Moisture & Humidity Problems #Live

In this first live podcast episode, Bryan responds to audience questions and discusses moisture and humidity issues in HVAC.

Moisture leads to other problems, including fungal growth. We often see moisture problems where the surface temperature meets the air dew point, not where hot meets cold. When the customer drives the temperature down too low, many surfaces in the home can meet the dew point and begin sweating, especially ductwork in unconditioned spaces and air handlers.

When you increase airflow, you derate the HVAC system's dehumidification. That's because the evaporator coil can't get cold enough for moisture to condensate on top of it, meaning that the moisture stays in the air. If there isn't enough dehumidification, we may end up seeing a moisture problem. These problems are especially prominent on wood and finished surfaces and can damage those severely.

When assessing a home, you also have to think about internal moisture gains, including from cooking, showering, and doing laundry. However, external moisture gains are a major concern from infiltration. Drawing poor-quality, unconditioned air from attics and the outdoors through cracks will increase those gains. You must also keep in mind that the dew point can be different throughout the house. Dew point will also be different on the ceiling compared to the floor. Some stratification occurs with height, so that can complicate matters and must be accounted for.

Bryan also covers:

• Multi-stage compressors
• Dew point vs. relative humidity
• Infiltration, leakiness, and negative pressure
• The problem with bath fans
• Water in slab structures
• Boot sweating
• R-value and insulation in the attic
• Commercial buildings with fresh air requirements
• Condensate blowoff in horizontal installations
• Dealing with wet insulation

 

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