BOC HVAC Systems and Controls 2

Question 1

An air-side economizer in fixed dry-bulb mode should use outdoor air for free cooling when:

Accepted Answer

Outdoor air temperature is below the changeover setpoint and cooling is needed

Answer

Dry-bulb economizers open outdoor dampers when outdoor air is cool enough to offset the cooling load.

Question 2

What is the primary purpose of a freezestat on an air handling unit?

Accepted Answer

To shut down the fan or close outdoor dampers when air entering the coil nears freezing

Answer

A freezestat, typically set near 38°F, protects water coils from freeze damage.

Question 3

An enthalpy economizer differs from a dry-bulb economizer because it considers:

Accepted Answer

Both temperature and moisture content of the air

Answer

Enthalpy is total heat content, which accounts for sensible and latent heat.

Question 4

In a VAV system, the duct static pressure sensor that controls the supply fan is typically located:

Accepted Answer

About two-thirds of the way down the longest main supply duct

Answer

Placing the sensor downstream ensures adequate pressure reaches the far terminal units.

Question 5

A VAV box with hot water reheat typically opens its reheat valve when:

Accepted Answer

The zone needs heat and airflow is at its minimum setting

Answer

Reheat is used after the box has throttled to minimum airflow and the zone is still too cool.

BOC - Building Operator Certification Practice Test