Characterization of Mechanical Ventilation Systems in New US Homes: What types of systems are out there and are they functioning as intended?

As the airtightness of homes improves to meet energy efficiency goals, it becomes more important for mechanical ventilation systems to help maintain a comfortable and healthy indoor air environment. ASHRAE Standard 62.2 provides national guidance for mechanical ventilation system design and installation, however adoption of those guidelines into local building codes has occurred at different rates. Once provisions for mechanical ventilation are adopted in a local code, are mechanical ventilation systems properly designed, installed, commissioned and operated according to code or above-code program requirements? This paper presents results from field studies that include characterization of whole house mechanical ventilation (WHMV) systems in 150 occupied homes in CA, CO, FL, GA, OR, and SC built between 2011 and 2018. In each of the study homes, homeowners were asked how they operate the system, system airflow was measured, and operation of the system was monitored for one week. Resulting installed performance was compared to inferred design intent. Results show that the installed performance of WHMV systems is related to complexity of the system itself, with systems that are simpler to install and operate more likely to be capable of meeting ASHRAE 62.2-2010. The frequency that systems were operating as found did vary regionally, and was related to the presence of clear labeling, and complexity of system controls. Results show there is a need for further homeowner and industry education to ensure behavior that results in operation of WHMV systems as intended.