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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).

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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 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
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
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

slide5

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

Summer cooling of greenhouse with fogging system

High-pressure fogging

heat of fusion
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
Heat of fusion from ice formation protects citrus crops exposed to freezing temperature in Florida
cell damage by low temperature
Cell Damage by Low Temperature
  • Ice crystals rupture cell walls
  • Intracellular or intercellular event
  • Leakage of cell contents
  • Readily occurs in tender plants
  • Influence of “extensin” on cell wall

Ice crystals

Cell wall ruptures

Extensin

(rupture-resistant)

cryogenic storage
Cryogenic Storage
  • Liquid nitrogen (-196 oC, -320 oF)
  • Permanent storage of pollen, seed, meristems
thermal belt
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

cold

warm slope

warm slope

Normal Condition

Temperature Inversion

slide16

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

slide17

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

slide20

Frost Damage on Strawberry Plants in California

A

B

Normal

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.

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

ice nucleating active ina bacteria on strawberries
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

plant growing structures

Plant Growing Structures

Controlled Environment Agriculture (CEA)

Cold Frames

Hotbeds

Cloches and Plastic Tunnels

Greenhouses

Shade and Lath Houses