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Heat Load Calculation
heat load calculation formula

Heat load or heat gain

heat load calculation formula, A building or room receives heat from many sources. Inside, computers, copiers, machinery, and light all produce heat. Hot air from outside enters the structure though through open doors and windows or as a leak ‘outside’. However the biggest source of heat is solar radiation from the sun, which falls on the roof and walls, and heats the internal surfaces through windows.

The sum of all these heat sources is known as the building’s heat gain (or heat load), and is expressed in either BTU (British thermal unit) or Kw (kilo Watt).

For an air conditioner to cool a room or its output must exceed the heat gain. Before purchasing an air conditioner it is important that heat load calculations are done to ensure that it is adequate for the intended application.

heat load calculation formula

There are many different ways to calculate the heat load for a given area:

heat load calculation formula Quick count for offices

Heat Load Calculation For offices with average insulation and lighting, 2/3 living and 3/4 personal computers and a photocopier, the following calculations will suffice:

Heat Load (Btu) = Length * Width * Height * 4 IN Feet

Heat load (BTU) = Length * Width * Height * 141 IN Meter
Add 500 BTUs for each additional stay.

If there are any additional significant sources of heat, for example south-facing windows from floor to ceiling, or equipment that produces too much heat, the above method will reduce the heat load. Instead the follow method should be used.

More accurate heat load calculations for any room or building
The heats gain of a building or room depends on:

Area size is being cooled
The size and position of the windows, and whether they have shading
Number of occupants
Heat generated by equipment and machinery
Heat generated by light
By calculating the heat gain from each individual item and combining them together, an accurate heat load figure can be determined.

heat load calculation formula First step

Calculate area in square feet of space to be cooled, and multiply by 31.25

Area Btu = Length (feet) * Width (feet) * 31.25

heat load calculation formula Second stage

Calculate the heat gain through the windows. If windows does not have shading, multiply the result by 1.4
North side window BTU = Area of ​​north facing windows (meter.sq) * 164

If there is no shading, then the north window BTU = north window BTU * 1.4

South side window BTU = area of ​​south facing window (meter. Sq.) * 868

If there is no shading, then south window BTU = south window BTU * 1.4
Add results together.

Total windows BTU = North side window + South side window

heat load calculation formula step Three

Calculate the heat generated by occupants, allowing 600 BTUs per person.

BQU = Number of people * 600

heat load calculation formula Step four

Calculate the heat generated by each item of machinery – find power in watts for each item such as copiers, computers, ovens etc., add them together and multiply by 3.4

Equipment BTU = Total Equipment Watt * 3.4

heat load calculation formula Step five

Calculate the heat generated by light. Find the total wattage for all lights and multiply by 4.25

Lighting BTU = Total Light Watt * 4.25

heat load calculation formula Step six

Add the total heat load which you find.

Total heat load BTU = Area BTU + Total window BTU + Surcharge BTU + Equipment BTU + Lighting BTU

heat load calculation formula Step seven

To determine how many air conditioners are needed, divide the heat load by the cooling capacity of the air conditioning unit in the BTU.

heat load calculation online

Number of required total unit of A/C = Total Heat load BTU / Cooling Capacity BTU


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