4

Inlet Moisture (gr/lb)

Fig. 39-26 Performance Plots for System Example. Source: Munters Cargocaire and Mason Grant Company ture at various locations. Note that the 800 cfm (22.6 m3/m) of incoming outside air (Location A) balances 500 cfm of exhaust (14.2 m3/m) at Location G and 300 cfm (8.5 m3/m) of air leakage. This system's controls are as follows:

• Room air pressure is controlled by a differential pressure controller, which automatically adjusts the fresh air intake damper. As air pressure exceeds the set differential, the damper begins to close to reduce incoming air.

• Dehumidifier capacity is controlled by a bypass damper that passes air around the system as humidity levels are less than design conditions. As a dewpoint controller signals a humidity change, the bypass damper is modulated.

• Desiccant system energy use is controlled by a temperature controller in the reactivation airstream. This minimizes energy use by reducing the energy of the reactivation heaters when the temperature rises above the set point of 120°F (49°C), which indicates that all of the moisture absorbed on the process air side has been desorbed in reactivation.

• Chilled water flow through the outside air precooling coil is controlled by a three-way valve, which responds to a controller located downstream of the coil that is set at 50°F (10°C). The post-cooling coil, which sets the final delivered air temperature, is controlled in the same manner, with the temperature sensor located in the conditioned space to maintain constant temperature. In a variable flow system, two-way valves could be used to accomplish this control function more economically.

• A supply air heating coil is used to provide heat whenever room temperature drops below 68°F (20°C). This is controlled by the same sensor that controls the post-cooling coil.

Bypass only at low load m

300 cfm leaves the room through cracks and doors

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