ThinFin output

Gordan

Hiya,



I have some questions about ThinFin output. Radiant Engineering has output charts for ThermoFin C, but none for ThinFin. When I called them I was told that I should estimate ThinFin output to be about 12% fewer BTU/ft^2, as this is roughly the reduction in coverage between the two plate types (3.5" vs. 4"), but Viega's ClimateTrak (rebadged ThinFin, from what I heard here) installation manual suggests a drastically reduced output, even adjusting for factors like downward loss and possible differences in ambient temperature (unspecified in the case of Viega's charts; 65 deg. F in ThermoFin chart) and supply temperature (again, Viega doesn't specify whether the "Supply Water Temperature" is really supply - and what's the delta-T - or the average water temperature.) For instance, at .5 R of finished floor above subfloor, the ThermoFin C chart indicates 40 BTU/ft^2 at 120 deg. F average water temperature (90% = 36 BTU/ft^2) and the ClimateTrak chart indicates 15 BTU/ft^2. So, what should I really expect from an 8" on-center application of ThinFin vs. ThermoFin, all other things held equal, and how does that square with what the two manufacturers are saying?



Also, is there any kind of handy formula to estimate output at different spacings? I have a single room which, due to cathedral ceilings, has a higher heat flux requirement than the rest of the house. It's not a huge room, however, so it would be economical to pack three runs of plates per joist bay, for roughly 5.5" on-center spacing. How much of a boost in output could I expect?



Thanks in advance,



Gordan

NRT_Rob

fun stuff

additional plates aren't going to help much.



you have be sure of whether the charts are looking at supply temp or average temp, and what room temperature they are assuming. if the viega chart is supply temp and 70 deg room, that could be 10 degrees of water temp shift by itself... maybe 15.

Gordan

Right you are...

Rob, thank you for chiming in. I know that you use a lot of ThinFin. Would you feel comfortable quantifying the "slight" reduction in output when compared to ThermoFin?



Also, I take back what I said about Viega not specifying the room temperature - it's 68, so that alone would shave 6 BTU/hr ft^2 (going by the rule-of-thumb) from the output. Also, I did call them and the supply temperatures are the actual supply, with 20 deg. F delta-T (who designs for 20 deg. delta-T in a radiant floor?) so the average temperature would be 10 deg. F less. They did provide charts for different spacing in Appendix E (the document I'm looking at is IM-PRCT-0208) but the graphs for 6" and 8" are identical, which looks like an editing error given that they also show output to drop by 5% at 9" o.c., compared to 8" o.c.

CMadatMe

Did You Try

To download the free Viega radiant design software from their web site? You could run the loss via the program with this application and get your anwser.  I use Wirsbo Joist Trak Plates and don't see them being that much different. I ran my dining room 250 sqft. Using plates in bays and a 1.68 R-Value (5/8" sub with a 3/4" oak) I get a water temp of 135, 22 btus sqft.  Heat loss is high due to crawl space underneath, 12' ceils, skylights, slider, 2 3x5's. Changing the R-value to .5 The water temp drops to 109, 22btu's a sqft. I used 68 as my setpoint 0 degrees outside and a 10 degree delta-t, 8" on center. Using a 20 the temps rise 5 degrees but the btu output per sqft doesn't change.

Gordan

Radiant Wizard

Chris, thanks for the suggestion - I meant to try that. I downloaded the free design program and, unfortunately, it's worth every penny - to be generous. According to its parameters, sheet aluminum plates are just as good as the extruded ClimateTrak - the supply water temperature doesn't change no matter which one I choose. I yi yi.



Basically, my design heat output (10 outside, 68 inside) for that room needs to be 31 BTU/hr-ft^2. Everywhere else I'm comfortably in the high teens (downstairs) - low twenties (upstairs, radiant ceiling) zone, but this room has a small footprint and a cathedral ceiling. I'll probably wind up just using ThermoFin and supplementing with small areas of radiant wall, such as right under the windows, where the enclosed convectors presently are. (Obviously, insulate the heck out of the cavity behind the panel.)

NRT_Rob

heh

we design for 20 deg DT in radiant floor standard. works great.



We basically fudge thermofin output as requiring 5 degrees lower water temperature than thinfin. for thinfin we use wirsbo's joist trak chart which is likely similar to viega's.



6" o.c. spacing doesn't help you much so I don't think it's a typo. as you widen it out you lose output quickly but if you already achieve "heat saturation" at 8" o.c. more plates don't really help.

Gordan

Thanks again!

Looks like I'm really better off with more area for the radiant panel... and the wall will provide more output with the same plates and tubing and water temperature, anyway! Less cruft for heat to work its way through. Thanks for the reality check!