Development of an Integrated Residential Humid Climate HVAC System

Marc Hoeschele, and
David Springer, Davis Energy Group

Keywords

Abstract

Standard residential vapor compression cooling systems provide a mix of sensible cooling (lowering indoor temperature) and latent cooling (removing moisture at the evaporator coil). These systems operate at a sensible heat ratio1 (SHR) of about 0.75 to 0.85, depending upon indoor and to a lesser degree, outdoor conditions. In humid climates this often leads to indoor humidity exceeding typical comfort levels of 55-60%. This is especially true in energy efficient homes where sensible loads are reduced through the implementation of measures such as low solar heat gain coefficient glazing, improved building envelopes, and use of energy efficient appliances and lighting. Some advanced vapor compression cooling systems provide two-stage cooling or lower the airflow through the evaporator coil to increase dehumidification, but this control strategy may not improve comfort under low sensible load conditions, leading homeowners to further reduce their cooling setpoint or install a dehumidifier.

This project involved the design, construction, and testing of an advanced appliance that provides space conditioning, fresh air ventilation, and integrated dehumidification. The system was designed to respond to changing indoor temperature and humidity conditions by varying the supply air temperature, humidity, and airflow level. During conditions with elevated indoor relative humidity and no sensible cooling loads, supply airflow can be reduced to as low as 150 cfm/nominal ton, and a second refrigerant coil can be used to reheat supply air. Preliminary results from a Florida field test site are encouraging in terms of improved comfort and overall performance, although additional laboratory and field testing is needed to fully validate system performance.