HVAC Controls and Thermostats 3

Question 1

What is the typical main air supply pressure used in a pneumatic HVAC control system?

Accepted Answer

15–20 psi

Answer

5–10 psi

Answer

25–30 psi

Answer

35–40 psi

Question 2

How does a Variable Frequency Drive (VFD) control motor speed in HVAC applications?

Accepted Answer

By varying the electrical frequency supplied to the motor

Answer

By varying the supply voltage only

Answer

By adjusting the motor's internal resistance

Answer

By cycling the motor on and off rapidly

Question 3

What is two-position control in HVAC?

Accepted Answer

Simple on/off control where the output is either fully on or fully off

Answer

Control with two independent setpoints for heating and cooling simultaneously

Answer

A system that controls two separate zones independently

Answer

A thermostat with dual temperature sensors for averaging

Question 4

What is the purpose of Demand-Controlled Ventilation (DCV)?

Accepted Answer

Vary outdoor air ventilation based on actual occupancy using CO2 sensors

Answer

Maintain a constant outdoor air flow rate regardless of building occupancy

Answer

Control the heating demand of the building during peak load

Answer

Reduce duct static pressure at low occupancy

Question 5

What steady-state control problem does the Integral (I) term in PID control eliminate?

Accepted Answer

Steady-state offset or residual error from setpoint

Answer

Rapid oscillations and hunting

Answer

Derivative kick on setpoint changes

Answer

Initial overshoot on startup

Question 6

What is the primary function of a Building Automation System (BAS)?

Accepted Answer

To centrally monitor and control multiple building systems including HVAC, lighting, and security

Answer

To control only the heating systems in a building

Answer

To replace individual zone thermostats with a single control point

Answer

To manage only outdoor air damper positions

Question 7

Why do smart and WiFi thermostats typically require a 'C' (common) wire?

Accepted Answer

To provide continuous 24V AC power for their electronics, displays, and wireless communication

Answer

To enable two-stage heating and cooling operation

Answer

To connect the thermostat to a building automation system via BACnet

Answer

To allow compatibility with millivolt heating systems