Window frame integrable air recuperation minichannel/minigap heat exchanger

Abstract

This article describes an evaluation of mini heat exchangers operation as a decentralized mechanical ventilation system with recuperative heat recovery that can be integrated into the window frame. The relatively small yet efficient air recuperation system allows for retrofitting existing buildings by reducing the overall energy consumption and thus the CO2 emissions. The proposed design, unlike existing systems, is easy to scale up to various room sizes and is a promising solution for buildings where a centralized recuperation system cannot be implemented or interfering with the building’s facade is not allowed. Theexperimental research was carried out enabling to collect temperature, pressure drop, and volumetric flow rate measurements in a recuperation system with various minigeometries, namely minichannels withahydraulic diameter of 3.00 mm, minigaps with a hydraulic diameter of 5.82 mm, and minigaps withahydraulic diameter of 1.98 mm. The system was tested for a room air temperature of 22 °C and three values of outside air temperatures, namely 5 °C, 10 °C, and 15 °C. The volumetric flow rate for a single heat exchanger ranged from 4.1 m3/h to 20.4 m3/h. The results showed that higher temperature rise of supplied air andhigher energy efficiency of the heat recovery can be achieved for smaller airflows and higher differences between outside and room temperatures. For an exemplary 34 m2 office room, the 0.8-fold air exchange rate can be provided and 1 667.1kWh of annual energy savings can be achieved, corresponding to 50.3 % of total energy required for heating the air. Heat exchangers equipped with 3.00 mm minichannels recover a similar amount of heat as the ones equipped with 5.82 mm minigaps, even though the hydraulic diameter ofthe minichannel is almost 2 times smaller. Meanwhile, a 5.82 mm minigap reduces the pressure drop by 76 % compared to a 3.00 mm minichannel.