiency increased from 18% to 60% when changing from cross flow to counter flow in flat plate design, while it increased from 25% to 77% in enhanced plate designs. For enhanced designs, counter flow heat exchanger is 52% more efficient than cross flow heat exchanger. Also, improvements to increase the surface area and turbulence in both flow types have increased heat transfer and thermal efficiency.