Dew point is the temperature at which air becomes saturated with moisture and water vapor begins to condense into liquid water at constant pressure. Dew point is a critical parameter in HVAC design and operation, determining when condensation occurs on cooling coils and building surfaces, affecting both system performance and indoor air quality.
Dew Point Calculation and Properties
Dew point depends only on moisture content, not on temperature or pressure independently. Air at 75°F with 50 percent relative humidity has a dew point around 55°F. When this air cools to 55°F, condensation begins. Every 1°F drop in dew point approximately reduces the absolute humidity by 0.5 grains per pound of dry air (a standard measurement in HVAC). Summer outdoor dew points commonly reach 70-75°F in humid climates.
HVAC Significance
Cooling coils typically operate with surface temperatures 10-15°F below room dew point to ensure condensation and dehumidification. Dehumidification systems target specific dew points for comfort and process control. Understanding dew point prevents surface condensation on windows, ducts, and pipes that can cause water damage and mold growth.