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.