# Air conditioner size and temperature lowering speed

• posted on June 25, 2007, 7:30 pm
Hi,
I have searched over the Net, but couldn't find what I have been looking for. AFAIK, all AC systems are measured using BTUs (or a variant of). Now, what BTU means? Here is the most common definition: "amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit" (from Wikipedia). Yep, I understand this and it is the most useful thing in the world. What does this mean to me? Absolutely nothing. I understand that someone making ACs must know this, so he can compare or test or whatever, but to a normal user, this is absolutely useless. Are you going to cool your pool with AC?
What the normal user might need is the answer to this question: How much time do I need to cool my A x B sized room from X to Y degrees Celsius? Yes, there are other things to worry about (for example: building insulation, geographic location, north-south orientation, etc.), but is there some rough measurement for a common domestic building to be relatively sure that XXXX BTU AC will do it job or not. I don't care if I miss for 10%, but I care if I don't know if I missed at all (because I cannot "translate" the above BTU definition).
I didn't find something similar - all the calculators are saying: you will "adequately" cool your XXX m2 room if your AC has this many BTUs. What is adequately? Does it mean that a 30m2 room can be cooled from 30*C to 20*C in 20 minutes or 2 hours or 20 hours? Will it run for the whole day if the outside temperature is 30*C or will it stop after 1 hour?
In fact, the real question would be - how BTUs (or, to be precise, day- tons) project into "degrees Celsius per hour"? What is the margin that one should be always holding in order for AC not to run the whole day, but to run reasonably (e.g. 30% of the time - is 30% a good measure)?
If you have any good answers or links to sites explaining this, that would help many people on this world, I presume.
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• posted on June 25, 2007, 8:22 pm

http://www.refrigerationbasics.com/1024x768/definitions1.htm
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• posted on June 26, 2007, 8:46 pm
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• posted on June 26, 2007, 9:51 pm

I don't think there is a more basic answer to your question or anything laid out in layman's terms better than the one you just read. Read again about sensible and latent heat and how temperature in degrees is qualitative vs. BTU's which are quantitative. Or don't waste any more time worrying about it and hire someone who knows. Your quote: "In fact, the real question would be - how BTUs (or, to be precise, day- tons) project into "degrees Celsius per hour"?
Answer: They don't ... directly.The A/C system has to remove moisture (latent heat) as well as reduce temperature (sensible heat).
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• posted on June 26, 2007, 9:57 pm

On second thought start here and work up to the other section. http://www.refrigerationbasics.com/1024x768/rb1.htm
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• posted on June 27, 2007, 1:34 pm
Paul, I disagree that a-d are whining. I am trying to be ignorant about all things I can, since trying to know everything in this world just doesn't work. http://en.wikipedia.org/wiki/KISS_principle. I try to concentrate on the things I need every day. I was trying to get the answer from the people who know what they are doing. I assume people on this group are - at least kool seems to be good at it and, at the end, not trying to analyze/judge my personality, but answer the question, which really is the right thing to do.
kool, thanks for the answer. You are right about hiring someone who knows, but what "someone who knows" told me was - you have type A AC system which is "this, this and this" and type B which is "that, that and that" - choose (one is 2x more expensive, that is everything meaningful I can see). Tried few of them. That's how it's where I live. Wouldn't waste time at all if I could, but seems inevitable.
That's why I was looking for a simple transformation from things commonly used to describe AC systems (BTUs, for example) to something I (and all people I know) commonly use to describe their feeling about how fast the room is getting cooled - degrees C per hour. I don't care about being 100% precise or so - I just need enough info to make a decision.
There must be a way, since HVAC people are doing it. The question is - is it simple or complicated? If there is a simple method which makes < 10% error, that's good. From what you have said:

there doesn't seem to be. Thanks again, I'll consider the options.
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• posted on June 26, 2007, 12:20 am

Its not rocket science........................
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• posted on June 26, 2007, 1:28 am
:)
Actually, some of my best customers are "Rocket Scientists."
--
Zyp

"Noon-Air" < snipped-for-privacy@comcast.net> wrote in message
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• posted on June 26, 2007, 1:38 am
Zephyr wrote:

Hi, LOL! Case of a puch knowledge without experience, right on! Knowlege with experience rules! No experience, nothing.
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• posted on June 26, 2007, 1:57 am
ok, I'm stupid. what's a [puch?]
--
Zyp

"Tony Hwang" < snipped-for-privacy@shaw.ca> wrote in message
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• posted on June 26, 2007, 2:00 am
Zephyr wrote:

Foreign language for much?