HVAC System Design and Operation 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 HVAC System Design and Operation flashcards as text
Which equation gives hydronic heat transfer in Btu/h for water?
Answer: Q = 500 × GPM × ΔT
500 comes from 8.33 lb/gal × 60 min/hr × 1 Btu/lb·°F.
How is cooling tower approach defined?
Answer: Leaving water temperature minus entering air wet-bulb temperature
Approach is how close the cold water leaving the tower gets to the ambient wet-bulb temperature.
How is cooling tower range defined?
Answer: Entering water temperature minus leaving water temperature
Range is the temperature drop of the water across the tower.
What does a variable primary flow chilled water system require to protect the chillers?
Answer: A minimum flow bypass so evaporator flow stays above the manufacturer's minimum
A controlled bypass keeps evaporator flow above the minimum when coil valves close at low load.
What is the main job of an expansion tank in a closed hydronic system?
Answer: Absorb water volume changes from temperature swings and hold the system pressure
The tank takes in thermal expansion of the water, which prevents relief valve discharge and keeps pressure stable.
To prevent pump cavitation, how must available NPSH (NPSHA) relate to required NPSH (NPSHR)?
Answer: NPSHA must exceed NPSHR with a safety margin
If NPSHA drops below NPSHR, the liquid flashes to vapor at the impeller eye and the pump cavitates.
Under the pump affinity laws, if impeller speed rises 20%, what happens to flow?
Answer: Rises about 20%
Flow is directly proportional to speed; head follows the square and power follows the cube.