1 or 2 zones for a garage and snow melt system

achoyna

Hi gurus,

When I built my garage and did the landscaping I laid 3 x 250' rolls of pex in the 4" garage slab (with 2" of foamular insulation below it), and 2 rolls of 5/8" Alum-a-pex outside in packed sand, with reflective insulation underneath, with 1" thick stone tiles 1" above the pex.

My main question is, should I:

• Build the water distribution with 2 zones (separate pumps and manifolds), 1 zone for each purpose?
  
• build only 1 zone, using actuators on each valve to control the water flow for each systems pex?
  

I only intend to keep the garage at 55 degrees, and run the water/propylene glycol at between 110 - 130 degrees. Would a 4.4 gallon expansion tank be sufficient for this system?

I intend to model the system on something like this Home Depot distribution system. Any thoughts on that design?

Thanks for any advice.

Alan

GroundUp

Whether actuators or manifolds, it's still 2 zones no matter how you slice it. If it were me, I'd use two manifold sets with two circ pumps as the requirements are drastically different. What is the heat source for this system? The 4.4 gallon tank is more than sufficient unless the heat source has a lot of volume. Did you also wrap the outside edges of the slab/foundation with 2" of foam?

Tim_D

Pumping requirements may be significantly different for these applications and the expansion tank question can not be answered without knowing the length of the 5/8" runs, glycol mix, starting temperature, etc.

motoguy128

With the wide temp range of the snow melt I’d go up one size on the expansion tank to be safe.

Not sure how well the snow melt will work with minimal insulation under it. If you lack the heat output , snow melt becomes a ice rink system. Usually 3/4” is recommended with narrow spacing and you need a LOT of heat. The PEX should have been right under the stone tiles with 2” further down.

No perimeter insulation on the garage slab wire require 20-30% more heat.

You need 2 pumps for this system with primary/secondary piping.

achoyna

Thank you @motoguy128, @GroundUp, and @Tim_D for your advice.

No I did not insulate the perimeter of the slab. I didn't think of that sadly

Looks like a 2 zone (2 sets of manifolds and 2 pumps) it is.

I'll be using a condensing boiler as the heat source, and I'm not sure what the mix of water and glycol will be. This is for Chicago. Any recommendations on mix?

GroundUp

Don't bother trying to heat it until you insulate the perimeter, 90% of the heat loss is through the slab edges. With snowmelt in MN I typically run 40% concentration for a cold start system.

Tim_D

Pull down the ASHRAE design data for your area to determine the glycol mix. More glycol means more flow to achieve the same output so do not go overboard or you will need a really big pump. Edge loss can be a big deal. You may want to address that.

hot_rod

Really the glycol only needs to protect the piping down to the lowest temperature you want to melt snow. If at 0 or below you do not typically need to melt, maybe a 35% would protect from burst.

Some glycols show freeze, ice crystals form
Slush, no longer pump-able but does not freeze solid
Burst....

Circulators may need to be up sized, both distribution and boiler side if it is P/S or a separator.

achoyna

Thanks again @GroundUp, @Tim_D, and @hot_rod.

3 of the sides of the slab are concrete paths, and the concrete apron on the garage entrance/exit, so I can't insulate them darn it, but I will insulate the back of the garage that thankfully is accessible as it is a garden bed.

I was thinking of using the Grundfos UPS26-99FC 1/6hp pump for each of the zones. Would that be able to support 2 x 250' 5/8" Aum-A-Pex with a 40% glycol mix?

Zman

Are your garage loops 5/8 or 1/2?
On paper the Grundfos 15-58 would work well for both zones. The snowmelt loops would flow about 2.3 gpm on speed 3.
I think if this were mine, I would use a 26-99 on speed 1 for the snowmelt. It would be nice to have the speed 2 and 3 options if the snowmelt loops turn to slush.

Big Ed_4

Give it a whirl and if you need more expansion then twin in a second at the same location

GroundUp

My experience with cold glycol is that less pump is better. A 15-58 will be more than plenty for only 2 loops, hot or cold IMO. Overpumping tends to cavitate the circ when the fluid is super cold.

DavidinKenai

You think you're only going to keep the garage at 55F and you might do that most of the time, but there will be times you're out there working on something for a few hours, fixing the car, or times you want to thaw the car quickly and then you'll crank the thermostat to 70F, so that's your design temperature.

It's pretty easy to install and use an ice melt system (rather than a snow melt system). What I mean is: shovel / blow / plow the bulk of the snow away and then run the system to leave it clean and dry and thawed. If you don't bother to remove the snow (the appeal of such a system, I know), then where does the melt water go? Your drain lines and surface drainage will ice up as that melt water leaves the warm pavement. Do you run electric heat trace (I hate that stuff) in the drain lines until they're below frost depth?

For a high-end ski resort or a hospital entrance area, throwing lots of BTUs at it to melt the snow can be worth the luxury or reduce slip hazard (and liability). For residential applications, I've found it more reasonable to plan on ice removal by heating AFTER bulk snow removal has been done.