Radiant heat boilers

[moobeast2]

Have a few questions about shop heat. We are building a pole-barn type shop for the farm with radiant floor heat. I've pretty well decided to go with an electric boiler as we are on municipal electric and average about $.05/kwh. I know, lucky us

Here is our shop plan: 40x60x16 R-19 in walls R-30 in ceiling two big O/H doors (20x15, 12x12) R-10, 6 4x5 dbl-paned windows, 1 entry door. Floor will be concrete slab on grade with 2" pink board under all and around edges. I plan on using 3/4 PEX 18" on-center, 1 zone 4 circuits about 400' each.

I am looking at a HydroShark3 electric boiler, either a 14 or 19 KW (49K BTU or 65K BTU). Or a boiler from Electro industries, an EB series 15KW (51K BTU). The Electro seems like a better built sturdier unit but is almost twice as much money. However you can get the Electro with outdoor reset. Our local fuel company tried to talk us into a Buderus propane boiler and described outdoor reset and how it works. The Electro website doesn't recommend outdoor reset for shop type buildings.

Is outdoor reset worth the extra money on an electric boiler or in a shop building? The HydroShark looks like an easier setup; they make pre-assembled boards for connecting the boiler and I've found several other places that sell pre-assembled manifolds. We aren't plumbers but my mechanic is pretty good at anything so I'd like us to hoop it up if possible.

Any opinions or comments welcome. Any questions just ask; I'm in and out of the office so I may not get back right away. Apologies for length, just trying to get out as much info as I can. Thanks!

 

[danski0224]

Has a heat loss calculation been done?

 

[moobeast2]

Yes; the fuel company rep came up with about 95800 BTU total heat loss. I used LoopCAD to do my own calculations and came up with 43,000BTU heat loss. (See my other post about LoopCAD and its accuracy).

 

[danski0224]

I think your number is low.

 

[stingry]

Yes; the fuel company rep came up with about 95800 BTU total heat loss. I used LoopCAD to do my own calculations and came up with 43,000BTU heat loss. (See my other post about LoopCAD and its accuracy).

What design parameters did you use (interior temp, outside temp, etc.)? I ran your numbers thru a program that I got from Watts Radiant and come up with a slightly less than 43,000 BTU heat loss at a -3 deg F outside temp, 7 mph wind and an interior temp of 68 deg.


Steve

 

[moobeast2]

I used -2, no wind (didn't see an entry for it) and 55 inside temp

 

[danski0224]

I did a load calc on a house. Chicago area.

Ranch on a slab, ~1400 sf, no edge insulation, forced air ducts in the slab, R9 in the walls and not much more in the ceiling, long axis of the house faces east and west, -1* ODT 72* IDT and came up with 56,416 BTU.

Changing indoor temp to 55* F changes the heat loss to 43,278 BTU.

Cubic volume ~11,200 cu ft.

Your space is ~38,400 cu ft- 3.4 times as big.

Floor area is 2400 sf, 1.7 times larger.

But, the high ceilings means you have more air to heat and more loss through the walls.

Those overhead doors are a killer. Lots of loss.

Yes, you have better insulation all around but a 43,000 btu load?

It doesn't make any sense.

I'd believe the fuel rep calculation. Something isn't right with yours.

 

[stingry]

Apples and oranges??? Do a calc using his parameters and see what you come up with.

Cheers
Steve

 

[danski0224]

Apples and oranges??? Do a calc using his parameters and see what you come up with.

Cheers
Steve

Some ways yes, some ways no. It's still a conventional building in the same general climate zone as me.

As far as me running a calc goes: (1) not enough info and (2) not something I do for free.

The OP can spend $50 at (www) HVAC-Calc (dot com) and do his own.

Infiltration is a huge variable. There are ASSumed numbers used in some load calc software and procedures. Problem is, you can't have a set of measured infiltration numbers for a building that exists only on a set of plans.

Some will say that even Manual J has a fudge factor built in, over and above the infiltration assumptions.

You can design for a set of numbers, but then that must be verified.

I believe there has been a discussion on this forum about insulated premium garage doors that fail (miserably) to perform as advertised. So, if you design for a huge hole in the wall to be R25 and it is really R5, and the load is *right there* at R25, will it work?

