PVC tubing 
The power of evaporation
This year, we’ve all been working from home. I’m very lucky to have a man shed to work in. In very hot weather though it can become far too hot to work in. The roof is dark and in direct sunlight on a hot day we are looking at 40C.
The shed has a gutter and a water butt, so I decided to create a water cooling circuit with some PVC pipe arranged as a spray bar. I used a PWM motor speed control circuit and a 12V bilge pump from eBay.
On a hot day the roof would reach 66C. With the water cooling it would bring that down to 28C. Its not so much the water cooling the roof as the evaporation of that water, so I don’t need to spray a lot of water, just keep it damp. The specific latent heat of evaporation of water is staggering so the cooling effect is very real and quite dramatic. On the hottest days, the roof evaporated 25l of water which is many megawatt hours of energy, powered directly from the sun – that otherwise would have cooked me.
Refinements
The evaporation was so effective that I had to add a float switch to prevent the pump running dry and I had to top up the water every other day unless it rained.
I added an irrigation inline filter to stop debris clogging the jets. Again, where else, a fiver on eBay.