Horticulture Science
Lesson 43
Controlling the Greenhouse
Climate
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.
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.
Student Learning Objectives
•Describe methods of heating
greenhouse structures.
•Contrast major greenhouse
cooling and ventilation systems.
Student Learning Objectives
•Discuss how energy curtains are
used to maintain greenhouse
temperatures.
•Analyze greenhouse climate
controls.
Terms
• analog controls
• computer controls
• computerized environmental
management systems
• energy curtains
• environmental controls
• fan-and-pad cooling system
• fog system
Terms
•
•
•
•
•
•
•
•
hot water heat system
infrared heating system
polyethylene tubes
short-day curtains
steam heating system
thermostats
unit heaters
vents
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.
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.
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.
What methods are used to heat
greenhouse structures?
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.
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.
What are the major greenhouse
cooling and ventilation systems?
• The number one cooling system used today
is the fan–and–pad 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.
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.
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.
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.
How are
energy
curtains used
to maintain
greenhouse
temperatures?
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 shortday effect.
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.
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.
Review/Summary
•What methods are used to heat
greenhouse structures?
•What are the major greenhouse
cooling and ventilation systems?
Review/Summary
•How are energy curtains used to
maintain greenhouse
temperatures?
•What are the common
greenhouse climate controls?