Snowmelt Control?

Chris Holley_2

help me out here. I’m quoting a small snowmelt job..1,000 sq. feet of sidewalk and poured concrete staircases. It’s a commercial application and we’re designing for Class 2…about 200 btu/sqft in this area.

My question is control. We’re Tekmar people here so it’s a question of which Tekmar. The client has made it clear that he’d be fine monitoring conditions and running the system as needed if it would save him some system cost. So….we probably will not be quoting the 090 snow sensor and housing.

At the cheap end we could use the Tekmar 650, essentially a slab setpoint control, or at the other end we could use the Tekmar 662 with all it’s bells and whistles,like viscosity compensation,ramped start up, and so on.

Boiler protection isn’t an issue as we’ll probably use a condensing unit like say a Munchkin or NTI Trinity. Slab protection is the question. How much of an issue is ramped start up? Is concrete cracking ever really an issue without it? I’m more concerned about the concrete stairways, than the sidewalk.

What say you guys?

Chris Holley

John_21

snowmelt

use the best one with all the bells. Have installed 3 that way very good results. Slow warm up very important. You have many options with better controls. They will do more than you can. Once setup it takes humans out of the picture. John

hot_rod

energy consumption

will be the big issue. With the setpoint, only, control the system runs regardless of sun, snow, sleet, or hail

Possibly if this slab is in a shady spot of you have a lot of snowfall.....maybe

A precipitation sensor with a spring wound 12 hour, manual control sounds like a better system.

Shop around there are other brands of slab precip sensors out there if price is the concern. Although tekmar has the nicest features, in my opinion.

Won't take long to "burn up" the price difference in fuel costs with a 1000 square foot at 200 btu/ sq. ft. running whenever it's below 32 degrees "Heating the great outdoors" comes to mind!

hot rod

Chris Holley_2

Well actually

The low end control, the Tekmar650 is more than an a setpoint control. It has an integral timer, can maintain an idle temperature, and has both warm and cold weather cut offs.

But...it doesn't do the gradual warm up routine (based on amaximum DT) that the 662 does. The 662 also changes the maximum DT based on fluid temperature to compensate for the viscosity changes of the glycol solution....whew

But..again..it's the ramped warm-up feature that interests me most. Is stress cracking of snow melted concrete stairs or slabs really an issue without it????

Chris

Ken Wickre_6

tekmar 362?

If you use a dedicated boiler sized to match the load, Delta T protection should be automatically provided with the tekmar 650. The temperature rise across the boiler will be offset by an equal temperature drop in the return fluid. Concerns to watch out for with any boiler is the minimun allowable return it can see. A cold slab, at say 20°F, may be unacceptable for even a condensing boiler.
Another option would be to consider the tekmar 362 in mode 2 and provided with the otional 092 snow melt kit. It is a variable speed injection or floating action control, your preference, and provides minimum boiler protection, Delta T protection for the slab, mixed system reset, viscosity compensation, idling, and more. It is a simple system to apply and for a building owner to understand-if they will take responsibility to manually start it.
I have applied several snow/ice melting systems including the 650/356, 661, and 662. I have never seen a slab destroyed by high temperature differentials, but I always promote awarenes of this possibility. I don't want the first system I see to be one I helped design. If you haven't investigated the 362, it may be a good application for you in this instance.

Chris Holley_2

Thanks for your thoughts guys

and Ken, of course you're right on the inherent Delta T limitation using a matching load boiler. In fact it occurs to me (duh) that these modulating boilers modulate based on Delta T so any load less than the boiler max would still be DT limited.

We are suggesting, but not supplying the heat source here. I hadn't realized that the tekmar 362 had a mode 2 snowmelt option. Looks good! That's what we'll quote. It will give them then option of a high or low mass boiler, remote start, idling, run time, and all the other goodies

Thanks again.

Chris

hot_rod

Unless the boiler

is grossly oversized, I can't imagine shocking the slab. Consider 1000 square feet of concrete 4" thick is @ 12 yards of concrete. More if steps are involved. 12 yards of concrete weighs about 48,000 lbs. To raise that slab from a start up of 32 degrees to a maximum of 90- 100 degree (supply temperature) would take awhile, especially if the snow continues to fall.

The bigger concern is shocking the boiler. You really need a control that can both mix the boiler supply, and watch, and respond to the return temperature to the boiler. A thermostatic 3 way would one way, but I too, prefer a VS mixing control, or a VS mixing pump with sensors on the boiler return.

Idleing the slab will certainly help the response and melt time, but it will cost you additional energy, regardless of the control. The beauty of the slab precip sensor is it will start the slab as soon as the moisture hits the sensors. This way it would start and shut down without an operator being present. Worth the extra bucks by far, especially in a liability prone icey stair situation
Wouldn't it be ironic if the person responsible for start up slipped on the dock or stairs on his way in


Condensing boilers thrive in these applications. Start up will be gentle regardless of the heat sourse due to the thick viscosity of glycol at temperatures below freezing. This will greatly effect the pump capacity until things warm up and the fluid thins to a more "pumpable level.

hot rod

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