What differences and benefits does a counter flow heat exchanger have over a cross flow heat exchanger for energy recovery?
Counter flow and cross flow and heat exchangers are two heat transfer configurations within energy recovery technology for ventilation application. Choosing a counter flow heat exchanger over a cross flow heat exchanger depends on application, size, desired heat transfer efficiency, pressure drop limitations, and installation cost. Below is a comparison.
Counter Flow Heat Exchanger
- Counter flow heat exchangers generally offer higher heat transfer efficiency compared to cross flow heat exchangers
- As the air flows in opposite directions, there is a continuous temperature difference between them along the length of the heat exchanger, providing 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
- The hot air flows in the opposite direction as the cold air
- The counter flow exchanger is longer and turns the air at the entrance and exits to the exchanger; the airflow within the exchanger is along the same plane but in opposite directions
Cross Flow Heat Exchanger
- The hot and cold air flow perpendicular to each other (at a 90-degree angle)
- The hot air enters the heat exchanger from the opposite end as the cold air and the hot air and cold air 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; the heat transfer effectiveness can 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
Key Differences and Considerations
- Heat Transfer Efficiency: Counter flow heat exchangers generally offer better heat transfer efficiency because they maintain a larger temperature difference between the hot and cold air along the entire length of the exchanger
- Effectiveness: Counter flow heat exchangers tend to have a higher heat transfer effectiveness, meaning they can transfer a greater amount of heat between the air streams
- Temperature Approaches: In counter flow heat exchangers, the outlet temperatures of the hot and cold air streams are closer to each other compared to cross flow heat exchangers
- Pressure Drop: Cross flow heat exchangers typically have lower pressure drops compared to counter flow heat exchangers, which can be advantageous in some applications
- Size: Cross flow heat exchangers are longer. They require space to make the change in airflow direction at entrance and exit
- Equipment Cost: Counter flow heat exchangers are typically more costly than cross flow heat exchangers
Engineering calculations and simulations can help determine the most suitable heat exchanger configuration for a given situation.