ASHRAE Material Properties 3

Question 1

What is the approximate specific heat of dry air at constant pressure in I-P units?

Accepted Answer

0.24 Btu/lb·°F

Answer

For dry air, cp ≈ 0.24 Btu/lb·°F, which gives the 1.08 constant in the sensible heat equation (0.075 × 60 × 0.24).

Question 2

What density does ASHRAE use for standard air at sea level?

Accepted Answer

0.075 lb/ft³

Answer

Standard air is taken as 0.075 lb/ft³, which is about 1.2 kg/m³.

Question 3

A 2-inch layer of insulation has k = 0.25 Btu·in/h·ft²·°F. What is its R-value?

Accepted Answer

R-8

Answer

R = thickness / k = 2 / 0.25 = 8 h·ft²·°F/Btu.

Question 4

Which piping material has the highest coefficient of linear thermal expansion?

Accepted Answer

CPVC

Answer

Plastics like CPVC expand about 3-4 times as much as copper and about 5 times as much as steel, so they need more room for expansion.

Question 5

Compared with open-cell spray foam, closed-cell spray polyurethane foam has which characteristics?

Accepted Answer

Higher R per inch and lower vapor permeance

Answer

Closed-cell SPF is rated at about R-6 to R-7 per inch and can act as a vapor retarder, while open-cell is about R-3.5 to R-3.8 per inch and lets vapor through.

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers Certification Practice Test

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers Certification Practice Test

ASHRAE Material Properties 3