Wall R Value Activity

Construction Context
rvaluewall We spend the most money for energy heating and cooling our home. Insulation reduces that cost and saves money. The effectiveness of insulation is designated by its “R” value. The higher the R Value the better the insulation. “R” refers to the “resistance” to heat flow.

See http://www.cellulose.org/HomeOwners/WhatR-valueMean.php for more information about insulation. Understanding how well a home is insulated is complicated by the fact that a wall in your home is usually a combination of wall-framing, windows, doors, and other interruptions in the insulation.

Optional Materials
Infrared Thermometer

Activity Description
This activity can be conducted as a qualitative analysis of the number and kind of interruptions in the walls of a room or house. For example, students count the number of windows, doors, vents, and electrical wall outlets in the outside walls of their home. This provides a qualitative assessment of home insulation.

A more meaningful assessment of insulation would be to compute the total square feet of wall interruptions and of what type: windows, doors, vents, and electrical wall outlets. Students could compute the total square feet of outside walls and then compute the ratio of square feet of interruptions to the total wall area.

Included in this activity is a description of computing the total R Value of a wall considering typical features of a wall (link to PDF: http://theselsproject.org/wp-content/uploads/2013/02/wall_assembly_problem_key-copy-2.pdf or scroll to the end of this activity for a picture). This quantitative treatment of the problem can provide the basis for a rich discussion of heat flow through walls and energy efficiency in a home or building. Such a discussion shows the interconnection of science concepts in real-world problems.

Science Concepts
Heat Conduction [relations to Convection and Radiation]

Next Generation Science Education Standards
Scientific and Engineering Practices:
– Asking questions (for science) and defining problems (for engineering)
– Using mathematics and computational thinking

Crosscutting Concepts:
– Patterns
– Scale, proportion, and quantity
– Energy and matter: Flows, cycles, and conservation

Discussion Questions

  1. Ask students to reflect on the effectiveness of insulation in a home. Guide discussion so that students come up with the effect of windows, vents, etc. on home insulation and energy efficiency.
  2. What can be done to improve efficiency after introducing insulation in the walls? (e.g. thermal pane windows, Low-E glass, plug covers for outlets, heavy window covers, etc.)
  3. Ask students to interpret what the ratio of wall-interruptions to wall area tells you about energy efficiency. (e.g. the higher the ratio the poorer the energy efficiency.
  4. Watch the classroom video that examines the effect of insulation around a box on heat flow out of a box with and without insulation.

HOW TO CALCULATE WALL R VALUE

wall_assembly_problem_key-copy-2

(Download the activity in PDF, Word)