HVAC and Building Envelope Flashcards
7 cards from real CEM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 HVAC and Building Envelope flashcards as text
What is the purpose of demand-controlled ventilation (DCV) in commercial buildings?
Answer: Modulate outdoor air intake based on CO2 or occupancy sensors
DCV reduces outdoor air ventilation when spaces are less occupied, cutting heating and cooling energy while maintaining acceptable indoor air quality.
Which of the following best describes 'thermal bridging' in a wall assembly?
Answer: A highly conductive element that bypasses insulation layers
Thermal bridges are elements like metal studs or fasteners that conduct heat more easily than surrounding insulation, reducing the effective R-value of the assembly.
What is the Integrated Part Load Value (IPLV) used to evaluate?
Answer: Chiller efficiency across a range of part-load operating conditions
IPLV is a weighted average efficiency metric for chillers that accounts for the fact that they rarely operate at full load, providing a more realistic performance comparison.
In a cooling load calculation, which load component accounts for heat from occupants, lighting, and equipment?
Answer: Internal heat gains
Internal heat gains are heat generated inside the conditioned space by people, lighting, and plug loads, all of which must be removed by the cooling system.
What does an air-side economizer's 'high-limit shutoff' control?
Answer: Outdoor air temperature or enthalpy threshold above which economizing is disabled
The high-limit shutoff closes the outdoor air damper to minimum position when outdoor conditions (temperature or enthalpy) exceed a threshold where free cooling is no longer beneficial.
Which insulation material has the highest R-value per inch of thickness?
Answer: Spray polyurethane foam (closed-cell)
Closed-cell spray polyurethane foam achieves approximately R-6 to R-7 per inch, the highest commonly used insulation, due to its low-conductivity blowing agent.
A building's heating system is sized using outdoor design conditions. What temperature is typically used for heating design in the U.S.?
Answer: 99% or 99.6% heating dry-bulb from ASHRAE weather data
ASHRAE recommends using the 99% or 99.6% heating design dry-bulb temperature, meaning outdoor air exceeds this cold temperature only 1% or 0.4% of annual hours.