The pot-in-pot works by evaporative cooling. One large clay pot is placed inside another with a boundary layer of sand between the two. Tender crops are packed into the inner pot and covered, then water is poured into the sand. The water slowly evaporates, drawing the heat from the contents of the pot and keeping the vegetables fresh for days.
The same principle is used in simple cooling devices the world over. A company in Ohio has been making the same style of passive water cooler for more than a century, based on an Amish design. This is simply a porous clay urn, which quietly sweats its contents, helping to keep what remains cool. Terracotta wine coolers work in the same way, as long as you remember to give them a good soaking first.
There is a limit to the potential of such simple evaporative coolers in the kitchens of Britain. After all, a pot-in-pot is never going to look as good as a 6ft-high bright pink retro-chic fridge-freezer, the unassailable accessory of all domestic food designers worth their coarsely ground sea salt.
Perhaps, though, there is a middle ground. This is what we are seeking at Tree House, where the outline of our kitchen is taking shape amid the general hubbub of wiring, plumbing and plaster-boarding. With the FSC birch-ply carcasses installed, Ford and I have had our first impression of life in the culinary laboratory that looks over our living space, through the glazed boundary of the house, across the pond and into our courtyard garden. If this view proves to be too distracting, we will be able to pop our amputated fingers into our energy efficient under-counter fridge (www.aeg-electrolux.co.uk) while we wait for help to arrive.
We will have a small freezer too, but this will be tucked away under our staircase. Its installation is on hold as the staircase is one of the few key items of the building yet to take shape, though Mark has been doing a good job plaster-boarding the curving interior of the trunk of Tree House where it will rise.
The most important eco-choice when buying a fridge or freezer is to check the energy rating: nothing less than A is acceptable and A+ or A++ is desirable (the energy efficiency logo is now only given to appliances rated A+ or better). Regrettably, however, the energy rating can be misleading because it is based on the energy use per cubic metre of space inside. This approach favours bigger appliances because, as the size of a fridge increases, the additional energy required to cool the interior decreases. But extra energy is still extra energy, so an A-rated mega-fridge will use far more power than a B-rated under-counter fridge.
So don't just check the energy rating when making comparisons between products, check the annual energy consumption, too. Then think very hard about how much powered cooling you really need. Really, really need.
If any entrepreneurs out there think that the pot-in-pot might catch on here, do get in touch. A little retro-chic detailing and I'm convinced we'll be millionaires.
Will Anderson's complete 'Diary of an Eco-Builder' will be published by Green Books in Spring 2006 (www.treehouseclapham.org.uk)Reuse content