Components of a Commercial HVAC system Flashcards
What is the purpose of the damper?
To regulate the flow of air
Mixed air is a mixture of _______ air and ______ air
return, outside
Wiring for the HVAC control components is usually ___V
24V
To double the airflow rate, the fan hp should be increase _____ times
eight
What is the difference in operation between an opposed blade damper and a parallel blade damper?
In an opposed blade damped, adjacent blades turn in the opposite directions. In a parallel blade damper, all of the blades turn in the same direction
What are the fail-safe positions for the outside, exhaust and return air dampers?
- Outside and exhaust air damper: NC
- Return air damper: NO
How does the damper actuator achieve its fail-safe position?
When power fails or is cut off to the actuator, a coiled spring returns the motor to its fail-safe position
What are the two general classifications of control valves?
- Two-way
- Three-way
What are two methods of providing mechanical cooling in an HVAC system?
- Chiller cooling tower
- Refrigeration
What is the typical set point for a mixed-air controller?
13°C
What is the purpose of the minimum position device?
The minimum position device prevents the outside-air damper from closing before the minimum outside-air requirement (specified in the Building Code) is met
What does the term economizer control mean?
When the outside air is warmer than the return air, the dampers revert to their minimum positions, letting in less air, thereby reducing the operational costs of cooling hot outside air
What are the typical fail-safe positions for the hot and chilled water valves?
- Hot water valve: NO
- Chilled water valve: NC
Is the freeze-stat usually a manual or an automatic reset device?
Manual reset
Under what conditions is it permissible to mix Class 1 and power circuit wiring?
If both circuits are connected to the same equipment and all conductors are insulated for the maximum voltage present
