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Variable Air Volume vs. Constant Air Volume for Commercial HVAC System

by Tod Althoff | Dec 19, 2017 | HVAC, Facility Maintenance, Facility Manager, Mechanical Ventilation | 0 Comments

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Commercial HVAC systems can be designed with variable air volume (VAV) or constant air volume (CAV). The type of system your Chicago building currently has depends on the size of your building and the initial HVAC budget as well as your energy saving and air quality goals.

Understanding Commercial HVAC Ventilation System Configurations

HVAC systems are designed, installed and configured according to the specific building and its use. ASHRAE Standard 55 outlines the guidelines that should be used to establish comfortable indoor environmental conditions. In general, HVAC systems are configured to be comfortable for occupants who are dressed in average attire for the season and who are lightly active while inside the building. They are also configured in accordance with indoor air quality building codes and standards, meaning a certain amount of fresh, outdoor air must be periodically vented into the building and stale air must be vented to the outside in order to manage indoor air pollution.

Constant HVAC Air Volume (CAV)

As indicated by the name, constant air volume controls (CAV) provide a constant volume of air to all parts of the building when the system is in operation. CAV systems are either “on” or “off”. When the system is on, heated or cooled air is blown through the air ducts at a constant rate. When the system is off, no air blows through the air ducts and registers.


  • Can Be Purchased in Multi-Zone Variations
  • Great for Single-Zone Buildings
  • Less Expensive to Install
  • Offer Great Reliability and Durability


  • Less Energy Efficient
  • No Specific Supply Air Modulation
  • Only Two Settings

Variable HVAC Air Volume (VAV)

Variable air volume (VAV) systems contain controls within the box to control air flow. At their most basic, these boxes contain dampeners that open and close according to sensors and thermostats that are located within the VAV box. Advanced systems may also contain heating elements to help control indoor temperature.


  • Air Supply Modulation Systems Are Built-In
  • Building Temperature Can Be Precisely Controlled
  • Can Be Used for Dehumidification
  • Extremely Energy Efficient
  • Great for Multi-Zone Buildings


  • More Expensive to Install
  • May Be Noisy, Depending on System Design
  • Contains More Moving Parts and Electronics

Choosing CAV vs. VAV for Your Building

If you have a CAV system in your building, you may want to consider VAV, especially if you have multiple zones or certain rooms that have to be kept at precise temperature settings. For example, you may want computer rooms and rooms will with equipment or electronics to be cooler than the rest of the building, and you may want lounge areas and offices slightly warmer. If your commercial building isn’t very big, you may simply want a CAV system. When deciding on which HVAC system is best for your building, it is best to conduct a building inspection to gauge what is best based on operational needs. Applicable air quality tests can also be perfomed to ensure you are adhering to all applicable building codes.

Optimizing Your Commercial HVAC System with Althoff

If you are worried that your HVAC system isn’t operating normally or you have noticed wide temperature variations within your building, our HVAC technicians are here to assist you. We can examine your current heating, cooling and mechanical ventilation equipment to determine if it is working for your building. If you would benefit from upgrades and/or retrofits, we can recommend certain items that can improve your indoor comfort and air quality while saving you money on your heating and cooling bills.

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