Suspended tube vs. plates (SE)

Steve Ebels

OK guys, don't get all wrathy with me before you hear this all the way through. I'm doing a design for a log home using panel rads as the primary heat source in each room. The couple doesn't have the budget to do infloor type radiant so that can't be considered. The problem I've run into is that the missus doesn't like the "look" of the panel rads up against the log wall in the great room. Heat loss in the area is a tad over 37 btu's per sq ft.

The solution I would like to propose to them is to use fewer and discreetly located rads as the primary heat source and supplement what we can't get out of the rads with a suspended tube setup under the whole floor of that room. This is primarily due to cost. I have never used suspended tube (always plates). My thinking is that with careful sizing of the rads, I can match the required water temp for the suspended tube to the water temp of the rads. This would eliminate the need for a mixing valve, let them keep the critical wall area free of radiators and give them the required btu output.
The suspended tube would be controlled by a wall stat/ flooor sensor combo ( RTI p/n 4018) that will kick on the pump on air temp drop and limit the floor temp so as not to ruin the 3/4" oak they are installing.


Looking for anything you think I'm overlooking with this design.

Thanks in advance as always.

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hr

What about

Putting the suspended tube on the first stage maybe getting 10-15 BTUs per square foot and have the panels come on when needed. The new tekmar 511 could do all this for you. Two stage for the floor/ panels and you can set a not to exceed temperature for the floor using the floor sensor. Probably a good portion of the heating season could be handled by the floor alone.

While not all agree with suspended tube, there are some applications where it is acceptable, in my opinion.

Log homes are a challange, and I can understand why log owners don't want panels or baseboard everywhere.
hot rod

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Alan(CaliforniaRadiant)Forbes

I don't see

where the money savings is. Radiators/suspended tube/2-stage thermostats sounds like more work than staple-up with plates.

Don't fall into the trap of trying to save money for the owners by making your job ten times harder.

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hr

In Steves case, Alan

I'm not convinced plates would get him to the required 37 BTU/ sq. ft. Dale's Thermofin sheets show 31 BTU at 160 degree supply under plywood and hardwood (1-1/2") with 88 degree surface temp 9" o.c.

With that in mind why not give them the unmatched comfort of warm floors, with the least amount of panel radiators. If they are concerned about the "look" of panel radiators all along the beautiful log walls, then the mix of the two MAY be a good resolve. At over $1.00 per foot for aluminum tracks, I'll bet the numbers would come real close.

Balance the owners "wants" with the system design, that should be part of the goal also.

hot rod

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Steve Ebels

You're right

Hot Rod, The "look" is the big thing. After that is the cost which is way less with a couple rads and suspended tube than with plates. Also, even with plates the floor would be running hotter than I want to see it in order to hit that btu/ sq. ft. target. I appreciate what Alan is saying though also. Sometime it's easy to fall into the trap of over-complexity whilst trying to defy the laws of physics. (I always come up on the short end of the stick when I do that)

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Duncan_2

A non-wrathy idea

It sounds like you're thinking of running a separate piping run for rads and for suspended, each with it's own thermostat.

Another possibility is to run them in series, and divert water away from the floor loop when joist space temperature gets too hot, and use radiators only, until the floor loops cool down.

One room thermostat, a diverter valve and a simple air temperature sensor for the floor temp.

The drawing below shows radiator heat only if the valve fails closed (figured that's a safe way to go). If the floor approaches the high limit, the diverter valve swings to the "A" position and you get radiator heat only. If the floor is below high limit, both rads and floor get heat.

Floor heat is run piped in AFTER the rads have dumped most of the heat (if you use a small enough circulator), to maximize floor on time.

Dunno if this fits in with your plan, I just thought one room tstat, and piping the floor AFTER the rads dumped most of the heat might be a workable idea.

Wrathy, huh? *chuckle*

Mike Kraft

Mr Able Ebel............

Try this link and let me know what you think:)

http://www.reggioregister.com/

cheese..........I've used em in a post and beam.They love em!

Steve Ebels

Thanks for the input

Everyone! It's like having a group of experts at your beck and call, 24/7. After reading all your posts I thiink that I'm going to set it up as folloows.

