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Posted by Tony Hwang on June 13, 2007, 12:19 am
gofish@gonefishin.net wrote:
> bubbabubbs@yahoo.com wrote:
>
>
>>On Jun 12, 4:07 pm, vze8f...@verizon.net (v) wrote:
>>
>>>On Mon, 11 Jun 2007 08:20:55 -0700, someone wrote:
>>>
>>>>...Someone who is thorough, will use correct
>>>>inputs, and won't cut corners on the formulas.
>>>
>>>To what end is the need to be that precise? They will just size it to
>>>the nearest ton (or maybe half ton) anyway. It's not like it's going
>>>to make much difference if it comes out 38,052 btu/hr for the anal
>>>retentive guy, or 41,019 btu/hr for the good enough for government
>>>work guy.
>>
>>And what if it's more like borderline - "back of napkin" calc will
>>suggest 2-ton, but Manual J suggests 1.5-ton.
>
>
>
> there's one tiny facet of information the average homeowner is unaware
> of, that being an ac unit Does Not have the same capacity across all
> ranges of outdoor temperature. A 2 ton unit might have an output of
> 24,000 btu at an outdoor temp of 90F, but watch that output plummet
> like a rock when the od temp gets above 100.
>
> This is where the manufacturers Engineering Data for each condensing
> unit comes into play and the contractors extrapolation of such data
> with desgn temps to determine total tonnage required.
>
> The load calc is merely the starting point to apply the engineering
> data to. Gee I oversized it & now I gotta worry about mold vs Gee I
> undersized it and now the customer complains on hot days that they
> just cant get cool enough.
Hmmm,
Experience rules!
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