Number of units used in the past: none

Number of units currently in use: one at Dehra Dun and one at Banswara ,

Rajasthan, Latitude? 25°N

Periods of Operation:

(a) On experimental basis': January 1971 to May 1972

(b) In field operations: June 1972 to date

Drying Data;

TABLE A - individual tests with 3,54 cu.m. charges of 25 mm planks of furniture and joinery woods.

Material Drying Time (Days)

Green to 12% moisture content

Mundani (Acrocarpus fraxinifolius) 28 to 32

Toon (Cedrela Toone) days for

Hollong (Dipterocarpus macrocarpus) all the

Haldu (Adina cordifolia) species Chir (Pinus roxburghii) cut as

Kanju (Holoptelea integrifolia) stated

Sissoo (Dalbergia sissoo) in (a)

TABLE B - Mixed 3,54 cu.m. charge of 75 x 100 mm framing of structural woods.

Material Drying Time (Days)

Green to 12% moisture content

Laurel 42

Hollong (Dipterocarpus marcocarpus) 26

Hollock (Terminalia myriocarpa) 30

Sissoo (Dalbergia sissoo) 25

Safed siris (Albizzia procera) 34

Eucalyptus hubrid 55

Furniture timbers were dried within 40% of the time required for normal air drying.

Operating Conditions;

Kiln Temperature Excess: Over ambient on clear days (oc)

May - June Novenber

With green charge 10 15

With charge nearing completion of 20 28


Fans worked during daylight hours only, with baffles adjusted to produce;

(a) a recirculating system with partial air venting, or

(b) a single-pass flow-through drying system for use in early stages of drying wet timber or quick drying plankigg.

See Figure 3.

2. Timber for wall and roof stands, framing and foundations - 1,05 cu.m. 62,50

4. Polyethylene sheet - 0,25 ran - 122 cm wide - 50 m 28,13

5. Screws, nails, angle iron, etc. 18,75

6. Fan 91 cm - with auxiliary equipment 141,25

7. 1 HP electric motor 84,37

8. Black paint - 9 litres 9,00

9. Labour charges, 30 days 75,00

TOTAL 618,50

$1.00 U.S. worth approximately 8 Rupees Annual Operating Expenditure;

Considering that a solar kiln will be effective only for about 8 months in the year in most part of the country, the annual operating costs will be as follows:

Electric power for running fan (2 cents per Kwh) 79,63

Labour charges for stacking and unstacking of timber 12,50

Cost of replacing sheeting every 2 years 25,00

TOTAL 117,13

Output of seasoned timber in 8 months: 28,32 cu.m.

The operating and construction costs are respectively 60% and 75% lower than those required in a standard steam heated kiln.

Cost of Drying Related to a Unit of Material Dried:

$4.00 U.S. per cu.m. for planking $6.25 U.S. per cu.m. for framing

Estimated Life of the Dryer:

Polyethylene sheeting needs to be replaced every two years. Wood frame if made of durable hardwood or preservative treated timber is likely to give a life of at least 15 years.


The kiln does not require skilled or full time operators indispensable in a steam or electric heated kiln and its initial cost is relatively low.

It is ideal for small saw millers and manufacturers of furniture who are operating on a small-scale. These people often use partially air seasoned or unseasoned tinker for two reasons:

1) because of thw widespread use of low shrinkage species such as teak and

2) because efi.a lack of awareness, on the part of the wood industry, of the need for properly seasoned wood for domestic uses.

The performance on cloudy days is rather poor.

A suitable device for storage of solar energy for night tiiiie use would result in further drying time savings and make the process more attractive, in India, the large scale timber industry has so far been seasoning properly only special wood products, if proper seasoning was to be extended to all the wood products, drying units would demand a fast turnover for economical operation.

An efficient arrangement for additional humidification of the kiln air remains to be developed to.prevent cracking of the more refractory or thick section timber during the solar kiln drying process.

Principal investigator(s): Sharma, S.N.

Nath, Prem

Wood Seasoning Branch Forest Research Institute Dehra Dun U.P. India


(1) Sharma, S.N., Nath, Prem, Bali, B.I., Journal of Timber Development

Association of India, volume XVIII, No. 2, April 1972.

(2) Gupta, C.L., Draft for Action Plan for Solar Drying, ACES Occasional

Paper No. 5, Auroville Centre for Environmental Studies, Pondicherry 605002, India, 1973

Plenum Chamber Closed

Plenum Chamber Closed



Vents closed



Back Fan "Cover Removed

Vents closed

Plenum Chamber Opened

Baffles Closed

Back Fan Cover On

Vents Openod (A)

Baffles Closed

Back Fan Cover On

Vents Openod (A)

Figure 3. Drawing Showing the Kiln Working as

(A) A Single pass Forced Air Dryer?

(B) A Recirculating Air Dryer with Partial Ventilating




Status: experimental Heating mode: hybrid

Type: chamber dryer Air circulation: electric fan forced convection

This dryer has been tested and operated in Puerto Rico, it is one of a series of similar solar lumber kilns tested throughout the world, (United States, Philippines, India, Madagascar, Uganda, japan and South Africa). The results of the many different tests have shown that the solar lumber drying is particularily effective and attractive in the tropical regions. The solar kiln dried lumber was found to have moisture contents lower than than can be expected with air drying.

Figure 1. This Drawing Illustrates the Main Components of the Lumber Dryer: the Four Fans, the Blackened Metal Sheet Absorber and the Louvered vents

Characteristics :

The luaber dryer is aligned lengthwise on an east-west axis with its lower side wall facing south. The roof is sloped southward at an angle of about 16°, The structure rests on a reinforced concrete slab, to which it is anchored by bolts through sill plates. The north wall is covered with plywood sheets. All other walls and the roof are covered outside and inside with transparent plastic films which provide an insultating dead air space. Small louvered vents are set in the lower corners of the east and west walls.

This dryer has a blackened metal heat absorber, which is about 60 cm below the roof and parallel to it. Four fans, powered by a 1,1 kw motor mounted outside the north vail, are located in the upper back part of the dryer. These fans blow the air over and under the black absorber sheet, for taking as much heat as possible from it. Baffles are set around the fans and between the heat absorber and the top of the lumber pile (located centrally within the dryer). These force the air flow to circulate in the following path: from the heat absorbing surface, downward on the south side, through the lumber pile, and back upward on the north side into the fans.The slight pressure differential created on the two sides of the wood pile produces slow air movement through the vents.

Dimensions: Hie overall dimensions of the dryer are:

3,05 m wide and 6,10 m long, the south wall is 3,0 metes high and the north wall 4,1 m high diameter of fans: 40 cm air space between plastic sheets: 4 cm

Materials of construction: Drying Chaafcer:

Transparent cover: roof and walls - transparent plastic film Frames: conventional 5 x 10 cm lumber insulation: none

All imported materials.

Location: San Juan

Puerto Rico

Latitude: 18°28'N Longitude: 66°06"W

Practical Operation:

Number of units used in the past: one Nuriber of units currently in use: none

Periods of Operation:

(a) On experimental basis: the unit was tested only from December 1961 to

April 1965

Drying Data;

Mahogany (Swietenia macrophylla) and Guaraguao (Guarea) were dried.

Quantities dried: 7 charges with 2 000 Bd. ft, each; and 1 charge with 5 000

Bd. ft. (For Drying Times, Operating Conditions, and Climatological Data, see tables 1, 2, 3, and 4).

TABLE 1 - Mean Monthly Climatological Data for the Rio Piedras - San Juan area (1900-1964)
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