Wort Chiller - How many feet start to be counter-productive?

[Bobby_M]

The more surface area of the cooling element you have, the more efficient the cooler will be. However, it has to be understood that a 100’ chiller won’t necessarily chill more efficiently than a 50’ chiller.

Nice first post.

Here's the thing, people throw the word "efficient" around a lot when talking about IC lengths and diameters but I always have to ask exactly what the context is. That is, we have to define the priorities for which efficiency will be measured.

Efficiency measurement will be completely different if the goal is FASTEST chilling vs. Least water use vs. cheapest upfront materials cost.

Fastest? Assuming enough kettle capacity to deal with the displacement, 100' of 5/8" OD copper will absolutely cool faster than 50' of 3/8 but at the cost of materials and water usage.

When it comes to the question about coil length for a given diameter, longer is better up to the point where tap water pressure can no longer deliver the same flow rate. However, this ignores the question about the upfront cost vs. cooling gains.

I suppose you could look at efficiency at the maximum cooling speed with a sweet spot of water usage and upfront costs (the diminishing returns problem). If absolute efficiency is really that important, go with a plate chiller instead.

Specifically to the original post's question, the only way I could view a longer tube length as counterproductive is if you mean cost to value. For the most part, longer always means equal to faster cooling given a fixed coolant temp and flow rate. However, I read "counterproductive" as SLOWER cooling after a certain length. In the context of how we use these chillers, it's never counterproductive.

 

[audger]

people are getting bits and pieces of the equation, but in just skimming over this thread, i havnt seen all the pieces yet. there are four main pieces of the equation that influence the efficiency of any chiller, radiator, heat exchanger, etc...

-flow rate of the cold side
-temperature of the cold side
-flow rate of the hot side
-temperature of the hot side

given those four variables, we can conclude...

-when flow rate of the cold side increases, efficiency increases, but more water is wasted
-the greater the temperature difference (delta) between hot and cold, the more efficient the heat transfer
-if you either decrease the flow rate, or increase the time the cold water contacts the hot water (with a longer tube), the more efficient the design becomes (more heat transfered per unit of cold water), but the longer amount of time it will take to cool the hot side
-as you lower the temperature of the hot side, the temperature delta, and therefore thermal transfer efficiency, per unit of cold water, decreases. meaning your efficiency from start to finish is not linear but more logarithmic.

if you were actually doing the math, you would want to factor in the heat capacity and permisivity of the materials (kettle, copper tube) and other secondary factors, but for overall discussion, those four variables are the important ones.