(Slides)
Different ways to ventilate
greenhouses
·
Ridge vents with sidee vents
·
Older greenhouses have hand crank vent openings
o
Most modern greenhouses are pretty well automated
·
HAF = horizontal air flow
o
Fans at crop level
o
Vents opposite and at some height
o
Only works for short, even plants
·
Exhaust fans are not enough to cool in hot climates
o
Usually combine evaporative coooling in hot areas
§
Excelsior pads
·
life is one season
§
Cell-dec
·
longer life: up to 5 years
o
especially if use pre-filters
·
twice as expensive as Excelsior
·
Big tubes (fan tubes)
·
Whitewash
o
Sprayed on outside of greenhouse (use laytex paint)
o
Reflects sun out
o
Before laytex paint, used mud
o
Washes off (partly natural)
o
Need to scrub at the end of the season to remove
all that didn't come off naturally
o
See handout #2
·
Shade Cloths
o
Internal
§
Add junk to top of greenhouse
§
Don't remove heat from greenhouse
§
Shade plants & keep them cooler
o
External
§
But can't use with top vents on the greenhouse
o
Can get cloths that block 10% to 90% of the sun
§
But if less than 30% it will unravel; you need to have
it custom sewn to prevent unraveling
·
Paddle (ceiling) fans
o
mix up air
o
pull up cold air from bottom
o
most efficient are those that suck air up, rather than
push it down.
{end slides}
Cooling: high pressure fog systems require
1.
Water free of silt sand, high mineral loads
2.
Speciall pump capable of delivering very high pressures
o
used in Hawaii a lot
3.
A control system to activate the pumps
o
Usually cycles 30 sec on, 30 seconds off
4.
Nozzles capable of delivering high pressures (500-600 psi)
o
rate of delivery = 0.6 gpm
o
spaced about 10 feet above crop
o
process of evaporation = cooling
o
all vents and exhaust fans working + cooling to keep
the humidity down
Flowing water shade
o
Water is pumped to the ridge of the greenhouse
o
Enters a PVC pipe along ridge
o
Pipe has holes in it
o
Water trickles down the greenhouse on outside
Air Conditioners
1.
Too expensive for most commercial greenhouses
2.
Must be rated at 50-100 ton
o
--most home units are rated at 1/2 ton.
Good rule of thumb for ventilation
·
To maintain greenhouse air temperatures 11-13 F (6-7 C)
above outside air temperature
o
Air exchange 0.75 times the greenhouse volume per
minute
·
To maintain greenhouse air temperature 10-12 F (5-6 C)
o
One complete air exchange per minute!
Fans are rated in cubic feet
To determine size
·
Determine the volume of air to be moved
(see flow chart on the Handout)
Light May cause or regulate
·
photsynthesis
·
chlorophyll synthesis
·
chloroplast formation
·
anthocyanin formation
·
seed germination
·
seedling and vegetative growth
·
flowering
·
phototrpoism - light induced movemnt of plants
·
photoperiodism
·
regulation of "biological clocks"
3 aspects of light that are most important
1.
Intensity
2.
Quality (red...green...etc)
3.
Quantity (duration)
PAR = photosynthetically active radiation
·
400-700 nanometers wavelength
See handout #1
Lighting considerations:
·
Choice of structural materials, framing members and
site orientation
·
Plant spacing and layering
·
Choice of planting time
·
Use of shade cloth and black cloth to limit light
Other factors that decrease transmission of light
·
Overheat equipment (ventilators, shading, heating
equipment, etc)
·
Plants and plant supports -- hanging baskets
·
Choice of glazing materials (see materials HO from
awhile ago)
·
Erosion of or dirt accumulation on
o
Glass should be cleaned once a year
·
Plant spacing
o
usually a compromise between providing adequate light
and maximizing profits
o
closer spacing = thinner stems, smaller flowers, tall
leggy plants
·
Choice of planting time
·
Use of shade cloths
o
White latex paint
o
mix white paint with water
§
heavy = 1 part paint to 10 parts water
§
moderate = 1 part paint to 15-20 parts water
§
applied with paint sprayer
Shade sometimes needed for one stage of growth, not others
§
seedlings
§
only during flower initiation
Latitude makes a difference
Shade plants in south, full sun in north
§ columbic, some ferns, coral bells, some violas, solomon's seal
Supplemental Lighting
§ 1893 L.H. Bailey - first reported the benefits of supplemental light in greenhouse = electrohorticulture
§ Slow to catch on
§ Mostly used in Canada, Alaska, north Europe, UK, Netherlands
Lamp types
3 basic types of lamps are used for lighting plants
1. Fluorescent
2. Incandescent (tungsten filament)
3. HID (High Intensity Discharge)
§ High pressure mercury
§ Metal halide
§ Low pressure sodium
§ High pressure sodium
Incandescent lamps
§ Not used to increase light intensity
§ Currents only 7% of energy used is turned into light
o The remainder is given off as heat
§ Greenhouse application is primarily for photoperiod control
Fluorescent lamps
§ Growth rooms & small germination areas rather than whole houses
§ Most efficient types = cool and warm white tubes
§ Convert 20% of electrical energy into light
§ Mix of phosphors change spectrum
o Goal is 400-700 nanometer spectrum range for plants
§ Plant group A - enhanced red pigment
o Grow lights (original)
§ Plant group B - even more red
o Today's grow lights
§ Lots of shade from reflectors
§ Not as much heat
§ See handout #3
Handouts
1. radiant energy & effect of light intensity on the rate of photosynthesis
2. Cleaning solutions for greenhouses (glass)
3. Light and temperature data for various lights
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