Considerations for providing healthy, comfortable, energy-efficient whole-house mechanical ventilation during humid weather in near zero energy homes

Abstract

Whole-house mechanical ventilation (WHMV) is necessary for adequate ventilation in healthy near zero energy homes in most cases. Ventilation standards such as ASHRAE 62.2-2016 call for more ventilation than can be provided by natural ventilation in new homes built better than minimal building code requirements. A very troubling matter is that different studies in different climate locations have shown that a majority of WHMV evaluated in occupied homes has found them to be turned off, broken, or delivering too little ventilation when operational. Some homes with adequate ventilation may have increased potential for comfort complaints, moisture control issues, and even higher than expected energy usage. Higher energy usage will occur when supplemental dehumidification is needed. Balanced ventilation provided through a heat recovery ventilator or an energy recovery ventilator may be a good approach for many climate zones, however supplemental dehumidification needed for homes intended to maintain relative humidity around 50% during mild humid weather. Recent studies found that the highest efficiency variable air conditioning systems do not dehumidify as well as lower efficiency single stage systems, but some may be capable of very good dehumidification negating the need for costly supplemental dehumidification. This paper will use recent lab and field research studies to discuss details of issues that engineers and builders must consider to design WHMV with good potential of providing healthy, comfortable and energy-efficient ventilation.