Design Principles for Retained Heat Cookers
Dean Still, Aprovecho Research Institute, March 2005

Guesses at Design Principles for a Retained Heat Cooker

1.) Air exchanges are more important than insulation
A.) Make the enclosure as air tight as possible
B.) Use R-7 insulation at a minimum

2.) The mass of the insulation and any mass within the envelope of
insulation will rob heat from the pot of food
A.) Keep insulation and inner walls of the retained heat cooker as light
as possible.
B.) To work well insulation should not be less than R-3 per inch of
thickness.

3.) Conduction looses more heat than convection. Convection looses more
heat than radiation.
A.) Lift the pot up off the floor of the box using a non-conductive
material. Leave an air gap of .5 inch.
B.) The walls and ceiling of the box optimally should be .5 inch bigger
than the pot.

4.) Insulation looses its ability to slow the passage of heat when
slightly moist.
A.) Do not allow moisture to contact the insulation.
B.) Use a moisture proof barrier between the pot and the insulation.
C.) Use closed cell insulation.

5.) The inner box will grow mold.
A.) The inner surface should be easy to clean.
B.) Cloth will become unsanitary if unprotected.

6.) To cook pinto beans
A.) They need to be pre-soaked
B.) The retained heat cooker needs to be able to keep 5 liters of water
above 90C for 90 minutes.

Best,

Dean
Posted to Stoves March 1, 2005
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