I want to build a closed immersion wort chiller system. Does any one have a suggestion for the type of pump I should get? I figure since the water isn't actually going in the beer it doesn't have to be food grade. Any suggestions would be appreciated.
Just about any submersible pond pump will work for 33°+ coolant.
If your intent to a closed system is no water/coolant loss these are my experiences.
I've tried a closed system with glycol at 20°F using a counter flow chiller. Worked great at first dropping out put wort to 35°F but quickly lost effenciency from returning hot glycol to the cold glycol reservoir. Was chilling 13.5 gallons of wort with 15 gallons of glycol. This problem can be fixed by simply having a hot reservoir, so it doesn't heat up the cold reservoir. But then your chill volume is a one shot chance to complete the chill. I've opted for future system to adopt what commercial systems use, as a double chiller system using ground water through the first chiller to knock the temp down most of the way then the glycol chiller to reach even lager pitching temps in one pass. Then I think a single reservoir glycol system will work. But at the expense of water loss.
Before the glycol system I tried the ice chest thing with ice water and again the hot return defeats the ice in the first 10% of the chill process.
All in all any system to be closed and not waste water will need to have a coolant volume several times larger than the volume of wort being chilled. This volume ratio is reduced by the greater temperature differentials between coolant and the wort.
The main concept to keep in mind is that you are only transferring heat. Mass (wort/coolant) will continue to have its' heat energy until absorbed by other mass. The only heat that is lost in a system is the miniscule amount transfered to the atmosphere.
Some basic math. If your wort volume and coolant volume are equal you can expect the final temp of both to be the average temp of both. So 20° coolant 212° wort can expect 116° of both masses. (CTxCV)+WT/CV+1 = final temp. Coolant Temp, Coolant Volume unit, Wort Temp, formula assumes wort volume unit of 1 and CV evenly divisible by WV. So to get 10g of wort to 68° you need 30g of 20° coolant in a closed system that returns hot to the cold reservoir. This doesn't factor the glycol refridgerators contribution to cooling incoming hot coolant.
You could literally use any pump that will move water at a rate that you're satisfied with. In fact, I would consider one of the fountain pumps from Harbor Freight (if you're in the US). With a fountain pump, you could simply drop the pump into, for example, a cooler filled with ice water, run the water through some tubing, through your chiller and return it to the cooler. You will have a lot of ice melt very quickly though.