Insulation under snowmelt?

kevin_5

I know that many large commercial jobs and even some residential don't insulate under the entire slab, and I know why. The question is: Isn't it a non-negotiable to insulate under snowmelt? This is a car wash, two open wand bays (not even a door) and one outside bay. One zone, 5/8 tubing, 12" on center. (includes the three bays and front apron.) It has a slab sensor and will activate from air temp I believe. A local "expert" claimed without insulation it would heat up a lot of dirt and then you would have all that "free" heat when you shut it off. I agreed that was true, except for the fact that you pay dearly to heat up that dirt in the first place, and by the time you get actually get any heat (next week) the Nebraska weather cycle could easily be back to hot and will naturally melt everything anyway. THEN you can shut down the system and enjoy all the "free" heat you no longer need. Am I too narrow minded to see the bigger picture here, or is this indeed a stupid place to try to save $500 on foam?
Thanks for the opinions. Kevin

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Earthfire

I agree it's dumb

Use the insulation. I would go with 2" foam .The idea with a car wash is quick response, to keep the cars out of the bay walls and the customers off their kesters on the slopped floors. Insulation will help push max btu to the surface. The ground heat sink works in garages or warehouses that have doors going up and down all day.

hot_rod

The insulation

will make quite a difference in start up time, which is critical in a wash to prevent ice build up.

I have been retro fitting a carwash where every year they chop and replace one bay. The difference between the new system I install with foam compared to the older bays is substancial.

A slab sensor is a fairly common way to control these ramp it up around 32- 33F slab temperature to prevent ice build up.

Typically most carwashes have an attendant checking daily, they can fine tune the setting on the slab control to their location.

$500.00 is a cheap number considering the performance difference.

hot rod

smoore

snow melt

what make and model control do you like to control your snow melt with?

hot_rod

A simple

setpoint control with the sensor in a well near the top of the slab. I like a control with an adjustable differintal. I keep it tight at 3-5 degrees so turn on at 32F and off when it hits 40. Or what ever suits your fuel budget, since you are heating "the great outdoors"!t

I have also seen carwashes with the sensor wall mounted inside the bay, up high. In fact this wash used to be that way. Sometimes however the air temp at night falls below 32F but the slab still has plenty of warmth. Really no need to fire the boiler yet.

The slab sensor is a more accurate way to know when ice starts forming.

If possible, locate the sensor near where the car door opens and the wands are located. It's the slip and falls you want to avoid. Also many hand washes have drip systems to prevent wand freeze ups. You want the heat on under that drip when the slab starts to hit freezing temperatures.

Goldline has a very dependable no frills setpoint, SP- 32 I believe. Ranco, Honeywell, Johnsone Controls, Heat Timer, tekmar, etc all have nice digital electronic setpoint controls out there. A Johnstone Supply catalog has 4 or 5 options. Watch their monthly flyers, seems every month has one or another on sale

Wash bays are expensive snowmelts as they rarely see the sun for any "free melt" energy.

hot rod

Jack_23

where to locate sensor

Where are placing your slabsensors in this type application?