A chiller is one of the last things I need to build or buy before I can get my new brew house up and running. I used immersion and counterflow chillers in the past, all of which I built. If chilling wort in the least amount of time using the least amount of water and while remaining relatively easy to clean was important, counterflow was the obvious choice before JaDeD started to produce outside of the box immersion chillers. Yesterday, I started to think about JaDeD's claims. It is obvious that the Hydra chills wort faster than a single 25' coil of copper tubing of the same diameter. It does so by increasing the volume of coolant and the amount of surface area that is in contact with the wort. However, one thing that it does not do is increase the surface area to volume ratio and that is what makes a chiller truly more efficient, especially as Delta T grows smaller. By more efficient, I am not talking about speed of cooling. I am talking about the amount of heat being being draw off by the coolant per unit of volume. Time in heat exchanger only becomes important as Delta T grows smaller. A 50' immersion chiller is not more efficient than a 25' chiller when Delta T is large because temperature equilibrium is reached fairly early. However, as Delta T grows smaller, a 50' immersion chiller is more efficient than a 25' immersion chiller because the coolant has longer to sink heat from the wort; however, it does so at the cost of time.

With that said, the Mantis is truly a more efficient immersion chiller than a single 25' coil of 3/8" copper. Here is why:

25’ 3/8” copper tubing chiller

Surface Area = 300” (25 feet) * 0.375 * 3.14 = 353.25 sq. in.

Volume = 300” (25 feet) * 0.1875 ^ 2 * 3.14 = 33.12 cu. in.

Surface Area-to-Volume Ratio = 353.25 / 33.12 = 10.67

2 x 25’ 1/4” copper tubing chiller

Surface Area = 300” (25 feet) * 0.25 * 3.14 * 2 = 471 sq. in.

Volume = 300” (25 feet) * 0.125 ^ 2 * 3.14 * 2 = 29.44 cu. in.

Surface Area-to-Volume Ratio = 471 / 29.44 = 16

As one can clearly see, a 2 x 25 x 1/4” copper tubing chiller is 1.5 times more efficient in terms of surface area to volume than a 25’ 3’8” chiller for any given volume of water. That is not as important when Delta T is large, but it conserves water when Delta becomes small. We have all seen an immersion chiller drop wort from boiling to around 150F quickly. From that point, cooling speed slows as Delta T become smaller. The only way to increase thermal transfer is to slow down coolant flow or increase the length of the chiller. However, there is another way; namely, increase the surface area to volume ratio. Turbulent flow through the chiller will allow for better heat transfer for any given surface area to volume ratio, but the limiting factor will be how small can we make Delta T before we reach diminishing returns with respect to coolant usage.