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
Under the ASHRAE Standard 62.1 Ventilation Rate Procedure, how is breathing zone outdoor airflow (Vbz) calculated?
Answer: Vbz = Rp × Pz + Ra × Az
Vbz sums a people component (Rp × Pz) and an area component (Ra × Az).
Under ASHRAE Standard 55, which PMV range is generally used to define acceptable thermal comfort for general occupancy?
Answer: -0.5 to +0.5
A PMV of -0.5 to +0.5 corresponds to a PPD under 10%.
A space has a sensible cooling load of 36,000 Btu/h and a latent load of 12,000 Btu/h. What is its sensible heat ratio?
Answer: 0.75
SHR = 36,000 / (36,000 + 12,000) = 0.75.
In the equal friction method for low-pressure supply ducts, which friction rate is commonly used?
Answer: About 0.08 to 0.10 in. w.c. per 100 ft
Low-pressure comfort systems usually use about 0.08 to 0.10 in. w.c. per 100 ft.
If a centrifugal fan's speed is cut to 50% of design, its shaft power will be roughly what fraction of design?
Answer: 12.5%
By the fan affinity laws, power varies with the cube of speed: 0.5³ = 0.125.
What is the main design purpose of an airside economizer?
Answer: Using cool outdoor air for free cooling when conditions allow
An airside economizer brings in more outdoor air to cut mechanical cooling when the outdoor air is cool or dry enough.
A cooling coil has a bypass factor of 0.15. What is its contact factor?
Answer: 0.85
Contact factor = 1 − bypass factor = 0.85.