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3000 sf 6" sip wall, 10" roof, floor, 600,000 BTU's/day?

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Posted by AstickfortheMULE on February 28, 2006, 10:07 pm
 
Assuming a 30 deg difference from outside to inside?  Boy that seems
like alot of energy for a moderate climate.  The reason I ask is that I
am trying to anticipate my energy needs/consumption so I can plan my
solar size, etc.

Does this seem accurate?


Area (ft2)         H.M. (BTU/Hr.)         Heat Loss
1. Windows & Doors    20    X    41    =     820
2. Net Walls    3380     X     4    =     13520
3. Ceiling    1056     X     2    =     2112
4. Floor    1056    X     2    =     2112
5. Infiltration    26400     X     .81    =     21384


Posted by nicksanspam on February 28, 2006, 10:41 pm
 


The arithmetic seems OK. What does it mean? If a 6" SIP wall is R24,
3000 ft^2 would have a thermal conductance of 1000/24 = 125 Btu/h-F.
With dT = 30 F, 125x30 = 3750 Btu/h or 24hx3750 = 90K Btu/day would
flow through the wall. Where does your 4 come from? What's H.M.?

Nick


Posted by AstickfortheMULE on February 28, 2006, 11:52 pm
 Wait.  You have 90k btu/day.  What gives.  The chart above was from
HVAC company calc and that was some coefficient.

Are we talking 90k btu/day for walls, roof, floors and does not include
infiltration and windows?

Thanks, Nick


Posted by AstickfortheMULE on February 28, 2006, 11:53 pm
 Wait.  You have 90k btu/day.  What gives.  The chart above was from
HVAC company calc and that was some coefficient.

Are we talking 90k btu/day for walls, roof, floors and does not include
infiltration and windows?

Thanks, Nick


Posted by Ecnerwal on February 28, 2006, 11:01 pm
 

H.M. (whatever that may be) appears to be lumping several coefficients
which are clearer if not lumped, IME. But you are probably in the
ballpark.

Are you really looking at a (mere) 30 degree F differential, or are you
further confusing the issue by looking at 30 degrees C and working in
BTUs at the same time? Also, you should adjust the floor for loss to
ground temp, not air temp, unless the floor is exposed to the air on the
bottom...

My shop is of roughly similar size, 8 inch SIPs, but also more windows,
and works out to 22,000 BTU/hr at an 88F differential (28F for the
floor) plus 37,000 BTU/hr for 1 air change per hour (making an
air-to-air heat exchanger look like a very good idea). A 30F difference
will scale directly - 7,500 & 12,600 BTU/hr for radiant and air exchange
losses, 482,400 btu/day, or 3.5 gallons of heating oil. That air-to-air
still looks like a good idea.

I run my spreadsheet thus:

(Feet, Farenheit, "English" R and U values)
Building part,length, width, area, R-value, U-value (1/R-value),
BTU/HrDegF (area times U-value), Max Delta-T (Furnace sizing design temp
- interior temp minus extreme outside temp), average Delta-T (how much
fuel and/or solar collection do I need).

Btu/HrDegreeF times either delta-T gives max or average heat loss rate
per hour for each building part.

--
Cats, coffee, chocolate...vices to live by

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