Idle musing - is our planned shed too far from the house for a wood boiler?

[mesuno]

Having recently bought some land adjacent to our house we are considering building a large workshop/shed. I figured it was worth at least contemplating building a boiler/heat storage system at the outset so we can get some idea what is feasible.

It is particularly appealing because our main wood storage area is a fair old trek from the house so it would be nice to be able to walk out, load up a big boiler once every 2 days or so and then rely on the thermal storage for heating the house. We'll be able to get vehicles right to it so it would be a substantial time and effort saver re handling/moving/stacking firewood.

A quick estimate (based on google maps on my pc screen, so not terribly accurate) is that the pipe run would be 450ft each way - quite a bit longer than others I have seen discussed in the sticky thread. Is that distance itself a show stopper? What kind of heat drop would we expect?

How do we go about calculating sizings of everything? Thermal storage, boiler size, pipe dimensions?

How can we integrate thermal storage in the workshop with our domestic hotwater and central heating? Do we need a small HEX and tank at the house?


Cheers for your input!

Mike

 

[joecool85]

You'd have to run big lines (I'd suggest something like 1.25" as a bare minimum) and a large pump. It could be done if you bury it deep enough and insulate well with spray foam but the install cost will probably make this idea a non starter.

 

[Tennman]

Ouch! I thot mine was bad at ~450' round trip. First I've read of anyone here wanting to go that far. I wrote a small spreadsheet based on the Taco TD for pump sizing. If you want a copy PM me. My limiting factor was not only the underground cost, but I refused to have joints underground. I bought 300' rolls of 1 1/4" pex with a lot of waste to avoid underground joints. You can do it, it will ultimately cost you more wood and walking about time. And a big pump.

 

[woodsmaster]

That would be vary expensive.

 

[mesuno]

<double post>

 

[mesuno]

I guess the real question is whether it would be more expensive than carrying all our firewood for the next umpteen years that distance :~|

The site we are considering is the absolute ideal for us to drop our logs straight out of the back of the 4WD and from there eventually into the boiler. Moving them from that site to the house to burn is a PITA; narrow paths, steep slopes, steps and distance which basically means carrying it all in your arms as we can't get vehicles closer without major landscaping work which we will never get planning permission for.

 

[heaterman]

Rough estimate of your cost for that using 1-1/2" tube would be around $9,000 at a bare minimum provided you do it with something that has decent insulating properties. There is no way you can buy premade tube of good quality for under $25/ft from what I have seen.

Using a 26-99 Grundfos with 1-1/4" tube and a few misc fittings thrown in for rough calculation you would see a flow of about 8gpm with head running a little over 27 feet. Differential pressure is high enough that you would have to seal and pressurize that part of the system in order to avoid losing pump after pump due to cavitation. 8gpm will give you around 80,000 btu's to play with under normal circumstances. If you have all low temp emitters like a radiant slab floor you may get as high at 120,000 out of that flow rate.

Going to 1-1/2" tube and using the same pump brings the gpm up to nearly 13 and drops the head by about 15%.

So.....simple answer is, yes it can be done. Whether such a thing is cost effective is something I cannot tell from here.
BTW, I would not be hesitant one bit to splice underground provided you use a good fastening system like Rehau, Uponor or Viega. My 1st "weapon of choice" for that application would be Rehau Everloc fittings. The tube will fail before those fittings come apart or lose their grip. We once pulled over 300'of 1-1/4" through a conduit that had some unexpected kinks in it using a 1/2" nylon rope and my van to tug it through. That was 8 years ago.

 

[mesuno]

Heaterman - I was thinking along the lines of using spray in place closed cell foam in a trench with cheaper pipes. According to the sticky thread it has higher insulating value and works out cheaper.

 

[joecool85]

Heaterman - I was thinking along the lines of using spray in place closed cell foam in a trench with cheaper pipes. According to the sticky thread it has higher insulating value and works out cheaper.

Still going to be quite expensive. I can't imagine doing the job for less than $5k but I haven't actually run the numbers.

 

[Jim K in PA]

Heaterman - I was thinking along the lines of using spray in place closed cell foam in a trench with cheaper pipes. According to the sticky thread it has higher insulating value and works out cheaper.

Something to think about with long run spray in place piping insulation is expansion. Check the specs from the manufacturer for the tubing you plan to use for its rate of expansion (mm/M/deg C). I used spray in place closed cell foam for my underground run, but I had less than 60' of pipe run. Even with a good quality pre-insulated product like Microflex, et al., plan ahead at the terminations for a fair amount of movement of the pipe (use strain relief as much as possible).

As to the justifiability of such a project, if you plan to be there for a long time, it may make economic as well as practical sense. That is something you will have to determine and decide.

 

[Hunderliggur]

I would use $10/ft as a ballpark. Using your labour (I lived in the Cotswolds for two years) and the spray in place you make get it down to $5/foot. I have 80ft underground and 80ft in the basement. 1 1/4 PEX underground and 1 1/4 copper in the basement. Works fine with a Taco-0011.

From Mark at AHONA for my 320ft round trip: If you were to use 11/4 copper along with the wirsbo pex you would be fine with the fluid velocity at 3.6 feet per second on the copper and 3.47 on the pex and a total head loss of 13.28 total dynamic head loss including the Danfoss valve so 14GPM @ 13.3feet of head a Taco .0011 IFC pump will work well- IFC is internal flow check built in.

Where are you in the UK. And I though I had problems with local government permissions!

Mark

 

[mesuno]

Thanks for the more promising figures!

We are based in Kent (SE UK) - all our infrastructure problems come from my parents buying part of what used to be an old manor house. The building and grounds are all protected as Listed Buildings which is why we have to look outside the property boundary for the workshop/boiler install

 

[Hunderliggur]

My forester prepared a forest management plan for me for our 44 acres. He estimates that I can harvest about 10 cords/year from the living trees with a sustainable forest. There is also a lot of down wood that would add to that. 10 cords is more than I need personally so a sell a little to friends. What can your 12.5 acres produce and how much do you need? Don't forget the possibility of scrounging outside of your land (with permission of course). Our local landfill has a "yard waste" area. Log rounds are in one pile and are free for the taking if you want them. I picked up a truck bed of red oak that way. Many (most) people in our area (outside of Washington DC) can't be bothered with splitting their own wood, they would rather pay $200/cord cut/split/delivered.

It looks like your boiler needs justify the outbuilding. Just get good prices on you costs so you don't get caught short. Storage will be in your house, right? 450 ft of COLD or cool water is a lot to circulate when you have a call for heat and the storage is in the outbuilding.