Sensible and Latent Heat

The distinction between dry air and the moisture content of the air and between dry-bulb and wet-bulb temperatures is extended to the two types of heat carried by the entering air and the air already contained in the space: sensible and latent heat.

Sensible Heat:  is the amount of heat in air that can be measured by an ordinary thermometer. The daily weather report gives us sensible heat temperatures, but it does not represent the total heat we experience. It constitutes a portion of the heat resulting from air infiltration, ventilation and internal heat sources such as people, electric lights and electric motors. Sensible heat also results form heat leakage or solar radiation.

Latent Heat: is the amount of heat contained in the water vapor (moisture) in the air. It constitutes a portion of the heat resulting from infiltration and ventilation and any internal sources capable of adding water vapor to the air. The amount of latent heat in the air can be determined by using a psychometric chart.  The amount of excess latent heat so determined will indicate the amount of moisture that must be removed from the air in order to obtain comfortable conditions.

Above is an example of a Psychrometric Chart

Both sensible and latent heat gain are expressed in Btu. When the total of the two are added together, their sum represents the total heat gain in Btu that must be removed from the air each hour by the air conditioner.

Sensible heat gain is represented by a change in the dry-bulb temperature readings, where as latent heat gain is represented by a change in the web-bulb temperature.

This post was published by Tucson air conditioning service but was written by James Brumbaugh in the book "HVAC Fundamentals: Air Conditioning, Heat Pumps and Distribution Pumps (Volume 3)"