Jason wrote:

Does anyone have any tips on where I can look for details on how to go about
designing/specifying/building a passively-cooled larder for a kitchen? We
are having some structural work done, and being able to incorporate
something like this would be great.

I've done a little search, but not really come up with anywhere good to
start.


Great idea Jason. This should be one of those desirables for a well
designed house.

There are a few options. I'd go with a small fan and differential
thermostat for a start. IME this has knocked 4-6C (and occasionally as
much as 10C) off evening and night time indoor temp without any
insulation. Add insulation and lots of thermal mass, eg cast in situ
concrete, and you'll see a temp reduction all day as well.

The diff stat is important, running a fan on a timed schedule did not
deliver anything like as much benefit. A cupboard would only need a
tiny 3" computer case fan, with 2 exterior holes for air inlet and
outlet. Holes should have metal mesh to keep rodents out and insect
mesh to keep bugs and debris out.

You'll want the puter fan to be silent, so I'd mount it on rubber
bushes so it doesnt use the all as a sounding board. Use a variable V
wallwart to power it, so you can select 12,9,7.5 or 6v. This reduces
consumption and noise if full power isnt needed, and it probably wont
be. A simple labyrinth over the fan is the best way to kill fan noise,
so if you find your heavily constructed cupboard doesnt silence it, you
can make a very effective labyrinth out of sheet steel with 2 layers of
cardboard glued onto it. Or chipboard would probably be easier.


If you want to take the cooling further, there are 2 simple ways to
chill it.

1. Take the inlet air through a plastic pipe sitting in a trough of
water. A standard ballcock keeps the trough filled. The water
evaporates, cooling the inlet stream. The pipe barrier keeps the inlet
air dry, you dont want to get the cupboard damp.

2. Bury a plastic pipe underground and bring in the air through that.
Temp underground is well below ambient in summer. Cooling a house this
way needs an awful lot of pipe, but a small cupboard doesnt.


If you must have something totally passive, larger air holes with one
way dampers would work, waiting for the wind to blow through. But this
would require more vent area than forced air, plus actuators to keep
the dampers shut when required. I'd go with the fan, its much easier.

There are of course other options. Heat pipes act like one way heat
valves, and are fully passive, but a fan and stat are a lot simpler and
controllable. Heat pipes have been used in custom fridges to provide
this type of cooling during winter, reducing energy consumption.

I wouldnt use air from under the house as it'll be damp and musty, not
whats wanted. If using evaporative cooling, keep the damp separate to
the intake air. Plastic pipe makes a very simple heat exchanger.

Lastly, I suppose another alternative is to run the cold water supply
pipe to the house through the larder before it goes anywhere else. This
comes in at a nice cold underground temp. If you do that, you'll need a
drip tray, as condensation may form on the pipes. Add fins to the pipe
for greater heat exchange.


NT