The design heat loss of the room is 19,400 btu's. Given the floor area I have to work with I can get about 9,500 from the floor. The balance will come from rads in the room that can be placed in discreet locations. The max water temp before exceeding a floor temp of 80* (as high as I like to go with hardwood) is 175-180* (good for 22 btu's per ft at r-value of 1.5). I'm going to put TRV's on the rads, let them just pick up the slack when the floor is not able to carry the load. The rads and the floor will all be on a common manifold with the floor running "wild". The whole system is going to be run on a Vitodens which gives me full reset and WWSD. The rads can be sized to hit design output at my target water temp for the whole building so there will be no mixing or lower water temp required. ( Nice what a condensing boiler can do for you). All the rest of the rads in the building will be piped home run style back to a common manifold also.

Make any sense?

Thanks again

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Mike T., Swampeast MO

Just what I've done except at lower temps

and with more massive emission devices. I know the principle is sound but...

I had it easy because massive devices operating at low temperatures behave nearly linearly through their range of supply temperature operation. A simple mechanical reset with its flat reset curve was just fine.

With a suspended system, the prospect of linear radiation surface temperature change with changing supply temperature is dead. I'd try to select or set a curve similar to the below to start testing. Your goal is to set a "wild" temp that keeps the surface of the floor comfortable to the touch--never overheating--while the TRVs take up the slack. If you meet these conditions, you have no need for further control of the radiant--big savings in cost.

My minimum sizing standard for the panel rads would be sufficient to keep the space at 50 degrees at design temperature with 150 average supply temp.

If you want to know why I believe this is an appropriate guess of the curve shape for "wildly" controlled suspended radiant floor warming ask and I'll try to keep it short.

Mark Eatherton1

OK, I'll bite....

I want to know why you believe this is an appropriate guess of the curve shape for "wildly" controlled suspended radiant floor warming, and keep it short...

I fired my radiant walls project at the Habitat for Insanity today. It had actually been running since I purged it, I just hadn't been back there in a while. It was COMFY!!

The bigger the surface, the lower the maximum required temperature.

Got solar?

I sat there in awe today and watched as the electrical meter spun backwards from the roof mounted Photo Voltaic storageless system.

This home will probably win the award for the most energy efficient home in the state of Colorado built in the last year.

Anyway, it was cool to see the walls running at an idle at 75 degrees F.

Course the MRT differential was only 6 degrees, and the MRT was around 68 degrees F in the bed rooms and 70 in the common living spaces. This systems is going to be awesome. I may take some of the funds from the local RPA and donate a solar/hydronic interface. Might as well make it THE greatest energy efficiency home in the world...

Ok, Ok, I'm cutting it short, now its your turn.

ME

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Mike T., Swampeast MO

Sorry for delay

Ramp up...Maintain...Compensate

Initial steep curve gets the supply temperature high enough for minimum useful floor-warming temp from the suspended floor system. With steady outside temp in this zone, the floors will be providing most of the heat requirement. The TRVs will be nearly shut (plenty of reserve).

Relatively flat zone is where the TRVs open and provide the balance of the heat requirement. That initial rampup gave them plenty of headroom. The panel rads will supply more and more of the heat requirement with the floor remaining relatively constant in temp. The panel rads will be operating relatively cool with a high proportion of radiant output. This should be the most efficient zone of operation for the system. A second purpose of this is to prevent floor temp over-shoot as this outside temp range represents the "transition" zone in many climates. The floor will be fooled into thinking that the outside temp has remained nearly steady. The TRVs have taken up the slack and will respond quickly to rising outside temp.

The second steeper curve is there for two reasons. First, the headroom of the initial boost will become exhausted. A greater increase in supply temp will be required. Second, as the temp of the panels increases, so does their proportion of convective output. As convective currents reinforce themselves, more and more heat is drawn from the floor. Ideally this part of the curve will allow a gradual increase in the floor temp with dropping outside temp.

Please offer criticism!

Mike T., Swampeast MO

MRT???

Mean Reference Temperature?

tcutler

3 way

Why not use a 3 way mixing valve for the in floor manually set. The mixing valve will move up and down following the high temp curve and act as a high limit for the floor. Set the heating curve on the Vitoden for the rads. If the heating curve is set correctly the customer achieves the highest comfort level through constant circulation. This removes any additional wall thermostats and controls. You still have thermostatic valves on the rads to prevent over heating.

The best part is the floor is allways warm.

Have you installed the Vitoden before? (You need to put an ear on the cover to hear it run) It's Awsome!!!!!!!!!!!!!!!

