Governing Equation for Sensible Heating and Cooling

Example

Calculate the amount of sensible heat that must be added to 100lb of air at 85°F dry bulb and 75°F wet bulb to raise the temperature of air to 100°F dry bulb.

Solution

a) Locate the 85°F dry bulb and 75°F wet bulb – this corresponds to 62% Relative humidity.

b) Move from point established in a) above to right to 100°F on a horizontal dry bulb temperature scale – this corresponds to 39.6% Relative humidity.

The condition of the air is changing from state 1 to state 2

c) Read h₂ and h₁

•         h₂ = 39 Btu’s/lb dry air

•         h₁= 43.5 Btu’s/lb dry air d) Estimate heat addition : Q = m [h₂ – h₁]

•         Q = 10 x [43.5 – 39]

•         Q = 10 x 4.5

•         Q = 450 Btu’s