Horticulture Science Lesson 43

Controlling the Greenhouse Climate

Horticulture Science Lesson 43

Controlling the Greenhouse Climate

Interest ApproachInterest ApproachAsk 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 ApproachInterest ApproachThen 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 ObjectivesStudent Learning Objectives•Describe methods of heating greenhouse structures.

•Contrast major greenhouse cooling and ventilation systems.

Student Learning ObjectivesStudent Learning Objectives•Discuss how energy curtains are used to maintain greenhouse temperatures.

•Analyze greenhouse climate controls.

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

TermsTerms• 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 short-day 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/SummaryReview/Summary•What methods are used to heat greenhouse structures?

•What are the major greenhouse cooling and ventilation systems?

Review/SummaryReview/Summary•How are energy curtains used to maintain greenhousetemperatures?

•What are the common greenhouse climate controls?