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Heating /cooling system sizes for residential building 1
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DonPhillips
Structural
Based on the 2003 International Residential Code (2003 and 2006 are widely adopted across the United States).
"M1401.3 Sizing. Heating and cooling equipment shall be sized based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methodologies."
You may want to Google this and see if you can find trial versions of Manual J software.
Don Phillips
"M1401.3 Sizing. Heating and cooling equipment shall be sized based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methodologies."
You may want to Google this and see if you can find trial versions of Manual J software.
Don Phillips
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Most salesmen will give you a one ton/500 sqft value. And that may, or may not, work for your application; "your mileage may vary."
In Southern California, even a 3-ton A/C for 2000 sqft might be a bit much, since the air is so dry. But, you have to put up with relatively long run cycles, compared to running a 4-ton A/C in the same house. For power efficiency, you want longer run cycles, but for faster cooling or more drying, you might want the higher tonnage.
TTFN
FAQ731-376
In Southern California, even a 3-ton A/C for 2000 sqft might be a bit much, since the air is so dry. But, you have to put up with relatively long run cycles, compared to running a 4-ton A/C in the same house. For power efficiency, you want longer run cycles, but for faster cooling or more drying, you might want the higher tonnage.
TTFN
FAQ731-376
DonPhillips
Structural
So much depends on the building envelope, you really need to run the Manual J.
Don Phillips
Don Phillips
Wareagl487
Mechanical
From my experience, Manual J results are very conservative with results. I've done comparison testing running loads utilizing Trane Trace and Manual J on the same condominium unit with Trane results indicating +/-550 ft2/ton and Manual J results of +800 ft2/ton. I believe it has to do with the "assumptions" built into the Manual J programming.
As stated, it is best to run the load calc's for accurate estimates of capacities required.
Andy W.
As stated, it is best to run the load calc's for accurate estimates of capacities required.
Andy W.
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With E+ I get : Heating load of 16016 Btu h. - with 1.25 capacity margin the system would be 20,020. Does it look reasonable? For cooling it would be 15,800 Bth ( approx 1.5 Tons). Assumed lighting load of 0.6 W/ft2 and equipment (internal) load 0.4 W/ft2.. the ventilation was o.35 ach.. Both wall and roof are R22.. It looks very small as compared to the values suggested here.. Is there anything I may be missing in my calculations..
thanks..
MSB
thanks..
MSB
DonPhillips
Structural
I did a load calc on a 4 family building reconstruction project and based on the 2003 IECC requirements, I got heat losses so small, I think the smallest furnance was still about 3 times too large for a 5F design temperature. The building was not air conditioned so I did not run the cooling load.
Don Phillips
Don Phillips
A couple of things:
IRstuff: You get better humidity control from longer running cycles. This is why it is bad to oversize units - when a unit is oversized, it will cool the space in too short a period of time to remove the moisture.
MSB: That's why we run the numbers. With good insulation and glass, it's not unusual to get low-sounding numbers anymore - even here in FL where I am. That's one reason I didn't pipe-in earlier with a btuh/SF number/range.
IRstuff: You get better humidity control from longer running cycles. This is why it is bad to oversize units - when a unit is oversized, it will cool the space in too short a period of time to remove the moisture.
MSB: That's why we run the numbers. With good insulation and glass, it's not unusual to get low-sounding numbers anymore - even here in FL where I am. That's one reason I didn't pipe-in earlier with a btuh/SF number/range.
example,
I have an 1800 SF house in teh mid-atlantic area. 1958 vintgae, double pane windows. split level home.
I have a 2-1/2 ton AC unit - that's 720 SF per ton.
I set the stat at 72F in the middle of summer, the unit still cycles.
As Pat says, do not oversize or else you will have that damp feeling in the basement. Let teh compressor work all day to dehumidify proerly.
With today's energy efficiency and all (assumming a regular house) - a 2-ton unit (750SF/ton) is a good rule of thumb you are looking for.
You still need the Manual J.
I have an 1800 SF house in teh mid-atlantic area. 1958 vintgae, double pane windows. split level home.
I have a 2-1/2 ton AC unit - that's 720 SF per ton.
I set the stat at 72F in the middle of summer, the unit still cycles.
As Pat says, do not oversize or else you will have that damp feeling in the basement. Let teh compressor work all day to dehumidify proerly.
With today's energy efficiency and all (assumming a regular house) - a 2-ton unit (750SF/ton) is a good rule of thumb you are looking for.
You still need the Manual J.
If this is YOUR house... or someone close... or a high end user, don't neglect considering a variable speed model. This could give the Owner the best of both worlds... enough capacity to keep the home at set point on the hottest days, and the ability to turn down, and have long run cycles for dehumidification.
Jabba
Jabba
thermodynut
Mechanical
Most of the ideas proposed have to do with AC ... in MA you are probably more concerned with heating. 20,000 btu/hr seems minimal, and probably too small, to me, but numbers like 500 BTU/hr/ft2 * 1500 ft2 = 750,000btu/hr are way too large. Your local library probably has do-it-on-paper versions of the calculations that go into Manual J.
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