Hands-on Activity: Model Greenhouses
Educational Standards :
Pre-Req Knowledge (Return to Contents)
A basic understanding of the properties of light, including the visible spectrum, reflection and refraction of light. Students should concurrently be taking Algebra 1 in order to complete the worksheet calculations.
Learning Objectives (Return to Contents)
After this activity, students should be able to:
Materials List (Return to Contents)
Each group needs:
For the entire class to share:
Introduction/Motivation (Return to Contents)
Have you ever noticed that often, after entering a car that has been in the sun all day, the interior is very warm, and may even be uncomfortably hot. This is not just due to hot weather; it happens because the design of the car lets heat enter, but not escape. This situation is not to be confused with the greenhouse effect. Although the situations are similar, the analogy is incorrect. The greenhouse effect refers to the process by which radiation from the sun is absorbed and reflected by the Earth's surface; some of the reflected radiation makes its way back through the atmosphere, and some is absorbed by greenhouse gas molecules that then re-emit the radiation in all directions in the atmosphere warming the surface of the Earth. As you have probably heard many times, the greenhouse effect has the potential to harm the Earth due to its contribution to global warming — but without it, our Earth would not be warm enough for us to live on!
The process by which a greenhouse works is very different from the greenhouse effect. A greenhouse consists of a structure made entirely of a highly-transparent material, such as glass or plastic. The transparent material lets heat enter in the form of radiation, but does not let this heat escape (at least not very quickly). Heat is absorbed by inside objects and materials through radiation, and then released to the rest of the interior space through convection. The most important aspect of a greenhouse is that a person can control the interior environment, which is helpful when growing plants, especially in climates in which gardening would not normally be favorable.
So how can using a greenhouse improve the energy efficiency of a typical house? To start, it uses the light and heat emitted by the sun to create an exceptional environment for plant life. To do this with conventional heating and lighting would cost quite a lot. It also allows people to grow their own vegetables, herbs and flowers rather than buying them from a market. Designing a greenhouse as an addition to any home gives the inhabitants the opportunity to grow their own vegetables and plants at usually less cost than a grocery store. This saves energy in the form of electrical lights and heaters, as well as the energy that would be used to package the store-bought foods and transport them to the grocery store and to your home.
In the future, engineers may design and build enormous skyscraper greenhouses that are able to grow all kinds of fruits and vegetables, eliminating the need for goods to be transported into major cities. These would allow cities to become self sufficient and help to prevent widespread deforestation.
Vocabulary/Definitions (Return to Contents)
Procedure (Return to Contents)
How Greenhouses Work: Greenhouses operate on four principals: radiation, transmittance, absorption and convection. Through this process, people are able to harvest energy from the sun and use it to maintain a warm and humid indoor environment conducive for plants to grow.
The result of this process is an indoor environment much warmer than normally achievable without a greenhouse. If the temperature gets too high, it is easy to adjust it by opening a window or door to let out some heat.
A greenhouse design can be modified to account for specific capacitance or temperature needs. While changing the slope of the walls and roof does not change the amount of radiation entering, changing the dimensions does. A larger surface area leads to a larger amount of transmitted radiation. To harness all this radiation, a large absorptive surface is also required. For a higher-heat greenhouse, the floor surface area should be maximized while the volume of the overall greenhouse should be minimized (to allow for less space to be heated with the same amount of radiation). Of course, engineers must remain within certain constraints while designing them this way. For a larger capacity, a greenhouse simply needs more volume with a considerable amount of radiation still being transmitted. Greenhouses should be designed to optimally suit the specific needs of the user, so engineers must understand any necessary design modifications.
The Greenhouse Effect and Climate Change: The greenhouse effect is often confused with the process that occurs within an actual greenhouse. The greenhouse effect refers to a process in which reflected radiation from the Earth's surface is absorbed and re-emitted by greenhouse gases, rather than getting passed back into the atmosphere. It prevents the loss of heat by radiation, rather than convection, as in a typical greenhouse. It is important to distinguish between the two because they are easily confused.
Climate change refers to a significant change in average weather patterns over a long period of time in a particular region. It is attributed to several factors such as variations in solar intensity, and the Earth's orbit, and more recently, greenhouse gas emissions. Studying how the climate changes helps to distinguish between natural dynamic climate patterns and more recent forced climate patterns such as those caused by global warming. This kind of information is critical in analyzing the worldwide problem of global warming.
Vertical Farming: Vertical farming is a conceptual form of agriculture suitable for implementation in urban high-rises. These multi-story greenhouses would enable year-round crop production with exceptional benefits. Food for urban centers could be produced without the trouble of weather-related failure or transportation expenses. These buildings could make cities of the future completely self sufficient, reducing deforestation by returning farmland to nature. Currently the concept of vertical farming has not become a reality, but it is likely to revolutionize food production in the next 50 years.
Solar Geometry: It is important to consider the position of the sun and place the greenhouse on the land so that it receives sunlight during all times of the year. For this to happen, it must be completely exposed to the south (assuming its location is in the northern hemisphere). Placement should take into consideration any nearby trees or structures to the south of the greenhouse that may block the winter sun, which is much lower in the sky.
Before the Activity
With the Students
Attachments (Return to Contents)
Safety Issues (Return to Contents)
Troubleshooting Tips (Return to Contents)
If a model greenhouse has difficulty retaining heat, make sure it is completely sealed so no air can leak out.
Investigating Questions (Return to Contents)
What are some ways to use a greenhouse other than for gardening? (Possible answer: You could install a duct and fan system to pull warm air out of the greenhouse and heat your house during the winter [this would mean it would no longer work for gardening].)
Assessment (Return to Contents)
Question/Answer: Have students first discuss amongst themselves, and then discuss as a class.
Activity Embedded Assessment
Worksheet: Have teams complete the Greenhouse Design & Testing Worksheet; review their answers to gauge their mastery of the subject.
Re-Engineering: Ask students how they could improve their model greenhouse and have them sketch or test their ideas.
Concluding Discussion Question/Answer: Ask students and discuss as a class.
Activity Extensions (Return to Contents)
Have students work as a class to design and build a larger greenhouse that can hold more plants.
Have teams evaluate their models considering solar geometry, thinking about the position of the sun in relation to their greenhouses. Where would they place their greenhouses next to a house? For example, a greenhouse is best placed in an area that receives sunlight during all times of the year.
Activity Scaling (Return to Contents)
References (Return to Contents)
Greenhouse Effect. Updated December 4, 2008. Wikipedia, The Free Encyclopedia. Accessed December 4, 2008. http://www.gov.mb.ca/agriculture/crops/greenhouse/bng01s04.html
Greenhouse Heating and Venting: A guideline for determining heating and venting requirements of a greenhouse. March 2006. Manitoba Agriculture, Food, and Rural Initiatives. Accessed December 3, 2008. http://www.gov.mb.ca/agriculture/crops/greenhouse/bng01s04.html
The Vertical Farm Project - Agriculture for the 21st Century and Beyond. 2008. The Vertical Farm Project, Environmental Health Science of Columbia University, New York, NY. Accessed December 3, 2008. http://www.verticalfarm.com/
ContributorsLandon B. Gennetten, Lauren Cooper, Malinda Schaefer Zarske, Denise W. Carlson
Copyright© 2007 by Regents of the University of Colorado. This digital library content was developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326.
Supporting Program (Return to Contents)Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder
Last Modified: March 12, 2014