A lot of customers have asked over the years how many watts of power they need for their electric brewery. I've been able to give estimates based on the actual BTUs needed to heat water + 30% for loss, but my answer has never been exact. So, when I finally sat down and calculated real world losses I decided to use a converted beer keg or keggle because they make a great brew pot & a lot of 10 gallon brewers use them. Keggles hold 14.5 gallons of beer which makes them the perfect size for a 10 gallon batch.
To calculate BTUs needed and heat loss we need to start with the basic stats:
30# - Weight of a empty beer keg
16.5" - Keg diameter
23.3" - Keg height
12 gallons - Batch size these calculations are based on
0.12 BTUs - to heat one pound of steel 1 degree F
3.6 BTUs - to heat the keg 1 degree F
8.34 BTUs - to heat one gallon of water 1 degree F
1.5 sq ft - Water surface area of keg
8.38 sq ft - Side surface area of keg
1.5 sq ft - Bottom surface area of keg
3.41 BTUs - Heat generated by one Watt/hr of electricity
Then I found the standards above in a published Engineering table. The table lists BTU/hr loss per square foot in a steel tank with no insulation, assuming the temperature outside the tank is 70F.
Find more electric brewery tips at www.kegkits.com