greenhouse structures and operations - … structures and... · greenhouse structures and...
TRANSCRIPT
GREENHOUSE STRUCTURES AND OPERATIONS (HEATING, COOLING & ENVIRONMENTAL CONTROL SYSTEMS)
R. Allen Straw Specialist
Virginia Cooperative Extension
GREENHOUSES
Hobbyist, spare time Supplemental income Full time income
The intended use of the structures
determine the type, size and quantities of greenhouses.
How is the structure to be used? Retail sales Sole structure Retail sales area/ greenhouse
Wholesale sales Based on market demand Contract grower
Educational Hobby Public display Research
Trace your market before deciding on structures
Transplant/ Liner
Propagators
Nursery Growers
Landscape Contractors
Residential Construction
Commercial Construction
Wholesale Customers
Retail Garden Centers
Commercial Small Fruit Producers
Increased Crop Inventory
New Varieties
Crop Renovation
Commercial Vegetable Producers
Field Inventory Needed Per
Crop
2nd and 3rd
Planting per Season
New Crops
Greenhouse Growers
Wholesale Customers
Retail Customers
Greenhouse Size
Length 96 ft. (120 – 144 ft.) Ideal
< 96 ft. Increases your expense
> 96 ft. Makes air movement and
ventilation difficult
Width Freestanding 30 – 32 ft.
Gutter Connect 24 ft. 30 – 32 ft.
Overall 24 ft. X 96 ft. (gutter) 32 ft. X 96 ft. (free)
Greenhouse Components
Structures and Framing Glazing End Walls Heating Cooling and Ventilation Systems Thermostats and Controls Floor Benches
Structures
Structures- Free Standing Quonset
Structures- Free Standing Gable or Gothic
Structures- Gutter Connect
Greenhouse Types - Homemade
Inexpensive Often used in soil
culture Difficult to heat Difficult to ventilate
Greenhouse Types - Quonset
Moderate expense Unusable production
space on edges Machinery utilization
difficult
Greenhouse Types - Short Sidewall
Moderate expense Less unusable space
on edges than Quonset houses
Equipment utilization (?) – dependant on height of sidewalls
Greenhouse Types - Sidewall
More expensive Load Rated structure 70 mph / 10 lb/ft2
80 mph / 20 lb/ft2
Long Life $20,000 plus
Greenhouse Types – Gutter Connect
More expensive
Load Rated structure 70 mph / 10 lb/ft2
80 mph / 20 lb/ft2
Long Life
$20,000 plus
Good for multiple houses
More efficient to heat
Structure Variations
BELOW GROUND Studebaker Nurseries, Lancaster, Ohio
Framing
Materials for framing: •Galvanized Steel •Rigid Conduit •Thin wall Conduit •Structural Aluminum •Wood •Other materials & combinations
Framing Materials
Galvanized Steel Extruded Aluminum
Galvanized Conduit
Greenhouse Coverings (Glazing)
Glass Fiberglass Polycarbonate Double wall plastic (Poly) Film Plastic
Glazing, ctd.
GLASS
Glazing, ctd.
POLYCARBONATE
Glazing, ctd.
Glazing (covering)
FILM PLASTIC- (single layer)
Glazing ctd.
DOUBLE POLY COVER (Inflated)
Inflation System for Double Poly
Greenhouse Plastic Inflation
Position to keep about 2 inches of air between the layers of plastic
Use outside air to reduce condensation
Use jumper hoses for end walls
Do not over inflate Cancels the effect of the
dead air space Makes the plastic more
prone to wind damage
End Walls
POLYCARBONATE
PLASTIC
WOOD
FIBERGLASS
Greenhouse Coverings
Plastic 4 mil. (no!) 6 mil. Single layer (no!) Double layer
Affordable
Fiberglass (no!) Yellows and reduces
light penetration
Polycarbonate Single layer (no!) Twin wall Triple wall Expensive Good for end walls
Glass Longevity Very Expensive!
Greenhouse Heating
Heat need equations Heat required = U x A x (Tinside – Toutside) Where U = heat flow coefficient Single layer of plastic = 1.2 Double layer of plastic = 0.8
A = surface area of the greenhouse T = temperature rise
Calculating Heating Needs Heating systems are rated in British thermal units
(Btu) per hour (h). The Btu capacity of the heating system equals Q
The total exposed (outside) area of the greenhouse sides, ends, and roof in square feet equals A
The heat loss factor that quantifies the rate at which heat energy flows out of the greenhouse is equal to u ( A single cover of plastic or glass has a u factor of 1.2 Btu/hr. Double poly is .8 and polycarbonate is .53)
(Ti-To) is the maximum temperature difference between the lowest outside temperature (To) and the temperature to be maintained inside (Ti)
The formula is Q =A x u x (Ti-To)
Example (Small GH)
A 16’ wide by 24 ‘ long, 12’ ridge, 6’ sides, single layer glass greenhouse.
