Btu/hr/ft2 For Various Floor Layouts

PhotoGuy

So my thirst for RH is still in high gear! Knew nothing coming in but learning much from cruising the web and getting all kinds of info. I know to take everything with a grain of salt that I'm reading so I checking in here when I have questions,

So … along the way I ran into a RH study (LINK HERE) out of Virginia Tech. The list below shows the type of layout utilized with the “Btu/hr/ft2” listed at the end.

Joist Space, AL louvers in air cavities, 24" spacing (Ultra-Fin) - 5.6
Joist Space, no heat transfer plates, 8" spacing - 7
Structural plywood with AL facing, 12" spacing (WarmBoard) - 17.5
Thin plywood with AL backing, 7" spacing (Quik-Trak) - 18
Gypsum cement overpour 1 1/2" thick, 8" spacing - 18.5
Expanded PS base with AL plates, 6" spacing (Roth) - 19.1
MDF board with foil face, 8" spacing (ThermalBoard) - 19.5
RAUPANEL 8" spacing - 28
RAUPANEL 6" spacing - 30

Knowing that “WarmBoard” seems to be the Cadillac systems others are judged by, I was surprised to see:
1) How close “Quik-Trak” and “WarmBoard” are in output.
2) That “Raupanel” isn’t mentioned more over “WarmBoard.”

Your thoughts appreciated!

Ironman

Interesting study. And, I suspect very accurate ( we Hokies are known for that).
What water temps were used? Can you post a link?

PhotoGuy

Oops ... thought I did. Now added above. Or ..... HERE

bmwpowere36m3

I thought btus/sqft was based on floor surface vs. air temp... The big variable being supply temp needed to drive those btus thru the flooring material.

Gordy

You have to remember, and think about how each "system" is installed. WB eliminates some new construction steps when implemented.

1. the cost of sub floor material is deducted from the cost of the WB material. Your not using both.
2. The labor costs to lay conventional sub flooring, and then lay an alternate panel system is decreased by the use of WB. all though labor is going to be a little more to lay down the WB verses regular sub floor it would be far less than doing it the other way....basically twice.

Some of the products above are for remodel, or after thought radiant implementation into construction.

Gypcrete requires some strucutural enhancement to carry the extra loading for the weight of the gypcrete.

Finally a lot has to do with cost. Some people THINK they can get away with spending less, and still have the most benefit radiant has to offer. Sadly to find out you will never get a system that is efficient,comfortable, for cheap all though some would try, and have a customer believe that.

There are diminishing returns on dollars spent to ROI. How much will be gained in efficiency, and output going from 12' to 8" to 6" centers on tubing lay out. I think WB has that figured out as to why they maintain their 12" oc layout with their system. That being said some of it is structural integrity of the panel itself, The manufacturing process of tighter center grooves along with making the aluminum form to that lay out could be challenging. This all would add more cost to the panels.

Gordy

bmwpowere36m3 said:

I thought btus/sqft was based on floor surface vs. air temp... The big variable being supply temp needed to drive those btus thru the flooring material.

Thats why when ever possible keep the radiant on top.

Most under floor methods, are for remodel jobs where build up is not an option, or someone thinks they will get over the top performance for under the floor cost. Not so. The less r value between the radiant, and the room, the lower the water temps, and/or the higher the output.

Sometimes under floor is enough to off set the loads in low load scenerios.

hot_rod

I am a big fan of the Warmboard system. In addition to a nice HX surface across the entire sheet, it provided one heck of a nailing substrate for hardwood, cement board, or what ever the final coverings are. If the joists are sized appropriately it gives you a rock solid floor with virtually no flexing, very close to a concrete floor in that respect. If there is one ares I'd improve it would be tighter tube spacing.


I like the Roth panels for that tight tube spacing, and still the entire aluminum surface.


My next project will be all 6" OC tube spacing. the goal is not just very even temperature gradient across the surface, even on quick startup and short run cycles, but it allows the lowest possible supply temperatures.

With todays low loads and wide assortment of on-top, or below the floor products we should be able to heat spaces with 120°F or even 100°F temperatures, with dry systems. Tight tube spacings is one of the keys to that end.

The low, low temperatures allow for very high efficiencies from condensing boilers, but also allow for high COP from heat pumps, and allow solar input even in the coldest climates we have, top of Minnesota for example. with a typical plate style solar collector 100- 120 is very do-able in severe climate zones, when the sun shines.

Take a look at some of the "cheat sheets" we put in this issue of Idronics showing how tighter tube spacing and lower AWT relate.
to heat output and heat emitter selections.


http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_6_0.pdf

Gordy

I agree hot rod tighter tube spacing is huge. As you say it opens doors to heat sources that may not be usable in higher temp required layouts.

The difference being only 10-20* can be huge in opening those doors. Especially at design conditions.

Rich_49

Photo ,
Maybe we could shed some light on the comparison which you mention above and why Warmboard and Quiktrak ( I am a Uponor guy) should not be mentioned in the same sentence .

