Commercial HVAC Systems Flashcards

What is the primary function of a cooling tower in a commercial HVAC system?

Answer: To reject heat from condenser water to the atmosphere

A cooling tower rejects heat absorbed by condenser water to the atmosphere through evaporative cooling.

In a Variable Air Volume (VAV) system, what component controls airflow to each zone?

Answer: VAV terminal box with a damper

A VAV terminal box contains a motorized damper that modulates airflow to maintain the zone's setpoint temperature.

What does the term 'tons of refrigeration' measure in commercial HVAC?

Answer: Heat removal capacity (1 ton = 12,000 BTU/hr)

One ton of refrigeration equals 12,000 BTU/hr of heat removal, derived from the heat needed to melt one ton of ice per day.

Which refrigerant is most commonly used in modern large commercial chiller systems due to environmental regulations?

Answer: R-134a

R-134a is widely used in centrifugal chillers as it is an HFC with zero ozone depletion potential, compliant with modern regulations.

What is 'economizer mode' in a commercial air handling unit?

Answer: Using outdoor air for free cooling when conditions are favorable

Economizer mode uses outdoor air instead of mechanical cooling when outside conditions (temperature/enthalpy) are suitable, reducing energy costs.

In commercial HVAC, what is the purpose of a 'chilled water reset' strategy?

Answer: Raising chilled water supply temperature during low-load conditions to save energy

Chilled water reset raises the chilled water setpoint during part-load conditions, improving chiller efficiency (COP) significantly.

A commercial rooftop unit (RTU) serving multiple zones typically uses which distribution strategy?

Answer: Constant volume ductwork with zone dampers

Multi-zone RTUs typically use constant or variable volume ductwork with zone dampers to distribute conditioned air to multiple spaces.