PLANNING & DESIGNING OF GREENHOUSE
A
greenhouse, is basically the purpose of providing and maintaining a growing
environment that will result in optimum production at maximum yield. The agriculture in the controlled
environment is possible in all the regions irrespective of climate and weather.
It is an enclosing structure for growing
plants; greenhouse must admit the visible light portion of solar radiation for
the plant photosynthesis and, therefore, must be transparent. At the same
time, to protect the plants, a greenhouse must be ventilated or cooled during
the day because of the heat load from the radiation. The structure must also be
heated or insulated during cold nights. A greenhouse acts as a barrier between
the plant production areas and the external or the general environment.
LOCATION OF GREENHOUSE
Selecting a “good” site for the location
of a greenhouse is crucial. But what constitutes a “good” site? There are
several things that should and must be considered in order to increase the
chances of a successful operation and business. Things to Consider While Selecting a
Greenhouse Site:-
1. Solar Radiation:- Plants require sunlight for
photosynthesis. When plants experience cloudy days their photosynthetic rates,
and therefore their ability to grow and yield a product, such as tomatoes,
cucumbers, peppers, etc., will be reduced. Therefore, a region and location
with high light intensity year-round is desired.
2. Water – Water quantity and quality is
crucial. Water will be needed for irrigation. Water will be needed for the
evaporative cooling system and can equal or exceed the irrigation water amounts.
However, due to more strict regulations and a desire to avoid ground water
contamination with high concentrations of salts, large greenhouses are now
recirculating the nutrient solution. Recirculating the nutrient solution also
saves water, nutrients & money. Therefore, excess nutrient solution should be recycled
and/or mixed with the bleed-off water and redirected into designated areas,
such as grass, shrubs, trees/windbreaks, etc.
3. Elevation – will affect the summer maximum and
the winter minimum temperatures. Choosing an appropriate elevation will
minimize heating costs in the winter and cooling costs in the summer.
4. Micro climate –
· Latitude – Unless the global climate changes
drastically, sea level at the poles will be colder than sea level in the
tropics. Hence, latitude makes a difference!
· Trees,
mountains or other obstructions – may cast shadows on the greenhouse, especially in the
morning or afternoon hours. Mountains can also effect wind and/or storm
patterns.
· Clouds
and fog – Note that
certain areas (e.g., on the lee side of certain mountain ranges, or near
coastal regions) may develop clouds or fog during certain times of the day or
year that will reduce potential sunlight.
·
High
Wind Areas – High
winds can “suck” heat away from the greenhouse and therefore increase the
heating energy needed to maintain the temperature inside. High winds can
also cause structural damage to greenhouses.
· Blowing
dust/sand – High
winds can “kick up dust or sand”, especially in desert regions, which can
damage some greenhouse glazing.
· Snow – The weight of heavy, wet snow on a
greenhouse could crush it. However, high winds in snow areas can also blow snow
up against the greenhouse structure (snow drifts) and cause damage to it.
This danger can be reduced by using windbreaks (trees, snow fences, etc.).
5. Pest Pressure – Choose a site away from existing
agriculture production areas which could harbor insect pests in the
fields. Insect pests of concern include white flies, aphids, spider mites
and thrips.
6. Level and Stable Ground – The ground upon which the greenhouse
will sit must be:
·
Graded
for routing surface water to a drainage system or a holding pond.
· Compacted
so there will be no settling after the greenhouse has been constructed.
7. Utilities – Availability of utilities should
include telephone service, three-phase electricity and fuel for heating and
carbon dioxide generation. Note that, when compared to propane, electricity or
fuel oil, natural gas is a fairly economical heating energy source.
8. Roads – Need access to good roads to
transport the “product”. Good roads close to a large population center or
to a brokerage center aids wholesale and retail marketing.
9. Greenhouse Orientation –
·
In
Free Standing greenhouse more sunlight is available in winter in East-West
oriented greenhouse.
·
In
Naturally ventilated greenhouse, the ventilator should open on the leeward
side.
·
A
free standing greenhouse should have its long axis perpendicular to the wind
direction.
