Seed
Germination
·
optimum 60-86 degrees F (15-30 C)
·
temperature influences:
o
% germination
o
seedling vigor and shape
o
future crop performance
Greenhouses
·
heat the air, not the plants
·
heating costs are second only to labor costs as the
biggest greenhouse expense
·
Original source = solar energy
·
the solar energy enters the greenhouse
·
It is absorbed by the surfaces it hits (benches,
plants, floor, structure, etc)
·
It looses energy and is re-radiated as heat energy.
·
This longer wavelength energy is reflected by the glass
(thus the greenhouse effect)
·
Since the energy is trapped, it heats up the greenhouse
·
Plastic is more transparent to long wave radiation
·
Plenty goes out
·
So how does a greehouse get hot?
a) trapping of long wave radiation
·
25% of the heat
b) heating a relatively small volume of trapped air
·
greenhouse restricts movement of air; keeps in in once
heated
·
radiant energy heats up trapped air
c) supplimental heat (furnaces)
Slides of:
·
gas fired boiler
·
pipe and fin orientation
o
location hard to get ideal
o
location sometimes depends on cost of heat
·
types of unit heaters
·
tubes for moving air
o
holes must be pointed downward for proper air
circulation
o
IR heating systems
§
only heats surfaces
§
can save 30-40% in heat costs
§
but depends on plants
·
won't work for tomatoes (too much shading)
·
will work for bedding plants
·
use of waste heat as an energy source
·
heating control center
o
should at least have temperature min/max
o
should have humidity
o
should be at plant height
o
should be away from drafts and direct sun
·
if using ground beds then a good idea to have soil
thermometer
·
aspirated system for temperature control
{end slides}
Type of heating system depends on
1.
Season of operation
2.
Size and shape of greenhouse
3.
Type of glazing materials
4.
Crop grown and heating requirements
5.
Available types of fuel
How do you figure heating requirements?
Need to know:
1.
Heating season
2.
Fuel source
3.
Greenhouse structure
3 reasons why you need to ventilate a greenhouse
1.
Reduce air temperature--maximum air temperature for plant
growth is 95 F (35 C)
2.
Supply CO2
3.
Lower relative humidity
Types of ventilation systems
1. Natural ventilation
o
vents, windows and doors
o
Ridge vents create a chmney effect
§
breeze blowing over top of greenhouse creates area of
low pressure and pulls air from greenhouse at ridge and pulls air in at sides
o
In general
1.
Ridge vents only - should be used on houses less than 21 feet
wide
2.
Ridge and side vents required on larger houses
3. Vent opening (area) should be 25% of the floor area
·
but size goes way down if you have fans
Need 0.75 to 1 full air change PER MINUTE!
(Depending on temperature requirements
Handouts
1.
Greenhouse heat loss calculations
2.
Overall heat transfer coefficients for greenhouse glazing
materials and systems
3.
Heat content for fuels
4.
Estimating heating loads
5.
Ventilation requirement for control of solar heat in
greenhouses
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