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Humidity occurs in indoor environments due to building related causes. Porous walls, rising damp, and leaks in the building are determinants for structural dampness due to elevated humidity levels. [4]: 185–187 The construction of the building can also lead to humidity and unwanted moisture in the indoor environment. [15]
The control system can compare the temperature of the outside air vs. return air, or it can compare the enthalpy of the air, as is frequently done in climates where humidity is more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economizer mode.
The most common indoor pollutants monitored in DCV systems are carbon dioxide and humidity. [1] This control strategy is mainly intended to reduce the energy used by heating, ventilation, and air conditioning (HVAC) systems compared to those of buildings that use open-loop controls with constant ventilation rates.
Ventilation is mainly used to control indoor air quality by diluting and displacing indoor pollutants; it can also be used to control indoor temperature, humidity, and air motion to benefit thermal comfort, satisfaction with other aspects of the indoor environment, or other objectives.
Plumbing systems also service air distribution/control, and therefore contribute to the mechanical part of MEP. Plumbing for HVAC systems involves the transfer of coolant, pressurized air, water, and occasionally other substances. Ducting for air transfer may also be consider plumbing, but is generally installed by different tradespeople. [11]
By comparison, thermal comfort standard ASHRAE 55 requires systems designed to control humidity to maintain a dew point of 16.8 °C (62.2 °F) though no lower humidity limit is established. [44] Water vapor is a lighter gas than other gaseous components of air at the same temperature, so humid air will tend to rise by natural convection. This ...
Therefore, an in-room dehumidifier will always warm the room and reduce the relative humidity indirectly, as well as reducing the humidity more directly, by condensing and removing water. Diagram showing airflow through a heat-recovering dehumidifier. Warm, moist air is drawn into the unit at A in the diagram above.
For instance, the dew point temperature of air at 20 °C (68 °F) and 80 percent relative humidity is 16 °C (61 °F). The dew point temperature falls to 9 °C (48 °F) if the relative humidity is 50 percent. [4] A related, but quite distinct, technique of obtaining atmospheric moisture is the fog fence.