The big question is will LoopCad guarantee their numbers? I'm not saying their numbers are wrong, but they are a whole lot lower than I would expect.

 

[jvitez]

There's no negative to oversizing an electric boiler except the instalation cost. I'd go with the largest boiler. How often will you be opening and closing the doors? You might consider a smaller boiler and a forced air unit heater to quickly heat the air after a door is opened.

 

[z28toz06]

There's no negative to oversizing an electric boiler except the instalation cost. I'd go with the largest boiler. How often will you be opening and closing the doors? You might consider a smaller boiler and a forced air unit heater to quickly heat the air after a door is opened.

going with an oversize boiler is usually not recommended, at least with a standard boiler system, electric maybe not so much?

a space heater will be unecessary if the floor system is working (sized)properly. room temp will recover quickly due to the giant 2400 square foot heater you are walking on.
moobeast:
400 foot runs sounds long. water in the pex will cool off by the time it hits that last 100 feet, creating cool spots. most everything I've read says 250 to 300 feet per loop max.

 

[jvitez]

z28tox06, you're correct on all points. I was trying to keep my post simple and to the point.

An oversized fuel burning unit heater or boiler will be inefficient if it's single fire, meaning one btu/h output only, either on or off. It takes a certain time period for the combustion chamber/plenum/etc to heat up and reach steady state, at which point all the heat being created by burning fuel will be going into the building. A modulating/multi-fire boiler is different again: it can vary it's output depending on input required, so here a bit oversized gives you wiggle room if you get a particularly cold snap.

For electric heat it's far less of an issue. A resistance element heats up at a certain (fast) rate, and there it sits until it's turned off. More KW output simple means a larger number of elements. Electric elements are essentially 100% efficient, not cheap but efficient depending on your POCO's pricing.

My comment about adding a unit heater was meant in case the OP puts in the 14 KW boiler he mentioned for his floor heat. That would be defintitely undersized and would give poor performance, which could be obviated by a unit heater. But your reply is the best: install a boiler with enough input and size the PEX loops properly, and you shouldn't need another heat source unless you need really fast recovery.

Our local hospital did a big renovation including the ambulance bays. They now have a big spacious drive through off load area, front and rear garage doors, with a heated floor plus forced air unit heaters. Makes sense here to keep patients from getting an arctic blast as they're coming out of the rig by having rapidly heated air, not direct radiating heat from the floor which they won't feel, just the air temperature.

 

[Bigrhamr]

Can anybody with heat loss calc experience comment on the difference between a free one like this:

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

And some of the more expensive and presumably pro quality software?

To me the one in that link seems pretty complete but I don't see what it uses for an inside design temp or how to change that. I can say that it gives me numbers very similar to those obtained through a HVAC supplier.

As mentioned above infiltration seems to be the biggest wild card and guessing there can change the results dramatically. How does a pro come up with the infiltration number? Some kind of pressure or flow test?

 

[danski0224]

That link has no provisions to orient the structure. Lots of windows on the south side is different than the same thing on the north side.

Even between "pro" versions, there are differences. There are only a couple of "pro" versions that are ACCA accepted: Elite and Wrightsoft. Both supposedly have very steep learning curves, but are very comprehensive.

As far as infiltration goes, you have a design target set when the plans are drawn (test when construction is complete), or you test in a completed structure.

 

[tdkkart]

Can anybody with heat loss calc experience comment on the difference between a free one like this:

http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm
And some of the more expensive and presumably pro quality software?

To me the one in that link seems pretty complete but I don't see what it uses for an inside design temp or how to change that. I can say that it gives me numbers very similar to those obtained through a HVAC supplier.

As mentioned above infiltration seems to be the biggest wild card and guessing there can change the results dramatically. How does a pro come up with the infiltration number? Some kind of pressure or flow test?

I can tell you that I put in a set of pretty conservative numbers for my 30x40 pole building and came up with 24,000btu. Conveniently enough, my radiant floor system uses an electric demand water heater which is 7KW, or just short of 24K btu. Has no problems whatsoever heating the building is -20* temps.

 

[BadgerBoilerMN]

Any electric boiler should include a weather sensitive control for increased comfort and lower fuel bills.