This document presents information on a greenhouse dryer. It discusses how greenhouse dryers work on the principle of the greenhouse effect to dry materials using solar thermal energy inside a greenhouse structure. The document categorizes greenhouse dryers based on air flow, covering material, structure, and floor type. It then describes a case study of a large parabolic roof greenhouse dryer that was able to dry 300kg of chili from 75% moisture content to 15% in 3 days, compared to sun drying which only achieved 42% moisture reduction in the same time. The greenhouse dryer provided higher drying rates and quality than natural sun drying.

1. GREEN HOUSE DRYER
Presented by
Mr. DINESH
Roll no. 18AG63R17
Department of Agricultural and Food Engineering
IIT Kharagpur

2. Content
• Drying
• Introduction
• Working principle
• Classification of Green house dryer
• Advantages of Green house dryer
• Case study
• Graphical representation
• Results and discussion
• Conclusion
• References

3. Drying
• It is the removal of moisture from the food
product to safe level.
• It increase the shelf life of the product.
• It is the basic unit operation used in the food
processing.

4. Drying
• Drying rate depends on external parameters
• It also depends on internal parameter.
• It involves two phenomenon:
1. heat transfer
2. mass transfer

5. Introduction
• Sun drying is the most common method used to
preserve agricultural food products.
• Due to drying of products on open grounds or
mats, it is influenced by birds, rodents, rain and
microorganisms.
• So, the quality of the dried product is lowered.
• As a result, dried product could not get the better
price.
• To avoid this situation and post harvest losses, a
new concept of green house solar dryer arises.

6. Green house dryer
• Greenhouse structure used for drying is
called greenhouse dryer.
• Inside greenhouse dryer materials are dried using
the solar thermal energy.
• It works on the principle of Green House effect.

7. Working principle
Green house Effect
•

8. Classification of dryer
• On the basis of air flow
1. Passive (Natural convection)
Greenhouse drying under passive mode

9. Greenhouse drying under active mode
2. Active (force convection)

10. Hybrid photovoltaic-thermal (PV/T)
integrated greenhouse dryer.

11. Classification of dryer
• On the basis of covering material
1. Polythene covered
2. Polycarbonate sheet covered
3. Glass covered
• On the basis of structure
1. Even span roof type
2. Parabolic shaped
• On the basis of floor
1. Concrete floor
2. PVC sheet floor
3. Rock bed or sand floor

12. Polycarbonate covered greenhouse solar dryer

13. Advantages
• The advantage of solar greenhouse is the use of
renewable energy sources, which reduces the cost
of drying .
• Greenhouse dryer have a better quality product
than open sun drying.
• Greenhouse drying reduces moisture content in a
very less time compare to open sun drying.
• It has also advantages that the material to be dried is
protected from dust and rain.

14. Case study
Description
• Parabolic roof structure
• Polycarbonate sheet cover (thick=6mm)
• Concrete floor
• length= 20m,width=7.5m,height=3.5m
• Capacity= 1000kg
Large greenhouse solar dryer

15. Case study
• Materials used:-
1. Chilli (300kg)
2. Pyranometer
3. Hygrometer
4. Anemometer
5. Thermocouple

16. Fig : The dimension and the positions of the thermocouples (T)
hygrometers (Rh) and product samples for weights (M)

17. Observation
1. Solar radiation
Time (hour)
Graphical representation

18. Observation
2. Air flow rate
;
Time (hour)
Graphical representation

19. Observation
3. Relative humidity
Time (hour)
Graphical representation

20. Observation
4. Temparature
Time (hour)
Graphical representation

21. Observation
4. Moisture content
Time (hour)
Graphical representation

22. • The moisture content of chilli in the green
house dryer was reduced from an initial value
of 75%(wb) to a final value of 15% (wb)
within 3 days.
• Whereas the moisture content of the natural
sun-dried samples was reduced to 42%(wb) in
the same period.
• Dried chilli colour in green house dryer was
better than open sun dried sample.
Result and Discussion

23. • Moisture removing rate is more in green house
dryer compare to natural sun drying.
• Max. temperature is obtained up to 57-59 °C.
• High quality of dried products.
• Drying is uniform.
• Large quantity of crops, grain, etc., can be dried in
less time.
• The greenhouse dryer under forced convection
mode is found to be best for high moisture
content crops.
Conclusion

24. References
• Hossain MA. Forced convection solar drying of chilli,
Ph.D. thesis. Bangladesh Agricultural University,
Bangladesh, Mymensingh; 2003.
• Janjai S, Keawprasert T. Design and performance
evaluation of a solar tunnel dryer with polycarbonate
cover. International Energy Journal 2006;7:187-194.
• Muhlbauer W. Present status of solar crop drying. Energy
in Agriculture 1986;5:121-137
• Sharma VK, Colangelo A, Spagna G. Experimental
investigation of different solar driers suitable for fruits and
vegetable drying. Renewable Energy 1995;6:413-424.