Useful for students

1. Md. I. A. Ansari
Department of Agricultural Engineering
(e-mail: irfan26200@yahoo.com)

2. Greenhouse technology is one way of the using
solar energy.
Ggreenhouses are the enclosures where crops,
vegetables or flowers are provided proper
environment under adverse climatic conditions
for plant growth and production.
So for growing off season crops, it is very
much useful.

3. Figure 2. A greenhouse for flowers.

4. Passive Greenhouse
• The greenhouse in which there are no any
moving components or active elements ie.
heating or cooling occurs naturally is
called passive greenhouse.

5. Active Greenhouse
The greenhouses in which auxiliary
energy is used for heating or cooling is
called as active greenhouse.
Active systems employ pumps and
other devices.

6. Greenhouse Drying
 Post harvest life fruits and vegetables is low due to
perishable nature.
 Fruits and vegetables being high moisture foods are
spoiled due to microbes, enzymes and biochemical
reaction.
 Low temperature storage could extend post harvest
life but maintenance of cold chain is a must.
 Hence fruits and vegetables can be dried to prolong
shelf line and dried products can be kept under
ambient conditions.

7. Moisture Content

8. Food Sample =
Mass of product = Mass of water in food + Mass of dry solids
+ Food LiquidFood Solids
Mass of dry solid
Food Sample
Mass of water in food

13. • A food is initially at a moisture content of
90% dry basis. Calculate the moisture
content in wet basis.

14. Ans.: M: 567%

16. Water activity is an indicator of the availability of
free water.
Water activity is an important property for food
safety.
It predicts food safety and stability with respect to
microbial growth, chemical/biochemical reaction
rates, and physical properties.

17. • The ERH of a food product is defined as that
relative humidity of the air surrounding the
food at which the product neither gains nor
loses its natural moisture; that is, it is in
equilibrium with its environment.
• At a relative humidity above the ERH, the
product will gain moisture and at a humidity
below that level, it will lose moisture.
• A food with a aw of 0.6 will lose moisture at a
relative a relative humidity below 60% and
gain moisture above 60%.

18. Free water and Bound water
 Free water present in food acts as a solvent.
 Water which is bound by such minute
forces that its vapour pressure is equal to the
vapour pressure of pure water.
 It can be found as free water, in cavities
and wide capillaries. This can often be thought
of as the second and subsequent layers of
moisture attached to a surface.

19. A portion of the total water content present
in a product is strongly bound to specific
sites on the chemicals within the
product .
 It exerts a vapour pressure less than
that of pure water.
 It can often be thought of as the first
layer of water molecules attached to a
surface.
Total moisture content=bound moisture
content + free moisture content

20. Bound Moisture
Free Moisture

22.  Drying is traditional method for preserving the food.
It also helps in easy transport since the dried food
becomes lighter because of moisture evaporation.
 Drying prevents growth of fungi and bacteria.
 The traditional practice of drying agricultural produce
in the developing countries is sun drying, which is
seasonal, intermittent, slow, and unhygienic.

23. • To overcome the problems of sun drying,
mechanical drying is introduced with the
following advantages:
• (i) fast drying
• (ii) large volumes of produce can be handled
(iii) drying parameters can be controlled and
quality of the produce can be maintained.

24.  The energy demand of mechanical dryers is met by
electricity, fossil fuels, and firewood are becoming
scarce.
 Solar energy can be an alternative source for drying
of food and solar dryers are employed for the
purpose.
 The use of the greenhouse as a dryer is the latest
development.
 The drying capabilities of the greenhouse can be
utilized for curing tobacco leaves, while guarding the
harvest from rain damage.

25. In an efficiently managed greenhouse,
there will not be any time gap between
crops.
if crops are not grown in a particular
period, the greenhouse can be utilized as
a greenhouse dryer.

26. Importance of Drying
It can be processed during peak season and can be
utilized during off season.
Due to low water activity, shelf life of dried product
is more and it can be stored for longer duration at
room temperature.
Total volume of produce is reduced and it will help
in storage and transportation.
Added advantage is the large savings in packaging,
storage space requirements and transportation costs.

27. In general, the produce is spread as thin layers
in trays covering the greenhouse area.
The trays can be fabricated with sheet metal
and wire mesh.
Trays should be arranged horizontally on
existing growing benches or frames.
For better operation, proper ventilation should
be provided by either forced or natural
ventilation, to remove the moisture liberating
from the produce and to control the air
temperature inside the greenhouse.

28. The natural ventilation can be enhanced by
using a black LDPE chimney connected to the
greenhouse.
A dehydrated products remains stable only
when it is protected from the exposure to air,
water, sunlight, etc. hence appropriate
packaging of a dried product is an important
consideration.


