Development of a Seasonal Smart Ventilation Controller to Reduce Indoor Humidity in Hot-Humid Climate Homes

Controlling indoor humidity is important in homes, because high indoor humidity is associated with occupant health and building durability issues. Ventilation is often used to avoid peaks of moisture in homes, such as in kitchens and bathrooms. However, in hot-humid climates, outdoor air can have higher humidity than indoors, and continuous whole house ventilation can lead to increases in indoor humidity levels. This problem is exacerbated in high performance homes, because their efficient building envelopes limit the operation of the cooling system, which also provides incidental dehumidification. This paper analyzes a time-shifting approach to smart ventilation control that takes advantage of changes in outdoor and indoor humidity, essentially venting more when dryer outside and less when more humid outside. The changes in whole house airflow are controlled in such a way that exposure to air pollutants is equivalent to a continuously operating, fixed airflow system. Specifically, this paper presents the development and initial testing of a seasonal smart ventilation controller, based simply on the month of the year and the net-humidity balance for the month between inside and outside. We assessed high performance test homes with varying floor areas and moisture generation rates across a variety of hot- and mixed-humid climates in the south-eastern U.S., using ventilation simulation software specially adapted for this analysis. We present the results from baseline simulations, with continuous fans sized at 0%, 50% and 100% of the ASHRAE 62.2-2013 fan flow rates. From this analysis, we develop a seasonal control strategy. Finally, we present preliminary results from use of the proposed seasonal controller. The results include comparisons of IAQ, energy use and indoor humidity levels.