Larder cooling

[EccentricAnomaly]

Not to de-rail KLD's fan control topic (maybe rogeriko's comment can be moved here) I think it's worth discussing schemes for cooling larders as efficiently as possible.

Here's what I have in mind: a radiator ("absorber" actually) in the larder and another on the north facing roof above it plumbed in a loop so that thermosyphoning takes heat out.  The loop would probably be filled with quite a bit of glycol.  It'd need a small expansion vessel, of course.

The absorber could probably do with a drip tray under it to catch any condensation which runs off.  If it's an ordinary steel radiator then the paint would need to be kept in good condition.

A refinement might be to box in the sides of the radiator (the one on the roof) and screen the front with some material which transmits long-wave IR but reflects short-wave solar radiation.  White polythene seems, from my limited experiments, to suite.

[johnrae]

Surely a passive system like you suggest would not only cool the larder during the cool of the night but also heat it up during the heat of the day.  And a non-return valve to prevent the reverse thermo-syphon would inhibit all action due to the pressure required to open the valve.

In my limited experience the best passive cooling system for a larder is a nice thick concrete floor

jack

[johnrae]

The other form of passive cooling is a wet blanket.  The oldies amongst us will remember fitting a wet sock over a milk bottle tohelp keep it cool.  The latent heat of vaporisation cooled the milk (by extracting heat from the bottle contents) as the warm ambient air evaporated the water.  It didn't do much but anything was better than milk being poured from the bottle in lumps !!  Fridges were very much a luxury before the comparative affluence of the 60s.
jack

[EccentricAnomaly]

Surely a passive system like you suggest would not only cool the larder during the cool of the night but also heat it up during the heat of the day.

How would the heat travel downhill?  I'm proposing that the external radiator be above the absorber, probably by at least a metre or two.

A more extreme example using heat pipes: http://fourmileisland.com/IceBox.htm

[KLD]

EA

The one issue I see with your proposal is that the temperature difference between inside and out might not be large enough to drive the thermo-syphon. Our larder works well during winter; while it was below zero for two weeks or so last January, the larder temp fell to 3 or 4°C.
During summer, when even the night temps are around 20°C, no passive solution will work.
But now and in spring, when the nights are cool (say 10°C), you want the larder to use as much as possible during those maybe six hours available. Will the radiator circuit be able to shift enough energy?

Klaus

[EccentricAnomaly]

Klaus, yes, it would really only be on clear nights that there'd be much cooling in summer.  I did some experiments with trying to do some cooling with covered surfaces as I mentioned above but didn't really come to any conclusions.