A Variable Volume and Temperature (VVT) Control Strategy for a Liquid-Desiccant and Dew Point Evaporative Cooler-Assisted 100% Outdoor Air System (LDEOS) (ST-16-C048)

The main purpose of this study is to propose a variable volume and temperature (VVT) control strategy for a liquid-desiccant and dew point evaporative cooling-assisted 100% outdoor air system (LDEOS) and evaluate its performance on a Building Controls Virtual Test Bed (BCVTB). For decades, various alternative air-conditioning technologies have been developed to reduce refrigerant use and energy consumption. Among them, many studies have been conducted on a liquid-desiccant (LD) and indirect evaporative cooling-assisted system because it independently controls the sensible and latent load and reduces cooling energy by using latent heat of water vaporization. In previous studies, the LDEOS, which conditions a space by using 100% outdoor air, is proposed by combining membrane enthalpy exchanger (MEE), LD, and dew point evaporative cooler (DP-IEC). Unlike the energy performance and the design process, few studies were conducted on the control strategies of the LDEOS. In the control strategy of a general variable-air-volume (VAV) system, the controller maintains a constant supply air temperature (SAT) for dehumidification control. However, the SAT control is hard to be implemented for an indirect evaporative cooler if VAV fan is applied. In this study, a variable-air-volume and temperature (VVT) control is presented for the LDEOS. In VVT, the cooling capacity is controlled by the fan airflow, but the SAT is not controlled. In the LDEOS, the dehumidification control is achieved by the LD, and thus, the SAT does not need to be modulated. The VVT control was realized on a BCVTB in a one-minute time step and evaluated its performance. The simulation result revealed that the proposed control strategy maintained a space comfortable while saving 35% of fan energy compared to the reheating-based constant SAT control strategy.