A = 1056 ft2 exposed area
U = 1.2 heat loss factor Ti = 60 deg F To = 0 deg F
Q = 1056 x 1.2 x 60 = 76,032 Btu/hr Furnace Output
Heating Example (Larger GH)
Parameters U = 0.8 (double layer plastic) A = 4,600 ft2 (32 ft. x 96 ft.) T = 60 degree rise
Heat Requirement = 0.8 X 4,600 x 60 = 220,800 btu’s
80% efficiency = 276,000 btu’s Two (2) - 150,000 btu furnaces
Heat “Types”
Larger ranges with centralized heating Steam Hot Water Smaller ranges with individualized heat units Electric Natural Gas Propane Infrared vacuum units Wood / Coal
Heat, ctd.
Boilers
Hot Water Steam
Heat, ctd.
Hot Water Heat In Floor
Heat, ctd.
Electric
Heat, ctd.
Propane & Natural Gas
Heat, ctd.
Infrared vacuum unit
Wood / Coal
Calculating Ventilation Needs In the summer, a greenhouse needs a 1:1 air exchange per
minute- exchanging inside air with outside air. In the winter, it needs only 20-30% of this amount to avoid
chilling the plants. Cubic footage of the greenhouse can be estimated using
the floor area times the average height of the house (side height + ridge height /2)
Exhaust fans are rated at CFM’s (cubic feet per minute) The fan or fans need to push (exchange) the total cubic
footage of air from the greenhouse each minute. The reduced amount of air exchange for winter is
accomplished by using a two stage fan/ thermostat control.
Greenhouse Ventilation/Cooling
Minimum of 1 air exchange / minute
Calculate volume (ft.3) of the greenhouse 32 ft. x 96 ft. 30,000 ft.3
Two 15,000 cfm fans 48 in. fans
Inlets Ft.3/700 (wind velocity at
inlet in ft./min.) 30,000 / 700 = 43 ft.2
Two 5 ft. square shutters Rule of thumb Inlet shutters should be
1.25 to 1.5 times larger that fan dia.
Cooling and Ventilation Systems
Cooling Wet pad system Shade Cloth
Ventilation Motorized shutters Exhaust fans Horizontal Air Flow (HAF) Convection Tube system Mechanical side curtain Hydraulic Roof System
Cooling- Wet Pad System
Cooling- Wet Pad System
Cooling- Shade Cloth
Ventilation Layout
Ventilation
MOTORIZED SHUTTERS
EXHAUST FAN WITH SPRING SHUTTER
Ventilation
HORIZONTAL AIR FLOW FANS
Ventilation
CONVECTION TUBE
Ventilation
MECHANICAL SIDE CURTAINS
Ventilation
HYDRAULIC ROOF SYSTEM
Greenhouse Air Circulation
Horizontal air flow fans 12 to 18 in. 4 in the house Make a race track ¼ way in from side
walls ¼ to 1/3 way in from
endwalls
HAF and Heater Configuration
HAF and Heater Configuration
Humidity Control
Humidity control A full canopy of a
tomato or cucumber crops will produce significant amounts of moisture through transpiration
A closed GH maintains that moisture
Humidity control fan in the top of the house works very well.
Humidity Control (cont.)
As low as possible Optimum 60 – 70%
Realistic 80 – 90%
Humidity control fan Switch Timer Humidistat
Thermostats and Controls
NOTE: Make sure that any thermostat used is one that will register down to or preferably below freezing and above 90 deg F. Normal house thermostats only go down to 40 deg F.
Thermostats and Controls
NOTE: Greenhouse thermostats and controls should not be mounted on outside walls or in direct air currents.
Thermostats and Controls
Thermostats and Controls
Thermostats and Manual Controls
Floor
BARE GROUND
Floor
Woven Landscape Fabric
Floor
GEO TEXTILE/ GRAVEL
Floor
CONCRETE Note: Used brushed concrete to avoid slippage when wet. Floors have a crown to drain excess water.
Benches
WOOD FRAME/ HARDWARE CLOTH
Benches
PASSVIE SOLAR
Benches
HYDROPONIC SYSTEMS
Benches
ROLLING BENCH SYSTEMS
Greenhouse Growing Area
Goal should be to have more bench space/ plant growing area than walkways. Cost per plant will be related to populations of plant materials being grown.
Costs of Greenhouse Construction 30’x48’ Greenhouse Double Poly Glazing Inflator Fan Unit Polycarbonate end walls Modine Gas Heating Exhaust Fans Motorized Inlet Shutters HAF Fans (Wet Wall optional) (Benches optional)
$11995.00 Package $6800.00 Labor (57%) $18,795.00 Total
2010 Estimate 1440 Square feet
$13.05 per Sq. ft. Cost (Turnkey)
Is there a difference…
Questions ??
R. Allen Straw
Virginia Cooperative Extension
931.261.0973