randomhitz
Registered Users
Posts:10
 |
| 05/20/2008 12:43 AM |
|
Hi Everyone--thanks so much for the wonderful info shared here. I'm new here, been studying
hydronic systems for a while. Built my own baseboard system that has run without problems except for one valve replacement for 13 years. I want to do a saltillo tile over slab install, and I want to know if placing tubes closer to the top surface of the slab would be advantageous with tile above. Please let me know if I have left out critical information. I have many questions but this particular question is specifically about tubing placement in the slab.
Randy
|
|
|
|
|
|
|
whitealan
Registered Users
Posts:12
|
| 05/20/2008 8:32 PM |
|
There are two approaches to your problem over slab. One is if you want “thermal mass”. If so you probably know that you have to heat the whole slab, it is a big “mass” and takes hours to warm 1°F, but I also will take long hours to cool down. In this case the piping can be in the slab’s middle but it will be difficult to actually keep it in the middle when you start pouring the cement. Those plex tubes may very well end up at the bottom of the slab and you will be heating the soil and the slab 50-50. Better, if you align those tubes to be 1” inside the slab from the top, but also the problem will be when you start pouring cement and who knows where the tubing will end up settling.
If you start from scratch it may take a couple of days to reach the desired temperature. If you overshoot or undershoot you will have to wait and be uncomfortable a while.
If you want thermal mass for indoor comfort, the “mass” will take a while to warm up and will act as “cooling” source for a while. You may even run cooled water and have it to act as “cooling” but it is no comfortable due to the fact you’ll “have cold feet and hot heads”. It is a big failure to use it for summer cooling. It is very good for heating only and "old hat" in the US.
The building’s envelope is of the utmost importance. You may have to insulate the slabs sides, the sides facing outdoors and that is a thermal bridge and therefore loosing (winter) and gaining (summer) heat if you like it or not. It cost you money to compensate for any thermal bridge heat loss. If you live in a real cruel winter area you also will be well advised to insulate your slab from the to-be frosted soil. Heat will escape away very well through your floor.
The other approach is not to care for a “big thermal mass” and use the floor only for heating in winter without having to heat the whole slab. In this case it will pay to insulate (for temperature, radon gas, humidity, etc. from the soil) the floor from the slab. There are polyurethane insulating boards or isocianurate (Dow Chemical’s blue board), or other boards, some with tongue and groove connections, rigid and with a “R” value of 6 per inch. Cover the whole floor with that material, tape the joints thoroughly and then prepare the under floor (plywood, membranes, etc.) and then apply the “mortar” for your Saltillo tile in which you can imbed micro capillary tubes were water will run through. This way you only have a much, much smaller mass, just the tile and mortar mass, the floor will warm faster and transport heat to the tile faster and economically.
If you want to learn more about this system visit www.bekausa.com and go through the web site specially click on “slide shows” and “general presentation” where you will see micro capillary tubes applications in Europe. An image is worth a thousand words.
|
|
|
|
|
BillN
Registered Users
Posts:38
|
| 05/21/2008 8:50 AM |
|
I have done many thick and thin slab installations and I do not believe that there is any difference in performance relative to where the tube is in the slab. When I first started, I tied the tubing to the top of the rebar, which put it near the top. Then before construction was finished, a bobcat pushed a stone into a tube because it was too shallow. After that, I put the tubes in the bottom. The procedure that I use is to prepare the subgrade. Compact it and make it nice and flat. Then 2" rigid insulation, a heavy plastic vapor barrier, then 6X6 #10 wire. Lay the tubes out and tie them to the wire. Then put in the re-bar after that, 1/2" 1 ft spacing is what I use. I also use a 1/2" foam border around the perimeter. This will insulate the edge and serve as an expansion joint.
As far as controls goes, I recomend a reset loop. You need to maintain constant circulation with a high mass panel and vary the circulating water temperature based on the outdoor temperature. If you try to control it the same way you control the baseboard you will have a problem.
Cheers! |
|
|
|
|
NRT.Rob
Registered Users
Posts:384
|
| 05/21/2008 10:42 AM |
|
there is a slight performance hit with tubing at the bottom. but, it's small.
Bill, you only use 1/2" at the perimeter? we usually spec 2" There; edge loss is a big deal. |
|
-=Northeast Radiant Technology=-
NRTradiant.com |
|
|
NRT.Rob
Registered Users
Posts:384
|
| 05/21/2008 10:43 AM |
|
| for whitealan, it's pretty hard to think that anything can beat the simplicity and cost factor of simply tubing concrete. Even if you need fancy controls to make it work properly, you're out ahead when you're done. |
|
-=Northeast Radiant Technology=-
NRTradiant.com |
|
|
whitealan
Registered Users
Posts:12
|
| 05/21/2008 12:57 PM |
|
It is true that a simpler system is more economical than a more complicated one, not only at installation time but also as repair or maintenance in the long run. At decision time you have to put ALL the costs on the table and then make a judgment call and live with that decision.
I think that a careful cost analysis is smart and the only way to do that is to ask prices at the moment and not imagine them. It is your money anyway.
|
|
|
|
|
Don Regan
Registered Users
Posts:11
|
| 05/22/2008 7:42 AM |
|
| Have you ever looked at Crete-Heat to simplify your radiant installs? |
|
|
|
|
whitealan
Registered Users
Posts:12
|
| 05/22/2008 11:24 AM |
|
| Crete-Heat as I can see it in their web site is specific for PEX tubing installations. The BEKA USA micro capillary tubes won’t be able to use that product. If you go to www.bekausa.com and then click in “slides shows” and then “general presentation” you will see a lot of pictures of the capillary tubes and how they can be installed. |
|
|
|
|
BillN
Registered Users
Posts:38
|
| 05/24/2008 10:30 AM |
|
Rob, you are right.
In thin (1.5") slabs, I use the 1/2" perimeter insulation because its backed up to a wood plate. For full slabs, I use the 2" for the perimeter.
The problem with the 2" is that there is a big gap to fill. I typically use joint expansion compound made by Sika.
Lately I have been trimming the 2" insulation next the top so that there is only a 1" gap. Its easier to fill.
I checked out the Beka web site. Their setup looks nice, but I bet its alot more expensive then laying down PEX. Smaller tubes in parallel is interesting though. For slabs, I tend to use the 3/8" tubing instead of the 1/2" and run 2 or 3 loops in parallel. This way if a tube ever fails, that loop can be shut off with only a minor hit on capacity. |
|
|
|
|
NRT.Rob
Registered Users
Posts:384
|
| 05/31/2008 1:51 PM |
|
| I've never seen anyone use a perimeter insulation detail for thinslabs, that's pretty cool bill. I hate tapers but as you note, it is a big gap and sometimes you have to do what you have to do. It sure is nice when you get someone who is designing their structure with proper insulation in mind... and sadly, it's pretty rare too. |
|
-=Northeast Radiant Technology=-
NRTradiant.com |
|
|