Fixing too long loops..reversing valve technique

The Steam Whisperer

I've heard of the reversing valve technique and need to know more about it. I have a system with 4-3/4 inch 1000 ft long loops with a 410,000 btu/hr load (under a commercial meat freezer). How well has this worked for those out there. I figure I can get 3 gpm through each loop at 50 ft head ( 2 NRF-36 pumps in series). This works out to a 65F delta tee.

Harvey Ramer

You need the 4-way valve, actuator of your choice and a repeat cycle timer to make it all work. It's pretty straight forward. You can set the timer on something like a 15min. cycle.

The Steam Whisperer

Thanks,
I've done almost no hot water in the last 5 years and am a bit rusty.

I was wondering how effective it was.... does it perform like cutting the delta tee by 1/2 or somewhere in between.

SWEI

The BTU transfer should be about the same, it just moves from one end of the loop to the other, which charges the mass far more evenly.

hot_rod

Glycol? Those freezer floors are sometimes crazy thick, like 12"!

Here it is with a PL 55. 40% PG, Nowhere near the btus you need, however.
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Your dual PL 36 would give you a tad more

You basically warm the slab from two different directions, even out the temperature, no additional energy added.

This is a tekmar 721 with a Belimo actuator. Belimo has the operator and mounting kit to put it all together.

I used the strongest actuator they had as the 4 way valves tend to get sticky and hard to turn. I'd add a hydronic conditioner to help keep everything lubed up.

A simple lamp timer is fine, pull the pins so it changes every 15 minutes as Harvey suggested.

I wouldn't make any promises.

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The Steam Whisperer

Freezer floor from top to bottom Slab, foam insulation, slab, gravel. Tubing is in the gravel. Design load on prints worked out to about 110 btu/sq ft. Going much above 50 ft head doesn't yield much more flow. I think dual PL-55's (84 ft head)would only give about 3.5 GPM per tube. I also made the suggestion that they use the radiant system as a heat sink for the refrigeration....ever done that?

Thanks Hot rod

hot_rod

Heatway, then Watts Radiant was involved in a lot of freezer floor design. Really the tube is to prevent the subgrade from freezing and heaving, cracking and breaking the slabs. So the goal is just above freezing temperature, design was usually 40°

There are different temperature freezers depending on what was stored in them. What temperature is that running?
10 to -20°, as low as -30F for flash freezers. I used 10 in the calc.
Loads were typically low, 3- 7 btu/ ft

4-6" of insulation was suggested to keep that load low, 55- 75° supply temperatures typically, great for mod con performance you would see some serious condensate.

I don't think you can pump your way to that 410K load number, if that is accurate?
even with a hydraulic mining pump Although the friction from those elevated flow velocities in the tube could add some heat.

A great idea dumping the refer heat into the radiant, but your bottleneck is still in the tube.

If you take it on, be clear that it is a bandaid approach and may not get them where they want to be.

I have one of the original Heatway Refrigerated Warehouse Permafrost Protection design guides I could scan and share, if that helps.

The Steam Whisperer

3-7 btu/sq ft? I believe that it works out to about 110 btu/sq ft in this freezer.....looks like some numbers need checking.

The Steam Whisperer

After looking at how big a mess this system is, I think its wise to back away.... not worth the potential trouble.

hot_rod

Could be your most profitable option

Solid_Fuel_Man

In commercial ice rinks we use the waste heat from the glycol chiller for the same purpose, Preventing permafrost. Not sure what we calculated the actual load to be, but the indoor rink we service the cooling towers still run even with the sub-slab heat running. Built in 1978, so not sure what there is for insulation below the chilled slab. All sch80 welded steel