Example of Residential Heat Load Estimate/ Calculations

Now that we have seen the various heat loads inside the room and also surveyed the room, let us see one example heat load calculations for the residential building using the heat load calculations form shown below. To start with, fill the details given at the top of the form. These are given below:

Customer: Mr. Allan Smith

Address: New York

Buyer: Mrs. Smith

Installation by: Mr. Garry and Mr. Ronny

Estimate number: 0022

Estimate by: Ms. Sheena Roy

Equipment Selected: Manufacturer, Model and Size (to be filled at the end of heat load estimate): 2.5 TR Split type.

Direction House Faces: North

Gross Floor area (of the house): 1500 sq ft.

Gross inside volume (of the room for which heat load calculations are being done): 300 sq ft

Dry Bulb Temp (DBT) F

Outside 100

Inside 78

Difference 22

There are three windows in the room each of the size 6 x 4 = 24 sq ft. There is one window each in east, south and west direction. The glass of the all windows is single, there is no shading and no outside awnings.

Fill the details of areas in the heat load calculations form as shown in the attached form. Round off the proper associated factor with window in each direction for from no shading option. If the windows has shades or outside awning, one has to round of the factors from those columns. For this particular example the rounded factors have been shown in the form. For window in east direction it is 100, while for window in south and west directions it is 75 and 150 respectively.

Now multiply the area of each of the window by factor associated with it as shown in the form. For window in east direction it is 24 x 100 = 2400, for window in south it is 24 x 75 = 1800, for window in west it is 24 x 150 = 3600. The highest of all these, 3600 has to be selected and filled in the last column. Thus the total solar heat gained by the window is 3600 BTU/HR.

The total area of three windows is 24 + 24 + 24 = 72 sq ft and they are all of single glass. Fill this in the area column for single glass window as shown in the form. Since the difference between external and internal dry bulb temperature is 22F, the factor associated with it would be 27, so it has to be rounded of. The product of 72 and 27 is 1944. Thus the solar heat gained by the windows due to design temperature is 1944 BTU/HR.

Let the size of the room is 20 ft x 15 ft = 300 sq ft, which is the total floor area of the room. Let us suppose the height of each wall is 12 ft and none of them are insulated. Two walls of this room if length 20 ft and 15 ft are exposed directly to the sun, while remaining two are partitions.

The total area of walls exposed directly to the sun is 20 x 12 + 15 x 12 = 420 sq ft. Since the designed temperature difference is 22F and there is no insulation, the factor associated with it is 7. The product of 420 and 7 is 2940, which is the total BTU/HR gained by the walls exposed directly to the sun.