Heat Load Formula

The heating load is the quantity of heat energy expected to be introduced to particular space to retain the temperature within an appropriate range. The cooling load is the quantity of heat energy need to be extracted from space in order to maintain the temperature within an appropriate range.

There are two types of heat sources are known, one is resulting in the internal heat load on the conditional area and the second one is resulting in an external heat load.

Heat sources which result in an internal heat like heat conduction through the glass, walls, etc. Heat sources which result in an external heat load, heat from any source added in the air after it leaves a space.

The heat load formula is given as,

Heat load = Q = m × Cp ×ΔT


Q = Heat load (kW)

m = mass flow rate (kg/s)

Cp = specific heat (kJ/kg K or kJ/kg oC)

ΔT = change in temperature (K or 0C)

Example 1

Determine the heat load in the electric convector in which the rate of mass flow is 5.45 and Cp is 1000 and the enthalpy is from 21.5 to 26.55.



M = 5.45

Cp = 1000

T1 = 26.55

T2 = 21.5

Substituting in the formula

Heat load , Q = m ×Cp ×ΔT

                      Q = 5.45 x 1000 x (26.55 – 21.5)

                    Q = 27522.5 W

Example 2

Determine the heat load if the specific heat is 200 and enthalpy change from the temperature 31.5 to 26.55 and M is 4.45.



M = 4.45

Cp = 200

T1 = 31.5

T2 = 26.55

Substituting in the formula,

Heat load, Q = m × Cp ×ΔT

                  Q = 4.45 x 200 x (31.5 – 26.55)

                 Q  = 4405 W


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