The effect of buoyancy forces in buildings on the efficiency of unbalanced regenerative air handling units

Over the years, ventilation in old residential buildings has developed and modernized, leading to more efficient ventilation systems and heat recovery units. In individual rooms, small houses, one-two storey buildings, and greenhouses it is very appropriate to use small single Air Handling Units (AHU) with heat recovery. It has been established in the literature that such devices for heat recovery are influenced by external factors - the outdoor and indoor parameters of the air, and especially the pressure difference in the buildings. These factors cause an unbalanced operating mode of the regenerative AHU which can significantly change its efficiency. The main aim of this paper is to simulate the unbalanced operating modes of AHU with a fixed-bed regenerator for heat recovery in multi-storey buildings. Simulations were performed for two cases of room ventilation, the first case refers to a single device in a room, and the second case refers to a pair of devices in a room. The results show different ventilation modes for each of the cases, which leads to different pressure distributions, air change rates, room velocity vector fields, and different regenerators' thermal efficiency.