Fire Building Planning Tool

Due to overwhelming popular demand, I'm putting my fire planning tool on the web for anyone who wants to use it. It's at http://www.nofossil.org/weather/delphi.php and is somewhat documented. You'll need at least an educated guess for the following data:

- Your latitude and longitude. It doesn't do Zip Code.
- Your temperature-independent base heat load (DHW, primarily)
- Wind factor: how much wind affects your heat load. The default is probably fine.
- Temperature factor: BTU heat loss per degree day for your house. Can be derived from Slantfin or history.
- Approximate hourly boiler output: probably about 75% of rated capacity
- Degree day base temperature. Usually 65, though I use 60.

It will likely take a bit of tweaking to get useful results, but feel free to play with it. Comments and suggestions are welcome as always.

I've updated my private version so that it checks the amount of heat in storage. It then looks at the heat loss and figures out how long before the storage runs out, and tells you how long before you need to build a fire. Unfortunately I can't add that feature for the public version, although I could provide a place to put in your own storage numbers.....

smokinj said:

Very cool how much time you have in this?

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Couple of hours for original tool, another couple of hours to create the public version with the data entry form. I do some of this kind of stuff in my consulting business, so I pretty much knew what I had to do. Turned out a bit easier than I expected. Wish I had done it earlier.

If anyone wants the scripts, just drop me a line.

Haven't done lambda sensor yet - need a longer extension cord for my welder......

gorsuchmill said:

Nofo - This is great, but how do you calculate the temperature factor? I've used the Slant Fin heat loss program and am coming up with approx. 110k btu/hr; however, I don't see an output related to degree days. Is there a simple calculation I'm missing?

Thanks.

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I haven't used the Slantfin program, but I expect it gives you heat loss at a particular temperature, probably worst-case. I'll assume 0 F for your case, but try and find the actual number....

A day with an average temperature of 0 degrees would be 65 degree days (figured from a degree day base of 65, which is most common). If the number really is 110,000 BTU/hr, then your daily heat load at that temperature would be 2,640,000 BTU. Divide that by 65 (the number of degree days) and you'll get 40,615 as the number of BTUs per degree day. That's the number for my planning tool.

I'll agree with pybyr - that number seems extremely high for Maryland, unless you're heating the statehouse. That's more of an Alaska number.

Over time, you would probably want to adjust the number so that it matches reasonably well with your actual experience. My personal number is derived from an analysis of heat consumption at different temperatures and wind speeds.

I've got mine tied into a calculation of heat left in storage. Yesterday morning it said that I'd run out of heat by 6:00 this morning if I didn't build a fire. I skipped the fire and ran out at about 5:00 this morning. Pretty close for a 20 hour look-ahead based on a weather forecast. That's what I really wanted - a tool to tell me if I can skip, and to help me figure out how long of a fire I should plan.

Hope this helps.....

gorsuchmill said:

The 110k btu/hr figure is based on a worst case scenario, I believe, in which I input the outside temp. at 10*. I don't live in the statehouse, but an old millhouse of about 4000 sf, located at the bottom of a hill where I don't get much wind, but the sun sets early and the ambient temp seems a little cooler than when you start "up the hill". For what it's worth, I went through approx. 1350 gallons of oil last year with a 6 zone system (incl. DHW), and the thermostats programmed at 64* when we're home and awake and 58* when we're away or asleep.

To get back to the temperature factor then, should the input figure be based on the average load, which I've read is typically about 50% of the "worst case" heat loss estimate?

Thanks again.

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Two ways to get a temperature factor:

1) Take the worst case (10*) heat load. Divide by 55 (worst case is calculated for a day with 55 degree days) and multiply by 24. That gives you 48,000 as the temperature factor.

2) Take your oil consumption, multiply it by 143,000 and then by your oil boiler efficiency (assume .85 unless you know otherwise). This gives you an estimate of heat delivered by your oil boiler for a whole season - about 164,000,000 BTU. Divide that by the average degree days per heating season at you location (about 4500 at Annapolis). That would yield 36,500. Add some if you want to keep the thermostat higher.