In today's podcast, Bryan covers some of the facts about humidity. He also explains how to keep humidity under control in all climates. Humidity refers to water vapor in the air and is a component of the air. Changes in temperature and pressure affect the density of the air. The air density determines how much moisture air can hold.

Relative humidity refers to the ratio of water vapor in the air. An RH value of 100% indicates that the air is saturated with water vapor; it has reached the dew point. At that point, the wet-bulb and dry-bulb temperatures will be the same. We do not want to reach the dew point inside a building.

Many people associate high relative humidity with high temperatures, but that association is a misconception. Unless the moisture content is extremely high at high temperatures, the RH will tend to be lower in hotter environments; hotter temperatures can hold more moisture. The moisture content at 90 degrees with 55% RH will be significantly higher than the moisture content at 65 degrees with 55% RH.

If the indoor temperature is below the outdoor dew point, we need to make sure we keep outdoor air out. We can do that by using ventilation strategies like bath fans and kitchen exhaust, especially since construction companies have built homes much more tightly over time. However, we want to ensure that we don't draw in low-quality air from the attic. We find that many humidity control strategies overlap with ventilation.

Bryan also discusses:

• Wet-bulb depression
• Insulating spaces and the effect on humidity
• Dehumidifiers
• Attic and crawl space dew points
• Humidity drivers inside the home
• Coil temperature, airflow, and dehumidification
• Off cycle fan delay
• Sweating and equipment freeze-ups
• Running continuous fan

 

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