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12-19-2009, 12:17 PM   #16
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Quote:
 Originally Posted by Yoyizit Right sizing, or confirming Manual J This won't work with a variable output furnace. Toff = 65F, when you don't need heat. Tper is the 97.5 percentile cold temp, depending on your area, when your furnace is running all the time. The Slope = (Tper-65)/100 Tout = the average of 5 or 10 outside nighttime temps. Taking the average cancels out the effect of rain, snow, wind, clear weather, etc. The furnace Duty Cycle in percent at Tout = 100(on time/(off time + on time)) = (Tout-Toff)/slope Average this over a few cycles. E.g. Tper = 5F so the slope is (5-65)/100 = -0.6 Tout = 29F so the DC is 100(29-65)/(-0.6) = 60% If your furnace has this duty cycle at this outside temp. it is right sized.
only works on boilers

12-19-2009, 03:06 PM   #17

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Quote:
 Originally Posted by hvaclover Shill and conflict of interest!
He pays to advertise that program here.

 12-19-2009, 03:33 PM #18 Member     Join Date: Sep 2008 Location: PA Posts: 167 Rewards Points: 150 Here is another place for the heat loss. http://www.comfort-calc.net/home-page.html
12-19-2009, 03:57 PM   #19
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Quote:
 Originally Posted by hvaclover only works on boilers
Why?
I used
an always off [zero duty cycle] outside temp. for a furnace at 65F,
and an always on [100% duty cycle] for the design cold temp.

Excel calculates the slope of the temp/duty cycle line with the SLOPE function.

Then you know the duty cycle at any intermediate temp. for a perfectly matched house & furnace & climate by using the equation
Outside Temp = SLOPE x (Duty Cycle) + 65F
or
DC = [Outside Temp - 65F]/SLOPE

T
65.0 < enter Toff
36.0 < enter Tout

DC in %
0 < enter duty cycle
25 < enter duty cycle

-1.16 = calculated slope
65.0 = intercept

100.0 >enter DC
-51.0 = calculated Tout

Tdesign cold temp for Dist. Of Col. Is +14F, not -51F, so my furnace is oversized.

The furnace BTU output doesn't enter into the equation.

Last edited by Yoyizit; 12-19-2009 at 04:12 PM.

12-19-2009, 04:38 PM   #20
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Quote:
 Originally Posted by Yoyizit Why? I used an always off [zero duty cycle] outside temp. for a furnace at 65F, and an always on [100% duty cycle] for the design cold temp. Excel calculates the slope of the temp/duty cycle line with the SLOPE function. Then you know the duty cycle at any intermediate temp. for a perfectly matched house & furnace & climate by using the equation Outside Temp = SLOPE x (Duty Cycle) + 65F or DC = [Outside Temp - 65F]/SLOPE T 65.0 < enter Toff 36.0 < enter Tout DC in % 0 < enter duty cycle 25 < enter duty cycle -1.16 = calculated slope 65.0 = intercept 100.0 >enter DC -51.0 = calculated Tout Tdesign cold temp for Dist. Of Col. Is +14F, not -51F, so my furnace is oversized. The furnace BTU output doesn't enter into the equation. If your monthly avg. duty cycle and your monthly avg. outside temp. doesn't match these answers your furnace is undersized or oversized.
The latent hydro electron cyclic nature of the hydrogen atom in the water requires a a correction factor of Pi x Hy/7 xy.

12-19-2009, 05:42 PM   #21
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Quote:
 Originally Posted by hvaclover The latent hydro electron cyclic nature of the hydrogen atom in the water requires a a correction factor of Pi x Hy/7 xy.
I knew I left something out!

I have to fix this right-sizing-confirmation method.

If you know

you can check if your furnace is right sized for your house and climate.

If you know your furnace efficiency
at its monthly avg. duty cycle
you can calc. your house avg. heat loss.

Last edited by Yoyizit; 12-20-2009 at 12:45 PM.

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