An Open or Closed Dehumidification System?

2/1/2021 (Permalink)

The open drying system uses ambient outdoor air to reduce the indoor humidity. The most appropriate outdoor conditions for using an open drying system are when the temperature is high and the relative humidity is low. Always take an outside reading to check your dew point temperature. The open system is thus utilizing the principle of dynamic equilibrium for indoor humidity reduction. However, considerations must be made for energy loss and cost, building security, changing weather conditions, and all psychrometric data indoors and outdoors. The closed system utilizes air movers, dehumidifiers and psychrometrics to artificially control the indoor environment. The acceptable range of allowable humidity in an indoor environment for health and comfort is between 30%Rh and 50%Rh. The use of dehumidification equipment should always be considered in sealed structures to prevent equilibrium. In a flood damaged structure the Rh always seeks equilibrium and then the evaporation process stops. The vapor pressure equalizes in the contained space until the maximum humidity is reached or there is no more available water to evaporate. One of the best times to utilize a closed drying system and create positive pressure inside the building is when the outdoor humidity is high.