List of Topics

SfC Home > Physics > Thernal Energy >

 

Heating a Greenhouse

by Ron Kurtus (revised 9 November 2014)

A greenhouse is a building that is heated with solar radiation and insulated to prevent loss from convection, conduction and radiation, such that it can stay warm without external heating even during cold days of winter. Such a building is used to grow plants during the winter.

Light from the Sun passes through the glass roof of the greenhouse to heat the plants and ground inside. Objects heated by sunlight emit infrared radiation.

These objects then emit infrared radiation that is absorbed or reflected by the glass roof, thus trapping the thermal energy in the greenhouse instead of letting it escape. This helps keep the building warm.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion



Glass lets in solar radiation

A greenhouse is built with glass walls and a glass roof. Sometimes clear plastic is used instead of glass. One purpose is to provide light to the plants to help them grow and another purpose is to help keep the greenhouse warm.

Solar radiation or light from the Sun or passes through the glass and warms the plants, soil, and other things inside the building. Light is almost completely absorbed into the dark soil in the pots holding the plants, increasing the temperature of the materials.

Greenhouse heated by solar radiation

Greenhouse heated by solar radiation

Besides letting the light energy in, the glass walls and roof act as a thermal insulator to protect the inside from cold air and winds outside the greenhouse.

Warmed air warmed is retained in the building by the roof and walls. There is no heat transferred to the outside by air convection. The glass allows only a little heat loss due to conduction of heat through its material.

(See Heat Transfer for more information on that subject.)

Glass prevents infrared from escaping

Although the glass used for a greenhouse allows visible light and short wavelength infrared radiation to pass through it, it does not transmit the longer infrared wavelengths. This means the radiation is prevented from escaping, causing a loss of heat.

Greenhouse remains warm

Greenhouse remains warm

Typically, the greenhouse glass will transmit solar radiation of wavelengths between 280 nm and 2500 nm, while absorbing infrared or thermal radiation in the 5000 nm to 35000 nm region.

Note: nm stands for nanometer or one 10 millionth of a meter (10-9 meter). Some books denote wavelength in microns. A micron is one millionth of a meter (10-6 meter). Thus 2500 nm is the same wavelength as 2.5 microns.

Infrared radiation that does not pass through the greenhouse glass walls and roof is absorbed in the material. The glass then re-radiates the infrared back to the material inside the greenhouse, thus trapping the thermal energy inside the building and keeping it at a warmer temperature.

(See Infrared Radiation and Infrared, Gases and the Greenhouse Effect for information on those subjects.)

Ground slowly releases energy

Besides using the soil in the pots or on the ground of the greenhouse as a source of storing thermal energy, some greenhouses add materials such as containers of water or bins of sand and rock to absorb and store even more of that energy during the day. They help maintain a steady temperature in the greenhouse.

Since heated materials give off infrared radiation, the warm greenhouse soil, water, sand and other materials emanate this thermal radiation in longer wavelengths than the radiation that heated the materials. This energy is slowly released, even during the night.

Summary

A greenhouse is a building that is heated with solar radiation, such that it can stay warm even during cold days of winter. Light from the Sun passes through the glass roof to heat plants and the ground inside the greenhouse. These objects then emit infrared radiation, which is absorbed in the glass roof. Thermal energy is trapped in the greenhouse, keeping the building warm.


Be kind to your environment


Resources and references

Ron Kurtus' Credentials

Websites

Physics Resources

Books

Top-rated books on Physics of Heat

Top-rated books on Greenhouses


Questions and comments

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.


Share

Click on a button to bookmark or share this page through Twitter, Facebook, email, or other services:

 

Students and researchers

The Web address of this page is:
www.school-for-champions.com/science/
heating_greenhouse.htm

Please include it as a link on your website or as a reference in your report, document, or thesis.

Copyright © Restrictions


Where are you now?

School for Champions

Physics topics

Heating a Greenhouse




Thermal Energy topics

Temperature

Heating

Thermal insulation

Thermodynamics



Let's make the world a better place

Be the best that you can be.

Use your knowledge and skills to help others succeed.

Don't be wasteful; protect our environment.

You CAN influence the world.





Live Your Life as a Champion:

Take care of your health

Seek knowledge and gain skills

Do excellent work

Be valuable to others

Have utmost character

Be a Champion!



The School for Champions helps you become the type of person who can be called a Champion.