30. Greenhouse Heating
Temperature is one of the most important
factors in the production of horticultural crops.
Solar energy on sunny days is often enough to
keep a greenhouse warm, even in cold
weather.
During the night time, air temperature inside
greenhouse decreases.

31. The heat is always lost from the
greenhouse when the surroundings are
relatively cooler.
The requirements for heating greenhouse
depend on the rate at which the heat is lost to
the outside environment.
Heat losses can occur in three different modes
of heat transfer, namely conduction,
convection, and radiation.

32. Heat Loss

33.  Various methods are adopted to reduce the heat
losses, viz., using double layer polyethylene, thermo
pane glasses.
 Several different methods are used to heat
greenhouses.
 Heat must be supplied to a greenhouse at the same
rate with which it is lost in order to maintain a desired
temperature.
 For the purpose of greenhouse heating, apart from
conventional systems, solar energy can also be used
and the heat can be stored using water and rock
storage.

34. Most heat is lost by covering material by
conduction.
Different materials, such as aluminum
bars, glass, polyethylene, and cement
partition walls, vary in conduction
according to the rate at which each
conducts heat from the warm interior to
the colder exterior.
A good conductor of heat looses more
heat in a shorter time than a bad
conductor and vice versa.

35. There are only limited ways of insulating
the covering material without blocking the
light transmission.
A dead air space between two coverings
appears to be the best system.
A saving of 40% of the heat requirement
can be achieved when a second covering
in applied.

36. For example greenhouse covered with
one layer of polyethylene loses, 6.8 W of
heat through each square meter of
covering every hour when the outside
temperature is 1oC lower than the inside.
When second layer of polyethylene is
added, there is 40% reduction in heat loss.

37. A second mode of heat loss is that of
convection (air infiltration).
Spaces between panes of glass and ventilators
and doors permit the passage of warm air
outward and cold air inward.
About 10% of total heat loss from a
structurally tight glass greenhouse occurs
through infiltration loss.

38. A third mode of heat loss from a greenhouse is
that of radiation.

39. Heating Systems
• The heating system must provide heat to the
greenhouse at the same rate at which it is lost by
conduction, infiltration, and radiation.
• There are three popular types of heating systems for
greenhouses.
• The most common and least expensive is the unit
heater system.
• In this system, warm air is blown from unit heaters
that have self contained fireboxes.
• These heaters consist of three functional parts.

40. Unit heaters
• In a unit heater the fuel is combusted in the
chamber at bottom.
• Hot fumes rise inside the heat exchanger tubes,
giving heat to the walls of the tubes.
• Smoke exists at the top.
• A fan forces cool air of the greenhouse over
the outside of heat exchange tubes, where it
picks up heat and warm air is circulated.

42. Heat Distribution Systems
In the convection tube method, warm air from
unit heaters are distributed through a
polyethylene tube running through the length
of the greenhouse.
Heat escapes from the tube through holes on
either side of the tube in small jet streams,
which rapidly mix with the surrounding air
and set up a circulation pattern to minimize
temperature gradients.

44. Boiler
This system is used for very big
greenhouses and is a centralized system
of heating.
The fuel for boiler can be coal or fuel oil.
The heating of the greenhouse is
generally done through hot water at 85°C
or steam at 102°C.

45. Water or steam pipes are installed above the
beds of crop and along the side wall.
The steam system is cheaper than hot water
system.
To reduce the length of pipe to be used a
number of hot water or steam pipe coils can be
used and green house air circulated over them
by blower for heating.
A central heating system can be more efficient
than unit heaters, especially in large
greenhouse ranges.

47. Infra-red Heaters
The fuel gas (LPG) is burnt and the fumes at a
temperature of about 480°C are passed in 10
cm diameter pipes kept overhead at a height of
1.5m above plants.
Reflectors are provided over the full length of
pipe to radiate the infra red rays over the
plants.
The plants and soil get heated.

53. The fourth possible type of system is the
solar heating system.
Solar heating systems are found in small
commercial firms.
Both water and rock energy storage
systems are used in combination with
solar energy.

54. Solar heating system
Solar heating is often used as a partial or total
alternative to fossil fuel heating systems.
Few solar heating systems exist in greenhouses
today.
The general components of solar heating
system are collector, heat storage facility,
exchange to transfer the solar derived heat to
the greenhouse air, backup heater to take over
when solar heating does not suffice and set of
controls.

55. Normally flat plate collector are used.
This consists of a flat black plate (rigid plastic,
film plastic, sheet metal, or board) for
absorbing solar energy.
The plate is covered on the sun side by two or
more transparent glass or plastic layers and on
the backside by insulation.

