HVAC System Modeling

Complaints about poor air quality and high humidity levels at two Hillsborough County high schools prompted an analysis of the HVAC system design. The system controls incorporate a discharge air temperature reset, which increases air temperature at low cooling loads in order to decrease energy use. Furthermore, the reheat system had been turned off to comply with the Energy Code. Unfortunately, this resulted in decreased system dehumidification capacity at low sensible loads — just when humidity control is most critical. An hourly computer building simulation model was developed using DOE2.1E and Visual Basic to simulate control sequences and arrive at low cost modifications that will reduce humidity. The modifications will solve the air quality problem while reducing energy costs, as compared with reactivating the hot water reheat system.