A three sq ft area in a Warmbord house would contain 4 lineal feet of tubing . The same three sq ft area in a Quiktrak would contain 6 lineal feet . So in a 2,000 sq ft house we could say that you would require 1 1/2 xs the tubing . This tells me as I always knew that Quiktrak is not particularly EFFECTIVE .
Besides using 1 1/2 xs the tubing that tubing is 5/16" as opposed to 1/2" which would require you add more mechanical energy to pump through . this would increase your electric usage even though none system recommends a 10* Delta while the other recommends a 20* Delta . The Quiktrak is slower to respond being that the aluminum is at the bottom . You can also see a comparison here , http://www.warmboard.com/media/144 . lease take into account that the video was performed disregarding Uponor or Warmboards' recommended flow rate since it clearly states that they were done using identical flow rates .
Quiktrak will require shorter loop lengths to keep head in line although it will still be higher than an average 1/2" tubing system . This will increase the number of loops , manifold outlets , fittings . All of this costs money .
In the end , Quiktrak is specified by myself only when it will be more efficient than joist trak style products and only in areas where height is an extreme concern .
Hope this helps you understand how much goes into specifying one product as opposed to another and why we make the recommendations we do while customers have done much research and want what they want .
As far as Warmboard goes , I stand by this and have spoken to Terry Alsberg regarding the spacing . Warmboard is by far the best 12" spaced product there is , PERIOD . When designing though we may find that we really need 8" spacing and although Warmboard outperforms many other tighter spaced pre manufactured panel systems there are products that will shine brighter tha Warmboard when all things are considered . I , like Bob ( Hot Rod ) have spoken to Mr . Alsberg about making Warmboard with a 9" spacing . This may be not possible though with the structural product without increasing the thickness of the board for structural reasons . i have seen carpenters perform installs where there was a bit of bounce because the tubing ran parallel with the floor joists over long spans .

PhotoGuy

Ha! You guys all are starting to make much more sense! Thanks much for the detailed answers.

I'm actually starting to get it more ..... I know, a very dangerous thing!

SWEI

hot rod said:

I am a big fan of the Warmboard system.
...
If there is one area I'd improve it would be tighter tube spacing.

That (and the price.) It's a great product, but the total installed cost of similar-performing assemblies (including subfloor) comes in at almost 50% less around here.

My next project will be all 6" OC tube spacing. the goal is not just very even temperature gradient across the surface, even on quick startup and short run cycles, but it allows the lowest possible supply temperatures.

With todays low loads and wide assortment of on-top, or below the floor products we should be able to heat spaces with 120°F or even 100°F temperatures, with dry systems. Tight tube spacings is one of the keys to that end.

To my mind, the freedom to vary tube spacings as needed in order to achieve optimal system balance is critical. It's quite normal for us to use three or four different tube spacings in a single house. The result is a system that heats every room evenly with a single water temperature and needs very little balancing.

hot_rod

SWEI said:

hot rod said:

I am a big fan of the Warmboard system.
...
If there is one area I'd improve it would be tighter tube spacing.

That (and the price.) It's a great product, but the total installed cost of similar-performing assemblies (including subfloor) comes in at almost 50% less around here.

My next project will be all 6" OC tube spacing. the goal is not just very even temperature gradient across the surface, even on quick startup and short run cycles, but it allows the lowest possible supply temperatures.

With todays low loads and wide assortment of on-top, or below the floor products we should be able to heat spaces with 120°F or even 100°F temperatures, with dry systems. Tight tube spacings is one of the keys to that end.

To my mind, the freedom to vary tube spacings as needed in order to achieve optimal system balance is critical. It's quite normal for us to use three or four different tube spacings in a single house. The result is a system that heats every room evenly with a single water temperature and needs very little balancing.


When you say system balance are you referring to tube spacing adjustments so all zones use the same temperature fluid. The spacing regulates the output?

The tighter spacing really minimizes striping in the floor. In bathrooms or any tile surface you will feel a big difference between 6 and 12" spacing.

Carpet, as much as I hate it over radiant floors, really does help spread and minimize that stripping effect.

Perhaps the best system for even heat spread across the entire floor was the very early RadiantRoll. It was an EPDM mat system, very small tube. Also the tubes were counterflow design, supply next to return, so the average "mean" temperature was very consistent.

No doubt there are loads that we see more and more often in the low teens or single digits, perhaps that load could be covered with very low temperatures and 12" spacing. With a concrete slab that wide spacing will be noticed as you walk barefooted across the room.

But at some point for those very low loads, radiant floors is probably no longer a good match?

Gordy

That's where radiant ceilings come in. You can vary the coverage area to offset losses, and not worry about the foot comfort effects.

PhotoGuy

So I was doing some more reading about RH ( WAIT - I haven't stopped for three days now!). I found a thread (HERE) from 2008 on this board that discusses the report in my original question. Pretty much they went over it then and (along with some same responses here) debunked the report.

SWEI

hot rod said:

SWEI said:

To my mind, the freedom to vary tube spacings as needed in order to achieve optimal system balance is critical. It's quite normal for us to use three or four different tube spacings in a single house. The result is a system that heats every room evenly with a single water temperature and needs very little balancing.

When you say system balance are you referring to tube spacing adjustments so all zones use the same temperature fluid. The spacing regulates the output?

The tighter spacing really minimizes striping in the floor. In bathrooms or any tile surface you will feel a big difference between 6 and 12" spacing.

There is a small increase in output with tighter tube spacing. We adjust tube spacings as needed to closely match required water temps. Bathrooms almost always end up at 6" thanks to the limited floor space available for heating and the setting of a higher indoor design temp.

at some point for those very low loads, radiant floors is probably no longer a good match?

Absolutely, but most GC's just can't seem to get the "warm floor" meme out of their heads. That and the cost delta for ceiling mounted plates.