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Greenhouse Structures. GREENHOUSES. Structures covered with transparent material Allows sunlight to enter for plant growth and maintenance Artificially heated and cooled. Uses. Overwintering tender plants Starting seeds Starting cuttings Raising vegetables and flowers out of season - PowerPoint PPT Presentation
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Greenhouse Structures
GREENHOUSES
Structures covered with transparent material
Allows sunlight to enter for plant growth and maintenance
Artificially heated and cooled
Uses
Overwintering tender plants Starting seeds Starting cuttings Raising vegetables and flowers out
of season Growing specialty plants
Designed to local weather extremes
Minimum yearly temp. Max. wind speeds Max. snow loads Best light transmission
Environmental considerations for plants
Light Temperature Humidity
Headhouse
Office, storage, and work space from which greenhouses are located
Types of Greenhouses
Attached Freestanding
Attached Greenhouse
Connected to building Floral shop Garden center Office Home
Attached Greenhouses Advantages:
Less construction material needed Can be utilized to heat homes in
winter, cool in summer through heat and humidity change
Disadvantages Existing building can shade the
greenhouse, limiting light needed for plants
Ventilation and temperature are difficult to control.
Lean-To
Attached to building, usually on the south-facing side
Ridge to the roof is attached to the building side
Attached Even-Span
End wall is attached to a building Rafters are equal length
Attached Even-Span
Advantage More available space
DisadvantageMore expensive to build and heat
than a lean-To
Window mounted
Attached to windows as a pre-fabricated unit.
Disadvantage Limited space Plant environment
is difficult to control
Freestanding Greenhouse
Even Span Uneven- span Quonset Gothic Arch
Even-Span
Rafters of equal length
Usually clears spans w/ truss supports
ADVANTAGE: Allows more freedom of space/ movement and equipment
Uneven-Span
Rafters of unequal length Usually used for hillside placement
ADVANTAGES: maximizes sun light DISAVANTAGES: internal orientation of
greenhouse can make working in it difficult
Quonset
Curved roofs; military hut-style May or may not include sidewalls
Gothic Arch
Cathedral arch-forward style
Eliminates truss supports
Adds a double layer of polyethylene covering
Gothic Arch
Advantages Less construction material Less land needed for spacing Heat conservative due to less exposure Workers and equipment can move
through the buildings rather than between buildings
Gothic Arch
Disadvantages Creating different environmental
conditions for crops is more difficult Connected houses do not distribute
snowfall weight well and can collapse Require heating cables to melt snow to
prevent collapse Difficult to ventilate, requires fans to
circulate
Types of Connected Greenhouses
Gutter-connected – made up of even span greenhouses
Venlo or Dutch – twice as many ridges as gutter
connected Barrel Vault – quonset style with walls joined
Sawtooth – lean to style joined together
http://www.b2science.org/
Review
What is a greenhouse?
What are the four types of freestanding green houses?
Review
Three environmental considerations for Plants?
Objectives for the day
What are the structural components of a greenhouse?
What are five different ways of heating a greenhouse?
What are three ways of cooling a greenhouse?
What is a forcing structure?
Components of Greenhouse Structure
Frame Foundation Concrete Footings Sidewalls Covering
Frame
Pressure-treated wood
Aluminum Galvanized steel NOTE: glass
greenhouses require more structural support than polyethylene
Foundation
Continuous concrete bed upon which greenhouse is built
Water and electrical lines are placed before concrete is poured
Concrete Footings
Non-continuous supports located below the frost line (cannot be affected by frost heaves)
Take the place of foundations.
Spaced at intervals according to placement of support anchor posts
Sidewalls
Between the footings and supports
Greenhouse Coverings Glass Provides excellent light
transmission. Long-lasting. Double-strength, grade B weight
used for greenhouses except in cold areas, where thermopane (with a ¼ to ½ inch layer of trapped air between panes) is used.
Expensive installation and heating. Requires good structural support
of aluminum or steel. Sash bars Frame glass panes; held by glazing
compound. Bar caps Attached to outside of panes to
hold glass in place.
