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Member Posts: 44
I am looking at a design done by a PE and he isn't calculating any net effective floor areas for bedrooms, living rooms, etc.

Simply put, the entire floor is the effective radiant panel, regardless of furniture, etc. Cabinets and other built-ins are accounted for, but other rooms use the full floor surface for design parameters.

I was wondering what kind of "fudge" factor must be involved in order to get accurate data for the design?

Am I being too picky? The good folks at Wirsbo tell me that beds will radiate heat, and implied that tub and shower stalls won't if you install tube under them. I told them that this sounded backwards, as depending on the material of a tub or shower, the energy would transfer and some heat output could be gained. Beds don't radiate, IMO. Small air currents under a taller bed frame might be beneficial, but it ain't radiant energy being distributed, me thinks.

Wirsbo admitted that if you want to be accurate, you can deduct furniture...so how accurate should we be? Beds and other bedroom furniture can reduce radiant panel size by 50% in a heartbeat. I always allow for furniture.

Competing with not-so accurate PE's is not a fun place to live!

• Member Posts: 419
just my \$.02

Michael,

First some questions. Has the PE also accounted for floor covering? That seems most important. Are there multiple zones such that there is a thermostat to control the heat supplied to the rooms (rather than 1 for the house?) Is the system running near the floor temp limit (close to 85F) at design temperature? Does the design call for delta Ts of greater than 15-20F?

Here's the logic behind all the questions. If the system is one or another is running close to a limit, then the percentage of floor loss from furniture will become a factor. If the room is running with plenty of flow and radiation, what I would expect to happen would be that the heat output on other areas of the floor would become slightly higher and that the overall output would drop by less that the covered area ratio. If we make the assumption that the covered area emits no heat, then the mean water temperature for the pipe downstream of the obscured section increases, and with it the heat output.

You then have to deal with the controls, because a room without covered areas will satisfy faster than a room with coverage. How much has a lot to do with the operating design of the system. Thus the question about the size of the zones.

Radiant is actually a fairly forgiving heating design. IMO, the failures come from people choosing to greatly underdrive the floors in an effort to be cheap or simply refusing to consider the possible output of the radiating surfaces vs. load (or both.)

hope this made sense and hepled.

jerry
• Member Posts: 44
Jerry

Thanks for the thoughts, Jerry. I certainly agree with you.

Yeah, we are up against (and over IMO) some limits. He's running 138-degree water in a gypcrete overpour for some areas. No reset on the system side. "Dumb" thermostatic 3-way valve supplying 138-degrees all year long.

Man, don't make me describe the rest of the system. [grin]

Gonna have to scrap this one, I think.

Mike

• I haven't seen a problem with beds or sofas or the like, yet at least. Technically i suppose you could deduct something less than half of their area, assuming convective air transfer can still occur, which is still a substantial amount of output from a radiant panel.

Anything to-the-floor I deduct fully, except tubs. I deduct half a tub's area, typically, assuming that it will receive heat from below but not as effectively as the floor itself.

• Member Posts: 208
Spaces

Any object with an air space between it and the floor will have some radiant transfer and objects in direct contact with the floor will only have conductive transfer. One other consideration would be potential air movement or lack thereof.

So, a bed that is up off of the floor does not need to be deleted from the active floor area but a bed that sits directly on the floor such as the type with the drawers under it does need to be deleted. Bath tubs and showers will provide radiant transfer into the space depending on the surface temperatures that they are allowed to achieve, the method of delivering the heat into the object, air movement under the tub, insulation below, etc.

Call me if you want to discuss your project.

Tim D.
• Member Posts: 44
NRT.Rob

Thanks for the input and past exeperience, NRT.Rob. Much appreciated. I do feel much the same and use the same technique to estimate these things.

I haven't read anything of late saying that the convective transfer in low, long, cabinets is a very high percentage, so if you could point me to some documentation, it would be appreciated. I recall some past articles, but obviously they didn't impress me with the amount I could use to estimate these things.

What about convective currents over carpet as opposed to wood or another hard surface. More output? Does the surface area of the carpet strands come into play (can't see it in my mind, but my mind is rather cluttered).

