What wattage element is needed for hot liquor tank/heat exchanger, and what about brew kettle?

Question

I'm completely captivated by www.theelectricbrewery.com, love their directions, and have ordered the parts, so I'll have my experience soon, but what is your experience with selecting hot water heater elements for boiling/heating?

Edit: For anyone looking at this considering a move to electric, use the directions in www.theelectricbrewery.com as much as you can afford to. They ended up spending upwards of $5k on their whole setup, but their directions are really good, and you can make do with some of their setup without using it all. I highly recommend the 5500 watt ultra low density elements. The HLT can simply be plugged in and unplugged when it reaches the desired temperature. The brew kettle, on the other hand, really needs some form of control. Directly plugged in, my boil was extremely vigorous, and on a day when the temperature was below freezing, with a large fan directly on the boil, it was barely maintainable.

Answer 1

I wouldn't go any hotter than a 4500 watt element for a 15 gallon brew kettle. While the temptation to put a bigger element in to speed up the process is great, consider that once the liquid achieves boil, you will end up with a very localized 'hot spot' right on the element that causes the liquid to boil VIGOROUSLY. That locally hard boil will cause the liquid to want to boil over hard. Then the feedback controller (PID usually) will finally feel some of that heat and shut the element off for too long. The boil will disappear for a moment before the PID decides to turn the element back on.

Early on I had a lot of difficulty in getting a consistent boil that I liked.

One other thing that helps with this...

Make your controller switchable from two pole to one pole on the fly. Once you hit boil, there is no harm in dropping from 220V to 110V. The element will heat just fine and will not be as hot. That helps alleviate some of this problem.

Answer 2

The formula to determine wattage is as follows:

Gallons * Temp Rise (F)
------------------------------------ * 1000 = Watts Required
372 * heat up time (hours)

So, for a homebrew example of 7 gallons of wort at the beginning of your boil, and desiring to reach boil in 15 minutes, and assuming your wort temperature before boil is 150 degrees F after sparge runnoff:

7 * (212 - 150)
---------------------- * 1000 = X Watts
372 * .25 hours

Or 4666 watts.... or a 4500W element.

You'll have to tweak the formula to account for your starting boil size, typical sparge runnoff temp, and desired time to boil. Another limiting factor is going to be your available amperage to hook up the element. Since watts = amps * voltage, a typical 15 amp household breaker running at 110V will at most power a 1650W element.

The other main concern you'll want to watch out for is watt density of the immersion element. This is the measure of watts per square inch. Sugary water like wort tends to not conduct heat very well, so you want a low watt density to prevent the sugars from scorching. What qualifies as a 'low enough' watt density is something I've yet to figure out, but I suspect you'll be fine with anything at 40 or less watts/sq in. Keeping the wort moving (by stirring) will also mitigate this potential problem.