ASHRAE Material Properties 4 — Questions and Answers
Question 1: How does adding propylene glycol to a hydronic water loop change the fluid's properties?
- Specific heat goes down and viscosity goes up (Correct answer)
- Specific heat goes up and viscosity goes down
- Neither property changes noticeably
- Both specific heat and viscosity go down
Correct answer: Specific heat goes down and viscosity goes up
Glycol mixtures carry less heat per pound and are thicker, so you need more flow and more pump head for the same capacity.
Question 2: Low-e coatings on glazing mainly improve performance by changing which surface property?
- They raise surface density
- They lower long-wave infrared emissivity (Correct answer)
- They raise thermal conductivity
- They raise visible transmittance
Correct answer: They lower long-wave infrared emissivity
Low-e coatings cut radiant heat transfer across the glazing cavity, which lowers the U-factor.
Question 3: Which material gives a building the most thermal mass per unit volume?
- Fiberglass insulation
- Expanded polystyrene
- Softwood lumber
- Normal-weight concrete (Correct answer)
Correct answer: Normal-weight concrete
Normal-weight concrete is dense (~140-150 lb/ft³), so it stores far more heat per unit volume than wood or insulation.
Question 4: Why is a dielectric union installed where copper pipe connects to steel pipe?
- To allow for differential thermal expansion
- To electrically ground the piping system
- To prevent galvanic corrosion between dissimilar metals (Correct answer)
- To reduce water hammer
Correct answer: To prevent galvanic corrosion between dissimilar metals
Copper and steel are far apart on the galvanic series, so an electrical break is needed to keep the steel from corroding when the two are joined in water.
Question 5: Fibrous and cellular insulations work mainly by taking advantage of which property?
- The high density of the solid material
- The high reflectivity of the fibers
- The high specific heat of the fibers
- The low thermal conductivity of trapped still air or gas (Correct answer)
Correct answer: The low thermal conductivity of trapped still air or gas
Still air conducts only about 0.025 W/m·K, and insulation keeps that air from moving, which stops convection.
Question 6: What happens to the effective thermal conductivity of fiberglass insulation when it absorbs moisture?
- It increases, which lowers the R-value (Correct answer)
- It decreases, which raises the R-value
- It stays the same
- It drops to zero
Correct answer: It increases, which lowers the R-value
Water conducts heat about 20+ times better than air, so wet insulation loses a lot of its R-value.
Question 7: Which combination of surface properties makes a 'cool roof'?
- High solar reflectance and high thermal emittance (Correct answer)
- High solar reflectance and low thermal emittance
- Low solar reflectance and low thermal emittance
- Low solar reflectance and high thermal emittance
Correct answer: High solar reflectance and high thermal emittance
A cool roof reflects most sunlight and gives off the heat it does absorb, which keeps the roof surface cooler.
ASHRAE Material Properties 4
How does adding propylene glycol to a hydronic water loop change the fluid's properties?