Unknown

Comfort is second to none!

sounds like you need a set-point control for the floor for conditioning. Use the panel radiators to supplement on the really cold days. Try to keep it simple. Don't go crazy! I think Wirsbo's Advantage Program offers financing.

Make sure your customer realizes that comfort is the most important issue. the system needs to be asthetically (sp?) pleasing as well. Log cabins were often heated by fireplaces and wood burning stoves. A lot of panel radiation will only clutter things up and make the home look out of place.

DanHolohan

MRT

Mean Radiant Temperature

Steve Ebels

Job update

I met with Tom and Juanita for about 4 hours this evening and we agreed to turn the whole project into an experiment. It's going to go in like this.

The basic premise is that the floor will never be able to supply the heat needed regardless of the outdoor air temp because we are resetting the water temp. The rads and the floor will therefore always be "on".
We're going to do about 1,000 out of a total of 1,350 sq ft on the main floor with tube suspended under the floor. This will (on paper anyhow) give us enough btu's to eliminate the rads she doesn't want in the great room. (It really is a great room too, looking over a 180* bend in the river in front of the home). We can then use a total of 5 panel rads in discreet locations for the balance of the heat requirements for that level. I'm going to size the rads so the max water temp needed is 170*. This (according to the info I have) should give me a floor temp of 82* from the underfloor tubing at design temps. We're going to let the floor loop run wild with no control other than the full reset that the Vitodens will provide and whatever curve we plug into it. Constant circulation of course. The trv's on the rads will provide high limit control for the space being heated. The second floor will be all panel rads as well as the finished basement. We are going to keep the floor loops on a seperate manifold from the panel rads in case we have to isolate them and regulate them with a setpoint control if needed. My head tells me we're out on thin ice but my gut tells me it will work. I just need to get the rads sized right so the water temp they need mirrors what the floor temp requirements are. If I hit it right, I'm thinking there will be no need of a limit or mixing device for the floor. If I come up short heatwise we have a couple locations we can hide some additional radiators. If it's running to hot we can dial back the curve on the boiler to throttle the system back. We will know in a couple months how we did.

They are enthusiastic about it to say the least. They really wanted to do radiant floor in at least part of the home if not the whole thing, but had given up on the idea because of budget constraints. (Their insurance company REALLY gave them the shaft when their house burned to the ground last winter.) All they came out of that with was salvaged from the fireproof gun safe. They kept valuable papers, photo's, some cash and heirlooms in that. The total insurance check was $23,000 for their house and contents. I feel sorry for them so I'm trying to be creative as I can to help out. Tom (the HO) is going to do as much of the tube work as he can and we will do the boiler piping and other more technical end of things to help defray costs. I'll keep you all posted with progress reports and pics.

Here's to radiant, hydronical, hysterical, wetheaded, field engineering fun.

BTW they initially contacted me to provide ductwork for the Janijunk furnace their GC was telling them to buy. How's that for changing gears??

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Mike T., Swampeast MO

Sizing those panels

will be a bit tricky. I don't think you could--or would even want to--exactly mirror their temperature requirement with the suspended.

The TRVs will take care of any over-supply by shutting somewhat--I've also found that wide-open TRVs (at least Danfoss) make a very slight rushing noise like a distant toilet.

At all temperatures below design, you want some excess BTUs available to the TRVs. Since the floor will be running constantly (or very nearly so) it offers no control opportunity.

Without some excess capacity reserve at the TRVs, the temperature response would be extremely sluggish.

If you can determine (or someone can supply) the surface temperature of a suspended system of similar construction at a MUCH warmer outside temp and steady supply temp, your job will be a lot easier. Barring the actual data, I believe the website of [had a brain fart and can't remember the company name but the electronic reset company that's very popular--hate those--Tekmar] shows lots of graphs of supply temperatures for different systems. You might find inspiration there.

ross

did you consider...

radiant ceiling panels?

Steve Ebels

Mike

Either A: You are a really nice guy trying to help me out or

B: You realize I am way off the deep end here and are trying to get me back on the straight and narrow road of hydronic bliss or

C: You're just as nuts about this stuff as I am.

In any case, thanks for all the input. Good point on the rad sizing. I can understand why the rads should be oversized to provide a cushion and a little faster pickup. I haven't had any problems with TRV's making noise. (Oventrop exclusively) The nice thing about TRV's is the throttling effect on heat output. They're never really off all the way. Nice even heat.

