NREL and ORNL will work together to evaluate factors that can contribute to high relative humidity in low-load homes. This research will inform development of HVAC design guidance and standards, the Building Science Advisor (ORNL) and Building America Comfort Roadmap priorities.

Occupant-related internal gains are a significant source of uncertainty when it comes to selecting space-conditioning equipment and, as the efficiency of the building thermal enclosure improves, internal gains account for an increasing percentage of the total building conditioning load. In addition, equipment controls, airflow rates, and the chosen capacity can all affect indoor relative humidity. This project will use EnergyPlus to quantify the impact that variations in internal moisture loads, and air conditioner configuration can have on indoor relative humidity and the recommended equipment capacity. The project will:

• Use stochastically derived latent and sensible internal gain profiles to determine the sensitivity of internal gains on indoor relative humidity
• Evaluate the impact that air conditioner oversizing and air flow rate have on indoor relative humidity
• Determine recommended blower-off delays to better control indoor relative humidity in low-load homes

In addition, HVAC contractors are wary of installing low-capacity equipment in low-load homes because of concern that there may be insufficient capacity to handle unique "party" and setpoint recovery loads. This project will also investigate how well appropriately-sized equipment in a low-load home can handle these atypical loads that are not accounted for by current equipment selection procedures.