Using refrigerant gel packs to chill wort

[Brewmegoodbeer]

I have some thermosafe gel packs that im thinking of putting in a color with a sub pump to recirculate water through a chiller after getting my wort to about 85 or so (ground water temp of hot Florida) using ground water. Had anyone had experience with using these with a chiller in home brewing? They stay cold for literally days after being frozen. Thanks

 

[Robert65]

Once I get somewhere below 100F with groundwater, I switch to a pump and recirculate ice water. So same principle. If those packs turn out to be just as effective, at least you wouldn't have to keep making/buying ice. But I wonder how many you'd need. I can melt 20-30 lbs of ice getting 6+ gallons the rest of the way from the 90s to lager pitching temperature, but at least it goes very fast.

 

[Godot]

Yes, I've done this. No problems at all. I usually use frozen water bottles in water, but I have chucked in a gel pack to help matters along. I do it to preserve water.

 

[Robert65]

Yes, I've done this. No problems at all. I usually use frozen water bottles in water, but I have chucked in a gel pack to help matters along. I do it to preserve water.

That's a good tip. I don't like the amount of water I waste making and melting ice. Freezing in bottles would make it reusable and less expensive than the gel packs.

 

[ba-brewer]

I use an immersion chiller with tap water until it plateaus then switch to recirculating water over frozen blocks of ice. I tried frozen gel blocks once but they did not seem to work as well as the ice blocks.

In summer I can get down close to 80 with the IC and tap water so it does not take too many ice blocks to get down to mid 60s or lower(2 or 3 glad 6 cup containers frozen). I only use enough water get the pump to start flowing so I am not losing ice cooling power to excesses water.

The first tap water goes into a bucket for cleanup then rest into the pool.

 

[Robert65]

I've been thinking about this.

First, it isn't the mere presence of cold ice that removes heat from the system, but its actual melting. Freezing water gives up heat, melting ice absorbs heat. So also larger pieces will be preferred, as they will slowly melt away, rather than expending all their capacity to take up heat at once.

Second, this heat transfer depends on a direct interface between the melting ice and the coolant water. Without some intervention, an insulating boundary layer of fluid at an equalized temperature will quickly form, hindering further heat transfer. This is why you need to stir your wort or move your IC around, and is also the principle behind a convection oven.

Now, in your pump reservoir full of water and ice, the circulation of the water prevents the formation of this insulating layer, constantly renewing the interface between ice and water. But if you use frozen bottles (or gel packs,) the boundary layer will form INSIDE the bottle, where you can do nothing about it, and heat exchange will be rendered less effective.

So it would seem to me that the best option is probably to use ice, and find a way to put the melt water to good use.

 

[ba-brewer]

There is a way to figure out how much ice is required, Bobby from brew hardware post a formula once and I put it in a spread sheet which seem to get fairly close. The main part is it requires 144 BTU to melt 1 pound of water.

pounds of ice = (weight of water * gallons to cool * (start temp - end temp))/144

use 8.3 for a gallon of water

 

[Robert65]

That probably assumes perfect efficiency, whereas we'll actually lose some along the way in hoses, the coil, pump friction, etc. But it is a cool formula to have, thanks for posting. I'm going to pay attention the next few brews and see how close I get! If you're too far off, it probably means you could tighten up your rig (shorter hoses, etc.)

 

[RPh_Guy]

larger pieces will be preferred, as they will slowly melt away, rather than expending all their capacity to take up heat at once.

You do want large surface area of the ice so it absorbs heat faster, allowing you to chill faster. Smaller ice pieces are better.

I agree with everything else you said.

 

[ba-brewer]

That probably assumes perfect efficiency, whereas we'll actually lose some along the way in hoses, the coil, pump friction, etc. But it is a cool formula to have, thanks for posting. I'm going to pay attention the next few brews and see how close I get! If you're too far off, it probably means you could tighten up your rig (shorter hoses, etc.)

For sure a first approximation. I was already using my process when I seen the post so it was more of a curiosity thing for me go out and measure the weight of my ice blocks to see how close it was. You lose BTU to the reservoir and the water but I think you would get some of that back if you chill long enough.

I have wondered how much it matters if the ice sits in the reservoir vs be suspended over it and whether a insulated vessel would work better than my HLT but that seems like work to verify and a few blocks of ice to work OK for me. For lagers I raid the ice cube tray to get colder during summer. I do know ice in a bucket with a second IC as a prechiller was worst cooling then the gel packets in a recirculating setup.

 

[balrog]

I do this exactly, tap water IC to about 90-100, pond pump recirc in cooler
Always works better with 16lb bag ice than any number of frozen freezer gel packs or blocks as the gel pack interface, static, doesn't xfr heat to inner gel pack as easily as melting ice chips.

I recently did two batches one day, I had the ice for the first and used the gel packs for the second. Chill times were about 12m first batch, second similar size batch was more like 25m, both batches chilled to 64.

 

[Robert65]

I do this exactly, tap water IC to about 90-100, pond pump recirc in cooler
Always works better with 16lb bag ice than any number of frozen freezer gel packs or blocks as the gel pack interface, static, doesn't xfr heat to inner gel pack as easily as melting ice chips.

I recently did two batches one day, I had the ice for the first and used the gel packs for the second. Chill times were about 12m first batch, second similar size batch was more like 25m, both batches chilled to 64.

Data! Nice.