Energy saving potential and repercussions on indoor air quality of demand controlled residential ventilation strategies

Ventilation is ambiguously related to the energy saving rationale originating from the mitigation of global warming, the reaching of peak oil or health concerns related to fossil fuel burning. Since it makes up for about half of the energy consumption in well insulated buildings, it is an attractive target for energy saving measures. However, simply reducing ventilation rates has unwanted repercussions on the indoor air quality. Two main strategies have been developed to reconcile these seemingly opposing interests: heat recovery and demand control ventilation. This paper focuses on the energy saving potential of demand controlled mechanical exhaust ventilation in residences and on the influence such systems may have on the indoor air quality to which the occupants of the dwellings are exposed. The conclusions are based on simulations done with a multi-zone airflow model of a detached house that is statistically representative for the average Belgian dwelling. Four approaches to demand based control are tested and reported. Within the paper exposure to carbon dioxide and to a tracer gas are used as indicators for indoor air quality. Both energy demand and exposures are reported and compared to the results for a standard, building code compliant, exhaust system, operating at continuous flow rates. The sensitivity of the control strategies to environmental and user variations is tested using Monte-Carlo techniques. Under the conditions that were applied, reductions on the ventilation heat loss of 25 to 60% are found, depending on the chosen control strategy (with the exclusion of adventitious ventilation and infiltration). home owners tend to prefer demand controlled exhaust ventilation over heat recovery systems to comply with tightening energy performance legislation. However, little information is available in literature on the performance that can be achieved with different approaches to demand controlled exhaust ventilation. This paper presents performance and sensitivity results that can be used to understand and design appropriate residential demand controlled exhaust ventilation.