A ‘use factor’ for HRV in intermittently heated dwellings

When considering the performance of HRV systems, the discussion is generally focusing on the reported effectiveness of the air-to-air heat exchanger. Although some excellent presentations at the AIVC conference in the past have dealt with uncertainties related to the test of that effectiveness, the fact that the heat recovered by the HRV unit might not be useful in an intermittently heated dwelling without room-by-room based demand control is usually not considered. Therefore, the ‘use-factor’ for the recovered heat is quantified in this paper.
The goal of this project was to investigate the performance of heat recovery units in low energy buildings by simulating different buildings under varying conditions. The influence of several parameters on this performance is studied: the type of building, the insulation and airtightness, the ventilation flow rates, the ventilation strategy, the heat exchanger effectiveness, the occupancy pattern and the demanded comfort level.
The results suggest that, although a heat exchanger can have an effectiveness of e.g. 75%, only approximately 40% of the heat in the extracted air is recovered and supplied usefully to the rooms