How SolarWall solar crop and process drying works

By: Solar Drying  09-12-2011
Keywords: Solar Collector, Solarwall

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No matter what drying process is used, the basic principle is that water is drawn from within the item to be dried, up to its surface and then removed from the surface. How quickly this happens, and how much energy is required, depends on three things:

1) The type of material being dried (how dense it is, how much moisture it contains, etc.),

2) The volume, temperature and moisture content of the air passing over the “wet” material, and    

3) The initial and desired final moisture contents of the material. 

Whether being used in conjunction with an existing system, or as the sole source of heat, SolarWall solar panels can be easily configured to deliver sufficient heat to correctly and efficiently complete the task at hand. Whether batch type or continuous, solar air heating can be added to most existing dryer system types.

1) How it works

i)     Perforated metal cladding panels are affixed to a roof; in areas where snow accumulation is a problem, the minimum slope should be 45° to allow the snow to slide off. Equator facing slopes are the best, but other orientations are suitable, too. Walls can also work well if the roof is not suitable.

ii)     To get the most free heat possible from your solar roof panels, as much of the roof should be covered as possible. Maximum efficiency and heat gains can be realized by placing panels over every roof surface – even going around obstacles and openings. If photovoltaics (PV) are being considered, the PV panels simply get placed over the transpired solar collector panels.
iii)     When SolarWall solar heating/solar drying panels are affixed to the roof (or wall), a gap is left between the metal cladding and the roof surface. The metal panels are heated by the sun’s rays shining on the dark metal cladding. Thanks to fans which create negative pressure in the roof space/cavity, the heated air passes through the small perforations in the cladding and then travels to the nearest fan or blower intake. The air flows in such as way as to help simplify balancing and ensures that no solar heat is lost. Note: All driers have fans; SolarWall simply ties into that fan, bringing air that has been warmed before it hits the burner.
2) How big a gap is needed between roof and cladding?
The ambient temperature and material being dried will dictate the heat gain needed from the solar collector panels in any given application. How much the temperature rises in the SolarWall panels depends on the volume of air per square foot (or meter) moving through the panel. Individual needs can be worked out in advance by SolarWall engineers so that the optimal amount of paneling is added, and the right amount of space is left between the roof surface and the cladding. On average, though, the gap is about 8” (20 cm).
3) Mounting the panels
It is best to mount the SolarWall panels on the roof, either with twin solar roofs or with a single roof mount (depicted in the typical connection details).

4) When a commercial dryer or heater is also being used
On sunny days, the increase in air temperature ranges from 20ºC to 30ºC (36ºF to 54ºF); in some cases though, even more heat gain may be needed and a dryer is needed with the SolarWall panels acting as pre-heaters. When SolarWall panels are being used in conjunction with a dryer (new or existing), it’s essential that there be a means of modulating the flame so that…
a)     the burner can be turned down (or off) when the panels are producing enough solar heat, or
b)     the burner can be turned up to top up the solar heat when it’s cloudy or very cold outside.
The SolarWall system works equally well with trough driers, tunnel driers, belt driers and drum driers.
Trough Dryer:Is typically used for crops such as tea, nuts, and cocoa beans 

Tunnel Dryer: Is most often used for drying products such as fruit and fish which have a higher initial moisture content.

Belt or Drum Dryer: Used for coffee, seeds, etc.

5) To recap

Perforated, dark, metal cladding is placed on as much roof surface as possible. Air is warmed by the sun, and is drawn in through the holes. This pre-heated air is drawn into ducting and, if necessary, has its temperature boosted by a supplementary burner, before being used for crop or process drying. Yes, it is as simple as it sounds.
To receive our SolarWall Crop/Process Drying Design Guide which includes illustrations and case histories, please complete our .

Keywords: Solar Collector, Solarwall

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