10. Capability of Expansion – Purchase more land than you anticipate
using in the beginning so that you have the ability to expand your
operation. Locate the initial greenhouses such that future expansion will
utilize the land area most efficiently.
11. Availability of Labour – The grower needs people who will
want to work as labourers and who are “trainable” to become a retainable
workforce. Such skills included pruning/training the plants and
harvesting/packing the fruit. Speciality labour will include people with
additional training in such fields as plant production, plant nutrition, plant
protection (insects and diseases) computers, labour management, marketing, etc.
12. Management residence – The grower/manager residences
should be close to the greenhouse so that they can get to the greenhouse
quickly in case of emergencies.
Components of Greenhouse / Poly-house
The greenhouse is a structure made by
assembling different parts or components. Each part has specific role in
greenhouse structure. It is covered with a transparent material for admitting
natural light for plant growth. The main components of greenhouse like structure, covering/glazing and temperature
control systems need proper design for healthy growth of plants.
Freestanding (single) or ridge and furrow
(gutter connected) greenhouses are two common styles of commercial greenhouses.
The freestanding style is often a Quonset,
which will accommodate many growing situations but presents height restrictions near the side walls. Another
freestanding style is the single gable
greenhouse and its many variations. The ridge and furrow or gutter
connected greenhouses are joined at the eave by a common gutter. When several
of these buildings are joined they are often referred to as a greenhouse range
(Figure 1).
Fig.1 Commercial greenhouse structures: A) gutter connected, B) Quonset and C) single gable.
1. Foundation:-
The foundation must resist overturning and
vertical pressure from structural loads and snow, and should extend below the
frost line. Concrete is the most appropriate material for permanent structures.
Unless the grower is constructing a greenhouse without the use of a
manufacturer, specific recommendations are usually provided for adequate
durability of the foundation. The foundation stage of construction is critical
and consulting with appropriate personnel, such as experienced builders, is
highly recommended.
The foundation can be 60 cm x 60 cm x 60
cm or 30 cm diameter and one meter depth in PCC of 1:4:8 ratios. The vertical
poles should also be covered to the height of 60 cm by PCC with a thickness of
5 cm. This avoids the rusting of the poles.
2. Structural Components:
Fig 2. Basic Structural components of
greenhouse
2.1
Side Wall:
·
It
supports the trusses and bears the weight of the greenhouse.
·
Set
in concrete footings
·
Typically
spaced 10 feet apart
2.2 Curtain Wall:
·
The
first several feet of sidewall above the soil line.
·
Usually
made of some solid building material such as poured concrete, concrete blocks,
bricks, or treated lumber.
2.3 Sill: It is top of the curtain wall.
2.4 Eave:
·
Where
the sides of the greenhouse join the roof of the greenhouse.
·
The
“top” of the sides of the greenhouse.
2.5 Truss:
·
Structural
component that supports the weight of the greenhouse roof.
·
Consists
of rafters, struts, and chords.
2.6 Purlin:
·
Purlins
run along the length of the greenhouse.
·
Keep
the roof trusses aligned.
2.7 Ridge:
·
Where
the roofs come together at the top of the greenhouse.
·
Many
greenhouses have a ridge vent(s).
2.8 Side posts and columns:
These are vertical supports that dictate
the height of the production area. These range from one to ten feet in height
and should be given serious consideration since they directly influence efficiency
(Fig. 2).
2.9 Sash Bar: (Refer Fig.3)
·
Run
perpendicular to the purlins.
·
Attached
to the purlins.
·
Hold
the glazing in place.
·
Sometimes
built with a drip groove or channel to catch condensation that forms on the
inside of the glass panels.
Fig. 3 Sash Bars
3. Framing Materials
Aluminum is the most economical material
for constructing the greenhouse frame. It can be shaped as needed to form
various structural components of the greenhouse and needs no maintenance after
installation. Aluminum framing also has the longest life span and allows for
light reflectance.
Steel is commonly used but must be painted
or galvanized to resist high moisture conditions within the greenhouse. Steel
needs more maintenance than aluminum and is heavier, requiring additional
support.
Wood was once a common framing material,
but it has steadily lost popularity for number of reasons. The main
disadvantage of wood is that it deteriorates over time.
