Liquid flow rate control in run-around heat recovery systems

Journal article, 2025

Run-around heat recovery has been available for over half a century as an option to recover heat in ventilation systems, especially advantageous in buildings with significant space limitations or strict air cleanliness requirements. The core of the system is a liquid transferring heat from the extract air to the supply air. Improper control of the liquid flow rate causes underperformance increasingly as the systems are designed for higher heat transfer effectiveness and more often in combination with demand-controlled ventilation. The work presented in this paper is a combination of experimental measurements and simulations. The results show how much the heat transfer effectiveness can be improved (up to 6% under the studied conditions) by increasing the liquid heat capacity rate from being equal to the heat capacity rate of the air flows, which is the prevalent strategy today. In addition, a novel control method is demonstrated. It is based on measuring temperatures instead of volumetric flow rates, which is the prevalent method today. This method has potential to make the system more robust and accurate, which is key to be able to optimize the liquid flow rate in run-around heat recovery systems in practice