Heating the ground under a commercial freezer......

Steve Ebels_3

There's a chance I might get involved (sucked into) a commercial project this summer that has 28x36 freezer area which will be maintained at -20*. The architect suggested to the builder that he get in touch with someone who can give both of them some guidance. So guess who got the phone call......



I've done enough reading on the subject to be dangerous but I really feel like the one eyed man in the land of the blind. Not enough knowledge about it to be confident in what I recommend.



So I'm wondering if any of you guys have done sub-grade heating under a commercial freezer. What did you use for control? What type of substrate did you place the tubing in? etc etc.

meplumber

Be careful with this Steve.

I am in an area of Maine with a lot of commercial blueberry freezers.  Heating can cause excessive frost in the interstitial space between the freezer floor and the ground.  This causes instability in the soil conditions and can cause heaving of the slab.  Some of the freezers here actually use cooling in the tubes beneath the slab to maintain a constant temp for the soil beneath the slab in the summer.



I don't work on their stuff, but a poker buddy of mine, is the facilities director for a couple of them.  There are engineers that specialize in this stuff.  I will see if he can get me their contact info.

Steve Ebels_3

That's why I'm asking here first

Talking with the architect, his concern was that eventually, no matter how much insulation you put on the ground under the freezer, it will freeze up and possibly cause the floor to heave, buckle or crack. 

Mark Eatherton

Been there, done that, and got out alive :-)

We did the tubing on a 10,000 square foot deep freeze warehouse. We used 3/4" tubing at 2' O.C. There was 6" of extra heavy duty XPS insulation directly below the warehouse slab. One way trip from a large manifold on one end to another manifold on the other end of the warehouse. Our tubing was buried 16" below that. We used a gas powered trencher to place the tubing.



We didn't make the final connections to the tubing, but I understand that they were going to be using the waste heat from the refrigeration process to generate 150 degree F water, and keep the area below the slab between 35 and 40 F. We buried a sensor well for them make out of copper directly between two tube, directly below the slab. They used a set point control, with an additional sensor for alarm.



I guess they (the company building the freezer) does it this way all the time, and they are internationally known eggspurts in the field.



BTW, I got hired to be an expert witness on a system like this that the main circulator failed, and cause a frost heave, and lifted the column directly above it about 6"'s and did some serious damage to the structures roof, 25' above the deck. Might be a good idea to incorporate a fluid flow switch in the safety circuit, and keep the main circulator running 24/7, and activate an alarm if it fails.



Make sure you or someone does regular fluid/maintenance checks, That's what caused the pump on that job to lock up.



HTH



ME

Paul Rohrs_14

Flow Swith and NEMA enclosure

I agree with Mark.   We have done several roll-in blast freezers that needed soil conditioning below the slab.

We have used both flow switches and differential pressure controllers and wired them to some ice-cube relays and lights (alarm optional) so that if we lose flow in system pump or HX pump we will switch from green light to red light.  All of our equipment usually sat on on a high traffic dock and in a highly visible area. 

Tubing manufacturers will help you determine the OC distance of your tubing and it is based on the temp of the roll in blast freezer.  For instance, one blast freezer we did was minus 10F and at 24" OC and another was a 10F setpoint and at 36" OC. (If memory serves)  We did use HDPE with pex tappings on one project and it went very fast.  After that the GC "placed" 5" of crush limestone (Fines to 1/4") over it and then 6" of High Density foam was placed prior to the structural slab.

The Double Wall BPHX on the roof was our waste-heat recovery "vehicle" from the refrigeration process and I would recommend putting  some air bleeders up there.

Paul

(I have a ton of other pics, and if you would like more, I'd be glad to send them to you off-line)







 

Steve Ebels_3

Hey Paul...........

If you would be so kind, please send me the pictures you referred to along with any other info or notes about that project.



Thanks in advance!!



s_ebels@yahoo.com

Gordan

Question from a lay perspective

Why aren't structures for this purpose built elevated from the ground, with a "crawl space" beneath? It seems like a lot of expensive measures are employed to prevent heaving of the soil and cracking of the slab, which should be a non-issue if you don't build a slab on grade.



I come from a part of the world where reinforced concrete slabs are used between floors on family homes, so my perspective on costs and benefits may be off...

Paul Rohrs_14

Structural Slab

As this is a roll-in blast freezer, by definition, there is a lot of heavy forklift activity consistently throughout the day and the structural concrete slabs were 6" thick, some projects were 8" slabs and the shear weight of that would not be condusive to being above a crawl-space.  You would then have to account for the dead-load of the racking that is typically placed in these freezers as well as the weight of the products being froze and stored.



Paul

Mark Eatherton

Ice ball storage...

If there were a crawl space below the freezer space, you'd have to expend a LOT more energy, dehumidifying the crawl space below the freezer space, to say nothing of the structural requirements that Paul pointed out.



As far as energy consumption is concerned, soil conditioning is energy neutral, because they are constantly taking heat out of the space. Instead of rejecting it into the environment, they are recycling it underneath the building to avoid the production of ice balls.



An ingenious use of waste heat if you ask me :-)



ME

Steve Ebels_3

mmmm hmmm

I would have to agree on the weight. In this particular job, which is small in comparison to many commercial freezers, the calculated load for each section of pallet rack is near 40,000#. That's each section 42" x 120". The racks are going to be 24' tall with a ceiling height of 30'.  Pretty hard to suspend that much weight without some serious support underneath........like mother earth herself.



Hat tip to Paul for some excellent documentation and pictures sent my way.  Thanks bro.

icesailor

Freezing Ground:

Years ago, I read a book by Farley Mowat called "The Siberians". He got in trouble for writing about Canada's largest neighbor an a nice light. He pointed out (in 1969) that the Russians had a lot of experience with building in Attic areas. The southern most city in Russia is North of Montreal, CA. That when they built buildings in the Arctic tundra that were heated, they sunk into the permafrost. So, at first, they added stories as the lower floors sunk into the ground.  So, they started building the first floors off the ground and insulating the heck out of the first floor floor.

Why not build the freezers off the ground and avoid the problem of needing to heat the ground. You get a few months of really cold weather and the rest is warm. I'd be trying to think of a way to use all that cold and cool a building in the summer. Or, recycling that cold air for refrigeration use. Either way, the Russians raised the buildings to stop the problem you describe, only their problem was the reverse.

Gordan

Yep...

That's what I would expect, pretty much. The structural issue aside (where the elevated floor construction that would withstand the described load for the freezer, would be prohibitively expensive) good air circulation combined with decent insulation should just about guarantee that there won't be frost - there's no fixed, non-conductive mass to be slowly cooled so the surface should never drop too far below the ambient air temp.

Paul Rohrs_14

Waste Heat Recovery

As ME eluded to, this is Waste-Heat recovery at it's finest.



The refrigeration process waste heat is reclaimed and pumped thru the tubing embedded in the ground to only maintain soil temp.



IIRC, and depending on flow rates it was only a 15-20 degree Delta T and exiting water temp was around 40F.



Other than the initial install cost, the system doesnt cost much comparatively to run.   If you had a big enough ECM circ, it would cost even less.



 A standard pallet of ham or beef stacked 5 feet tall.  Any guesses as to how much that weighs?



I believe  this freezer we did would hold 108 semi's full of frozen Beef, Ham, and the occasional Mother-in-Law.

Gordan

Oh, I get that.

I've once again been enlightened. :-) I mean, a static mass of concrete SEEMS simple and cheap to the uninitiated, compared to a heat distribution system with many moving parts - but things often aren't what they seem. Which is why we have experts!



I'm just quibbling with Mark's notion of snowball storage now. :-)