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Correct sizing of a/c? Walter R. 07-26-2005
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Posted by Walter R. on July 26, 2005, 1:07 am


With the outside air at 90 and a RH of 50%, the inside temp at 80, with a
differential of 1.5 degrees, my A/C is on for 30 minutes and off for 40
minutes.

Is this 3t A/C sized correctly? I would like to know because the A/C is
getting old and I want to replace it with a new one. If this one is sized
correctly I will know what size to look for .

Thank you
--
Walter
www.rationality.net
-




Posted by Greg O on July 25, 2005, 8:45 pm



> With the outside air at 90 and a RH of 50%, the inside temp at 80, with a
> differential of 1.5 degrees, my A/C is on for 30 minutes and off for 40
> minutes.
>
> Is this 3t A/C sized correctly? I would like to know because the A/C is
> getting old and I want to replace it with a new one. If this one is sized
> correctly I will know what size to look for .
>
> Thank you
> --
> Walter
> www.rationality.net
> -
>

Looks to me to be a bit over sized. A Manual J is the only accurate way to
know for sure, anything else is a guess!
My AC runs constantly at 95 degrees and it will maintain a indoor temp of
74. Sized right on in my book!
Greg




Posted by TURTLE on July 25, 2005, 9:00 pm



>
>> With the outside air at 90 and a RH of 50%, the inside temp at 80, with a
>> differential of 1.5 degrees, my A/C is on for 30 minutes and off for 40
>> minutes.
>>
>> Is this 3t A/C sized correctly? I would like to know because the A/C is
>> getting old and I want to replace it with a new one. If this one is sized
>> correctly I will know what size to look for .
>>
>> Thank you
>> --
>> Walter
>> www.rationality.net
>> -
>>
>
> Looks to me to be a bit over sized. A Manual J is the only accurate way to
> know for sure, anything else is a guess!
> My AC runs constantly at 95 degrees and it will maintain a indoor temp of 74.
> Sized right on in my book!
> Greg

This is Turtle.

I can keep 70ºF indoors with it 107ºF outdoors. Now it will run about 100% of
the time during the day lite hours. The Manual J said 3.25 tons and I upped to
3.5 tons. That 1/4 ton would make the difference at 107ºF outdoors these days.
Also that 1/4 ton hurts me on a 85ºF outdoor temp with not enough of run time. i
then installed a humidistat to override and keep a 55% RH or below.

TURTLE




Posted by Stretch on July 26, 2005, 4:23 am


Turtle,

1/4 ton oversized should not hurt. In the old days we figured up to
25% oversized was OK. Now it is recommended to oversize no more than
15%. Of course, you are sometimes limited by available sizes.


Walter,

If the conditions stated by you are design conditions for your area,
you are WAY oversized! When you are at design conditions, inside and
outside, your unit should run constantle or nearly constantly.

Stretch



Posted by Tekkie® on July 25, 2005, 9:37 pm


Walter R. posted for all of us...
I don't top post - see either inline or at bottom.

> With the outside air at 90 and a RH of 50%, the inside temp at 80, with a
> differential of 1.5 degrees, my A/C is on for 30 minutes and off for 40
> minutes.
>
> Is this 3t A/C sized correctly? I would like to know because the A/C is
> getting old and I want to replace it with a new one. If this one is sized
> correctly I will know what size to look for .
>
> Thank you
>
Maybe
--

Tekkie


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