Transcript Chap 10. Temperature

Chap 10. Temperature
 Temperature and Heat Units
 Thermal Properties of Water
 Movement of Heat Energy
 Biological Influence of Temperature
 Dew Point and Frost
 Thermal Belt and Temperature Inversion
 Temperature Control for Crop Protection
 Controlled Environment Agriculture (CEA)
Heat of Vaporization
 Heat is absorbed from surrounding when water evaporates
 Heat of vaporization = 970 BTU per lb of water evaporated
 Greenhouse cooling by the pad-and-fan evaporative system
Pad-and-fan evaporative cooling system
• Evaporative pad on one side wall and fans mounted on the other side wall
• Flow of cooled air from pad area to fan area (one air exchange/min)
• Maximum distance from pad to fan = 200 feet
• Temperature differential (∆T) between pad and fan areas is usually 7 oF
• Greenhouse air can be cooled down to the wet-bulb temperature
Cool-cell pad
Exhaust fans mounted on the side wall
Psychrometric Chart
• Illustrates the thermal properties of air
• Dry-bulb temperature
Air temperature of sensible heat
measured by dry-bulb thermometer
• Wet-bulb temperature
Temperature of an aspirated thermometer
measured with the bulb encased in a water
saturated wick
Measure the room temperature
Dry-bulb temp: ________oF
Wet-bulb temp: ________oF
Greenhouse Cooling with High-Pressure Fogging System
• Use high-pressure (1000 psi) to generate fog (size 25-40 µ diam)
• Use stainless steel pipe to prevent corrosion problem
• Use low-salinity de-ionized water to prevent clogging of nozzles
• More efficient in cooling the ambient air where it is needed
• Less disease and algae problem, compared to misting system
• Cost of installation high
High-pressure fogging
Summer cooling of greenhouse
with fogging system
Heat of Fusion
 Heat is released to surrounding when water freezes
 Heat of fusion is used to protect citrus fruits from freezing
Heat of fusion from ice formation protects citrus crops
exposed to freezing temperature in Florida
Overhead water sprinkling on citrus crops in Florida to
save them from freezing
Transfer of Heat Energy
Temperature Influence in Biological System
Cell Damage by Low Temperature
Ice
crystals
 Ice crystals rupture cell walls
 Intracellular or intercellular event
 Leakage of cell contents
 Readily occurs in tender plants
Cell wall
ruptures
Extensin
(rupture-resistant)
 Influence of “extensin” on cell wall
Cryogenic Storage
 Liquid nitrogen (-196 oC, -320 oF)
 Permanent storage of pollen, seed, meristems
Thermal Belt
 Good site for locating an orchard
 Usually on a sloped hill side
 North-facing slope is better the south-facing slope
cold
warm
warm
slope
warm
cold
warm
slope
Normal Condition
Temperature Inversion
Peach orchard located on a thermal belt, Western Slope, Colorado
Fruit growing area in Oregon
Grape orchards (vinyards) in Napa Valley, California
Frost damage in vinyards is not as severe in other orchards because flowering of
grapes occurs after shoot emergence
Prevention of frost damage by movement
Windmills and helicopters are used to mix the air to prevent frost
damage on fruit crops during temperature inversion
Use of Plastic Mulch
Strawberry Production in California
Frost Damage on Strawberry Plants in California
A
B
Normal
A. Freezing of leaves is often
initiated by the presence of ice
nucleating active (INA) bacteria that
secrete proteins that act as primers
for ice crystal formation
Damaged
B. Crop failure often results from
freezing of flower parts that are delicate
and fragile. Stigmas and anthers are
easily damaged by light freeze and
become incapable of pollination and
fertilization.
Ice Nucleating Active (INA) Bacteria on Strawberries
 INA bacteria secrete protein on the leaf
 Protein serves as a primer for ice crystal formation
 Mutant INA bacteria secrete defective proteins (ice-)
 Mutant proteins are incapable of forming Ice crystals
Wild type
INA bacteria
Mutant type
INA bacteria
defective
protein
Ice crystals formed on the
leaf → frost damage
No ice crystals formed on the
leaf → no frost damage
Smudging in a fruit orchard to prevent frost injury
Plant Growing Structures
Controlled Environment Agriculture (CEA)
 Cold Frames
 Hotbeds
 Cloches and Plastic Tunnels
 Greenhouses
 Shade and Lath Houses
Cold Frame
Cloches or Hotbeds
Use of Hotcaps for Vegetable Production
Standard Peak Greenhouses
Gutter-connected Standard Peak Greenhouses
Construction of a Modern Greenhouse
Quonset House
Air Inflated plastic greenhouses
Air Inflated Greenhouse with no internal
support structure
Geodesic Dome Greenhouse