Farm­ers in dry re­gions can keep ve­get­able and fruit pro­duce fresh for more than a week using an en­ergy free wooden char­coal cool­ing cham­ber.

A char­coal cham­ber, which works best in re­gions where the air mois­ture con­tent is 30 per cent or less, re­duces the spoil­age rate and al­lows for more time for sale of per­ish­able goods by main­tain­ing low tem­per­at­ures.

Wind in areas such as North East­ern, East­ern, parts of Rift Val­ley and other low rain­fall areas in Kenya is warm, but dry. Warmth causes foods to go bad, with ripe to­ma­toes tak­ing less than four days.

Ac­cord­ing to the Queen’s Uni­versity of Mech­an­ical En­gin­eer­ing re­search, a char­coal cooler can boost the shelf life of to­ma­toes from two days to 20 days.

Dur­ing con­struc­tion of the hutch like cham­ber, a cav­ity cre­ated by a chicken wire-mesh is left all round.

The 5cm or so peri­meter cav­ity is then filled with com­pact char­coal pieces.

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A bucket or a tank placed on top of the struc­ture sup­pli­ers the water that keeps the char­coal wet. A drip pipe run­ning on top of the char­coal layer re­ceives the water and dis­trib­utes it evenly into the pieces.

Char­coal is a bad con­ductor of heat. Con­ven­tional entry of heat is lim­ited in this case.

At the same time, the wind that is blow­ing into the cham­ber while hot dry is cooled and sat­ur­ated with water particles. Its tem­per­at­ure is lowered as its en­ergy is used to va­pour­ise the water droplets in the char­coal. The pro­cess even­tu­ally lowers the tem­per­at­ure of the air in the cham­ber, where the farm pro­duce is.

The foods are spread on the shelves in the cooler.

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The ve­get­ables do not also lose shape due to loss of mois­ture as a res­ult of strong dry wind that is blow­ing.

Char­coal cool­ers work best in re­gions where the mois­ture con­tent in air is below the 30 per cent mark be­cause if the wind is warm and sat­ur­ated, it will have no room to ac­com­mod­ate more water vapor and heat.

Ex­cess water drip­ping from the char­coal can be col­lec­ted by an open pipe just below the layer, then dir­ec­ted into an­other con­tainer for reuse.