First trial with new hex setup that is approx 7L with 6m copper coil and a 2200W keg king element.
Don't have the controller hooked up yet, but got the HEX up to about 70C then started running cold tap water through it. Full speed on the pump it came out luke warm at the other end, when i choked the pump back to a drizzle it's coming out around 45. At full speed on the pump the hex is cooling, even though the element is on flat out.
Next test, bought the HEX to the boil and put 45C water though it. Again when its at full speed the HEX water is losing heat. The water coming out is too hot to hold my hand under but no where near boiling. Recirculating through the pump I've gained about 15C in 45 minutes for about 80L water.
So the problems I am encountering are:
- Big differential between HEX temp and liquid out of the HEX temp (more copper should solve this, but will make the 2nd problem worse?)
- HEX losing heat (more watts needed?)
Hopefully it will have enough guts to hold mash temp for a large batch as that is it's primary goal, however would be nice to be able to speed it up to heat strike water and sparge with. Reno'ing the house soon and i'm getting a new shed, so am going to put a lot of power down there!
While a larger copper coil will get you warmer water exiting the HEX coil than the current coil, I am not sure if your element is going to keep up, especially if the difference in temperature is too much.
I did some testing a while ago and with a modern 2000W insulated kettle boiling about 1.9L of water from 19.3C to 100C took 6 minutes and 9 seconds.
For a 2200W element directly in the water I would expect that to be about 10% faster so I would assume it would still take around 5:20 to heat water up by 80 degrees.
That means to warm up 1.9L, for each minute it rises by about 15 degrees. So to increase your 80L by 15 degrees means it will take more than 42 minutes, assuming there is really good insulation and it ignores the thermal mass of the grain bed.
In the case above, when you mention a dribble, to get the 25 degree continuous gain in temperature increase you would have to run the water through at 1.1L per minute which would be quite slow. Any faster than that, even with a larger copper coil and you would only get 45 degrees for the initial water and it would cool down the HEX faster than the element could heat it.
I don't believe you will have issues maintaining the mash temperature if the mash tun is insulated but you might be better off to heat some sparge and strike water separately.
I used to run 2 * 2.4KW elements in a 4L double walled pot to get the HEX up to temp very quickly and HEX coil is stainless tubing (not as thermally conductive as copper) which is about 5 meter long.
It achieved the temperatures quite quickly but I didn't use it to heat the strike water or the sparge water. I used a separate hot liquor tun (Keg King 60L double walled urn) and once I had the mash at 78 degrees, I bumped up the two elements to just below boiling point to heat the wort as much as possible as it was pumped through the HEX to the kettle. The Kettle only had a 3600Watt element and it was insulated, which was enough for a rolling boil of the batches I made.
My setup was for up to a 80L wort, however most often I only made about 50L.
I hope it helps
Roller