Flow calc help pipe/pump size for 600' loop.

[MrEd]

I have my tarm 60 at my house, all up and running. Next project is to get some heat out to my workshop, which is a 24x30 wood frame building with currently no insulation and 12' ceilings. My plan is to pour a radiant slab, and run underground pex out with antifreeze and a liquid-liquid heat exchanger by the tarm. I really only need to heat the shop occasionally (thus the anti-freeze) and when I do, just needs to get upto 50-55 degrees or a bit more. Insulation is a future possibility as well.

The round-trip would be about 600'.

What size heat exchanger, pex and pump might I need to make this work?

This is a next year project, so just in the planning phase now.

 

[hayrack]

I think 600' is too far. You would be better off to put a seperate boiler or stove in the unattached building. It seems like I have heard that 80' is about as far as you want to be from the boiler

 

[Gooserider]

I have my tarm 60 at my house, all up and running. Next project is to get some heat out to my workshop, which is a 24x30 wood frame building with currently no insulation and 12' ceilings. My plan is to pour a radiant slab, and run underground pex out with antifreeze and a liquid-liquid heat exchanger by the tarm. I really only need to heat the shop occasionally (thus the anti-freeze) and when I do, just needs to get upto 50-55 degrees or a bit more. Insulation is a future possibility as well.

The round-trip would be about 600'.

What size heat exchanger, pex and pump might I need to make this work?

This is a next year project, so just in the planning phase now.

Well obviously you will need to do some serious heat load calcs, and then apply that to the sizing and so forth formulas - start with that Taco tech paper I mention in the "Tidbits" sticky... Note that 600' is a LONG way, and as such you are going to need a lot of very large diameter PEX to make the round trip with enough BTU's to do the job. It can be done, there is no real limit on distance, but it gets more expensive the further you go, both because the cost per foot x the number of feet, and because you need bigger tubes to deal with the flow resistance. It may well be that when you crunch the numbers, you would find it cheaper to do a second boiler or stove...

Whatever you do, don't make the mistake we see so often of not putting enough tubing in the ground to carry the load with a reasonable pumping effort....

A couple of other points...

While I agree with the folks that say you should probably put in tubes and properly insulate any time you pour a slab, just because you can't go back and do it later, I don't think in-floor is the best approach for a shop that is only going to be occasionally heated.... Slabs tend to take a lot to heat up and be very slow responding, then take a long time to cool back down again, so you'd be spending a lot of time heating the place for the short time you'd be there... I would look more at doing a "Modine" style heater - either commercial or home brew, to do the main heating, as that will give a much faster response, and maybe just use the radiant to take the chill off the slab...

I would also put a LOT of effort into improving the insulation situation - lowering the BTU/hr requirements for the building would make a BIG difference in the costs for your heat lines...

Gooserider

 

[Jim K in PA]

I concur with Goose. The distance issue can be calculated/dealt with, but it seems a false economy to spend thousands of $$ on getting warm water from the Tarm to the shop. For the use and building type you describe, propane fired Modine-stye space heaters will be more efficient and much more practical. If you go with in-floor radiant, you will have to run it for days to get the building up to temp. You could save a lot of $ by just installing a large wood stove in the shop, perhaps even one of those beastly double 55 gal drum units, and firing it when needed.

Dont mean to rain on the parade, just trying to help.

 

[heaterman]

From an economic and operational standpoint................

600'........strike 1 lot's of cost

intermittent heating with a radiant slab...... strike 2 too much flywheel effect in tons of concrete to operate it on/off

cost of mixing controls to drop water temp for slab heating............strike 3........ time to explore plan B

If you are going to use the shop frequently/daily, then I would consider using a radiant slab to heat it with. if you don"t ever foresee that happeing then I think your best choice is to insulate the Bejeebers out of it and install some alternate form of heat that can be turned on instantly when you need the building.

 

[MrEd]

Yea, hadn't thought of it, but trying to bring the slab upto temp for an afternoon of work on a Saturday probably doesn't make a lot of sense, though I love the idea of a nice warm slab to do woodworking projects on. I'll consider a water to air exchanger, or maybe just go with a dedicated unit in the shop. I really *hate* to put any new fossil heating sources in though, even thought it may in fact be the cheaper option. Maybe just a lot of insulation and a good old fashioned woodstove maybe the best route.

And by the way, the 600' was round trip, 300' in each direction, still a long ways though.

BTW: My original plan when I first set out to buy a tarm, was to install it in the workshop, and run the heat the 300' to the house (and 300' back) using 1" underground pex...glad I didn't end up doing that. Not sure I ever would have been able to get enough heat to the house. Never did do a heat-calc on my house before the tarm install, but plain old dumb luck everything still works perfectly - in fact, it wasn't until after I bought my tarm that I knew there was such a thing as a heat-calc (mostly because of this website/forum).

 

[heaterman]

"though I love the idea of a nice warm slab to do woodworking projects on"
Indeed!! there is nothing nicer to do any kind of work on than a heated floor and I completely understand your thinking in desiring to go that way. I think I would for sure tube the floor anyhow just in case the use of the building changes in the future. One never knows...............

 

[ewdudley]

Or some low-mass radiant flooring even.