56. The enclosing layers serve to hold the
collected heat within the collector.
Water or air is passed through the copper
tubes placed over the black plate and
absorb the entrapped heat and carry it to
the storage facility.
Based on the locations, the heat derived
can provide 20 to 50% of the heat
requirement.

57. Water and rock storage
Water and rocks are the two most
common materials for the storage of heat
in the greenhouse.
To store equivalent amounts of heat, a
rock bed would have to be three times as
large as a water tank.

58. A water storage system is well adapted to
a water collector and a greenhouse
heating system which consists of a pipe
coil which contains a water coil.
Heated water from the collector is pumped
to the storage tank during the day.
As and when heat is required, warm water
is pumped form the storage tank to a hot
water or steam boiler or into the hot water
coil.

59. Flat plate solar heaters are used to heat
the water during day time.
The hot water is stored in the insulated
tanks.
The hot water is circulated in pipes
provided along the length of the
greenhouse during night.
Supplementary or emergency heating
systems are provided for heating the
greenhouse during cloudy or rainy days.

61. A rock storage bed can be used with an
air-collector and forced air heating system.

In this case, heated air form the collector,
along with air excessively heated inside
the greenhouse during the day, is forced
through a bed of rocks.
The rocks absorb much of the heat.

62. The rock bed may be located outside the
greenhouse, and it should be well
insulated against heat loss.
During the night, when heat is required in
the greenhouse, cool air from inside the
greenhouse is forced through the rocks,
where it is warmed and the passed back
into the greenhouse.

63. A polyethylene tube with holes along
either side serves well to distribute the
warm air uniformly along the length of the
greenhouse.
The water or rock storage unit occupies a
large amount of space and a considerable
amount of insulation is provided.

64. Hydroponics

65. What is Hydroponics?
Plants grow in water.
Soil less growing!

66. Soil Less Growing?
What is used as a growing media?
Gravel -Rockwool
- Sand -Styrofoam
Vermiculite - Anything Inert!

67.  The term hydroponics was first used
in the 1930s by a California
researcher named W. F. Gerike.
 It is a combination of two Greek
words—hydro means “water” and
ponics means “labor.”
 Together they mean “water labor.”

68.  Simply defined, hydroponics is
growing plants with their roots in a
medium other than soil.
 Sometimes, hydroponics is
referred to as soilless culture
because soil is not used.
 In recent years, there has been
widespread expansion in
hydroponic systems due to a better
understanding of plant growth,
nutrient needs, and technological
requirements.

69. Advantages
Faster Growth- Hydroponics works by
automatically getting the complete nutrient
mixture and water to the roots without
drowning the plant.
Plants get everything they need all the time, so
they do not grow a lot of roots searching for
nutrients.

70. Advantages
No Weeds or Pests- Gardening without soil
eliminates the weeds do you do not need weed
sprays.
Because hydroponics does not use soil, harmful
insects that live in soils cannot damage
hydroponic crops.

71. The amount of nutrients needed by plants can be
adjusted as they grow.
– As plants mature, the type and amount
of nutrients can be easily adjusted in a
hydroponic system.

72. Hydroponic systems allow the pH
levels available to plants to be
adjusted quickly.
– Adjusting the pH of the nutrient
solution helps in nutrient
uptake.
Hydroponics allows for high-
quality yields

73. Disadvantages
 Cost of initial investment on hydroponic systems is
high.
 Hydroponic production is capital and labor intensive.
 A high level of expertise is required.
 Daily attention is necessary.
 Specially formulated, soluble nutrients must always
be used.
 Some diseases can spread rapidly throughout a
hydroponic system.
 Some water born diseases can spread rapidly in
recirculation system.

74. Plant Needs
What is needed for a plant to survive?
• Water
• Sunlight
• Air
• Nutrients (usually soil)
• Anchorage (root system)

75. Requirements For Plants To Grow
• Hydroponically grown plants have the same basic
requirements as plants grown in soil.
• All hydroponic systems must supply support, water,
nutrients, and air.
• The major differences between hydroponic systems are the
way in which plants receive support and
the method in which nutrients
are made available.

76. 1. Temperature—Since most hydroponic
systems are in greenhouses or confined areas,
specific temperatures can be set.
– Each type of plant has an optimal
temperature range for maximum growth.

77. 2. Light—All vegetables and most flowering plants
need large amounts of light.
– Hydroponically grown vegetables require 8 to 10 hours of
direct sunlight daily for healthy growth.
– Commercial operations sometimes use high-powered
lamps to increase light intensity and duration.

