GREENHOUSE COOLING

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Chapter 4

• GREENHOUSE COOLING

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SUMMER or WINTER
40-50oF hotter inside than outside
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TWO TYPES OF COOLING

• SUMMER COOLING
• Evaporative Cooling
• Smooth flow of cool air at plant level
• WINTER COOLING
• Fans only, imports outside air
• Turbulent air flow to mix frigid outside air with
  warm inside air, then reaches plants

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Principle ofEvaporative Cooling
Liquid Water
Water Vapor
Latent Heat of Vaporation
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FACTORS AFFECTING COOLING RATE

• Rate of Air Exchange
• Measured as CFM
• Std. Rate 8 cfm/ft2 of floor area if
• _at_1000 elevation
• _at_5000 fc light intensity
• _at_7oF rise between pads fans
• w/ 100-200 greenhouse
• Size of Pad

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ELEVATION

• As elevation increases,
• air flow must increase
• WHY?
• Air becomes less dense (lighter) at higher
  elevations and does not remove heat as quickly

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LIGHT INTENSITY

• As light intensity increases, heat build-up
  inside increases
• Max. Light Intensity on a bright July/August day
  10,000 fc
• Most plants need 3000 fc, but 5000 is generally
  acceptable to achieve 3000 fc in foliage canopy

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Pad to Fan Temp. Increase

• Std. value 7oF
• If can tolerate more, can slow air movement down
• If require less, must speed air flow

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Air Velocity

• Air velocities are adjusted for a 100-200
  Greenhouses
• If a GH is only 50, what happens to air
  velocity?
• Increase or Decrease ?
• Decrease

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Summer Cooling Example

• 30x100 Greenhouse
• LxWx8 cfm Unadjusted cfm
• 30x100x 8cfm 24,000 cfm
• If
• Elevation 700 Felev1.00
• Light Intensity 4500 fc Flight0.90
• Pad/Fan temp 7oF Ftemp 1.00
• Fhouse Felev x Flight x Ftemp 21,600 cfm
• Always use the higher of Fhouse or Fvel to adjust
  the std. cfm

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FANS Number Size

• Rules
• 1. Fan Spacing - at least 1 fan for each 25 of
  greenhouse width
• 50 wide 2 fans
• 60 wide 3 fans
• 35 wide 2 fans
• 2. Divide total adj. cfm by of fans
• 3. Evenly space fans
• (Use table 4-5 for fan selection)

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FAN SELECTION

• Example
• To move 24,000 cfm in a 30 wide greenhouse, need
  2 fans _at_ 12,000 cfm each
• 42, 1/2 hp

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Evaporative Pad Size

• Using Table 4-5
• Example
• With 2-12,500 cfm fans
• Need 168 ft2 excelsior
• 100 ft2 4 cellulose
• 72 ft2 6 cellulose

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Rules for Pad Installation

• 1. Pad should run entire length of wall
• 2. Water should be applied to top of pad on 3
  intervals
• 3. Should apply 0.5 gpm/linear ft. of 4 pad or
  0.75 gpm/linear ft. of 6 pad
• 4. Water storage tank should hold 1.5 gal/linear
  ft of pad

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WINTER COOLING

• Brings in cold outside air
• Mixes cold air with warm air in upper part of
  greenhouse
• Air blows down on plant leaves
• (Fan-Jet System often used)

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Calculating Winter Cooling

• Std cfm 2 cfm/ft2 of floor space
• Adjustments to winter cooling std values
• Felev (Table 4-1)
• Flight (Table 4-2)
• Fwinter (Table 4-6)
• Std. 15oF max. differential

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No. Size ofWinter Cooling Tubes

• Number of tubes depends on width of greenhouse
• lt 30 ft. 1 tube
• gt 30 ft. 2 tubes
• Diameter of tubes depends on length
• (See Table 4-7)

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Integrated Heating Cooling