Swamp cooler science: pimp my swamp cooler

I have a swamp cooler. I will provide all the background information first and put the real questions at the bottom for those who want to skip the volume of text.

It currently works as follows:

40 quart cooler containing tap water and ice jugs, drilled to fit input and output hoses.
[pumps via submersible water pump to --->]
rubbermaid roughneck trashcan, 1 inch drain bulkhead 9 inches from the bottom
[drains via 1 inch ID vinyl hose back to --->]
40 quart cooler.

A ranco controller monitors the water outside the fermenter and turns the pump on and off when cold water is required. Maybe one day I'll invest in one of those stainless steel temperature probe fermenter bungs, but for now I don't like the idea of putting more stuff than I have to into direct contact with my beer. Call me crazy: I know it's nuts.

Right now room temperature in that room can get up to about 85 F or possibly higher. Ice doesn't last long in the cooler. I suspect because it's drawing up heat from the fermenter and through the uninsulated trash can. To fix that I've cut the trash barrel down to 18 inches tall and I'm building a heavily insulated (and constructed) wooden box to fit the barrel inside. I'm also going to make an insulated cover to try to eliminate as much air convection as possible. There will be a hole in it so the airlock can poke through, so it's obviously going to have a draft.

QUESTIONS:

1) Salt changes the freezing temperatures of water. It also supposedly makes ice water colder (who knew?) and causes ice to melt slower (talk about counter intuitive). Will using salt water in my cooler improve it's efficiency?

2) Would salt water wreck a pond pump?

3) Do you have any other insulation, efficiency, or swamp cooler tips? If so, why are they?

Thanks as always HBT.

DSorenson said:

QUESTIONS:

1) Salt changes the freezing temperatures of water. It also supposedly makes ice water colder (who knew?) and causes ice to melt slower (talk about counter intuitive). Will using salt water in my cooler improve it's efficiency?

2) Would salt water wreck a pond pump?

3) Do you have any other insulation, efficiency, or swamp cooler tips? If so, why are they?

Thanks as always HBT.

Click to expand...

1) While ice does lower the melting point, the amount of heat it takes to melt said ice remains very close to the same. I've never heard about ice melting slower with ice. Got a reference? I don't believe the salt will improve your efficiency. It will take x BTU to drop the temperature of your beer a certain amount no matter what the temperature of your ice/water is.

Also, if I understand your system correctly, the ice water will just sit there until needed. Being at a lower temperature will cause it to lose heat to the environment faster. I believe your overall efficiency might be lower even.

2) This depends in what your pump is made of. Salt is going to make the water more corrosive to metals (including any metal pieces used to connect plastic pieces)

3) I made a swamp cooler once when my ferm fridge was taken up by a lager. I used an old tshirt fit over the carboy with an aquarium pump putting water on the top. I set up a fan to blow onto the tshirt for some forced convection / evaporation. I was able to keep the temperature at 65 F in my ~73 F apartment without any ice. You might be able keep decent control on your temps with a combo of ice and a fan. You could use the controller to turn the fan and pump on an off.

It sounds like you have more $$ invested in your automated swamp cooler than I have in my fermentation chamber. It is a plywood, 2x4 and pink foam insulation box with a minifridge in one end controlled by a Johnson A419 controller. \

I can't advise on the salt, Ice, water, pump configuration but would think that the salt would not harm the pump unless the parts are mild steel. You might use the pink foam-board for insulation. I used the 2 inch thick stuff.

Honestly, I would re-purpose all that equipment and make a fermentation chamber. You could use your temperature controller with a chest freezer. No pumps, no water, no salt, just electricity.

Ryush806:

Thanks for the response! I didn't believe it either, but a quick google search pulls up solid information. I'm still not sure I understand it completely. Here:
http://wiki.answers.com/Q/Why_does_rock_salt_make_ice_colder

Sadly I'm not sure evaporative cooling is an option: the air in my house is regularly 85% humidity during the summer. Thanks for the idea though!

kh54s10:

Thanks for the response. It is a lot of money for the whole operation (or at least more than just buying a chest freezer and controller, possibly). It started as just the trash can for a swamp cooler and it's been getting more elaborate over time by necessity.

I haven't insulated my 20x20x18 inch box yet and I was hoping someone would have a thought on insulation to pick. Thanks for the reference to the pink stuff. I hope it's cheep!

I use a 25' 3/8" immersion chiller. Temperature variation is unmeasurable, within .1° C, as measured with a thermowell. I use 4 liters of frozen water bottles every 12 hours.

I call it a water cooled fermentor, not a swamp cooler. Mine is a thermostatically controlled ice cooled waterbath. It’s a closed system, no evaporation, No swamp involved.

Yeah, I agree, forget the salt. It will lower your freezing point a little, but we don’t care about that. It’s the large amount of heat required to melt ice that makes it work.

What Ryush806 said is exactly right.

As far as the wet t-shirt method (an actual swamp cooler) it doesn’t work for me. You need low humidity for that.

Thank you, Wynne-R. Your setup looks something like mine! Mine is probably just more expensive. Do you use a lid on either vessels? Also, if you have any information on the temperature difference between your thermowell and the actual water in the 'ice bath'? Thanks for the picture.

It’s nice to hear from someone fermenting in a water bath. It’s more precise than cooling with air and I think tight regulation pays off. I have been able to drink my ales quite young. I just don’t have green beer.

I use STC-1000's so my temps are in Celsius. Usually the thermowell is about .3 -.5°C warmer than the waterbath. After the first few days the difference tapers off to zero.

I keep the sensor in between the first and second coils, where generous overshoot keeps my pump cycles at about 15 seconds. This keeps the water temp well within ± .1° C. I figure what happens in the water, half of it happens five minutes later in the beer.

There’s a certain amount of guesswork in measuring temps, though water is easier than air. My thermometers can’t measure less than .1 ° C. There are eddys and stratification. It’s about impossible to stir the water, with wires and hoses sticking out.

Excellent information! Thanks for the data; that will really aid me as I get used to using my water bath. I'm going to keep it at 58 F with a 2 degree tolerance assuming there will be a few degree difference between the water and beer. My water levels at most rise to 10 inches up the carboy so it's not as submersed as yours. I can only assume then that there will be a larger temperature difference.

So far my insulated box for the water tub has no trouble keeping a difference up (currently) up to 27 degrees lower than ambient- it looks like the hard work paid off.

Also: I understand what you mean when you talk about eddys and stratification. I've tried to set up my input hose so it shoots down into the bucket and induces a whirlpool. I hope that helps keep things more even.