Back up a few steps. How much heat energy are you trying to move? What is the heat load? If you run a heat load calulation it will spell out how many BTU/ hr. required. With that number you size the loops, supply temperature needed, and the pump size. The key number for sizing the loop output, and required pump size is the BTU/ square foot required. Do all you can to the building to keep the number below 20 BTU/ sq. ft
If you use a load calc from one of the radiant manufacturers it will spell out total load in btu/ ft. required, flow rate needed, supply temperature, and feet of head. Usually the amount of tube, and tie downs required is also provided.
The RPA guidelines suggest
1/2 pex, max. flow .6 GPM, loop length 300 feet, 9-12" on center
So 11 loops at .6 GPM each = 6.6 gpm at a 20 degree delta T.
From the Uponor Design Guide 1/2 pex flowing 100% water at 120F supply, multiply 300 feet (loop length) X .0137 = 4.1 feet of head. So you need a pump to move 6 gpm at 4-5 feet of head.
Many installers got to 330' loops as you can get 3 loops from a 1000' coil of pex. Borrow or rent an uncoiler if you go with 1000' coils
A Grundfos Alpha circ, for example could power that system, 7 gpm at 6 feet of head, with about 45W of electrical consumptiuon. Or a 007 Taco or 15-58 Grundfos @ 80W.
IF your load is 20 BTU/ sq. ft. or under I would consider 300- 330 foot loops at 9" on center.
For your 5600 square feet of building X 1.40 (factor for 9" on center) = 7800 feet of tube. Add a bit for leader lengths to get to the manifold location, and you need to buy 8000 feet of tube.
At 12" on center = 5660 feet of tube required round to 6000 for leader length.
So you are talking the price difference between 6000 or 8000 feet of tube, at $.30/ ft. (online prices) $600.00 more to go to 9". I would highly reccomend spending the extra $$ to tube it at 9" on center, maybe 6" if the load is great than my assumptions?
hr
Thanks.
The house will be very well insulated and very tight/low air infiltration.
Attached is what was sent to me by the designer of the 500ft loop system. He says the loss will only be 80,000 BTUs while others have calculated it at 147,000 to 169,000 BTUs. All of them received the same info... (House info pasted below). The variation in BTU loss is making me bonkers and I'm about out of cash as it is earmarked for everything else... DOH!
I told them the closest place to base outside temps and HDD was Alamosa, CO. HDD of between 7500 and 8700 per year.
Either way, when I asked him about the difference in BTU requirements, he wrote back :
"Your spray foam insulation will give you a heat loss of about 12 Btu's per Sq. Ft., 12" spacing in concrete will put out over 30 Btu's per Sq. Ft. if needed."
I already bought 15 rolls of Pex-B. They are 500ft rolls. Bought an extra 4 rolls than his design required...just in case.
So I'm in a little pickle. Do I continue with his design which he says he has done thousands of... or cut the rolls in half and go with a much larger number of smaller pumps.
I AM off-grid, but "should" have adequate power w/my set-up.... either way I thought one bigger pump would be better than a hand full of smaller pumps. I would assume two zones will call heat at bout the same time engaging more smaller pumps which add up to be more than the one single pump.
Taco says the one big pump
can push the number of loops he is suggesting for my design including his claim of 16 loops under the gpm load he has suggested would be needed. It's just so far outside the box from what I've been reading that I'm a nervous nellie now. If that one Taco dude said it was impossible this all would be a moot point, but he has said it could be done... BUT he/they were not designers, etc... add more lawyer-ease...yadda yadda yadda.
Anyone ever run across this system; and if so, how did it work?
At a loss and running out of time,
S+W
----start of paste for house info/rough info----
NOTE/UPDATE of below.... Going with all wood framing with ICF stem walls now. Galvalume exterior and still foam insulation. There will only be one garage door now... the 16x12.
Structures:
50x100 building (half living space and other half garage)
12x54 adjoining building (breezeway/pseudo greenhouse)
14ft eves
4:12 pitch to create 22 ft peak.
Living area ceilings 8’
Garage avg ceiling 16ft’? (UPDATE... will prob be 14ft)
Breezeway ceiling 13’
Manifold option to upgrade another building in future (add 3 zones later.. maybe 4?)
Floor:
All slab… 3 slabs all three 5” thick with 4” DOW under it. Perimeter will have 4” also… Closed Cell 2# spray foam prob…… or DOW??? Each slab thermally separate from each other. [UPDATE: ICF stem wall will have a total of 3 to 5 inches between wall and slab inside the building]
Thermostats:
In slab type
4 zones?
1 in garage, 2 in house, 1 in breezeway… open to suggestions.
Windows:
Roughly 272 sq ft of windows. Fiberglass framed Serious 725 series w/total window perf of supposedly .16U… 6.3R
· Four 4x6 windows in living area… all picture frame facing south (High SHGC, etc for solar gain)
· Four 4x6 windows in breezeway… all picture frame facing south (High SHGC, etc for solar gain)
· Two 3x6 casement. One east and one west
· One 6x2 picture window in bathroom close to ceiling for natural light
· One 6x4 picture in garage
· Garage door has four lights… 2x1… supposed to be R19.9 Amar door???
Doors
· Living area… 60 sq ft between two doors (not picked yet)… but will be fiberglass and mid grade R… Not much glass… R11? To R19? Both doors will NOT lead to outdoors. One will go into breezeway and the other into the garage.
· Breezeway…. 40sq ft of steel door. 6.5R? 2 3x6
· Garage door… 16wx12h… R19.9
· Garage man door 1 4x7 steel door.. 6,5R?
Insulation:
2LB Closed Cell spray foam… 4” walls and 6” ceiling on all.
May add fiberglass batts on top of foam in living area?
Building exterior:
Right now it’s all steel construction… may go with 2x6 framed conventional wood but w/same galvalume metal exterior and roof
[update: all wood building w/metal exterior]