Energy and air quality implications of passive stack ventilation in residential buildings

Ventilation requires energy to transport and condition the incoming air. The energy consumption for ventilation in residential buildings depends on the ventilation rate required to maintain an acceptable indoor air quality. Historically, U.S. residential buildings relied on natural infiltration to provide sufficient ventilation, but as homes get tighter, designed ventilation systems are more frequently required – particularly for new energy efficient homes and retrofitted homes. ASHRAE Standard 62.2 is used to specify the minimum ventilation rate required in residential buildings and compliance is normally achieved with fully mechanical whole-house systems; however, alternative methods may be used to provide the required ventilation when their air quality equivalency has been proven. One appealing method is the use of passive stack ventilation systems. They have been used for centuries to ventilate buildings and are often used in ventilation regulations in other countries. Passive stacks are appealing because they require no fans or electrical supply (which could lead to lower cost) and do not require maintenance (thus being more robust and reliable). The downside to passive stacks is that there is little control of ventilation air flow rates because they rely on stack and wind effects that depend on local time-varying weather. In this study we looked at how passive stacks might be used in different California climates and investigated control methods that can be used to optimize indoor air quality and energy use. The results showed that passive stacks can be used to provide acceptable indoor air quality per ASHRAE 62.2 with the potential to save energy provided that they are sized appropriately and flow controllers are used to limit over-ventilation.