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tomtoth
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Posts:4
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| 06/29/2009 8:51 PM |
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Hello All,
So. I thought I had it all figured out.. I had all my heat calculations done, and a loop design done.. Then I changed track methods. I'm now running thermal board (8" apart, 3/8 pex) this is what I have bought already.. I've attached and linked my loop design for using thermalboard (original was quicktrac, 7" apart 1/2" pex).
I also had planned to install 3/8" engineered hard wood on top of thermalboard (House is rancher on concrete slab).
I'm willing to pay for some assistance but haven't found anyone to help.
Am I going about this all wrong?? I was looking to start putting down thermalboard/wood floor this week.
Any & All suggestions welcomed!
Tom
http://bitteroldsoul.com/1609_4.pdf
The plan was to have dual coil water tank, (1 coil has backup boiler+radiant floor heat)(other coil is closed with 2 panel solar heater) with potable water going thru tank seperate of coils..
Way over my head at the present :( |
Attachment: 1609_4.pdf
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NRT.Rob
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Posts:733
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| 06/29/2009 9:08 PM |
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What kind of per-square-foot heat loads do you have? and where are you?
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-=Northeast Radiant Technology=-
NRTradiant.com |
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tomtoth
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Posts:4
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| 06/29/2009 9:14 PM |
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I'm In Sterling, VA.
I belive my average heat load is about 19.5 btu/hr/ft2.. IF thats then number you're looking for?
http://bitteroldsoul.com/HeatLossDetail.pdf |
Attachment: HeatLossDetail.pdf
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NRT.Rob
Registered Users
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Posts:733
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| 06/29/2009 9:20 PM |
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well, with that load, thermalboard will require some fairly significantly high water temps... not ideal for solar utilization. I don't know how much solar heating you're really trying to do here, but neither quik trak nor thermalboard are particularly ideal for it with your kind of heat loads. maybe, if you add some wall or radiators.
your loop layout looks good though, perhaps a bit conservative, and I'm not sure what you plan is in that hallway to get all those runs in.. slicing up some plywood infill?
what's the plan for the bathrooms, mortar? If so, zone them separately.
Finally, is the slab insulated? |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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tomtoth
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Posts:4
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| 06/29/2009 9:27 PM |
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House was built in 1973, not sure under the concrete, but I do have 2" styrofoam between slab and footer for outside wall.(outside wall looks to be poured footer with block
I thought the loops were a bit conservative too, but shorter loops are easier to heat(I assume).. and I Won't need the high heat temps going into the floor. My other concern was the 20' difference in loops..
For the hallway, you are correct in using some mdf/plywood sleepers/fillers. I was curious to see if the hall would be sauna due to all the ins/outs of the manifold.
So I would get little to no benifit with a solar heating system? |
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NRT.Rob
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Posts:733
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| 06/30/2009 7:31 AM |
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| well, with those really short loops you might have a 110 max water temp here, that's not too bad, and you're doing the right thing with floor coverings. but if 19 is an average... meaning some of your loads are higher than that... then you'll run into "little benefit" territory pretty quick.
edit: if the slab is not insulated downward, Roth panel would have been a much better choice though. at least you got the perimeter though, that's very good and better than most. |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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Dana1
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Advanced Member
Posts:702
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| 06/30/2009 12:39 PM |
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The presumptions in your heat load analysis of over 10.4KBTU/hr infiltration (based on 18mph wind @ 18F outdoor temps) seem overly conservative to me for Richmond, and it's nearly 40% of the design heat load(!). Getting an actual blower-door test and doing some remedial air-sealing can probably cut that factor in half or more for relatively short money. (Real world, I suspect you don't get 18mph wind concurrent with 18F temps anything like 0.5% of the heating season, let alone a 97th percentile condition.)
I'm betting that your real 97th percentile biinned hourly heat load is under 20K, not 27k+ (or could be, with some pressure-envelope improvement tweaks.) Most Manual-J type heat loss calcs run ~25% margins, and knocking 10-15% is generally "safe".
