CEM HVAC Systems & Building Envelope 3

Question 1

A variable-air-volume (VAV) system reduces airflow to a zone at part-load conditions. What energy benefit does this provide over a constant-volume system?

Accepted Answer

Fan energy decreases cubically with airflow reduction

Answer

Fan power follows the affinity laws: reducing airflow to 50% cuts fan power to approximately 12.5% (cube of flow ratio), yielding large energy savings.

Question 2

What is the purpose of a thermal break in a window frame or curtain wall system?

Accepted Answer

Interrupt conductive heat transfer through the metal frame

Answer

A thermal break is a low-conductivity material inserted in the frame to interrupt the metal conduction path, reducing heat transfer and condensation risk.

Question 3

In psychrometrics, what does the wet-bulb temperature primarily indicate?

Accepted Answer

Evaporative cooling potential and enthalpy of air

Answer

Wet-bulb temperature reflects the air's evaporative cooling potential and correlates closely with air enthalpy, making it critical for cooling tower and economizer analysis.

Question 4

Which strategy best addresses the 'stack effect' that drives air infiltration in tall buildings during winter?

Accepted Answer

Pressurizing lobby and lower floors with conditioned air

Answer

Pressurizing the lower building (where cold outdoor air infiltrates) counteracts the stack effect-driven pressure differential that draws cold air in at the base.

Question 5

A CEM is evaluating heat recovery from exhaust air. Which device achieves both sensible and latent energy recovery?

Accepted Answer

Rotary enthalpy wheel

Answer

A rotary enthalpy wheel uses a desiccant-coated rotating matrix to transfer both sensible heat and moisture (latent energy) between exhaust and incoming air streams.

(CEM) Certified Emergency Manager Practice Test

(CEM) Certified Emergency Manager Practice Test

CEM HVAC Systems & Building Envelope 3