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Horticulture Crops - Greenhouse Structures

Greenhouse Structures

پست كننده :Mohammad Khalid
تاریخ:سه شنبه 18 بهمن 1390-03:10 ب.ظ

Greenhouse Structures

Types, Framework & Coverings

Objective:

Follow this lesson, the student will be able to:

1.      Define greenhouse structures

  1. Explain the various design styles of greenhouses
  2. Illustrate the structural parts of a greenhouse
  3. Explain the differences between the transparent coverings used for greenhouse. 

       I.      Introduce greenhouse operations

a.       Greenhouses – are structures that are covered with a transparent material that allows sufficient sunlight to enter for the purpose of growing and maintaining plants.

b.      Greenhouse Range – 2 or more greenhouses located together in a commercial operation

c.       Headhouse – Central building that the greenhouse is usually attached to

                                                              i.            Used for:

1.      office space

2.      storage

3.      workspace

    II.      Attached Greenhouses

a.       Define Attached Greenhouse – connected to a building

                                                              i.            Lean-to-greenhouse – constructed against an existing building

                                                            ii.            Attached even-span greenhouse – has rafters of equal length and the end wall is attached to an existing building.

                                                          iii.            Window-mounted greenhouse – is a prefabricated style that is available to fit many standard size windows.

1.      Found on side of house

2.      Usually in the kitchen area

3.      “Garden Window” 

 III.      Freestanding Greenhouses

a.       Define Freestanding Greenhouse – separate from other buildings consisting of sidewalls, end walls, and a roof

                                                              i.            Freestanding even-span – rafters of equal length – most common style of freestanding

                                                            ii.            Uneven-span – rafters of unequal length – found on hillsides

                                                          iii.            Quonset – curve roofs without side walls

                                                          iv.            Gothic Arch – styled in the shape of a pointed arch 

 IV.      Connected Greenhouses

a.       Define Connected Greenhouses – Several greenhouses joined together

                                                              i.            Gutter-connected – several even-span greenhouse attached together – aka  ridge-and-furrow

1.      eve is replaced with a gutter which aids in removal of rain and snow

2.      interior walls replaced with support posts

                                                            ii.            Venlo – “Dutch Houses” – differ from gutter-connected because they are wider and have twice as many ridges between supports

1.      Glass greenhouse

2.      known for excellent percentage of light transmission

3.      Used in the Netherlands for production of vegetables and flowers

                                                          iii.            Barrel vault – Quonset style structures with sidewalls joined together

1.      Covered with flexible plastic like polyethylene

                                                          iv.            Sawtooth – lean-to greenhouses joined together

1.      found in warmer climates

a.       California

b.      Texas

c.       Florida

2.      upper portions of roof are vented to take advantage of natural ventilation

 

   V.      Greenhouse Framework

a.       Ridge – top of the greenhouse

b.      Anchor post – side post – main structural support

c.       Trusses – added to framework for structural support

                                                              i.            Composed of

1.      rafters

2.      chords

3.      struts

d.      Purlins – runs the length of the greenhouse and are bolted to each truss

e.       Ventilators – movable units to allow for natural ventilation – they may be attached to the sides or the ridge

 

VI.      Greenhouse Coverings (most important function of greenhouse covering is to allow the maximum amount of light into the greenhouse

a.       Glass

                                                              i.            Best light transmission

                                                            ii.            Last a lifetime

                                                          iii.            Available in different grades, weights, and sized

1.      double strength, grade B is used often

                                                          iv.            Constructed structure made of aluminum or steel

                                                            v.            Require more structural support than others

                                                          vi.            Glass size

1.      original 16-inch by 18-inch

2.      now days – up to 32-inch by 36-inch

3.      Venlo greenhouse – 28-inch by 65-inch, allows more light to enter

b.      Polyethylene

                                                              i.            Most widely used

                                                            ii.            Lower fuel cost for heating the greenhouse

1.      40% lower than glass or fiberglass-reinforced plastic

                                                          iii.            Short life span

                                                          iv.            UV inhibitors, help the lifespan to be an average of 3 years rather than 1 winter season without it

                                                            v.            Various widths and lengths and thickness

                                                          vi.            4 mil or 6 mil thick is used

                                                        vii.            Now days, most greenhouses use a double layer –outer layer 6 mil and inside layer 4 mil

                                                      viii.            Can produce condensation

1.      this can increase chances of disease

2.      reduce amount of sunlight

a.       To reduce condensation

                                                                                                                                      i.      Sun Clear, can be sprayed on the inside to reduce condensation

                                                                                                                                    ii.      Use anti-condensation chemical manufactured into the polyethylene

c.       Fiberglass-Reinforced Plastic

                                                              i.            Not used as much as in the past

                                                            ii.            Lower in cost than glass

                                                          iii.            Easy to install

                                                          iv.            Strong

                                                            v.            Longer lifespan than polyethylene

                                                          vi.            Can last up to 15 years

                                                        vii.            51-inch width, various length

                                                      viii.            Allows almost the same amount of sunlight as glass

                                                          ix.            Susceptible to ultraviolet, dust and pollution degradation

                                                            x.            Must use clear panels

                                                          xi.            Highly flammable, therefore insurance rates maybe higher than other coverings

d.      Acrylic and Polycarbonate

                                                              i.            Rigid, double layer acrylic and polycarbonate panels have almost replaced fiberglass-reinforced plastic

