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Air conditioner size and temperature lowering speed freeunli 06-25-2007
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Posted by kool on June 26, 2007, 5:57 pm

>
>> kool, thanks for the link. The page is informative, but contrary to
>> what Noon-Air said later - this is rocket science, but shouldn't be. I
>> read some of the text on the page, but:
>> a) I couldn't find the answer to my question,
>> b) Even if there is an answer on that page, why is everyone talking
>> about BTUs, kJ, calories, etc. and not something much more familiar
>> like degrees per m2 per hour? Why don't we start expressing the speed
>> of our cars in light year/picosecond or measure time as "duration of
>> 9,192,631,770 periods of the radiation corresponding to the transition
>> between the two hyperfine levels of the ground state of the
>> caesium-133 atom at zero kelvins" (which actually is the definition of
>> a second)?
>> c) Again, even if there is an answer, it's hidden in tons of
>> specialized text - is there an FAQ, for God's sake? Come on, people,
>> we should be making our lives easier, not more complex. Whoever needs
>> to know of BTUs (e.g. HVAC people) - let them know. Anyone who doesn't
>> need - don't let them even near BTUs!
>> d) I spent 15 minutes just reading this. If I spend 15 minutes reading
>> all kinds of rocket-science-type texts, I'll probably die pretty soon.
>> Hey, I cannot be an expert for everything, so there are many things
>> pretty clear to someone from the field, but not to an average AC
>> buyer. Can anyone recommend a clear, average-human-readable answer or
>> text on this?
>> e) "OK, I'm stupid".
>
>
> 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).

On second thought start here and work up to the other section.
http://www.refrigerationbasics.com/1024x768/rb1.htm



Posted by on June 27, 2007, 9:34 am
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:

> Answer: They don't ... directly.The A/C system has to remove moisture
> (latent heat) as well as reduce temperature (sensible heat).

there doesn't seem to be. Thanks again, I'll consider the options.


Posted by Noon-Air on June 25, 2007, 8:20 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.
>

Its not rocket science........................



Posted by Zephyr on June 25, 2007, 9:28 pm
:)

Actually, some of my best customers are "Rocket Scientists."
--
Zyp

>
> > 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.
> >
>
> Its not rocket science........................
>
>



Posted by Tony Hwang on June 25, 2007, 9:38 pm
Zephyr wrote:
> :)
>
> Actually, some of my best customers are "Rocket Scientists."
Hi,
LOL! Case of a puch knowledge without experience, right on!
Knowlege with experience rules! No experience, nothing.

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