Mechanical ventilation is vital in modern homes to insure adequate indoor air quality. However, builders, homeowners and policy makers may perceive best practice as a risk, especially if invoked during peak outdoor thermal conditions which may compromise comfort and energy use. In North America, ASHRAE Standard 62.2- 2016 defines best practice, yet ventilation code specifications vary internationally. Although enthalpy heat recovery is advocated in efficient home design, taking advantage of the natural daily and seasonal temperature and humidity cycles can provide further comfort and energy reduction advantages.
We describe a smart ventilation system which uses the simple idea of modulating outdoor air depending on departure of prevailing weather from desirable indoor comfort conditioning. The system uses outdoor temperature and moisture based control. The main principle is to shift ventilation from time periods that have large indoor-outdoor temperature and moisture differences to periods when these differences are smaller and their energy and comfort impacts are expected to be less. Fan flow rates are reduced when the outside temperature and moisture falls outside of optimum levels, yet overall air exchange is maintained to ensure chronic and acute exposure to pollutants remains relative to best practice. Online weather and smart thermostat data can be used as control inputs, so no specific measurement devices are needed.
Using the smart ventilation scheme demonstrated 10% average cooling season energy savings in two full-scale identical side by side test homes in Florida. Parametric simulations show similar savings for heating and cooling across North American and European climates demonstrating smart ventilation as a robust efficiency measure, particularly for cooling. We posit that a weather-responsive ventilation scheme has world-wide application.