Not wanting to put a downer on this but...
I looked into the same idea a few years back. People do build these, and some are really excellent jobs. I'm also talking about the better ones with a thermostat than can regulate the temp and not one where you need to manually monitor it.
When I started asking around I found most had used them for a while, but long term didn't keep them. I recall one person here on AHB build a big flash cabinet, that if I recall correctly never got used.
My first thought was it would be a lot cheaper to run, than a fridge. Wrong! Think about basic physics here. Cooling a volume to a given temp requires a set amount of energy. A fermenting fridge at 18, or the chamber at 18 is the same temp difference from the ambient. So you can have 2 fridges, 1 as a fridge working medium, and a second fridge at 18 which is hardly working at all; OR you can make the main fridge work harder by having to freeze water bottles all the time. Same applies for heating.
The next issue is swapping out the ice bottles. It's something you have to manually check and do all the time. Fun for a while, but gets boring pretty quick. What happens if you want to go away for a week or two? With a fridge it's set and forget.
Then when you want to drop the temp to 2 for a week or so at the end of fermenting. Can this even be done with ice bottles? If so I assume you will need a lot of them to get the temp down and then maintain it. With a fridge it's just dial up the desired temp and walk away for another week or so.
Most the time you can pick up fridge free or pretty cheap. If it's stored in the shed (or anywhere that the looks don't matter as much) and you have one with the rear condenser the panels could be used to add extra insulation to the top and sides making it more efficient.
Otherwise they could make good bottle storage, where temp fluctuations is not as a high concern.
Just my 2c
QldKev
