HVAC Building Automation Systems 4

Question 1

What is 'optimal start' in a BAS control strategy?

Accepted Answer

Calculating the latest possible start time to reach setpoint by occupancy time based on conditions

Answer

Optimal start calculates the latest possible equipment start time to achieve setpoint by occupancy, saving energy over a fixed early-start approach.

Question 2

Which of the following BACnet object properties defines how often a controller reads a sensor value?

Accepted Answer

Poll Rate

Answer

The Poll Rate property defines the interval at which a BACnet device reads input values from sensors or other objects.

Question 3

A variable air volume (VAV) box controlled by a BAS fails to open beyond 30% even at maximum cooling demand. What should be checked first?

Accepted Answer

Actuator wiring, travel limits, and calibration

Answer

When a VAV actuator doesn't fully travel, the first checks are wiring integrity, actuator calibration, and mechanical travel limit settings.

Question 4

What does 'Change of Value' (COV) subscription mean in BACnet communications?

Accepted Answer

A device sends an unsolicited notification when a monitored value changes by a defined increment

Answer

COV subscriptions allow a BACnet device to push value updates to subscribers only when the value changes by a defined increment, reducing network traffic.

Question 5

In a BAS, what is the purpose of the 'priority array' in BACnet commandable objects?

Accepted Answer

Manage multiple competing commands to an output by assigning priority levels 1-16

Answer

The BACnet priority array allows up to 16 commands at different priority levels to compete for control of an output, with the highest active priority winning.

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC Building Automation Systems 4