                                                            ii.            Lightweight

                                                          iii.            Easy to install

                                                          iv.            Excellent heat insulating ability

                                                            v.            Good light transmission

                                                          vi.            Various width and lengths

                                                        vii.            Acrylic lifespan = 20 years plus

                                                      viii.            Polycarbonate  lifespan = 15 years

                                                          ix.            Acrylic panel is flammable

Reference:

Introduction to Horticulture, 4th Edition

            AgriScience & Technology

Types Of Greenhouses

After you decide that you want to build a greenhouse, you have to decide next what type to build. This should not be a difficult one to address, provided you know what kinds of plants you want to grow.  You will need to answer questions such as:

§  What will my greenhouse be principally used for?

§  Do I want a large or small greenhouse?

§  Will the greenhouse be the main attraction of my garden?

§  Is my garden exposed to strong winds?

§  Are there young children or wild animals in the area?

Factors such as cost and space will determine the type of greenhouse you build.  If you do live in a windy area, it may be worth to spend the extra money for a solid and sturdy greenhouse.  If you live near a large hardware store or a nursery, or even a do-it-yourself home center, go and visit some models.  The customer service representative should be able to provide you with valuable information before you make a final decision.

So as not to mislead you, while there may be different types of greenhouse designs, we’re talking about the same greenhouse.  You get to decide which type you want it to be. 

For example, if temperature is the main factor, because of the plant varieties you want to grow, then there are three types in terms of temperature control.  There are also different types of greenhouses based on structural design.  We’ll start with temperature control factors.

For temperature control purposes, three types of greenhouses exist: 

§  hot greenhouse

§   a warm greenhouse

§   a cool greenhouse.

Hot Greenhouse

 A hot greenhouse’s inside temperature is maintained at a minimum of sixty five degrees. You can at some future date increase the temperature, but a hot greenhouse is intended for growing tropical and exotic plants. If you live in a very cold region, you will need to install heating and lighting equipment to satisfy the requirements of tropical and exotic plant species.

Warm Greenhouse

The temperature inside a warm greenhouse, on the other hand, is at about fifty-five degrees F.  At this temperature, a larger variety of plants can be grown, perhaps as many as you would in your outdoor garden.  You may still need to resort to the use of additional heat and light during the winter months.

Cool Greenhouse

A cool greenhouse (frost-free greenhouse) is maintained at a temperature ranging from forty to forty five degrees F.  This temperature is ideal for growing seedlings or any plants that do not need warmer temperatures to survive.  A cool greenhouse is perfect for starting your plants and vegetables in anticipation of the summer months.  Generally, the use of heat or lights isn’t required for a cool greenhouse.

As for structure, there are generally three types: 

lean-to

detached

ridge and furrow or gutter connected.

Lean-To

The lean-to type of greenhouse is rarely used for commercial purposes because of size restrictions, but is the most popular among hobbyists.[6]

Detached

Detached greenhouses – as the name suggests – are independent and are stand alone structures.  However, they may still be attached to a work area or else provide access to another greenhouse via a passageway.

The Quonset is the most common type of detached greenhouse used for commercial production.  They are built from arched rafters and have solid walls for support. Quonset greenhouses are ideal for producing most crops, although the growing area is limited to the areas around the side walls, which diminishes efficiency and productivity.

Ridge/Furrow

Ridge and furrow greenhouses are attached at the lower edges of the roof by a gutter.  The absence of an inside wall below the gutter allows for increased efficiency. Ridge and furrow greenhouses may be built with gabled or curved arches. Gabled houses are appropriate for heavy coverings (i.e. glass, fiberglass) while curved arch houses are covered with lighter materials (i.e. polyethylene, polycarbonates).

You may encounter different classifications in your readings on greenhouses.  For example, another classification, which is similar to the ones just mentioned are:

Cold frame type

Roof cover may be poly or shade, end wall covering is either poly or rigid, available lengths come in 12 feet increments, and no gutter connections or vents.

Ground-to-ground

Roof covering is either poly or shade, wall covering may be poly or rigid, lengths available in 12 feet increments, no gutters, roof vents are available.

Gutter-connected, Gothic arch

Load rating may be either 10, 15 or 20 pounds, roof covering is poly, sidewall and endwall either poly or rigid, lengths available in 12 feet increments while heights available in 8, 10 or 12 feet, gutter connection and roof vents both available.

Gutter-connected Cable 

Load rating 10, 20 or 30 pounds, roof covering either poly or rigid, endwall and sidewall covering may be either poly or rigid, lengths in 12 feet increments, gutter connection and roof vents available.








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