SENSIBLE HEATING AND COOLING FOR HVAC CONSIDERATION BASIC AND TUTORIALS


Sensible Heating
Sensible heating is heat added to the air, which causes the air temperature to increase. Sensible heat is measured using a standard thermometer.

A horizontal line on the psych chart represents any heating process such as a typical residential or commercial office heating process that adds sensible heat only.

Air enters the heating coil at 50°FDB and 40°FWB (condition point A) and leaves the heating coil at 100°FDB and 62.5°FWB (condition point B). As the air is heated, the dry bulb and wet bulb temperatures increase but the dew point temperature and the moisture content (specific humidity) remain constant.

The relative humidity also changes from 40% to less than 10%. This change in relative humidity is because as the air gets warmer, the air can hold more moisture (per pound of air), but because the amount of moisture is the same, about 22 grains, the relative humidity goes down.


Sensible Cooling
Opposite of sensible heating only would be sensible cooling only. This is not common but is used in some applications. Chemical dehumidification is one example. Sensible cooling is heat removed from the air, which causes the air temperature to decrease as sensed by a thermometer.

A horizontal line on the psych chart also represents any cooling process that removes sensible heat only. Air enters the cooling coil at 100°FDB and 62.5°FWB (B) and leaves the cooling coil at 50°FDB and 40°FWB (A).

As the air is cooled (heat removed), the dry bulb and wet bulb temperatures decrease but the dew point temperature (27°FDP) and the moisture content (22 grains) remain constant. The relative humidity also changes from approximately 8% to 40%.

This change in relative humidity is because as the air gets cooler, the air’s ability to hold moisture (per pound of air) lessens, but because the amount of moisture is the same, the relative humidity goes up.

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