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Any Guesses

S Ebels
S Ebels Member Posts: 2,322
I have a number in my head as to how many $$.$$ will be saved on energy costs but I'd like to hear you guys' thoughts on this one just for curiosity's sake.

Some of you may remember last winter I posted about the HUGE old sorched air system in the local community center. At the time, I was looking for parts for an old Midco burner. You could literally park a small car inside the furnace, which had some severe cracks in the HX. (think 4 feet long through 1/2" steel) We patched it up to make it through the winter and now the crew is torching it out as we speak. The whole building totals 13,000+ sq ft and was run by a single thermostat. The "duct" is all poured concrete and runs underground throughout the whole building. At an estimated 10,000 CFM of air flow the heat loss from begining to termination of the duct was 170,600 btu's. (15.8* air temp drop from furnace plenum to the last register) The chimney flue was 22" square with a 16" connector coming off the open draft hood. Can we say....... suction?

We are going to replace the system as follows.

2 VB2-63 boilers, staged and controlled by a Vitotronic 200 using full direct reset of boiler temp.

Each room will have its own panel rad with TRV. The building is divided into 3 zones, two of which will have master thermostats to enable the circs. The remainng zone will run off the boiler control which is constant circ with setback capability.

We're going to use the underground duct as a chase for our radiator piping. Yes, it's big enough to crawl all 150' of each of the 3 main ducts right down to the ends. Main piping is 1 1/2" copper (wish I could have found PAP that size) insulated full length.

The gym will be constant circ rads that will account for 50% of the heating load. The balance of which will be provided by an air handler operated by a programmable setback t-stat.

The gas bill in January (1634 degree days) this past year, manually starting the furnace one time per day, was $1,867.00 This kept the building at about 55-60* on average.

Just curious, don't waste a lot of time thinking about it.


  • Ken_8
    Ken_8 Member Posts: 1,640
    It will take ...

    between 53 and 57 years for the payback of the system's conversion costs - so, unless gas goes to 50-bucks a therm, it will still longer than your lifetime to save one penny.

    No wait...

    If gas went to $2,000 a therm, it would only take a week to get the conversion costs back...

    No No, wait again...

    If you donate the labor and materials as a tax write off and get the furnace licensed by the Smithsonian as a National Historic Registered Monument, then the tax credits and one time exemptions would allow an Earned Income Tax credit of 61% of the total depreciated marginalized revenue base of the .....

    OK. I admit it. I have no clue. But you know what?

    I'll bet no one else does either.

    But I'm sure someone somewhere bantied about some absurd number - and I'll bet they bought that number hook, line and sinker.

    Only in America.

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  • J.C.A._3
    J.C.A._3 Member Posts: 2,981

    Will the fuel cost be lower? I bet it will. The more important factor....are the folks using the facility going to be more comfortable, and less likely to die from the new system? There's your payback! Chris
  • S Ebels
    S Ebels Member Posts: 2,322
    Here's what I was a-thinkin'

    I don't feel that this is far fetched at all, conservative in fact.

    The snow would melt in the middle of the winter to about 2 feet from the building where the underground duct (return air) ran along the exterior walls. The heat loss in the duct will be virtually eliminated due to no 140* air blowing through it any more.

    The old burner clocked at 880,000 btu's give or take a few thousand.

    The percentage lost in the temp drop through the duct figures to just shy of 20% of the total input. Assuming that there was some heat also tranfered up into the building, I've still got to think there was a 12-15% net loss there.

    Stack losses were 24/7, figure 3% easily. Draft hood opening measured 260 sq in.

    Combustion efficiency, old=76-77%, new=85-86% figure a conservative 5%.

    The new system will move the btu's using a max of about 900 watts (w/o the air handler) the old furnace had a 5HP 240V motor moving all that hot air. In the coldest three months it would run 12-16 hours per day. Figure 5,500 watts, yielding a difference of about 4,500 watts , a savings of $.42 per hour of comparitive run time. All the circs can run 5 hours for the same cost as an hour for the old system.

    All this should translate into the vicinity of 23-25% reduction in total energy costs or $450 during peak months.

    Ken, you are of course correct in saying that paying for the system on energy savings alone will be a looooong way out there unless a therm goes to $4.00. (presently at $.72 locally) Chris however, brings up THE reason for the changeout namely, people will not die. That by itself is all you need.
  • Weezbo
    Weezbo Member Posts: 6,232

    i have to say thinking is highly overrated:) you have nice boilers,...im thinking you would be suprised at what 1/3 of the btu,s would do for you. honestly. i'm thinking the stack size down, cut the burn cycle way way back... do some balancing on the air handler cut down to a drizzle the outside air intake, put a speed drive on it,and a really small boiler for colder weather, im guessing your fuel savings would be 60 percent of the previous debacle. as an obvious beliver in viessmann efficentcy:)
  • S Ebels
    S Ebels Member Posts: 2,322

    The actual calculated heat loss of the building, figured on the high side is 505,642 according to HVAC-CALC. I have found this program to be on the "cautious" side of things. The pair of Vitola's have a combined output of 498,000 so we are dropping the gross input by roughly 380K compared to what was in there. Is this what you were alluding to?

    The air handler we are installing is oversized so we can drop the air flow back and still get the required btu's.

    Both boilers will be common vented into a new 12" stainless stack.

    What do you mean by "cut the burn cycle way way back"? Are you talking about the new boilers? If you were talking about the old furnace, it was junk. There were 7 different cracks in the HX when we finally got the jacket all the way off. Some were about 3 feet in length and I could stick my fingers through the gap.
  • Weezbo
    Weezbo Member Posts: 6,232
    Sounds closer:)

    yup that sounds closer...we did something similar took 1.5 megs out put back 590:) no problemo:) sings and dances and hangs right in there:)the air handeler is a ridiculous waste in our case 30 hp 16sqft Hole in the wall 60 " rounds ..the sheet metal we no monkey with however i suggested three vanees or life breaths in the office areas,letting the shipping and receiving doors which open and close elebenty sik times a day to handel the wearhouse:)and nope gotta evacuate like 196000000 btus an hr with a thirty horse:)) thru half a wall. seems when you suggest reason out come the overkill experts and they get the job:)) *obs lived here too long:))
  • Weezbo
    Weezbo Member Posts: 6,232
    as it is a community center....

    You could let the neighbour hood kids play in the old concrete duct work:) send them in with a torch and a few 1 1/2 " fittings.... :) could work out:)
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