CEM Building Envelope and Insulation 1 — Questions and Answers
Question 1: What does the R-value of insulation measure?
- Thermal conductivity in BTU·in/(hr·ft²·°F)
- Thermal resistance to heat flow in hr·ft²·°F/BTU (Correct answer)
- Reflectivity of the insulation surface
- Density of insulation material in lb/ft³
Correct answer: Thermal resistance to heat flow in hr·ft²·°F/BTU
R-value measures the resistance of insulation to heat flow; higher R-values indicate better insulating performance.
Question 2: The U-factor of a window assembly represents:
- Solar heat gain coefficient
- Overall heat transfer coefficient in BTU/(hr·ft²·°F) (Correct answer)
- Visible light transmittance
- Air infiltration rate in CFM/ft²
Correct answer: Overall heat transfer coefficient in BTU/(hr·ft²·°F)
U-factor is the rate of heat transfer through a window assembly per unit area per degree of temperature difference, with lower values indicating better insulation.
Question 3: Solar Heat Gain Coefficient (SHGC) of a window measures:
- How much heat the window frame conducts
- The fraction of incident solar radiation admitted through the window (Correct answer)
- The window's resistance to condensation
- The visible light transmission of the glazing
Correct answer: The fraction of incident solar radiation admitted through the window
SHGC ranges from 0 to 1 and represents the fraction of solar energy that passes through the window as heat gain into the building.
Question 4: Air infiltration through a building envelope wastes energy primarily because:
- It increases lighting loads by introducing outdoor humidity
- Unconditioned outdoor air must be heated or cooled to maintain indoor comfort (Correct answer)
- It reduces the R-value of wall insulation permanently
- It increases plug loads from appliances
Correct answer: Unconditioned outdoor air must be heated or cooled to maintain indoor comfort
Infiltrating outdoor air at different temperatures from indoor setpoints requires the HVAC system to expend energy conditioning that air, increasing heating and cooling costs.
Question 5: A blower door test is used to:
- Measure duct leakage in HVAC systems
- Quantify building envelope air leakage at a standardized pressure (Correct answer)
- Test fire door compliance
- Measure indoor air quality and CO2 levels
Correct answer: Quantify building envelope air leakage at a standardized pressure
A blower door depressurizes the building to 50 Pa and measures airflow required to maintain that pressure, quantifying total envelope leakage.
Question 6: Thermal bridging through wall studs reduces effective wall R-value because:
- Studs have higher R-value than insulation and over-insulate the wall
- Wood or metal studs conduct heat more readily than insulation, bypassing its resistance (Correct answer)
- Studs prevent air infiltration and reduce convective losses
- Thermal mass of studs stores and releases heat beneficially
Correct answer: Wood or metal studs conduct heat more readily than insulation, bypassing its resistance
Metal and wood studs conduct heat far better than insulation, creating pathways that bypass insulation and lower the whole-wall effective R-value below the nominal cavity R-value.
CEM Building Envelope and Insulation 1
What does the R-value of insulation measure?