Arkansas HVACR NewsMagazine March 2024

HVACR NewsMagazine March 2024

Tech News

Humidity Control

Dilution Air

We need to control our indoor environment to maintain a moderate humidity level (30-60%) to reduce the risk of bacterial or fungal growth, allergens, and VOCs indoors. Humidity control can happen at the indoor unit, such as when we get a cold coil with long runtimes in the Southeastern United States, or with supplementary equipment, like a dehumidifier. Homes that are substantially airtight, and therefore have continuously running mechanical ventilation systems for dilution air (see below), will have VERY different dynamics of humidity control than typical older homes, and occupants may end up needing dehumidification in a 'dry' climate, or humidification in 'humid' climates in cold months. But then we need to circle back: do we need to filter the air before we dehumidify it? Then, how are we going to distribute and circulate that dehumidified air?

Now we're getting into the part of ventilation that really relates to ASHRAE 62.2. Dilution air comes from outdoors and dilutes the presence of indoor contaminants, including CO2 and odors (some of which are associated with VOCs in paints, furniture, etc.). The chart below shows what the generic CFM requirements would be for some homes based on ASHRAE Standard 62.2. But then we have to think about humidity control; how do we make sure the air we bring in is at an acceptable humidity level? Do we need to filter pollen and other outdoor contaminants out of incoming air? How will we tie that outdoor air into the duct system for circulation?

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