Gundruk pot and dhungro
Gundruk pots and dhungro are fermentation containers documented in Nepal and one Darjeeling household. FAO describes earthenware; a 2024 figure identifies a bamboo-made airtight dhungro buried in a pit within a cow-dung heap.
Equipment · Drying kilns and dryers
Solar-biomass hybrid cabinet dryer
A cabinet dryer that takes its heat from a flat-plate solar collector by day and from a separate biomass stove when the sun is not enough, with the stove's flue kept apart from the drying air.
A solar dryer with a stove for the cloudy hours
A solar dryer uses the sun to heat the air that moves across the food, and the air is then carried into a chamber where the food is set out to dry. Where the sun is reliable the arrangement is simple. Where it is not, the dryer needs a second source of heat, and this design gives it one: a biomass stove that burns briquettes and heats the same drying chamber when the collector cannot.
The cabinet has three working systems. A flat-plate solar air collector, with a single layer of glazing and an area of 3.2 square metres, warms the ambient air. A drying chamber holds nine trays and is loaded from three doors at the rear. A combustion stove, with its heat exchanger and a 1.7 metre flue chimney, supplies the heat when sunlight is short. The source describes this as a hybrid, and the hybrid is the point of the design: the dryer keeps working through a cloudy spell instead of stopping.
Sources for this section
How the air and the flue gas take separate routes
Ambient air is warmed in the solar collector and rises into the chamber, where it crosses the trays. Warm, humid air leaves through a chimney at the top. The circulation is natural, with no fan described in the source. When the stove is in use, its heat reaches the process air through a finned rectangular aluminium-pipe heat exchanger. The flue gases travel in their own chimney.
This separation is the central control. The source states that flue gas can carry smoke, soot and harmful gases, and that it must not come into contact with the product. The stove therefore heats the air through a wall rather than mixing its exhaust into the drying air. Whether the joints, hood and heat exchanger hold that separation is a question the source leaves for the builder to test, and the research lists flue leakage and soot deposits among the prototype checks.
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What is known about the stove
The stove is a small steel box: a 2 mm mild-steel plate, a body about 600 by 300 by 150 millimetres, and a grate of 5 millimetre rods set roughly 60 millimetres apart, about 50 millimetres above the base. It has adjustable primary-air openings and an upper hood that connects through the heat exchanger to the flue. The fuel is a briquette of charcoal and clay about 130 millimetres across and 90 millimetres high, and the stove takes up to eight at a time.
The source reports a chamber temperature of 50 to 60 °C for this system. Those figures describe one arrangement in one period, and the source gives them as observations. They are not a drying setting that a reader can copy, and they are not a safety limit for any food.
Sources for this section
Building one
The source names the parts: the collector, the cabinet and its stand, nine removable trays with their doors, the stove with its grate and sliding air covers, the upper hood, the connecting flue, the heat exchanger and the separate exhaust chimney. A builder would fabricate the cabinet and collector, mount them on the stand, fit the trays and doors, make the stove, join the hood and flue through the heat exchanger, and then check that the flue gas stays isolated from the process air. This order is inferred from the design. The source does not give the joints, clearances or hole positions, and those need the drawings in the original manual.
The tools the source names for comparable construction in the same booklet are a tape, square, straightedge, caliper, sheet-metal cutter, drill, riveting tool, screwdriver and hacksaw. Welding is implied by the steel stove and hood. The source does not list it as a task for every builder, and a qualified metalworker is the practical route for the steel parts.
Sources for this section
What is not yet established
The source gives the solar collector's area but not its dimensions, the cabinet's outer envelope, the chimney cross-section or the dimensions of the heat exchanger. Those figures are missing from the booklet's specification table, and this page does not supply them. The design is a documented precedent for a hybrid dryer, not a verified build, and no measured drying performance is recorded for it.
Anyone adapting it to food should treat the stove's exhaust, the temperatures and the product's own drying behaviour as matters for their own measurement. The source does not validate meat or fish drying with this equipment.
Sources for this section
History
The design appears in Package 7 of Technology Packages: Solar, Biomass and Hybrid Dryers, a 2005 booklet from the Regional Energy Resources Information Center of the Asian Institute of Technology. The booklet credits project teams in Nepal and the Philippines. It does not date the first prototype.
Equipment details
PowerSolar The collector drives daytime drying with natural circulation; the source describes no fan. A biomass stove burning briquettes heats the air through the heat exchanger when solar energy is insufficient. The stove holds up to eight briquettes of 130 × 90 mm.
How you get oneBuilt yourself The source describes the components and an assembly order, not a shop drawing. It refers to Package 5 of the same manual for the collector, chamber and stand.
CareThe source gives no cleaning or storage routine. It warns that flue gas carries smoke, soot and harmful gases, so the flue, chimney and heat exchanger need checking for leaks and soot. Those checks are prototype tests the research proposes, not steps the source sets out.
Made of
- Flat-plate solar air collector, single glazing — Warms the air that enters the drying chamber
Collector area 3.2 m² as the source states it. The source does not enumerate the collector's sections or its dimensions. - Window glass — Glazing over the collector
Listed among the materials. Thickness and fixing are not given. - Mild-steel sheet, 2 mm — Stove body and stove plate
Stove body envelope 600 × 300 × 150 mm. - Stove grate of steel rod — Holds the briquettes above the stove base
Rods 5 mm in diameter at about 60 mm spacing, about 50 mm above the base. - Finned rectangular aluminium-pipe heat exchanger — Passes stove heat into the process air without letting flue gas touch the air
The source describes the form. Its dimensions are not given. - Galvanised iron and aluminium sheet — Cladding and hood
The source lists both metals. It does not say which part each sheet forms. - Wood — Chamber frame and stand
Listed. Species and section are not given. - Glass wool — Insulation
Listed. Its position in the cabinet is not specified. - Aluminium screws and rivets — Fasteners
Listed for the cabinet assembly. - Flue chimney, 1.7 m — Carries flue gas away from the stove
Height 1.7 m as the source gives it. Cross-section is not given.
Risks and precautions
Keep the stove's flue gas and smoke out of the drying air. The source warns that flue gas can contain smoke, soot and harmful gases.
Limits
Flue gas can contain smoke, soot and harmful gases. The source says it must not touch the product, so the stove's exhaust has to stay on its own route.
Source →Solar heat alone depends on available sunlight. The stove is the design's answer for the periods when the sun is insufficient.
Source →The source reports drying-chamber temperatures of 50 to 60 °C for this stove system. These are historical observations of one arrangement, not a set point or a food-safety limit.
Source →Places
Nepal
Manufacture · Country evidenceThe design was developed with RECAST, Nepal, from an AIT regional programme. Only the country is recorded; no locality is given.
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Sources
Regional Energy Resources Information Center, Asian Institute of TechnologyEquipment · Method · History · Safety
Technology Packages: Solar, Biomass and Hybrid Dryers (Package 7, pp. 36-40)The hybrid cabinet has a 3.2 m² single-glazed flat-plate solar collector, nine trays, three rear loading doors and a natural-circulation air path.
The biomass stove heats process air through a finned rectangular aluminium-pipe heat exchanger; flue gas is carried away separately and must not contact the product.
The stove body is 600 × 300 × 150 mm in 2 mm mild steel; the flue chimney is 1.7 m high; briquettes are 130 × 90 mm and up to eight fit the stove.
The source reports 50-60 °C inside the drying chamber for this stove system as an observation.
Cited in: A solar dryer with a stove for the cloudy hours; How the air and the flue gas take separate routes; What is known about the stove; Building one; What is not yet established