BTU's oer Season formula

GW

Once I do a heat loss, how fo I convert that into BTU's needed per season? Thanks,Gary

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zeke

Roughly speaking, you get the loss BTUH for a particular reference outdoor temperature and the get the average outdoor temperature for the entire heating season. The total BTU is equal to the product of the number of hours, N in the heating season times the average temp during the season, Tav- Troom, times the BTUH you got for the reference outdoor temp, divided by the (reference temperature- Troom), or
BTU=N*(Tav-Troom)*BTUH/(Tref-Troom)
A more useful and simpler way is to get the estimated degree days from the weather bureau for the season and then
BTU=DEGdays*BTUH*24/(65-Tref)
Strictly speaking the Deg days as given are referenced to 65 deg, so the last equation should have to be corrected to account for the fact that the setpoint indoor temp could be higher than 65 deg, but it is close enough since you can only estimate the deg days anyway.

GW

thanks

I think the manual J program I use has that info, I'll check. thanks Zeke

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GW

Zeke

Could you please offer an example? I almost follos the formula; could you do up a calculation where 0* is the design temp, 30* is the average, and 70* is the indoor temp? Did I leave anything out? Thanks Zeke,Gary

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GW

Hours

The manual J program says 741 heating hours, 130 of which are at 30* to 34*.

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Dave_49

Estimated annual heating engegy

Quoting John Siegenthaler in "Moder Hydronic Heating" the formula is: E= (Q)(DD)(24)(Cd)/1,000,000(Delta T)
E=Estimated annual heating energy tequired by the building(MMBtu) 1MMBtu=1,000,000Btu
Q=design heating load of the building(Btu/hr)
DD= annual total heating degree days at the building location(degree days)
Cd= correction factor for the location of the building.(because of modern building practices the actuall heat needed is a portion of the areas Degree Days) The book has a chart and if you don't have access to this you can post the DD for your area and I will get you this number, but for future reference I would think you would want access to this chart.
Delta T= Design temp. difference at which design heating was determined.

GW

still don't get it

the degree days are 741 according to manual J. The heat loss is around 50,000. Heating desing is 0*

Thanks, gary

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zeke

For your example

Tdesign=0

Troom=70

Tav=30

Assume:Qd=80,000BTUH

N = 200 heating days


Then

Qtotal=24*Qd*N*(Troom-Tav)/(Troom-Tdesign)

= 24*80,000*200*40/70= 219,428,571 BTU

or about 1 million BTU per day average.

For this example the number of degree days would be
N*(65-Tav)=200*(65-30)=7000 Degree days. So, if you use degree days , you can use this formula to get the Tav.

Dave_49

This is what I get

If you plug your numbers into the above formula. Assuming an indoor temp of 68, and Cd of .08 (from the chart in "Modern Hydronic Heating") I come up with your seasonal demand of 10,460,000 Btus.