Some of the functions and methods of air introduction include: The pretreat unit nomenclature has been used for a long time, but is now more commonly known as the dedicated outdoor air system (DOAS). The introduction of pretreated OA and minimum ventilation requirements go hand in hand. Ventilation standards such as ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality have been in use since 1973 (originally as Standard 62) and are now updated regularly using ASHRAE’s continuous maintenance process. This pretreated air is also an excellent method to supplement other devices such as active and passive-radiant and convective cooling technologies. One of the primary reasons for the air pretreatment is to decouple the latent and sensible cooling loads of the OA from the space’s cooling loads. This design approach is especially useful in humid coastal climates. This approach also provides a positive introduction of required ventilation air, which results in positive building pressurization. It continues to be a good way to reduce the work of dehumidification of the air (moisture removal) a building air unit would need to perform and to achieve more effective energy use. With further filtration and treatment, the air is introduced into the space. The unit takes in 100% OA and then filters, heats, cools, dehumidifies (or humidifies) the air, and introduces it into a mechanical room plenum where it is mixed with return air. Air-handling units (AHUs) that provide pretreatment of outdoor air (OA also referred to in some localities as pretreat units) have been standard in HVAC design for a long time.
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