Being characterized by high heat transfer area per unit volume, compact heat exchangers are convenient for applications where space is restricted.
Ventilation is very important for the health and comfort of the residents. Sufficient fresh air supply is helpful for the prevention of epidemic respiratory diseases, but heat losses by ventilation without heat recovery are significant due to hot or cold environment outside. In order to at the same time satisfy the need for ventilation and energy saving, heat recovery means must be prepared.
What are the differences between cross-flow and counter-flow heat exchangers?
In a cross-flow heat exchanger, the hot and cold air flows are perpendicular (90o angle) to each other. The hot and cold air flows typically enter the heat exchanger from opposite ends and flow across each other. Heat transfer occurs through the separation walls between the hot and cold air streams.
The temperature difference between the air promotes heat transfer, but the heat transfer effectiveness may vary across the heat exchanger. The heat exchange is most effective in the half of the exchanger where the two air streams enter the exchanger. The opposite side has less opportunity to exchange the temperature.
In a counter-flow heat exchanger, the hot and cold air flows in opposite directions. Although it appears that the exchanger has a similar cross pattern, it does not. The counter flow exchanger is longer and provides the opportunity for the air to be turned at the entrance and exits to the exchanger. The airflow within the exchanger is along the same plane but in opposite directions.
As the air flows in opposite directions, there is a continuous temperature difference between them along the entire length of the heat exchanger. This method provides more surface area and time for temperature exchange.
Heat transfer occurs through the separation walls, and the temperature difference allows for efficient heat transfer from the hot air to the cold air. Counter-flow heat exchangers generally offer higher overall heat transfer efficiency compared to cross-flow heat exchangers.
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