Greenhouse Coverings
Polycarbonate Lightweight Ease of installation. Good heat insulation. Good light transmission. Available in clear,
corrugated single layer panels.
Good replacement for corrugated fiberglass-reinforced plastic.
Disadvantage: Flammable
Greenhouse Coverings
Corrugated Fiberglass-Reinforced Plastic
Low in cost. Ease of installation. Tensile strength. Longer lifespan. Good light penetration. Can degrade over time
from ultraviolet damage, dust, and pollutants.
Flammable and may increase insurance costs.
Greenhouse Coverings
Polyethylene Inexpensive installation. Low heating cost. Short-lived. UV inhibitors increase its
lifespan. Produces condensation
which increases wet plant foliage and disease possibilities.
Light reduction compared to glass.
Greenhouse Coverings
Acrylic Lightweight Easy to install Good heat
insulation. Good light
transmission. Long lifespan. Flammable.
HEATING
• Steam-produced in a boiler-Circulated by pipes in sidewalls and overhead-Used mostly when several greenhouses are attached-this steam can also be used to sterilize media
Heating (cont.)
• Hot water-similar to steam but used in smaller houses
• Forced-Air-Local Units force hot air into houses-Can be moved through plastic overhead tubing
Heating
• Infrared Radiant-Individual unit heaters-Directly warms the plants in the greenhouse-Conserves energy but is generally cooler than other types of heat.
Heating Con’t
Solar Restricted to passive designs Crops require little additional heat
Unit Heaters
Fired by natural gas, propane, fuel oil, coal, or wood.
Electricity not recommended, due to reliability.
Determining size HVAC
Climate Area of exposed greenhouse surface Type of construction and materials = # of BTU’s need maintain inside
temp.
Cooling
Fan and Pad
Exhaust fan draws air through moist cellulose pad.
Air is cooled through evaporation
For low humidity conditions
Fog evaporative
Fog is generated within the greenhouse Heat is absorbed by the water droplets
and evaporated, cooling the greenhouse environment.
Used in propagation houses
Ventilation
Ventilation
Natural Fan Tube
Natural
Air exchange is fostered through open ridge and side venting, under thermostatic control.
Not advised for winter cooling due to possible plant injury
Fan-Tube
Fans bring in cool air which is mixed with warm air and distributed though holes in plastic tubing running the length of the greenhouse
May be used in conjunction with heating systems
Shading
Fabric Compound
Fabric
Black polyethylene pulled over the greenhouse to reduce light intensity and temperature.
Comes in a range of shade percentages.
Compound
Liquid compounds applied to glass or polyethylene covered greenhouses to reduce light intensity and temperature
Forcing Structures Used in Raising Plants
Lath House/ Shade House
Provides some shade and wind protection for plants
Allows moisture and air to permeate structure
Used as an outdoor setting for plants with some protection
Cont’d
Much smaller than a greenhouse For plant establishment,
acclimatization, or plants requiring shade
Weatherproofed wood or galvanized steel
Frame is three sided: roof, back, two sides
Con’t
Covering Wooden roof is slatted to permit
weather and light, but not full sunlight Plastic net fabric is commonly used, in
a range of shade percentages
Overwintering Structures
Cold Frame
Hotbed
Cold Frame
Unheated Structures Wind protection and
moderated temp. control Placed partially below
ground level Frame is wood W/ hinged
or sliding glass top opening or covering of plastic film
Backs are higher and tops slanted down for weather protection
Insulation can be used on tops of plants or containers
Hotbed
Similar to a cold frame in structure, but with and underlying heat source
Used to start seedlings or cutlings
Heat from pipe (steam or hot water), heat coils (electricity), or natural sources are used (manure)
Hotbeds have brick or concrete sides and back with a glass top slide or hinged covering
Review
What are the structural components of a greenhouse?
What are five different ways of heating a greenhouse?
What are three ways of cooling a greenhouse?
What is a forcing structure?