Radiant Ceiling spacing effects

Robert_H

Our heating retro plan uses cast iron radiators throughout the first floor except in an attached office. The office is 99sqft (inside dimensions) with several layers of old floor over a well insulated crawl space. The perimeter is almost covered with two desks and many filing cabinets leaving little exposure for radiant floor, baseboard or a radiator. So I am looking at radiant ceiling for this room. In the rest of the house the radiators are oversized which should allow lower water temperatures and I don’t want to end up with this room over cycling the boiler if I can avoid it. I’ve done a few layouts in visio and with an 8” spacing I can run about 136’ of tube and with 6” spacing 173’ of tube.

In general does this kind of difference in tube quantity and spacing reduce the water temp requirements enough to make it worth wile? I’m not really concerned about the cost difference of the additional tube and aluminum plates.

If it matters the heat lose in the room is 5564 btuh.

STEVEusaPA

Quick question...

Are you sure about that heat loss number?  Seems high for 99 sq ft.  Are the walls, and ceiling not insulated?  Did you calculate insulating the ceiling before you put the tubing in?  Does this office have 3 exterior walls and/or lots of large windows?

If all of that is correct, then 56 btu/sq feet will require a pretty high water temp, if it's even do-able. 

hot_rod

So a heat load of

5564 btu/ hr with 100 square feet of heat emitter? Then you would need 55.6 btu/ sq. ft. A bit high for a ceiling output. Check your load numbers again.



A rule of thumb about .7 btu/ hr. / sq. ft. for every degree difference between room temperature and average supply temperature in the tube and plates.



So 130° supply - 70 room temperature X .7 = 42 btu/ sq. ft.



I've heard 130- 140° max for supply to sheetrock ceilings. 140° supply, 20°∆T would be an average of 130° supply.

Gordy

1/2 your calcs

I would say even 25 buts a sf may be high.



A side note IF your heat loss is that high, and you spend lots of time at a desk you may notice some shadowing effect. This is where the desk is blocking radiant output to your legs and can be noticeable when ceiling output is high. Not a huge deal, but does happen with higher water temps.



And yes tighter spacing lowers water temps, but there is a point of dinishing returns.

Rich_49

Small rooms

with windows have high loads , too much infiltration . Remember guys the best window is still a SH*&^y wall . This room can't be done from the ceiling .  I would advise using a floor convector from Smiths Environmental or similar .

Robert_H

Heat loss update

First off, I really appreciate your replies.

I’ve tried several programs to run the heat loss Uponor’s, Taco’s FloPro and a spreadsheet created by Andrew Ensminger(Crown).

After your prompting I realized I had not updated the heat loss calcs for the insulation I added and will add to the overhead.

Current heat loss calc is 4110 by Uponor and 4770 by the spreadsheet.  Uponor does something weird (to me) and the heat loss changes as you add a heat source.  



In case anyone is interested here are the the room construction details:

Built early 1900s mill town (budget) construction

99 sqft, three exposed walls, unheated crawlspace.



One wood panel entry door with storm, not used and sealed up pretty well.

Two 2.5*5 Anderson double pane wood windows



8’ ceiling that was originally a vaulted ceiling and a previous owner added the sub ceiling with no insulation and not enough nails in the drywall so it was falling in when I bought the house. The gap between the vaulted ceiling and the roof sheathing is also un-insulated. I have insulated under the vaulted ceiling and the exposed gable end with 2” pink board (R10) and sealed all with expanding foam then drywall over that to seal and as fire barrier.

I have removed the drywall from the sub ceiling and brought the framing to 16” OC (2x4). I plan to insulate with R11 batts or blow in cellulose after I get the heating system installed.  I’m calling the above space insulation R22 in my calculations.



Walls: three exposed, originally with 4” of blown in insulation. However, I had to remove the bead-board on one wall and the insulation had settled a foot or more so I squared the gaps and filled them with R11 and dry walled over.  The other two exposed walls probably have the same settling problem. Knowing I will fix it in a few years I just call the wall insulation R11.



Under space insulation is R19 fiberglass and the crawlspace is not insulated but it is has vapor barrier all around and very well sealed against infiltration



Thanks

Robert

hot_rod

Consider the Roth Panels

it is a foam board with grooves for the tubing and an aluminum layer. it is light and easy to install. get some foam adhesive in a caulk tube, make sure it is foam adhesive Liquid Nail and others will dissolve into the foam.



Then get some grabber screws with large washers. I use the plastic washers from those roofing cap nails, to screw the panels to the ceiling until the adhesive sets.



This would allow you to use the 6" spacing and give you wall to wall aluminum conductor.

Robert_H

re: Roth Panels

Thanks Hot Rod, I'm looking into that. what document did you get those second two images out of?

Robert_H

cool feet

Thanks gordy, I was thinking about the shadowing effect also. It seems that radiant ceiling would be great in bedrooms or living rooms but not places where you spend a lot of time with your feet under a table or desk.  I'm considering heating both the ceiling and the exposed part of the floor as an option.

hot_rod

Idronics 6

is the source of that picture. It is a technical journal on Solar Combi Systems and how to use low temperature emitters with solar thermal.



http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_6_us.pdf



A whole series of these helpful journals are available for free at www.caleffi.us

SWEI

Insulation upgrades

should be on your radar.  Find an applicator who does wet-spray (damp-spray) cellulose and have them replace the R-19 under the floor with that.  You can also blow way more than R-11 up above.  Even under a low-slope attic, you can usually get R-40 or better.

Gordy

ceiling output

My master bedroom is 252 sf. over crawl space r-19, Three exterior walls, lots of glass. 50's construction. 10857 btus heatloss.



Nothing but radiant ceiling 115* supply temps. And it works beautiful. But my ceiling radiant is copper tubing 6" OC embedded in plaster. Is it better than Roth dunno.



Its doable Rich easily.

Rich_49

Robert

  Ran your numbers on Uponor ADS 7.2 as stated above . 

Loops    2

Loop length  152' @ 6" centers

AWT     103*

Surface temp    82.1*

Design Temp Drop  20*

BTUh sq ft    22.6

Total heat load  3387 BTU/hr

Robert_H

ADS file

Interesting Rich, can you email me the ADS file so I can compare how you got your results vs how I got mine?

rhatcher757@snetDOTnet

or attach it here which ever is most convinient

Thanks

Robert

Robert_H

Thanks

thats a lot of good dope!

Robert_H

Rich

Why two loops in that calc? I would think in a small circuit like this one loop would be fine. But there are many things I don't know yet!

Thanks

Robert

Gordy

Loop lengths

If you did one loop it's length would be 300 plus feet. Doable but larger circulator would be needed do to higher head which in turn would increase operating costs.



Also more even temps with shorter loop lengths.

Rich_49

Robert

I sent those files to you but you have not opened them . Why?    Gordy's explanation is dead on .

Robert_H

makes sense!

Thanks Gordy

Robert_H

Because I have not recieved them

First off, thanks for taking the time to help me with this!



When did you send them and how?

I have checked my email and I haven't received anything, yet

I checked my inbox and spam folder.



Did you send them directly to rhatcher757@snetDOTnet  directly or through the "contact this user" feature here at heating Help? Ive been having some problems with that. 

Robert_H

Got them!

Rich, I received two files from you this morning and will look at them later today. Thanks!

Robert