Saving Energy Through
Ecological Landscape Design
1991 Woodrow Wilson Biology Institute
After completing this activity the student will display the ability to...
- transcribe to scale the plant features of a common landscape.
- determine true north and south.
- collect and record data on a table.
- calculate a rating for and describe a definition of insulation and insolation.
- determine the 'ecological quality' of a landscape in a quantifiable manner.
An ecologically sound plan for landscaping your home can lead to terrific savings in energy usage. Not only do you recognize a dollar savings on energy costs but you individually impact the ecosystem less traumatically in terms of resources used and wastes created.
In this activity you will analyze an existing landscape for energy efficiency in both a qualitative and quantitative fashion. That is, you will describe the features of the landscape related to the effects of plants on both insulation and insolation (heat retention and reflection respectively). You will then assign values to theses features based on described parameters that will lead to an insulation rating (Rsu) as well as an insolation rating (Rso).
- graph paper
- magnetic compass
- measuring tape (optional)
- keys for identifying trees and shrubs (optional)
- protractor, string, tape or thumb tack, oak tag or cardboard
- trigonometry text with trig tables including tangent (or calculator with trig functions)
- Using a standard piece of graph paper, draw a picture of your landscape to scale and include as much detail as possible. Include all the relative distances from each tree and shrub to the house. Step off the distances and record them on connecting lines. If no measuring tape is available, assume one step to be 3 feet.
- Use a compass to determine magnetic north and south as accurately as possible. Mark these directions on your drawing. Note: True north and south need to be adjusted for according to your latitude. You may contact the U.S. Geological Survey for that information in your area.
- Label all the trees and shrubs simply as leafy (deciduous) or evergreen (coniferous) and give each plant a number, eg. E1= Evergreen #1, L2= Leaf tree #2, etc. Then record the data on the table you will prepare in procedure 4.
- Prepare a table for collecting data as follows:
- Calculate the rating by giving each plant in the data table a value based on the information below. You may use tally marks in the table cells and then write the numerical value for each when you are through.
|Evergreen trees||2 pts. for Rsu, 1 for Rso|
|Evergreen shrubs||1 pt. for Rsu, 1 for Rso|
|Leaf trees||1 pt. for Rsu, 2 for Rso|
|Leafy shrubs||0 pts. for Rsu, 1 for Rso|
In addition, give any tree an extra point for being inside a 30 ft. radius of the house, and give any shrub an extra point for being within three ft. of the foundation. Similarly, give any leaf tree an extra point for being on the south or southwest side of the house. These values reflect high insulation for evergreens and high insolation for leaf trees with lesser values for small shrubs. To calculate the overall rating for this landscape, simply add the numbers as you see below.
- Total Rsu=_____
- Total Rso=_____
- Extra pts.=_____
- Sum =_____ (quality rating)
For comparison to a norm, let us suggest an average landscape containing 3 evergreen trees and 8 evergreen shrubs all receiving extra pts. for close proximity. The yard also has 3 leaf trees within 30 ft. of the house and 11 leafy shrubs, 9 of which are within the proximity radius for the foundation. Two of the leaf trees are also on the south or southwest sides of the house. This landscape should receive a sum total of 63 pts. Assume an average score is between 50 and 75. Any landscape below 50 is considered to be inefficient and any score above 75 is considered highly efficient. How would you describe the energy rating you achieved on your house?
- Determine the types of trees in your landscape to common name or species. This can be done by asking the homeowner or by using available tree and shrub identification keys. These may be procured from the local nurseryman, a library, or from the county extension agent for horticulture. Add 1 pt. for each tree that has a very dense growth pattern for insulation or insolation according to the information in the reference books or keys.
- Estimate the level of maturity for your trees using these same references. For example, a silver maple tree will be noted to reach a maximum height of 60 ft. for your area. If you have a silver maple that is half that tall you would say it is 50% mature. (To be exact on the height, use the triangulation method described below). Add 1 pt. for a fully mature tree, 1/2 pt. for a 50% mature tree, etc.
- Suggest a re-planting program for a poorly designed landscape. Do not cut any trees down. Plant only new trees that will not be shaded out or encroached upon by existing specimens.
- Draw and design a new landscape that would achieve a rating of 80 or above.
- How would you define insulation and insolation without using scientific terms?
- Why do you need to know true north and south for this activity?
- Would you penalize a leaf tree in determining it's Rso if it was in a landscape in Puerto Rico? Montana? South Florida?
- What change in Rsu would you suggest for 5 Blue Spruces growing in a tight row on the north side of a home in Minneapolis?
- What incentives could the government institute to encourage both tree planting and ecological landscaping in the United States?
* Notes on using triangulation to determine the height of a tree:
- Use a protractor to make a right angle on a piece of cardboard and mark the angles from 0 to 90.
- Take a 12" piece of string and attach it to the origin of the angle with a tack or tape.
- Hold the paper straight out from your eye so that the base of the paper is parallel to the ground.
- Align the string so that it is pointing at the top of the tree you want to measure.
- Record the angle created.
- Step off or somehow measure the distance to the tree in feet.
- Use the formula below to determine the height of the tree.
Tree Height= [(Base(ft.) x Tangent of the angle* )+ ht. of your eye above ground level]
*From trig tables in any trigonometry text or use the tangent function on an equipped calculator
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281