ASHRAE ASHRAE Thermal Comfort and Heat Transfer 2 — Questions and Answers
Question 1: In ASHRAE load calculations, what term describes heat that affects only the sensible load without changing room humidity?
- Sensible heat gain (Correct answer)
- Latent heat gain
- Total cooling load
- Effective heat fraction
Correct answer: Sensible heat gain
Sensible heat gain changes the dry-bulb temperature of the space air without adding moisture, directly contributing to the sensible cooling load.
Question 2: Which ASHRAE method is the current standard procedure for calculating residential and commercial cooling and heating loads?
- Radiant Time Series (RTS) method (Correct answer)
- CLTD/CLF method
- Transfer Function Method (TFM)
- Degree-Day method
Correct answer: Radiant Time Series (RTS) method
The Radiant Time Series (RTS) method is the current ASHRAE simplified hand-calculation procedure described in the Handbook – Fundamentals for cooling load calculations.
Question 3: What is the sol-air temperature concept used for in ASHRAE load calculations?
- To combine solar radiation and outdoor air temperature into a single equivalent outdoor temperature for wall and roof conduction calculations (Correct answer)
- To determine the supply air temperature for variable air volume systems
- To calculate the mean radiant temperature of glazed surfaces
- To estimate ground-coupled heat transfer beneath a slab
Correct answer: To combine solar radiation and outdoor air temperature into a single equivalent outdoor temperature for wall and roof conduction calculations
Sol-air temperature is an equivalent outdoor temperature that accounts for both the actual outdoor air temperature and the solar radiation absorbed by an exterior surface.
Question 4: According to ASHRAE fundamentals, convection heat transfer coefficient h depends primarily on which factor?
- Fluid velocity and flow regime (laminar vs. turbulent) (Correct answer)
- Color and emissivity of the surface
- Thermal conductivity of the solid material only
- Atmospheric pressure at the site elevation
Correct answer: Fluid velocity and flow regime (laminar vs. turbulent)
The convective heat transfer coefficient h is strongly influenced by fluid velocity and whether flow is laminar or turbulent, as described by dimensionless Nusselt number correlations.
Question 5: What is the significance of the U-factor (overall heat transfer coefficient) for a fenestration assembly per ASHRAE?
- It quantifies the total rate of heat transfer through the window assembly per unit area per degree temperature difference (Correct answer)
- It measures the fraction of solar radiation transmitted through glazing
- It defines the air leakage rate through the window frame
- It specifies the visible light transmittance of the glazing
Correct answer: It quantifies the total rate of heat transfer through the window assembly per unit area per degree temperature difference
The U-factor is the overall heat transfer coefficient (Btu/h·ft²·°F) that accounts for conduction, convection, and radiation through the entire fenestration assembly.
Question 6: In ASHRAE psychrometric analysis, which process describes cooling air below its dew point to remove moisture?
- Cooling and dehumidification (Correct answer)
- Sensible cooling
- Evaporative cooling
- Adiabatic humidification
Correct answer: Cooling and dehumidification
Cooling and dehumidification occurs when air is cooled below its dew point temperature, causing moisture to condense out and reducing both the dry-bulb temperature and humidity ratio.
ASHRAE ASHRAE Thermal Comfort and Heat Transfer 2
In ASHRAE load calculations, what term describes heat that affects only the sensible load without changing room humidity?