Snow Melt experts....

MikeJ

How fast can you or should you raise the temperature of your driveway?
If you raise the temperature too fast will it cause concrete to crack?

If you start out with 30 degrees return and three hours later up to 65 is that fast?

Was mention to me that snow/ice sensor 090 is made to protect the concrete.
keeps from raising the temperature too fast.

How fast is to fast?
Does anyone know?

If you good point me to any literature on the subject that would be great
Thanks

@hot_rod thanks for your prior post on the gutter sensor

STEVEusaPA

You might get it up to 65° return water, but do you don't really think you can heat a concrete slab from 30-65° in 3 hours?
Unless you're dumping a tremendous amount of btu's into it, like a hospital heli-pad, designed to melt and dry the slab. But usually they keep their slabs idling.

hot_rod

I wonder that it is possible to shock or crack an outdoor residential Class 1 (80- 125) btu/sq.ft.) snowmelt slab?

ASHRAE indicates Class 2 around 125- 250 btu/ft. typically
Class 3 as 250- 450 btu/ft

Maybe Gordy or some of the concrete chat rooms have data on slab expansion concerns.

Good snow detectors will watch and limit temperature mainly to keep the slab just warm enough to melt. Excessive temperature just increases fuel cost. Good controls can watch ∆T also to prevent over-heating. The best, most accurate control is a well placed tekmar, HBX type SIM detector.

Generally SWT is below 140F to get the job done. Tighter tube spacing can provide lower operating SWT and provide n even melt surface, also. Wind speed can have a big effect on the loads.

Gordy

It’s more about how fast that expansion takes place, and how fast it contracts while cooling than anything. There’s a lot of mass there to suck up those btus.

If proper expansion joints, and contraction cuts were installed when the slab was done shouldn’t be any issues.

Gordy

A lot of it will depend on the slab temp before snow melting starts, and after it’s shut down.

A rough scenario was this last polar vortex. 70 degree temp cycle with out snow melt. Insulated snow melt slabs are not utilizing much of the grounds heat to help that slab. Slabs going to reflect the ambient temps more. Temps were in the 20’s We got considerable snow so the snow melt would have been active if you had one. The temps dropped to -25 . So shut down, and slab cooling would have been brutal.

Gordy

If you want hard documentation there isn’t anything that I have found as to damage, or possible damage to concrete from snow melt systems.

Most times the issues are under performing systems rather than over performing.

Remember you have a slab mass that is in an unconditioned space sucking the btus right out of it from the air / slab delta alone. I highly doubt unless you were to really try by oversizing everything you could create a scenario that would cause damage.

Think of it this way the abuse from plowing, and salting concrete is far more damaging than slab expansion, and contraction. So the snow melt actually saves concrete damage.

Zman

I have seen one staircase that was damaged by thermal stress. There were many cracks in the risers. The tubing was run in the lower assembly, not in the treads like they should be. The supply water temp was 160 degrees.
Unless you have huge BTU/ft ratios, I don't think you will crack a slab if you keep the water temps where they belong <130 degrees. Lower is better both for even melting and longevity.

Gordy

“Properly installed” is the operative words. I think in that case Carl they had to up the temps because the tubing was to deep.

Gordy

On a different perspective stairs usually receive heavy doses of salts. Usually causing them to spall pretty badly, and corrode rebar which bleeds through over time.

GroundUp

Not a technical assertion by any means, but I've been playing with my sidewalk snowmelt for years and abuse the heck out of it TRYING to break it and I can't. It's 1/2" tubing 6" OC at the bottom of a 4" slab run off an outdoor wood boiler with a little 3x8" 20 plate exchanger. 45% Propylene glycol fed with an NRF-22 circ running at 10 psi. No mixing valve on the glycol side, but I can play with the temps by throttling the flow rate of the 180 degree water from the OWB across the plate. Running wide open, it picks up to about 165* on the sidewalk side with a ~20 degree delta and since I'm impatient, I run it there most of the time. The small plate and small/deep tubing allows it to heat up fairly slowly to lessen the thermal shock, but it'll melt a foot of snow in about 6 hours at 10 degrees outside (I just did it the other day). I've been doing this during every snowfall in MN for 4 or 5 years now and there isn't a single crack in the concrete. It's pretty tough to thermal shock a slab IMO, unless you run super hot water like I am with a ton of tubing and very cold ambient air which would raise and lower the slab temp pretty rapidly

Zman

Gordy said:

On a different perspective stairs usually receive heavy doses of salts. Usually causing them to spall pretty badly, and corrode rebar which bleeds through over time.

Agreed, especially with ineffective snowmelt.