Chap 10. Temperature

1
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)

2
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

3
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
4
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
5
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
6
Heat of Fusion

• Heat is released to surrounding when water
  freezes
• Heat of fusion is used to protect citrus fruits
  from freezing

7
Heat of fusion from ice formation protects citrus
crops exposed to freezing temperature in Florida
8
Overhead water sprinkling on citrus crops in
Florida to save them from freezing
9
Transfer of Heat Energy
10
Temperature Influence in Biological System
11
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)
12
Cryogenic Storage

• Liquid nitrogen (-196 oC, -320 oF)
• Permanent storage of pollen, seed, meristems

13
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
14
Peach orchard located on a thermal belt, Western
Slope, Colorado
15
Fruit growing area in Oregon
16
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
17
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
18
Use of Plastic Mulch
19
Strawberry Production in California
20
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
21
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
22
Smudging in a fruit orchard to prevent frost
injury
23
Plant Growing Structures

• Controlled Environment Agriculture (CEA)
• Cold Frames
• Hotbeds
• Cloches and Plastic Tunnels
• Greenhouses
• Shade and Lath Houses

24
Cold Frame
25
Cloches or Hotbeds
26
Use of Hotcaps for Vegetable Production
27
Standard Peak Greenhouses
28
Gutter-connected Standard Peak Greenhouses
29
Construction of a Modern Greenhouse
30
Quonset House
31
Air Inflated plastic greenhouses
32
Air Inflated Greenhouse with no internal support
structure
33
Geodesic Dome Greenhouse