Does it mater how fast or slow you run the water through an immersion chiller?
Yes,
A faster flow rate will increase the rate of cooling.
However the final temperature will not be affected. You just get their faster.
Does running it faster use the same amount of water since you are running it for a shorter period or is it a constant?
There is an optimum rate. Each chiller will be different and affected by the temperature of the chilling water. When the wort is hot, and the out flow is cold water, the flow rate is to high to efficiently absorb the heat. The wort will be cooled, but with more water more than necessary.
So it sounds like your saying start slow and increase over time. Now if I monitor the discharge temp to keep it a few degrees above inlet temp that would be more efficient?
Right, as long as the out flow is slightly warm cooling is happening.
Absolutely 100% correct, rules of thermodynamics conclude that your delta should be between 8 and 12 degrees f. eg 60 in, 68-72 out.
Absolutely 100% correct, rules of thermodynamics conclude that your delta should be between 8 and 12 degrees f. eg 60 in, 68-72 out.[/quote]
Optimum, efficient, and neccessary lie in the eye of the beholder. Whatever the rules might be that conclude 8-12F is any of those, they’re not one of the exactly four rules of thermodynamics:
0) The game is mandatory, but it’s easy (if two things same temp as third, they’re all same temp)
- Winning is forbidden (AKA conservation of energy)
- Ties are permitted only when cold enough (moving heat from cool to warm takes work)
- It never gets that cold (Hell will freeze over before you see absolute zero)
Rule (0) seems obvious but really isn’t; that went unnoticed for centuries after (1) had claimed its number. Rule (3) is so obscure it’s irrelevant for amateur play.
Whether time, water, or ice is more valuable is a question for you and your wallet.
TL/DR: Put water through the chiller as fast as practical. Chill cooling water as necessary to meet chill time and temperature requirements. Recycle cooling water as necessary to limit consumption.
Greater water flowrate will always cool the wort faster. The rate of heat transfer is proportional to the (local) wort-water temperature difference, which is greatest as cooling water temperature rise approaches zero. That every little bit of water takes away very little heat is more than compensated by very very many little bits of water.
Lower flowrate will always use less water through the chiller. At greater temperature rise, every little bit of water takes away more heat, but every bit of that heat takes longer to get into the water. For given chiller influent temperature and wort volume and initial and final temperatures, thermodynamics does impose a minimum chiller throughput requirement.
The (local) wort cooling rate is proportional to the (local) wort-water temperature difference. For the purpose of this discussion of the overall cooling rate, we can ignore the (local) aspect and consider some appropriate “average” temperature difference. The appropriate average depends on design and operational details, but that yields only a little more precision and zero more illumination than just considering the cooling water temperature rise.
When the wort is 100F hotter than the water, that 8F rise gives 92F delta to drive heat transfer. Increasing to lake-draining rates would only increase the cooling rate by 100/92, ~9% faster.
When the wort is only 10F warmer, that 8F rise allows only 2F “driving force”. Increased flow could make the cooling rate up to 5 times faster… and need more than 5 times as much water through the chiller.
Similarly, at the same temperature rise, pre-chilling the influent cooling water 10F would only increase the chill rate of the hot wort by 02/92 ~9%, but could increase the merely warm wart chill rate by factor of 6 (12/2).
That is, flowrate and influent temperature have more impact on final wort chill rate than initial wort chill rate.
If the effluent water is (or can be chilled) cooler than the wort and recycled through the chiller, demand on the cooling water supply can be reduced (at the cost of time and total chiller throughput if the recycled water is warmer than the supply). That’s easy if you feed the chiller from a pump in a bucket; not so easy if supply pressure drives water through the chiller.
If the influent (or recycled) water can be chilled before entering the cooler, both chill time and cooling water supply can be reduced. Making a supply water prechiller that’s easier and cheaper than dumping ice into a bucket with a $15 pond pump has been left as an exercise.
I use a 25’ coil of 1/2" ID tubing and a $15 pond pump (garden hose just barely outruns my pump). I stir the wort to increase that side heat transfer coefficient. When the temperature rise falls to (guess) 20F or so, I shut off the hose and recycle the effluent and dump ice into the pump bucket. Even with my 85-90F supply water (Houston. August.), that gets my 6gal from boiling down to 120F in about 5min, 60F less than 20min, and 50F less than 30min. I use about 2gal ice, and crudely estimate that I draw only 10-15gal from the hose before recycling takes over.
That is what I did last winter. I didn’t measure my outlet temp but as soon as it felt cool I started recirculated ice water. Chilled pretty fast. That was a 5 gallon batch. I’m moving up to 10+ gallon batches and plan on making a CFC when I have the time. In the warm months I just collect the water and water my plants in the winter its a problem with ice. I’m thinking about water efficiency. I’m thinking using my existing 25’ ic as a prechiiler
To truly minimize cooling water supply, fill the chiller, lines, and sump to start and then feed the chiller ONLY recycled effluent, cooling the effluent (or infeed sump) as necessary to keep chiller influent water “enough” cooler than the wort. Dumping ice into the sump is pretty darned easy, and ~32F influent should be cool enough.
It’s hard for me to see how a prechiller heat exchanger will maximize wort heat transfer rate or minimize supply water consumption more than just adding ice directly to the chiller pump’s suction sump. The prechill exchanger will present more thermal resistance than direct water:ice contact, from its own finite conductivity and the necessary two boundary layers, and the local temperature gradient will be less because the chiller-side fluid will get warmer without the phase-change latent heat needed to melt ice locally.
If you have a pump and have to use ice anyway, why not just melt it directly into the chiller influent water?
If you somehow have access to cold prechiller working fluid (tap into a cold water AC system?), you’ll get faster wort chilling by just giving that fluid directly to the wort chiller.
The only way a prechiller seems sensible to me is if you need supply pressure to drive cooling water through the chiller, leaving no opportunity to introduce ice into chiller influent. A pump and sump would let ice precool chiller water more effectively, and more cheaply than another heat exchanger unless you already have an extra heat exchanger but not a pump and a bucket.
Well I do have a pump that I use in the winter. I put snow in the chilling water and it cools to lager temps pretty darn fast. I’ll buy some bags of ice and fill a couple of buckets with ice water and see how that works. Thanks for the input.
