Cooling Load

What are the major cooling load in a typical building? Knowing the type of loads will help you to design your house or building in such a way that minimizes the type of load by using better materials, orientation of the house or roofing that reflects solar radiation or simply by planting trees nearby.

The increasing greenhouse effect and depleting natural resources are calling all of us to play our part in helping to conserve mother nature.

Solar Radiation Heat

A study showed that the solar radiation heat from the sun contributes more than 25% of the total load in a house. The heat is introduced into the building through the outside walls and roof. Some of the solar rays are reflected, some cause the surface temperature to elevate and is transmitted to the cooler interior. The interior is heated as a result of heat transmission.

The calory/hr is given by the equation: Q = K x A x Δt where: 

Q is Calorific in Kcal/h that enter through the walls or roof due to solar radiation.

K is the heat transmission ratio in Kcal/m2h°C.

A is the area of the roof or wall in m2.

Δt is the effective temperature difference in °C.

Heat Transmitted Due To Temperature Difference

Heat is also transmitted between the interior and exterior of the building through ceiling, partitions and floors when there is a temperature difference between both faces. Heat will transmit from the higher temperature to the lower temperature. This is another cooling load. Similar equation as above is used for calculation.

Heat From Glass Windows

A part of the sun rays that hit the glass windows is reflected and a substantial amount is transmitted. A portion of the transmitted rays heat up the glass and some enter the interior where it is reflected by blinds or curtains. A portion of the rays go into the interior and heat up the space causing the space temperature to rise.

Interior Heat

The interior heat is generated by the lighting, audio-visual equipment, fax machines, household appliances and human bodies. In a typical office environment, a person contributes about 50 kcal/h of latent heat and 50 kcal/h of sensible heat giving a total heat of 100 kcal/hr.

Fresh Air Intake

Fresh air intake also contributes to the cooling load as the intake air from outside is usually at a higher temperature than the conditioned air. Both latent heat and sensible heat contribute to the load. Typical formulas are:

Sensible Heat

Q(s)=0.29 x R x Δt where:

Q(s) is the sensible heat load in kcal/h.

R is the fresh air rate in m3/h.

Δt is the difference in outdoor and indoor temperature in °C.

Latent Heat

Q(L)=720 x R x ΔH where:

Q(L) is the Latent heat load in kcal/h.

R is the fresh air rate in m3/h.

ΔH is the absolute difference in outdoor and indoor humidity in kg/kg.

A typical fresh air flow required per person is about 20 to 25 m3/h.

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