A new dual-path HVAC system concept is proposed and reduced for practice in prototype equipment that meets the requirements for increased amounts of outdoor ventilation air in air-conditioned buildings. One path of the system cools and dehumidifies ventilation air alone—or 100% outdoor air— while the other path conditions recirculation air only. The ventilation air quantity in the outdoor air path can be controlled based on any sensor input such as CO2 level, occupancy, etc. This ability to vary ventilation air yields significant energy savings. The continuously cooled and dehumidified ventilation air provides excellent humidity control in the conditioned space. The ventilation air path’s part-load operation is designed and controlled in such a manner that it continuously dehumidifies incoming ventilation air above a certain dew-point temperature. The capacities of the cooling and dehumidification coils in the ventilation air path are continuously modulated so that the leaving air temperature is held below a target dew-point temperature. Required ventilation air quantities are provided continuously. Additional features, such as a continuously wet coil on the ventilation airstream and a dry drain pan in the recirculation air path, significantly reduce growth and transmission of mold, mildew, and bacteria in the HVAC system and further improve indoor air quality. Prototype units were demonstrated in a combination grocery/department supercenter with variable occupancy load. Data analyses show significant energy savings when compared to a conventional constant-volume ventilation air system while providing excellent space humidity control.

Paper from IAQ 1997 -- Design, Construction, and Operation of Healthy Buildings: Solutions to Global and Regional Concerns