HEATING & COOLING LOAD CALCULATIONS

Heating load calculations are performed when determining how large a furnace is needed to heat the space or your home. Several factors are taken into consideration.

One factor is the outside temperature. The generally used outside temperature which is listed by ASHRAE is minus six degrees Fahrenheit and is based on the temperature reading at O’Hare. We use the extreme temperature reading at O’Hare which is listed at minus 12 degrees Fahrenheit. (You may download a sample heat load calculation in acrobat reader format).

The second factor is the desired indoor temperature. We use 70 degrees as the desired indoor temperature unless you tell us different.

The third factor is the amount of insulation that is in the walls, the ceiling and the type of floor that you have. You may have different types of floors. Part of the house may be over a basement, part of the house may be on a concrete slab and part of the house may be over a crawl space, and some rooms may be over the garage.

The walls, ceiling and floors are measured and the square area of each is calculated. All factors are considered when doing heat load calculations. The windows and doors are measured and the square area of each is calculated. The type of windows and doors are noted. The direction that the windows face is also noted.

Cooling load calculations are used to determine the amount of cooling that is needed to cool the space or your home. Sensible and latent are terms used in cooling load calculations to measure cooling loads. Sensible heat can be measured with a thermometer.

Humidity is also considered when doing cooling loads. The latent load is the amount of cooling it takes to remove moisture (humidity) out of the air. Moisture removal is an important part of air conditioning and that is the reason that the cooling coil has a pipe called a condensate drain connected to it. The total cooling load is the sensible load plus the latent load added together.

The window direction is particularly important for doing cooling load calculations.You can take the same house and turn it 90 degrees and the cooling load calculations are considerably different. For instance if one house has windows facing north and the other house has the same windows facing west the cooling load will be very different.

For cooling loads there are also internal loads such as people, the refrigerator, and lights that need to be taken into account.

We typically use 96 degrees for the outside temperature and 75 degrees for the inside temperature with an inside relative humidity of 50% for cooling load calculations.

As you can see the square foot area of the space or your home has very little to do with the amount of heat or cooling needed to make your home comfortable.

Attention to detail is the difference between a system that works and one that works well.