If you have recently got a ducted reverse cycle air conditioning quote, you may wonder how they came up with that particular size of unit for your home. Some different companies may also vary in which size air conditioning unit you should run. Below is how the companies come up with what size air conditioner you need for your home.
Firstly, a company will size up your home and each of the rooms. Once they have worked this out they then table the results as it looks like below (results in meters squared):
Living Room 45m2
Theatre 20m2
Bed 1 18m2
Bed 2 11m2
Bed 3 11m2
Once done they will now times the result by a figure. Some companies work on 0.12Kw per square meter. Others work on higher ratings. I believe a company should work on around 0.15Kw per square meter for homes with standard ceiling heights. If the ceiling height is 32 courses or over (or raked) then work on around 0.16Kw per square meter. If you are quoting on a commercial property, this rating can be increased to 0.18Kw per square meter.
Once you have chosen what Kw (Kilowatt) rating you want to work at (usually 0.15 for most homes), times this by the square meters of the room (see below):
Living Room 45m2 * 0.15 = 6.75Kw
Theatre 20m2 * 0.15 = 3.0Kw
Bed 1 18m2 * 0.15 = 2.7Kw
Bed 2 11m2 * 0.15 = 1.65Kw
Bed 3 11m2 * 0.15 = 1.65Kw
The above calculations now give you how many Kw each rooms requires for cooling or heating. For instance, if you were to simply put a ductless (wall split) or wall unit into the theatre, you would need the unit to have at least 3.0Kw capacity. If you go under this, the unit may struggle on hot days. If you go to big, the unit may short cycle which means it constantly turns on and off as it is too big for the room.
With a ducted reverse cycle air conditioning system, the company quoting you will now make an estimate on what zones you would run at the same time. With this example, the company would probably assume that the most you would run at any one time would be the Living Room + Theatre. This would then equal 6.75Kw + 3Kw = 9.75Kw. The company would then quote you on a unit around the 10Kw range. They generally cannot get a unit to match the exact rating as most machines only come in a few different Kw sizes.
So why don’t air conditioning companies size the air conditioner to run the whole house at one time? Firstly, the unit would be large and would cost a lot of money to run. Secondly installation costs would be extremely high. Finally, most people really don’t need to run the whole house at once, just the rooms that they are located in.
So this is how an air conditioning contractor sizes up your air conditioning system for your house. So before you get a quote, consider talking to the salesmen to discuss what zones you would run at any one time. Perhaps in the above example you also use one of the bedrooms as a home office (lets say bedroom 3). In that case you would need to add another 1.65Kw to the size of the unit making it 11.4Kw that is required. Discuss this before getting the quote drawn up to ensure you get a custom designed air conditioner that will fit your needs.
And if you are not confident with the contractors recommendations, size up your own house and discuss your results with them directly.
Tags: Air Con, Air Conditioning, Ducted Reverse Cycle, hvac, HVAC Sizing Guidelines, Sizing Your Air Conditioning System