Energy and IAQ Implications of Residential Ventilation Cooling

This study evaluates the energy, humidity and indoor air quality (IAQ) implications of residential ventilation cooling in all US IECC climate zones. A computer modeling approach was adopted, using an advanced residential building simulation tool with airflow, energy and humidity models. An economizer (large supply fan) was simulated to provide ventilation cooling while outdoor air temperatures were lower than indoor air temperatures (typically at night). A typical new construction, low-mass, timber frame home with ASHRAE Standard 62.2 compliant ventilation was considered. The simulations were performed for a full year using one-minute time steps to allow for scheduling of ventilation systems and to account for interactions between ventilation and heating/cooling systems.

The results showed that energy savings from a residential economizer are moderate (up to 200 kWh of cooling energy per year) using a high performance brushless permanent magnet (BPM) air handler. A Permanent split capacitor (PSC) air handler led to less cooling energy savings, and in some climates a small (approximately 1%) cooling energy increase. The cooling energy savings were greatest in climate zones 3, 4, and 5. Economizers were found not to contribute to excess indoor humidity in hot, humid climates, but did lead to increased indoor humidity in more moderate climates (but still not to the level found in hot, humid climates). Economizer operation reduced annual relative exposure by about 5 to 15% indicating a significant potential for IAQ improvement. The improvements were greatest in climate zones 3B and 4B due to longer economizer operation time. One caveat with the ventilation cooling recommendations is that they were for a lightweight timber frame construction and may change for heavier brick/block structures not included in this study.