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Rainwater harvesting for cooling worm tub condenser


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Hi Folks

We're potentially in the great position whereby we can pump harvested rainwater from a single tank, run it through a worm tub condenser then return it back to the same collection tub. I'm aware that seasonally the temperature of water coming in will vary and therefore we might need to regulate with a chiller....and of course the returning water will heat up the supply tank. But by how much?

1) The supply tank is approx 8000 litres

2) Our worm tub will hold approx 150 litres

3) The gin still will be charged with a maximum of 200 litres wash @50%

4) The still will run for approx 4hr 30min

If anyone out there is using a worm tub, whats the temperature of your water coming off and importantly how does this compare to the temperature of your new make spirit.

Would we better just installing a second tank and simply transfer cooling water between the two (there would be a cool down period as we won't initially be distilling everyday.


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I'm sure someone will correct me if I'm wrong, but here's my thinking, assuming 100% efficiency, zero losses, etc.

You're going to be cooling 104 liters of 96% from 78C to 25C = 53C change

The specific heat capacity of ethanol is approx 2.5 J/g·°C
So the energy needed is 104,000 x 53 x 2.5 = 13.8MJ
Now work backwards through the water.
Specific heat of water is approx 4.2 J/g·°C
13.8MJ / 8,150,000 / 4.2 = 0.4C
So, unless my math (or science) sucks, your tank and tub should increase by 0.4C for each 200 liter run.
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