HVAC Commercial HVAC Systems 3

Question 1

What is the main advantage of a water-cooled chiller compared to an air-cooled chiller?

Accepted Answer

Higher efficiency (lower kW/ton) due to lower condensing temperatures

Answer

Water-cooled chillers achieve higher efficiency because evaporative cooling in the cooling tower produces lower condensing temperatures than ambient air cooling.

Question 2

In a commercial HVAC system, what does 'DOAS' stand for and what is its primary purpose?

Accepted Answer

Dedicated Outdoor Air System — provides ventilation air separately from sensible cooling

Answer

A DOAS handles ventilation (outdoor air) requirements separately, allowing zone equipment to focus on sensible load control.

Question 3

What is the typical chilled water supply temperature range in a commercial central plant?

Accepted Answer

44–48°F

Answer

Commercial chilled water systems typically supply water at 44–48°F to provide adequate dehumidification and cooling capacity at coils.

Question 4

Which control strategy best describes 'demand-controlled ventilation (DCV)'?

Accepted Answer

Adjusting outdoor air intake based on CO₂ levels as a proxy for occupancy

Answer

DCV uses CO₂ sensors to modulate outdoor air dampers proportionally to actual occupancy, reducing ventilation energy waste in partially occupied spaces.

Question 5

In a commercial building automation system (BAS), what is a 'setback' schedule used for?

Accepted Answer

Allowing space temperature to drift to a less conditioned setpoint during unoccupied hours

Answer

Setback schedules let space temperatures rise (cooling) or fall (heating) to unoccupied setpoints during nights and weekends, saving energy.

HVAC Practice Test

HVAC Practice Test

HVAC Commercial HVAC Systems 3