8. Capacity Estimation for Room AC

ANNEX A
8. Capacity Estimation Procedure¹ for Room Air Conditioners

This procedure estimates the heat gain from a variety of sources. For each component, enter a quantity that you have measured or determined for your house, and multiply it by a factor that is provided. If the air conditioner will only be used at night, use the factor in parentheses.

1. Doors and arches
If the room has a permanently open door or archway more than 1.5 metres wide, skip this step and treat the two rooms as one, making all the necessary measurements in both rooms. Otherwise, record the width of he door or archway in metres and multiply by the factor provided.

2. Windows
Calculate the area (length x width) of each window by measuring its height and width in centimetres, multiplying these together and dividing by 10 000 to give the area in square metres. Record the area for each window separately for use in step 6. Add the areas together and multiply by the factor that applies to your type of windows.

3. Walls
Measure the length of all walls in metres. Walls shaded by other buildings are considered to be facing north. Record the length in the box that applies to each of your walls and multiply by the corresponding factor(s).

Inside walls (to unconditioned space)

Light construction
Outside wall facing north

Other outside walls

Heavy construction
Outside wall facing north

Other outside walls

4. Ceiling
Calculate the ceiling area (length x width) in square metres. Record the value in the box that applies to your ceiling and multiply by the corresponding factors.

5. Floor
If the floor is on the ground or over a basement, skip this step. Otherwise, calculate the floor area (length x width) in square metres. Record the value in the box and multiply by the factor provided.

6. Solar heat gain
If all of the windows face north or if the air conditioner will be used only at night, skip this step. Otherwise, using the areas measured for each window in step 2, record the total window area for each orientation that applies to your windows in the appropriate box, and multiply by the factor for the shading type that best represents your house conditions. Multiply this value by the factor that represents your window type. Once numbers are calculated for each orientation, compare them and select the largest one for use in step 7.

* glass block: multiply by 0.5
  triple-glass: multiply by 0.7
  double-glass: multiply by 0.8
  single-glass: multiply by 1.0

7. Subtotal
Add the figures from steps 1 through 5 and the largest value calculated in step 6, and record the sum here.

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8. Climate correction
Enter the subtotal from step 7 in the box, find the climate correction factor for your area in Table A-1 and multiply the two together.

9. Heat from people
Record the number of people who normally use the room (minimum of 2) and multiply by the factor provided.

10. Heat from appliances
Record the sum of the wattages of all lights and appliances (used during air conditioner operation) in the room and multiply by the factor provided.

11. Total cooling load
Add the figures from steps 8, 9 and 10 to determine the total cooling load. This number is the maximum amount of heat that builds up in a room in an hour, in British thermal units per hour. When selecting your air conditioner, choose a unit with a capacity rating close to the estimated load. Remember that a smaller capacity unit operating continuously will result in greater comfort than a larger capacity unit operating intermittently.

Table A-1. Climate Correction Factors

¹ Adapted from the cost estimation procedure published by the Association of Home Appliance Manufacturers.