HVAC Systems & 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 Systems & Building Envelope flashcards as text
A facility engineer notes that cooling tower approach temperature has increased over several months. What is the most likely cause?
Answer: Fouled or scaled fill media reducing heat transfer
Scale or biological fouling on the tower fill reduces wetted surface area and heat/mass transfer effectiveness, increasing the approach temperature.
Under ASHRAE 90.1, what is the primary purpose of the building envelope compliance path using the prescriptive method?
Answer: Verify that envelope component U-values meet tabulated maximum requirements
The prescriptive path requires that individual envelope components (roof, walls, windows) meet maximum U-factors and minimum R-values specified in ASHRAE 90.1 tables by climate zone.
Which refrigerant property most directly determines the operating pressures of a vapor-compression system?
Answer: Saturation pressure-temperature relationship
The saturation pressure-temperature curve dictates the evaporating and condensing pressures at given temperatures, defining compressor lift and system design.
A building automation system (BAS) shows supply air temperature consistently 3°F above setpoint. What is the most energy-efficient corrective action to investigate first?
Answer: Calibrate or replace the supply air temperature sensor
A faulty sensor is the lowest-cost root cause; sensor drift or failure will cause the control system to maintain incorrect conditions wasting energy before mechanical changes are made.
What does the term 'thermal mass' refer to in the context of building envelope performance?
Answer: Capacity of building materials to absorb and store heat energy
Thermal mass describes materials with high heat capacity (concrete, masonry) that absorb heat during the day and release it later, moderating indoor temperature swings.
Which HVAC system type delivers 100% outdoor air to each zone and exhausts 100% of return air, making it common in healthcare settings?
Answer: Dedicated outdoor air system (DOAS)
A DOAS provides 100% outdoor air (no recirculation) to meet ventilation and infection-control requirements, often paired with radiant panels or fan-coils for sensible load.
In a hot and humid climate, which building envelope strategy most effectively reduces latent (moisture) load on the HVAC system?
Answer: Installing a continuous exterior vapor retarder on the warm side
A continuous vapor retarder on the warm-humid exterior side blocks moisture-laden outdoor air from diffusing into the wall assembly and reaching the cooled interior.