6.101 drawback is that, once saturated, water is commonly removed from the substance by heating, thus evaporating the water. The circu-- larity of the process is self-defeating in a closed system. Dehumidification by air compression happens when the volume of moist air per kg of water is reduced below the specific volume for saturated water vapor at the temperature of the mixture. This process is useful when the air must be compressed in any case, but otherwise is ~ot an energy-efficient technique. The third process involves cooling air below its dewpoint thereby condensing out water. Air is usually cooled below ambient air temperature and reintroduced to the conditioned space. The dehumidification process thus partially accommodates the sensible heat gain load. The third process is the most likely candidate for our applications. Before the design process for dehumidification can proceed, conditions of the ambient atmosphere must be specified. The design climate for the colony is 295°K (72°F) temperature and 60% relative humidity. The high humidity level compromises the desires of the growing plantlife with the comfort of the colonists. Section VI.10.3 calculated the Sensible Heat Ratio at .794. This SHR describes the slope of a line which locates possible temperature-humidity combinations due to environmental gain that the colony could experience relative to one fixed condition point (see Figure 6.38). The next step is finding the amount of air movement needed in order to properly control the temperature and humidity. In theory, there are two possibilities: remove the latent heat only in the cooling process (i.e., just condense out the water), or condition the total air mixture to remove both sensible and latent loads. A standard chilled water cooling coil acts by sensible cooling the mix until the dewpoint, where the dry bulb temperature equals the wet bulb temperature, is almost reached (see Figure 6.39, Step 1). Dehumidification then begins and continues concurrent with sensible cooling (see Figure 6.39, Step 2). Since pure dehumidification is not possible with this method, some of the sensible load is satisfied in any case. How far should the air mixture be chilled? The plot of environmental gain points in Figure 6.38 intersects the
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