Michael Ward
• Member Posts: 44
Tim Doran

Thanks, Tim.

I noticed in your program, Quik Trak seems to be the equal or better performer when compared to concrete and lightweight applications.

What do I choose for gypcrete? Obviously, no one in their right mind would choose certain types of lightweight concrete after reading Siggy's book. What type of lightweight does your program model? I couldn't find any information at the website.

Thanks,

Michael Ward

• I've just been working with the knowledge that something like 50% of the heat transfer from the floor comes from air convection (anyone feel free to fine tune that figure if you like). This should be equal regardless of floor surface covering, since that transfer is about warmer air rising from a warm surface, not a smooth surface. Warmer air will rise, somehow, as long as there is a path for it to do so.

With long, low cabinets you are still radiating to the cabinet (warming an object in the room), you still have oblique radiation from the floor under the cabinet out into the room (at an angle) though this is weaker than it would be directly over the panel of course, and any air warmed under the cabinet should be able to rise to some degree. So for these reasons I don't worry too much about objects that are not down to the floor or very close to it.

But it would do you well to ask your clients if they have preferences for those honkin' waterbeds! That bit me once..

• Member Posts: 208
QT/GYP

QT does perform very well comparitively. The key to choosing a poured underlayment from a heating performance standpoint is the K-value or thermal conductivity. I most cases lightweight concrete has better conductivity than gypcrete even with air entrained into it to reduce the weight. We would have to look at specific mixes and brands to be dead accurate.

Tim D.
• Member Posts: 44
QT/GYP

Thanks, Tim.

So what do I use to model gypcrete in the WADS?

What is the K-value of QT?

Since Wirsbo and Siggy seem to really be at odds regarding lightweight concretes, some clarification might be in order.

For example: What exactly is the K-value, etc. of the lightweight you are using in WADS? What about the concrete? Maybe give us a description of the lightweight? The density? What type of aggregates used?

Siggy recommends not using lightweights with a density below 110 lbs/cubic ft.

He says that gypcrete has only a slightly lower thermal conductivity relative to standard concrete, thus it results in slightly less heat output under the same operating conditions. Pages 340-342, Modern Hydronic Heating, 2nd Edition, ISBN 0-7668-1637-0.

The picture I'm getting is that Wirsbo and Siggy are worlds apart. Please help me fill in the gaps, so as to bring this sucker together. What am I missing?

Thanks,

Michael Ward
• Member Posts: 208
K values

ASHRAE lists the thermal conductivity of concrete as .54 btu/h/ft/f and the thermal concuvtivity of gypsum as .25 btu/h/ft/f. With that said, it really depends on the mix when discussing lightweight concrete. If the mix in question has a density of less than 78 lb/ft3 it can be assumed that gypsum would be a better choice. In ADS it seems to assume that the concrete ovepour is normal concrete and that all of the lightweight stuff is sort of averaged out. I have to check with the guys that wrote the program to be certain of the math. I will check it out and post my findings as soon as I have them.

Tim D.
• Member Posts: 44
K values

Thanks, Tim.

I will plod along in another program for the time being. -- Mike
• Member Posts: 208
Design Assistance

I have s tool that I use for my commercial projects that has a lot more variability than most packaged software, including our. Give me a call and we can run you project while you on the line. 952-997-5334 Catch me before 5pm Tuesday as I will be traveling for a while after that.

Tim D.
• Member Posts: 44
Tim--Thanks

Thanks so much, Tim. I really appreciate your efforts.

This is just a residential project with gypcrete. No biggie, although the owner has been working on it for a few years, getting things just right. The PE is using your residential program to design it, which doesn't do gypcrete, I have to surmise. So...

I will pass along the info and maybe he will give you a call.

I will look at some other programs and maybe make some calls to find out about what kind of K-values they are using in their programs.

I've looked at some gypcrete sites as well. As I dig into this, I will drop some information back into this thread if it seems interesting or pertinent.

Seriously, I think you should suggest to your people that a drop-down menu with better control over these K-values would be a great addition to your software. In my neck of the woods, gypcrete rules, and you will be missing out if you can't model it properly.

Thanks, again!

Regards,

Mike
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