Barn heating options?

[Jeff922]

Hi all, hope you guys had a good winter.  I've been sort of "out of the loop" on this forum for the last several months, but in the coming weeks I'll be back to my Victoria's project.  The next phase will be completion of the electrical work (I'm doing this myself also). 

I'm in the "daydream" phase of considering a future barn to go next to my Victoria's.  This is all theoretical at this point and I wanted to get a little feedback/ideas.  I'm thinking the space would be roughly a 20'x30' two story (or 1-1/2?) gambrel(?).  The first floor would be my woodshop/storage, and the second floor would be art studio/fitness room/whatever else.  My main question is heat.  I'm not sure what makes the most sense.  The Victoria's I'm building is a FPSF concrete slab with 7/8" pex for radiant heat.  I'll probably install a gas hot water heater for this (open system with one heat source for both heating and domestic water supply)  100,000 Btus?  (not sure of size, I need to do a better calculation).  I also have a huge 100,000Btu woodstove in the Victoria's as I like to get as much of my heat as possible from wood.  Initially, I thought I would extend a pex zone underground over to the barn (about 40' away), but I wonder if this is really the best idea.  Should I consider a different heat source in the barn?  It will be a similar set-up as the house; a propane (or whatever) heat system to keep things 50F -55F and a wood stove (another 78,000 Btu unit I have) to take the edge off when we're working over there.  What should I use as the barn's primary heat source?  I've had thoughts of an outdoor wood boiler instead of propane, but don't like the idea of installing a separate domestic hot water supply.  Ideas?  Thoughts? 

[JRR]

I would not combine my domestic and heating systems water.  The heating system would have anti-freeze in it for winter shut downs.  The domestic system would be drainable.  I know they make heaters that are supposed to keep separate two or more water systems ... but I just don't know why I should trust them.  Simpler, more flexible, just to separate the systems.

I think you want a separate heating system for the barn .... passing hot water through 40 feet underground would incur some losses, albeit small.

My opinion.

[Bob S.]

I would put some sort of earth source heat as the primary heat in the barn and back it up with the wood stove. If you only want to keep it at 50-55 Degrees, and if you plan it from the get go it would not be that expencive. the key is 50-55 degrees instead of 70-75 degrees.

[Jeff922]

JRR, I agree that the heat loss to the barn is unappealing.  I'm not entirely sure I understand your concern with an open system.  Basically, cold water enters the floor first.  Or in other words, the hot water coming out of the shower or sink has passed through the floor first.  There is efficiency loss when antifreeze is used because a heat exchanger is needed (an additional expense). 

Bob,  You are absolutely correct about using geothermal energy, however, my particular situation makes that difficult.  I have a very deep, low yield well that probably wouldn't be appropriate for a hydronic geothermal configuration.  A bermed earth structure would be a good idea too but I don't really have any extra earth on my tiny lot.  I could build an underground potato barn I suppose  .  On second thought, excavation cost about $100/hr.  Hummmm...back to the drawing board...

[Alan Gage]

Have you run any heat loss calculations? I don't know how accurate they are but it's a start (and fun).

http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

Your current heating options of 100,000 BTU sound like way too much to me. I'm building what I guess could be called a super insulated house (single story 1000 sq. ft.) and plan to heat with only a small woodstove (1.3 cu. ft. firebox) and electric backup.

If I figure -20 outside and 68 degrees inside (88 degree temp difference) my calculated heat loss is 16,500 BTU/hour. It drops to around 10,500 BTU/hour with a 56 degree temp differential, which would be an average for Dec., Jan., and Feb. here (northern Iowa).

My walls will be 10" double stud with dense pack cellulose. Slab on grade with 4" sub slab insulation and R-75 in the attic. Nothing fancy with the windows, vinyl double pane with a U-factor of .29. I don't remember exactly what the numbers were but in a house this small the heat loss wasn't all that much more than one with standard 2x6 construction.

Take what I say with a grain of salt though. This is my first build and I have no prior experience other than research.

Alan

[Alan Gage]

As for the shared DHW and floor heat the reasons I heard to avoid this were that the water for the in floor heat sits, uncirculating, all summer and gets stagnant. Then come winter, when that pump is turned on again, that bad water is mixed in with the house water.

I'm not sure how you're doing yours though, perhaps it avoids this. I know there are systems out there that can. It would be nice to have anti-freeze in the lines in case the house, for some reason, is left unheated in the winter.

Alan

[Jeff922]

Thanks for the advice Alan.  I also found that link you referred to.  I filled in all the info and ran the calculation, but I wasn't really sure how to use that info to size a heat source.  But you are correct, I think I've oversized my guesstimate at this point.  I haven't found a good way to get a calculation.  Manual J seems beyond my abilities and all the other calculators/charts are way too simplified.  After reading your example however, this makes a little more sense.  I'll have to run that calculation again.  Looks like you've really done your homework.  Good point about the stagnant water.  I'll take a look at my diagram and see if there is a way to avoid it.  Thanks for the input!

[JRR]

It's not the "openess" that concerns me.  Its the unecessary combining of the two functions...heating and water supply.  As Alan suggests, what happens to the heating system if the house must be left closed for the winter season?  Best to have a bit of antifreeze in it for peace of mind.  And I would have the (separate) water supply system easy-drainable.   Otherwise, some spring repairs are in store for someone.  And if pure water freezes in the heating loop and boiler ... perhaps extensive repairs!

[Redoverfarm]

Jeff I had a outside boiler for about 3 years.  It was great to have cheap hot water and heat.  Downside was firing it twice daily and having someone to fill in on short absences to ensure the fire did not go out.  With mine there was a anti-corrosive additive that had to be used to protect the boiler tank and tubes.  The domestic used the same heating space in the boiler but was seperate from the water used to heat the house.  You can eliminate the exchanger if you went to hot water registers rather than forced air.  You can set up seperate zones for the heat and domestic hot water.  I had about 90 ft run to the house and used insulated pipe with very little heat loss.   They are used in this area a good bit but I would attribute that to the avilabiliy of the wood.   Some even use them to heat swimming pools in addition to their house. 

[Jeff922]

Hummm...I think something got lost in translation.  I didn't mean to suggest forced air when I said heat exchanger.  The heat exchanger I'm talking about would take the domestic hot water and heat the antifreeze in the radiant heat system - that's the exchange of heat I'm talking about. 

As far as I'm aware (and please correct me if I'm wrong), there are three basic types of radiant heat systems.

1) Open System:  this system has one heat source that supplies radiant heat and domestic water.  The benefit;  it's theoretically the most efficient and the least expensive.

2) Closed System:  This system keeps the radiant heat and domestic separate, but two heat sources are needed.  The disadvantage here is obvious.

3)  The Heat Exchange System:  Only one heat source is needed but a heat exchange becomes necessary.  Disadvantage is efficiency loss

That outside boiler you describe Redover sounds interesting, I definitely consider it.