DOAS, Evaporatively cooled condenser, Heat wheel, Enthalpy wheel, Closed DOAS
Dedicated outdoor air systems (DOAS) make use of the sensible and latent capacity of the return (exhaust) air to cool and dehumidify the supply (outside) air. “Closed DAOS” is an advanced form of typical DOAS with desuperheater and evaporatively cooled condenser in the return air stream. The air entering the condenser in Closed DOAS is in the fully saturated state. In order to fully saturate the return air, it needs to be sprayed by water. Sufficient amounts of water is required for fully saturating the air and keeping the coils of the condenser wet during the process. This water is obtained internally as a result of condensation on the evaporator fins, not requiring additional water use at the buildings site. Closed packaged configuration requires to have a water balance of water obtained in evaporator to that required for saturating the air and wetting the condenser coil. This water balance can be achieved under most conditions by an optimal control of enthalpy wheel and heat wheel (run around heat exchanger) effectiveness to control the amount of water obtained in the evaporator. The optimal control of heat and enthalpy wheel effectiveness is not only important for making the necessary water balance but also to keep the latent load as low as possible. This paper discusses the Closed DAOS configuration with psychrometrics and water balance analyses.