Design Principles Flashcards
7 cards from real ASHRAE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Design Principles flashcards as text
A water-cooled chiller runs at a COP of 6.0. What is its approximate efficiency in kW/ton?
Answer: 0.59 kW/ton
kW/ton = 3.517 / COP = 3.517 / 6.0 ≈ 0.59.
Why is a building's block (peak) cooling load usually lower than the sum of its individual zone peak loads?
Answer: Zone peaks happen at different times of day
Load diversity means east, west and interior zones peak at different hours.
Why do designers usually keep a commercial building slightly positive relative to outdoors?
Answer: To reduce uncontrolled infiltration of unconditioned air
Slight positive pressure cuts infiltration, which affects comfort, humidity control and IAQ.
Which ASHRAE standard covers the safety of refrigeration systems?
Answer: Standard 15
ASHRAE Standard 15 covers the safe design, construction, installation and operation of refrigeration systems.
In a tall building in cold weather, how does stack effect usually affect air leakage?
Answer: Infiltration at lower floors, exfiltration at upper floors
Warm indoor air rises and leaves through the upper floors, pulling cold air in at lower levels below the neutral plane.
What is the main energy benefit of a 'dual maximum' control sequence for VAV reheat boxes?
Answer: It allows a lower minimum airflow in the deadband, reducing reheat and fan energy
Dual maximum keeps deadband airflow low and raises airflow only when more heating is needed, which cuts reheat energy.
With low air velocity, how is operative temperature approximated in ASHRAE Standard 55?
Answer: The average of air temperature and mean radiant temperature
At low air speeds, operative temperature ≈ (air temperature + mean radiant temperature) / 2.