4. Coverings:
Glass allows maximum light transmission in
greenhouse production. Despite this, there are several disadvantages to
consider. Glass is expensive and, because it is fragile, has to be replaced
more often than many other materials in the market today. Also, consider that
when using glass, the cost of structural components will be expensive because
of the added weight which must be supported. When glass is desired, check with
the manufacturer for double and triple strength ratings available. Also,
“hammered” or “frosted” panes will distribute incoming light better by dispersing
the rays, resulting in fewer shadows. This type of glass is not transparent
from the outside, which can be an added security benefit in certain
institutions.
A double layer of polyethylene, inflated
with air, is another option to consider for covering the greenhouse. One
advantage of using this material is that it is relatively inexpensive.
Materials have greatly improved and some manufacturers guarantee their
materials for up to four years. Look for ultraviolet stabilized products that
are slower to yellow and crack. Single and triple layer polyethylene coverings
are used less commonly. Replacement of a polyethylene covering as a result of
wind, hail, or solar damage will be more frequent than any other covering, but
the low investment and the need for less structural components make it a
material to consider when a temporary greenhouse is desired. Two additional
products, available commercially, to extend the life of a polyethylene house
are poly patch and anti-drip material. The anti-drip material reduces
condensation that can harm plants growing below. Condensation should also be
controlled to prevent lowered light transmission, especially during the winter
months when low light levels may limit plant growth.
Fiberglass is another material that has gained
popularity over glass. It is very durable, rigid, and available in various
light transmission levels. Ultraviolet light will cause fiberglass to
deteriorate in a few years from swelling and fraying of the
fibers. This in turn quickly leads to
lowered light transmission to the plants. However, there are products now
available that will help to reduce the fraying. These coatings should be
applied prior to damage to the fiberglass. Although the life span of fiberglass
can be as short as five years, choosing higher grade products and applying a coating may result in a twenty year life
span.
Polycarbonate is one of the newest
materials available and is still being evaluated. This material is rigid but
also flexible enough to be used in a Quonset style greenhouse. Although the
initial cost of polycarbonate is high, a ten to 15 year life span can be
expected. Polycarbonate can be purchased in double and triple walled forms
which are highly impact resistant.
Acrylic is also new and expensive but it
has a minimum ten year warranty from some manufacturers. Although many
advantages exist such as high light transmittance, high impact resistance, and
great strength, costs have proven prohibitive in most cases.
Remember to check with the covering
manufacturer for several factors.
1. Combustibility - Some materials may result in lower
insurance premiums if they are fire retardant. Other materials are highly
flammable, such as fiberglass reinforced panels (FRP), and that must be
considered. Fire retardant FRP panels can be purchased.
2. Durability - Not only will this differ among
materials, but also will be determined by whether they are one, two, or three
ply.
3. Insulation - Note insulation “R” factor and compare for fuel savings.
Heat retention from highest to lowest:
·
Acrylic
(double layer)
·
Polycarbonate
(double layer)
·
Glass
(double layer)
·
Polyethylene
(double layer)
·
Fiberglass
Keep in mind that this is relative to the number and thickness of
layers used.
4. Life span.
5. Care - Maintenance may be required to
realize life span claims from manufacturer.
6. Guarantee - Read warranties carefully as most
will be limited.
5. Shading Compounds
During the summer months, when solar
radiations are too intense for any crops to be grown to acceptable quality.
Shading is necessary to make greenhouses usable and to prevent overtaxing the
cooling and ventilation systems. Instructions are provided to reach the desired
percentage of radiation blockage. Liquid formulas are commonly used for glass
and sometimes fiberglass. However, frayed fiberglass may absorb the liquid,
making it impossible to remove when maximum solar radiation is again needed.
Another alternative is to use shade cloth. It can be purchased for the
per cent of solar radiation reduction desired, depending on the crops grown.
Hi. I’m Designer of Blog Magic. I’m CEO/Founder of ThemeXpose. I’m Creative Art Director, Web Designer, UI/UX Designer, Interaction Designer, Industrial Designer, Web Developer, Business Enthusiast, StartUp Enthusiast, Speaker, Writer and Photographer. Inspired to make things looks better.
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