Horticulture Science Lesson 43 Controlling the Greenhouse Climate

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Horticulture Science Lesson 43Controlling the
Greenhouse Climate
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Interest Approach
Ask the students what would happen to greenhouse
plants if there were no greenhouse heating or
cooling systems. Try to lead their thinking to
both excessive heat and extreme cold conditions,
and request the students to clearly state their
thoughts and reasons.
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Interest Approach
Then have the students develop a list of ways
greenhouses are heated and another list of ways
greenhouses are cooled. Compile class lists on
the chalkboard, whiteboard, or overhead for all
to see. When the students have finished with
their lists, state the objectives of this lesson.
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Student Learning Objectives

• Describe methods of heating greenhouse
  structures.
• Contrast major greenhouse cooling and ventilation
  systems.

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Student Learning Objectives

• Discuss how energy curtains are used to maintain
  greenhouse temperatures.
• Analyze greenhouse climate controls.

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Terms

• analog controls
• computer controls
• computerized environmental management systems
• energy curtains
• environmental controls
• fan-and-pad cooling system
• fog system

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Terms

• hot water heat system
• infrared heating system
• polyethylene tubes
• short-day curtains
• steam heating system
• thermostats
• unit heaters
• vents

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What methods are used to heat greenhouse
structures?

• The ability to heat greenhouses is important on
  cold, cloudy days and at night.
• Solar energy on sunny days is often enough to
  keep a greenhouse warm, even in cold weather.
• There are several different methods used to heat
  greenhouses.

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What methods are used to heat greenhouse
structures?

• 1. Hot water heating systems are the trend in
  modern greenhouses.
• A hot-water heating systems involve heating water
  in a boiler and pumping the hot water through
  pipes located in the greenhouse.
• The pipes are often placed under the benches.
• These systems have low maintenance and deliver
  even heat.
• 2. Steam heat involves boilers that bring water
  to a boil the resulting steam flows through
  pipes in the greenhouse.
• Steam heat is not as even as hot-water heat.

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What methods are used to heat greenhouse
structures?

• 3. Small greenhouses are often heated by unit
  heaters.
• Unit heaters heat air within the units and then
  blow the air throughout the greenhouse.
• Polyethylene tubes attached to the units help to
  evenly distribute the airflow.
• Unit heaters are inexpensive but cost more to
  operate than other systems.
• Unit heaters are commonly used as backup systems.

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What methods are used to heat greenhouse
structures?
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What methods are used to heat greenhouse
structures?

• 4. Infrared heating systems produce heat energy
  that is absorbed by plants, media, and benches.
• Infrared heating systems do not heat the air.
• Since these systems must be placed at the peak of
  the greenhouse, they are best suited for high
  greenhouse structures so the energy can radiate
  throughout the house.

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What are the major greenhouse cooling and
ventilation systems?

• To maintain optimal temperatures for plant
  growth, it is important to be able to keep the
  greenhouse cool when outside temperatures are
  warm or when the sun is shining.
• Sophisticated cooling and ventilation systems
  have been developed for this purpose.

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What are the major greenhouse cooling and
ventilation systems?

• The number one cooling system used today is the
  fanandpad cooling system, which is based on
  evaporation of water.
• Cellulose or aspen pads at one end of the house
  are kept wet, while fans at the other end of the
  house pull outside air through the pads.
• Air entering the house is cooled as water in the
  pads evaporates.

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What are the major greenhouse cooling and
ventilation systems?

• A less common cooling system is the fog system.
• Fog systems involve an atomizer that produces
  water vapor.
• The flash evaporation of this water cools the
  greenhouse.

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What are the major greenhouse cooling and
ventilation systems?

• Natural cooling is made possible with vents,
  which consist of panels that open and allow air
  exchange with the outside.

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How are energy curtains used to maintain
greenhouse temperatures?

• The use of energy curtains in modern greenhouses
  helps to maintain temperatures and reduce heating
  and cooling costs.
• Energy curtains are automated systems using
  fabrics that can insulate a greenhouse at night
  and shade the crops during the day.
• The curtains are installed from gutter to gutter,
  and they are opened and closed by computerized
  systems.

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How are energy curtains used to maintain
greenhouse temperatures?
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How are energy curtains used to maintain
greenhouse temperatures?

• Short-day curtains are similar to energy
  curtains.
• The function of shortday curtains is to provide
  darkness that will simulate a short-day effect.

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What are the common greenhouse climate controls?

• Climate controls give the grower the power to
  control temperatures within the greenhouse.
• Environmental controls are devices used to turn
  greenhouse systems on and off, including heating
  and cooling systems.
• Thermostats are low cost and easy to install
  environmental controls.
• 1. On-off thermostats control fans, heaters, and
  vents with the change of temperatures.
• 2. Proportioning thermostats provide continuous
  control of systems with the change of temperature.

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What are the common greenhouse climate controls?

• Analog controls use proportioning thermostats to
  run amplifiers and electronic circuitry.
• The heating and cooling operations are
  integrated, resulting in better performance than
  provided by just a thermostat.
• Computer controls use microprocessors to make
  complex judgments based on information from a
  number of sensors.
• Computerized environmental management systems,
  although expensive, are accurate and can control
  all the automated systems together.

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Review/Summary

• What methods are used to heat greenhouse
  structures?
• What are the major greenhouse cooling and
  ventilation systems?

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Review/Summary

• How are energy curtains used to maintain
  greenhouse
• temperatures?
• What are the common greenhouse climate controls?