But even with those assumptions, it's hard to get much heating benefit out of solar on a lossy uninsulated slab, even if it's pretty easy to get DHW benefits with solar at somewhat higher temps. (It's a lot easier to insulate a tank than retro-insulate a slab, eh?) And the total solar gain + collector-efficiency peaks in the early summer, not on heating design-day. Solar space heating works best on very-well insulated structures, and at temps well below DHW temps, since the collector efficiency rises with lower collector<-->ambient delta-Ts.
In the one of the Canadian Net Zero Energy experimental houses they run the space heating collectors well below room temp, dumping the heat in to a large low-temp buffer tank. A small heat pump draw the heat out at higher temperatures to drive a coil in the ventilation system. In that case it was necessary in order to keep the temp down for the higher collector-efficiency. Without being able to the solar at 40-50F there wouldn't have been enough space on the entire south face of the building to suck in enough heat to handle the load at the lower collector efficiency. (This approach would be extravagant here- not a recommendation, just an extreme example.) For DHW your collectors need to be running north of 130F, which is 100F+ above your sunny cold-winter day ambient. If you could get your space heating temp requirements down to under 90F or less your collector efficiency will be considerably higher (~30-50% more solar heat gained, for flat panels, 15-25% more from evacuated tubes.) |
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tomtoth
Registered Users
New Member
Posts:4
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| 06/30/2009 5:29 PM |
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I Guess I should Look at my heat loss.. That number could be completly wrong.. I just took the room loss rate in the heat load analysis and averaged them.. Probably very wrong..
I have to assume slab is fairly insulated as it does hold temp fairly well in the winter/summer compared to outside.
I actully already did have a blower door test which pointed out a few issues, but my leakage was very low. (Few old warped windows, which I'm replacing, and leaks to attic from some holes in walls for pumping)
So, if I shortened my loops more(added loops), I could get the water temp to 90%, which in turn would make Solar a benefit? I really appreciate the help!!
If no solar I will have to rethink the whole thing.. the other problem is that I'm a 1600sq foot house.. the WH/HVAC closet is very small and can't be enlarged... |
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Dana1
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Posts:702
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| 07/01/2009 10:13 AM |
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Slabs have significant thermal mass so you won't see huge daily temp variances with them when they're idling in conditioned space whether insulated or not. But when you're using it as the radianting element of your heating system you're raising the temp above the ambient temp, and WAY above the subsoil temp, and the losses to the ground are significantly greater than when the slab is just a floor.
If you're using the solar for both DHW and space heating, it still has to run the collector at the less-efficienct DHW temps no matter what the heating water needs to be, unless you only intend the solar to operate as pre-heat for the DHW. Any decent solar designer should be able to sort that out for you. If you can get the average heating water requirement under 100F it's enough to make a difference. You don't have much space for more mechanicals, but a small indirect-fired HW heater running as a separate zone off your backup boiler in series with the solar-store in series as pre-heat would increase your overall solar fraction by keeping collector & solar storage temps lower.
Also, there's no need to maintain the solar storage at design-day heating water temps using the boiler backup. Smart controls would use outdoor temperature as a rough gauge of the heat load to put a variable lower limit on the heating water temp. (You obviously don't need 130F water to maintain temp when it's 50F outside.) Modulating/condsing boilers come with "outdoor reset" controls built-in, but whether you can run the heating loop & solar store directly in series with boiler in series depends on the flow required and the limits of the boiler, etc. There are probably several system-topologies where you can utilize that function though. What's most optimal depends a lot on the details.
Design-by-forum or by-web-store isn't likely to get the most perfect/best performance, but at least you're asking and thinking more deeply about it now rather than calling for help mid-winter when you're freezing (as has happened on this forum from time to time.) |
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demitry
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Posts:1
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| 07/08/2009 11:28 AM |
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hmmmm....???
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