I have a chart from RTI that gives floor temps for suspended applications that I'm attaching to this post. See what you think of it. I'm looking to hit the 20 btu/ft mark at design temp. (-10*) With the outdoor reset on the boiler, the floor output should vary pretty much on the curve of the boiler which will match the 3rd column from the right on the chart.

Loops under the floor are going to be kept to 250' or less to insure even temp over the whole surface.

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hr

Wondering about a condensing

heat source. Seems that it will be out of the condensing mode much of the time if you need 172 at design. Maybe a cast iron would be a better and less expensive heat source?

hot rod

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Mike T., Swampeast MO

Guess I'm

A + C

Am heading to happy hour and probably won't be back until early tomorrow morning. Will study the attachment then.

Steve Ebels

Good thought

I design for -10* but 80% of our winter is between 15 to 25*. Most of the time the boiler is going to be at 150-155 or less. The Vitodens hits 94% plus at standard AFUE test temps so I think it's worth the extra bucks. It will also be firing an indirect tank all year so less mass will be a plus.

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hr

My MZ

in my shop ran 92-94% on my analyzer up until I hit about 140, at 150 it would run around 87-88%. I'd be curious to see that Vitoden run 94% at 150 and above Show us some analyzer printouts when she's up and running.

hot rod

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Mike T., Swampeast MO

Damn those temps are high...

But I think you can still do this (warm the floors, keep return temp at boiler in condensing mode near your 80th percentile, ALL with no control of the floors beyond the reset).

That is IF resets can be reset they way I'm talking about...

NOTE FIRST: There is a GLARING error in this graph. 3 rows up and 4th from left it has 129 degrees--IMPOSSIBLE given the rest of the data. I believe it should be 139. Hate to say it but such a terrific error makes me consider the entire thing suspect....

Here goes:

Work with your most troublesome room (the great room).

Calculate heat loss at 55 degrees--if my guess is right it's going to be around 5,000. Set your supply temp at this point to about 120 degrees. You should be able to deliver damned near all (90+ %) of this requirement via the floor alone if the graph is near correct.

There will be a trade-off if the outside temp fluctuates around this temp--it will take hours for the floor to reach temp--but luckily you have the panel rads to provide quick comfort.

The STEEP dropoff in reset below this point is important!!!

Now jump to near your 80th percentile temp--say 20 degrees. Use a 1/1 reset ratio between these points. Your supply temp will now be 155 degrees. With a 15 degree delta t, your return is at the condensing threshold. Heat loss has increased to around 16,000. The floor output has increased only slightly but the temperature is such that it could NEVER be called "cold."

SIZE THE PANEL RAD(S) TO DELIVER 11,000 AT 155 SUPPLY--ABSOLUTE MINIMUM. This is the point where the panel "headroom" is exhausted. Note that I did not consider the increase in output of the floor--it's not much in this range and it still gives a bit of play. That thing about the tendency to oversize often overwhelming the sex drive is only half true--it's oversized because of the sex drive...

From that point on, use a reset ratio that gives you 170 degrees or so at design. As I said before, it's getting damned cold outside... Warmer floors will be welcome and there's still headroom for the panels. If it's anything like here those cold time often occur with wind and in a log home...

Again, please criticize. It can't be so simple as Dan telling me to "imagineer!"

Mike T., Swampeast MO

Why it's NOT \"B\"

I'm trying copper inside of an oversized garden hose embeded in a shower mud base TO KEEP IT SIMPLE.

Earthfire

design

You stated that, If I read correctly , design out door is -10 deg. with a 55 deg indor setpoint, 80% of outdoor temp is 15- 25 deg outdoor . If HO turns up thermostat to 70 deg. (As people age they need more heat) would't that shift your curve very close to max with little reserve for that other 20% of below 10 Deg. temps. Also I would try to go with a radiant slab in that finished basement instead of the panel radiators ( Lower water temps for same btu's) more even comfort . With the probable shift in setpoint temp. in the home you may not get the efficency that you expect out of the Vitodens . Save a couple of dollars on the heat source and put them in the rad slab in the basement. If the rest of the house can't keep up at -10deg. with 70 deg.setpoint at least that basement will be cozy and they won't be talking nasty about you when they are 70. This and a dollar will buy you a cup of coffe .JMHO

Bill Clinton

wonder what would happen

if you put four passes of tube in a joist bay, effectively 4" oc. I know it wouldn't double output, but, how much improvement might one expect?

