LinuxQuestions.org - Air Conditioner

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Something not computer related (although you can send me the solution in a spreadsheet :) ).

I like to know how I can convert the capacity of an air conditioner (expressed in BTUs) to something more 'human readable' (like delta(temp) per cubic metre) so I can calculate which capacity I need for a room of 150 cubic metre and a temperature difference of roughly 20 degrees max.

Till now, I've only found what a BTU is :(

It's really more complex than that- a lot depends on the insulation and heat generating equipment. A room full of servers will take way more than a room with a TV :)

bryantrv is correct that it's very complicated, but here's some more help for you.

Find out how much electrical equipment will be in the room and calculate the total wattage used. Then multiply the wattage by 3.412. This is the number of BTU/hour that the electrical equipment will generate.

The prior two replies assume you're trying to cool a computer equipment room, not a house.

I just asked "Google" for "air conditioner capacity calculator," and the first hit was this. There were more than 2x10**6 "hits," so you might be able to find exactly what you want in the list. :)

Thanks for the replies. I forgot about insulation and it's a normal room. For a computer room I would indeed take the kWs and convert to BTU.

Quote:

Originally Posted by PTrenholme

Google for air conditioner capacity calculator

I did some searches but forgot about that one :(

I would assume that the capacity depends on the volume but most of the calculators that I found just take the floor surface. Will try some more.

Quote:

Originally Posted by Wim Sturkenboom (Post 2891341)

[snip]
I would assume that the capacity depends on the volume but most of the calculators that I found just take the floor surface.[/snip]

Yes, of course. And on other factors. But, clearly, volume is linearly proportional to floor area, and -- in the U.S., at least -- most homes are built with "standard height" flat ceilings, seven feet (the U.S. does not yet use metric measures) above the floor. So, in order to "simplify" things, that assumption is built in to the calculator.

So, to use it, just compute the volume you're interested in, convert it to cubic feet, divide by seven. Then tell the calculator that you're interested in a room x by y feet where x*y = volume / 7.

Alternatively you could just plug a few easy numbers into the calculator. If, as I suspect, the calculator is using a formula like BTU = constant * x * y, then log(BTU) = log(constant)+log(x)+log(y), so log(constant)=log(BTU)-log(x)-log(y). Thus just putting a couple of numbers into the calculator should recover the formula used since the only "unknown" is the constant. Note that log(x)+log(y) is just log(area), so, if the calculator uses "area" as the input variable, then a single calculation should give you the constant.

In fact, let me see what the calculator to which I pointed you, above, yields.

Hum, O.K., that calculator is "slightly" more sophisticated, taking into account insulation, sun exposure, and heating. But the basic formula is about what I suggested:

Code:

BTU = 100 * area * insulation * sun_exposure + added_BTUs



where area        = ciel(length * width,10), both measured in feet

      insulation  = (1.1, 1.2, 1.3, 1.4, 1.5)[excellent ... poor]

      sun_exposure = (1.1, 1)[yes, no]

      added_BTUs  = (4000, 0)[kitchen, not_kitchen]

delta temp will vary according to the humidity, the volume of the room, AND the speed of airflow across the coil while BTU/hr is a direct measure of the energy the AC can move.

To cope with your problem under any circumstances, you want to calculate the rate of energy influx into your room (radiative, conductive, and due to sources into the room) then choose a unit that can move energy arriving at that rate.