Applicability of a CO2-based Demand Controlled Energy Recovery Ventilator to a Test Bedroom with Varying Simulated Occupancy

Indoor air quality is a major area of concern in northern housing and could be influenced by ventilation. The required ventilation rate set by North American ventilation standards (ASHRAE 62.2, CSA-F326) is calculated on the basis of fixed floor area and number of bedrooms or people. The heat/energy recovery ventilators (HRV/ERV) on the market offer constant airflows and are selected to meet the required ventilation. The ventilation rate could be too low for northern housing experiencing varying indoor conditions and occupancy, producing higher indoor concentrations of pollutants (RH, CO2, etc.) that need to be controlled. This paper presents results from an experimental assessment of a CO2-based demand-controlled ERV unit to a test bedroom with varying simulated occupancy. Three strategies for demand-controlled energy recovery ventilation were implemented in a test bedroom with varying occupancy of up to four adults sleeping in the bedroom. The implemented strategies are based on sensing CO2-concentration in the indoor air and in both the exhaust and supply air. The CO2-concentraion was used to ensure adequate ventilation during varying occupancy in the test bedroom. The ventilation rate can be switched between four flow rates or between two flow rates. The control strategy based on switching the air flow between four levels (fan speed switched between four relative fan speeds) achieved the best results in terms of acceptable IAQ with indoor CO2 concentrations below the limit set by ASHRAE 62.2 of 700 ppm above the outdoor concentration and the demand-controlled ERV spent a bigger fraction of time on low fan speed (relative fan speed of 20%). The results also suggested that a threshold for difference in CO2 concentration between supply and exhaust air of 150 or 200 ppm is suitable to ensure switches to higher ventilation rate shortly after a change in occupancy, achieve a good control of the indoor CO2 concentration, and present higher potential for reducing the electricity consumption by the ERV unit (higher fraction of time on low fan speed).