Snowmelt questions

Low-grade

I will be required to replace my sidewalk this summer and would like to include snowmelt capability. As I've read numerous pertinent posts over the last few months, I've been intrigued with the concept, but it has raised a bunch of questions. So - - -

(A.) Are there other fluids avaliable for heat transfer? Obviously water is out but glycol has it's own set of problems (ie; it's tendency to degrade to acetic acid). These troubles seem to be accelerated by high temperatures, therefore if temps are kept below, say 120 degrees (F), will the life of glycol be significantly extended?

(B.) Has anyone used Dow Syltherm (silicone based fluids) in a PEX system? It seems as though a fluid that has the ability to operate in a range of temps as wide as this product along with the general "inertness" of silicone, that it should last a long time if subjected to only 15-125 degrees (F). The viscosity or cost of this product may be prohibitive and I don't know if it will work with PEX. I should need only about 3-4 gallons as this project is fairly small (220sqft) and the heat exchanger can be mounted on the inside of the wall adjoining the slab. Anyone have any thoughts?

(C.) I've been told that PEX can be damaged by direct exposure to sunlight for more than 24 hours, specifically the O2 barrier. Is this no longer a concern with the newer materials or is it something I will need to consider? The question arises because I have some areas of colored/textured concrete that will be poured at a different time than the balance of the slab and it will be difficult to incorporate those areas into a different loop.

(D.) The sidewalk on this corner property is occasionally subjected to loaded trucks jumping the curb and driving over it. My munucipality will not allow me to protect this area with a solid standard (a 10" pipe filled with concrete and sunk in the footers is what I'd like!) so I'm left with making the sidewalk 10-12" thick to hold the weight without cracking. My two questions here are: 1) where do I locate the PEX for the most efficient use of the heat? Still in the bottom of the slab as is common in "normal" snowmelt? Near the top; say down 3"? In the middle? Does this thick slab change the spacing requirements for the tubing? and 2) does anyone have any suggestions for an insulating base as styrene board would compress under truck weight, allowing the concrete to break? I've thought about a slurry of cement, perlite and lightweight stone, but I have no experience with such a concoction. Ideas?

(E.) Is there any advantage to using 3/4" tubing as opposed to 1/2"? Seems the surface area of the larger diameter tube would impart more heat to the concrete. From my research of snowmelt systems, it appears that you want to be able to throw a lot of BTUs at the slab quickly to get past the phase change of the water changing form from solid to liquid and that larger tubing would help achieve that. Am I on the right track here?

(F.) As a volunteer firefighter for 30+ years, I have a good grip conceptually of pumping losses (we call it friction loss) and it appears that in this business it is referred to as "head". But head is a term also referring to elevation change. I'm having trouble differentiating two very closely related concepts. Can anyone refer me to a good explanation of this or explain it in a way that even I can understand?

Thanks in advance for the help from all of you here at the wall. I've only posted here once or twice before but have been lurking for quite a while. BTW - I'm located in south central PA. It is interesting to me how the wallies are from all over the globe.

Bradford

Mad Dog

I'll wait for the snowmelt king to arrive

Oh Mark Eatherton...where are you. Mad Dog

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Nron

Brad where do you live ? tha amount of glycol will depend on the design temp , required for your area , the system can also be treated for ph to keep your system clean and from braking down , yes also the lower boiler temp will help I alvays recomend the vitola large up front cost but when you heat the ground efficence is king for control of long time costs , always insolate under your slab ,they make foam that will not break down under the load Beaver plastics in Canada is one , Sorry dont know about the silicone based fluid . I would like to see what wirsbo has to say , and ask them about exposure to the sun 24 hours wont damage the pipe but if you are worried cover it with a tarp . keep asking questions , till you get your answers
Nron

Mark Eatherton1

Answers...

Sorry for the late reply. I went and watched the Rockies bounce the D-Backs on thier ears 14-4. Thanks Dennis!

A. Stick with proven fluids, and maintain them. Not that hard to do. Check it annualy and buffer as needed. At the typical opeerating (less than 140 F) range that you will be in, and the exposure time, your glycol will last for a LONG time.

B. Your thoughts about the viscosity of this fluid are correct. It would be like trying to push mortar through the lines when cold. See A.

C. I think its capable of handling 30 days if I'm not mistaken, but its somewhat moot anyway, because you will be required to maintain the fluid, which means it could have been installed without an 02 barrier... Your call.

D.1 The closer you keep the tube to the melting surface, the less time it will take to get the surface to melting temperature. I wouldn't go closer than 2" of the surface.

D.2 I've done truck loading docks before with 6" cement, #3 rebar at 12" X 9" O.C. and 25 PSI foam below that with no problem. Ran it by an structural engineer on the project, and he said the insulation was capable of withstanding more PSI than the soil below it. If in doubt, you could use an even higher density insulation. Foamular 250 = 25 PSI, = 3,600 PSF.

E. 3/4" would put out more heat than 1/2", however... you would be hard pressed to install it at 9" on center. Use 5/8", 9" O.C. and you'll be cookin'. Figure on about 150 btuH per square foot .

F. Friction loss and operating head are one in the same. Go to www.hydronicpros.com and down load his free demo software. You can use it to size your pump. If that fails, come back here and we can use his professional software to do the sizing for you. His demo software is limited in breadth and scope.

Let us know how your project turns out.

Good Luck

ME

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Low-grade

Nron - I live in southcentral PA Lancaster County to be more precise. If you're on the bus trip to Burnham tomorrow, wave to me as you go by. My work place is between two Burnham plants! LOL
Design temp and atmospheric operating temps for this system are not commonly the same. I will mix the glycol for 20-30 degrees below zero. The lowest ever recorded here was 22 below and believe me, I remember that morning well. Normally when it snows here, temps are 20-30 above zero. It is very rare for it to snow when it's real cold.
The Beaver Plastics tip is interesting.
Thank you for your reply!

Bradford

Low-grade

Mark - I appreciate your reply! Your reply has raised a few questions for me. I'll refer to the lettered paragraphs as I ask.

A)How do you buffer glycol? Is there a specific product for the purpose? How do you then know when it needs replaced?

understood

C) Does o2 migrate through concrete or only into the PEX where it's exposed to air?

D-1) understood

D-2) Is 25 psi the approximate "strength" of standard styrene foam or is 25psi foam a separate and special product? With a front truck tire having a ground pressure of approx 6-8000 PSF, at your figure of 3,600 PSF it seems it would be more than it could bear - however I realize that the concrete would spread the force quite well. So you're saying that it should be quite sufficient?

E) While I understand that your recommendation for 5/8" on 9" centers is probably based on your experience, how do you know that it's more effective or more efficient than say 1/2" on 6" centers? Do you also have a recommendation for maximum loop length or min/max number of loops in only 220sqft?

F) I'll be trying hydronicpros software.

Thanks much for the advice from the "king of snowmelt".

Bradford

Nron_9

the weather

Sorry bradford wont be waving from the bus im in western Canada , i wont be on that bus , but there must be some one in your area who can help. and its looks like your getting good help here , have a good day Nron

Mark Eatherton

More answers...

A. It depends on the glycol manufacturers initial inhibitor package. They will tell you what tests need to be performed and what chemcials need to be added to maintain proper pH.

C. Yes, o2 will permeate through cementitious materials.

E. You could get the same output of 5/8" with 1/2", but the head (pressuredrop) would require a substantually larger pump to overcome the pressure drop.

I'm just doing my job:-)You're welcome.

ME