78. 3. Water—Providing plants with enough water is
not a problem with water culture systems.
– However, water quality can be an issue.
– The pH of water should be tested and, if necessary,
adjusted for the particular crop being grown.
– Softened water may contain harmful amounts of sodium
and should be avoided.

79. 4. Oxygen—The most critical factor is supplying
the root system with enough oxygen for healthy
root growth.
– Plants and plant root systems require oxygen for
respiration.

80. 5. Nutrients—Hydroponically grown plants have the
same nutrient requirements as those grown in soil.
– Since hydroponic systems do not use soil,
essential nutrients must be provided with a
water solution.
– The solution requires careful calculations to
ensure that the optimal amounts of
macronutrients and micronutrients are
provided.

81. 6. Support—Soil provides a firm anchor for
plants to grow upright.
– In hydroponic systems, artificial support can
be provided.
– This can be accomplished through string and
mesh materials.

82. The term hydroponics is used to describe many
different types of systems.
Generally, all systems can be classified as
either aggregate culture or water culture.

84. • Aggregate culture involves the use of aggregate or
substrate materials that help support plants.
• Such materials allow the plants to take root.
1. Common substrates include sand, perlite, vermiculite,
gravel, peat moss, and rock wool.
– Rock wool is a spongy, fibrous material spun from
molten volcanic rock.
– All these materials are considered inert.
– They do not provide nutrients to the plants.

85. Soil Less Growing?
What is used as a growing media?
Gravel -Rockwool
- Sand -Styrofoam
Vermiculite - Anything Inert!

86. Rock Wool
Perlite and
Vermiculite

87. 2. Solutions provide the plants with essential
nutrients.
– Common methods of supplying a solution
are through drip and trickle.
– One method involves flooding the aggregate
for 10 minutes.
– The aggregate is allowed to drain for 30
minutes and then flooded again.

88. • Water culture is also referred to as nutriculture.
– In this type of system, no substrate is used.
– Although plants may be started in rock wool,
most of the roots are growing in a nutrient
solution.
– A system of this type has a continuous flow or
mist of nutrient solution that is recycled.
– Such a system is referred to as a circulating
system.

89. DRIP SYSTEMS Hydroponic
 Drip systems are the most widely used type of
hydroponic system in the world.
 Operation is simple, a timer controls a
submersed pump.
 The timer turns the pump on and nutrient
solution is dripped onto the base of each plant
by a small drip line.
 In a Recovery Drip System the excess nutrient
solution that runs off is collected back in the
reservoir for re-use.
 The Non-Recovery System does not collect the
run off.

90. The non-recovery system requires less
maintenance due to the fact that the
excess nutrient solution isn't recycled back
into the reservoir, so the nutrient strength
and pH of the reservoir will not vary.
This means that you can fill the reservoir
with pH adjusted nutrient solution and then
forget it until you need to mix more.
 A recovery system can have large shifts
in the pH and nutrient strength levels that
require periodic checking and adjusting.

93. 1. The water culture system most commonly used
in commercial operations is called nutrient film
technique (NFT).
– In an NFT system, a continuous flow of nutrient
solution runs through a series of tubes or troughs.
– A pump raises the nutrient solution to desired levels,
and gravity allows it to drain.
– The system is constantly recycling the nutrient
solution.
– NFT is typically not used to produce root vegetables
or tuber crops.

94. The concept of Nutrient Film Technique
(NFT) was originally developed by Dr
Allen Cooper in the UK. Dr Cooper
described the concept as follows:
A very shallow stream of water containing
all the dissolved nutrients required for
growth is recirculated past the bare roots
of crop plants in a watertight gully.
 Ideally, the depth of the recirculating
stream should be very shallow, little more
than a film of water – hence the name
nutrient film.

95. Nutrient Film Technique (NFT)
It is a kind of hydroponic system.
The NFT systems provide a constant film of
water and nutrients along the bottom of a
channel.
In effect, part of the roots grow down in the
water/ nutrients and parts of the roots above
the water line getting fresh air and oxygen.
The nutrient solution is pumped into the
growing tray (usually a tube) and flows over
the roots of the plants, and then drains back
into the reservoir.

101. 2. Aeroponics is another type of water culture
system.
– In such a system, plant roots are suspended
in the air within a closed container.
– Inside the container, spray nozzles mist the
roots.

102. • The aeroponic system is the most high-tech
type of hydroponic gardening.
• The growing medium is primarily air.
• The roots hang in the air and are misted with
nutrient solution.
• The mistings are usually done every few
minutes.
• A timer controls the nutrient pump much like
other types of hydroponic systems, except the
aeroponic system needs a short cycle timer
that runs the pump for a few seconds every
couple of minutes.