Hey, guys, I'm just wondering. No need to insult my ancestry over it!

Mike T., Swampeast MO

PROBLEM WITH ABOVE

I knew I should have stayed away to do this early in the morning when I'm at my best. Woke up thinking, "it might run out of heat near design temp!"

If you design for -10, the reset ratio from 20 degrees to this point would be too shallow.

Solution: use a .75 reset ratio in the middle. That will put the supply at about 145 at 20 degrees outside. THE PANEL(S) MUST NOW BE SIZED TO DELIVER 11,000 at 145 SUPPLY--MINIMUM.

If the floor temps attained by this scheme don't seem high enough to you at higher outside temps, you can put the initial boost temp a bit higher and flatten the middle more--prudence tells me not to go below .5 reset ratio. Just don't forget to recalculate everything else.

Steve Ebels

Heat loss numbers and other thoughts/questions

Here are the final heat loss numbers at various temps. We finally got a few construction details hammered out.

45*=9,159

35=12,430

25=15,701

15=18,972

5=22,243

-5=25,515

I'm figuring r-11 for the sidewalls of the home which are 12" diameter pine. Sound right???

The roof system is calculated at R-51. 12" of foam plus 1" of cedar tongue and groove cieling and 3/4" osb roof deck.
My heat loss program doesn't allow actual r-value inputs so I used the next one closest, R-44. Also the program is based on manual J and is not a true radiant calculation so I think the numbers are a little high.

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hr

It's the infiltration number

that will kick your butt with some log and timber frame construction. I have found round logs to be among the worse. Just not much of an R value where the round logs meet. They may be tight and look good right after construction and chinking. Years later as they dry and shrink it is not unusual to see cracks open large enough to stick your hand in! Some you could see daylight through

Square kiln dried log or round milled on two sides to provide a better "gasket" between the logs do much better. Still no match for stick frame and tyvek wrap.

I've found the round, right out of the forest, logs to be a heating contractors biggest challange. Allow enough fudge factor for changing infiltration with those babies.

hot rod

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Steve Ebels

Infiltration

I used a figure of .8 air changes per hour on the calculation. (inbetween what I would call average and poor) The logs are squared top and bottom with foam pad between and what appears so far to be an excellent chinking job. The chinking material itself is a pliable, very tough material. A crew of Amish log home builders came in and did the log wall and framing construction. The logs themselves are white pine.

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M.D.

LogCabin

I quickly read all the replies you have received and liked some, didn't agree with all.

One product that wasn't mentioned, and that I believe is the solution, was Ultra-Fin. It is a product from B.C. that has proven itself in -17F design conditions with excessive R-Valued floors. It is economical, using louvered fins riveted on 1/2" PEX tubing @ 30" O.C. runs. I have been using Ultra-Fin in W.PA for the last year with lots of jobs working better than Alum.Plates, or Hanging Method. (I've used them all since 1988.) Try their website "ultra-fin.com" They did a log home with 3" Subfloors and it worked! Matt or Malcolm will be glad to talk to you.

Your infiltration factor of .8 air changes is not realistic for a log home, or any tightly construced home, unless there are holes where windows shoould be. I don't care what the design manual says. I use .33 Air changes pretty exclusively.

The only way I can imagine your heatloss being so high per square foot is infiltration and/or high ceilings and/or lots of glass. If you also have high ceilings, the ceiling area will be cooler than the comfort area at the floor which averages the btu's/s.f. to your favor. We could talk about that, it is my opinion.

If there's a lot of glass, I would then add some panel heat with TRVs at the glass areas only, if possible. Two-Stage stats will not let the floor heat work until it is cold enough outside to need more than the panels. They won't have toasty floors until it's really cold outside. Remember, the heatloss at 35-ish outside is about half of what it is at 0-ish outside.

I can't be sure without seeing the actual prints of the home, but I would venture a guess that floor heat alone would heat that house quite effectively. I have put supplemental heat in many projects that never got turned on after the fact. The only jobs I have added supplemental heat, after the fact, were ones that didn't stick to the prints and added glass or skimped on insulation, etc. In all cases the owner agreed to pay for the added heat.