VAV vs CAV in HVAC

Did you know that HVAC systems in commercial buildings are responsible for 40% of the building’s total energy use? 

Given how much there is at stake, it’s no surprise that building owners are always on the lookout for new systems and technologies to reduce these costs as much as possible.

When it comes to energy savings on heating and cooling, business owners will have two primary options to choose from: constant air volume (CAV) and variable air volume (VAV) systems. Both options are viable ways to set up an energy efficient HVAC system, and the most appropriate choice will depend on your specific facility’s needs.  

Let’s compare VAV vs CAV and why a building owner might choose one over the other.

A Summary of VAV vs. CAV

CAV and VAV are types of ventilation systems that supply air to each building region (or “zone”) and help regulate internal air temperatures.

CAV is the older of the two options, leveraging a centralized duct system and compressor to supply constant air flow to different zones. 

While CAV systems can vary a building’s heating/cooling rate to create a comfortable and constant temperature, it has a harder time regulating temperature across multiple zones. Airflow volume is fixed, meaning that it’s less able to be adjusted to the requirements of each zone.

In contrast, VAV systems supply variable air flow at a constant temperature, using fans and dampers to manage cool air flow and maintain temperature and humidity conditions of different zones. This type of system requires installation of more HVAC components, such as:

• VAV boxes
• Fans and fan speed controls
• Duct dampers

VAV systems automatically adjust dampers to accommodate the airflow and temperature needs of each zone, making it a great option for larger facilities with varying temperature needs. It’s an approach that uses mixed air to balance heating and cooling in each region and offers a more flexible, cost-effective HVAC system.

Comparing the Pros & Cons of VAV vs CAV

When comparing these two HVAC systems, why would a building owner choose one over the other?

CAV Benefits 

CAV systems are older but remain viable ways to manage HVAC needs. Benefits include:

• Simple design
• Easy installation
• Lower up-front installation costs
• Ideal for single-zone applications

CAV Drawbacks

However, the simplicity of CAV systems cuts both ways, making it less ideal for more extensive HVAC needs:

• Provides only fixed volume airflow
• Limited options (such as manual dampers) for zone-level air flow adjustment and adaptability
• Lower energy efficiency overall
• Poor humidity control

VAV Benefits 

As the newer of the two HVAC options, VAV offers distinct benefits for commercial building owners, which include:

• Better control over airflow, temperature, and humidity
• Multi-zone conditioning through built-in dampers
• More cost-effective ventilation overall - less fan power is needed to maintain each climate zone

VAV Drawbacks

Although VAV offers big benefits to HVAC efficiency, this type of system comes with drawbacks as well, such as:

• More complicated infrastructure design that leverages more advanced fan controls and dampers
• Higher up-front costs than CAV installations

Despite its drawbacks, note that these up-front costs tend to be offset by the lower operating costs of the system itself.

Which Type of System Is Best?

CAV may be the best option when a building’s ventilation load needs are constant for long periods. In other words, CAV works best when a building must be heated/cooled to a specific temperature with little variability. 

This applies to single-zone applications, such as small warehouses. Or, multi-zone applications with similar thermal requirements, including small office buildings with multiple rooms

Additionally, CAV is an energy efficient choice for facilities with similar climate needs that operate 24/7, including :

• Manufacturing facilities
• Call centers
• Convenience stores
• Smaller retail establishments

CAV is ideal for applications where ventilation load shows little variation. 

Conversely, VAV is best for situations where ventilation is subject to part-load conditions. Generally, VAV is ideal for big, commercial areas where ventilation demands are continually changing, such as:

• Large-scale retail businesses
• Hospitals
• Airports
• Colleges
• Restaurants

In general, VAV offers better climate control and energy efficiency over the long-term through its more advanced regulation features, making it the more viable option for the majority of large, commercial HVAC applications. 

In most cases, when comparing single zone vav vs constant air, single zone VAV may offer in-depth control features that never get used. When only one zone needs to be regulated, CAV offers an approach that’s quicker to implement and cheaper to install.

Of course, CAV and VAV aren’t the only HVAC options available to businesses. Cutting-edge solutions such as underfloor air distribution (UFAD) offer substantial advantages over traditional HVAC and represent a superior way to manage air flow throughout a building.

Underfloor Air Distribution (UFAD): A Superior Alternative to Traditional HVAC Systems

UFAD is a revolutionary approach to HVAC that leverages underfloor HVAC installations accessible by raised access floor panels. Unlike with traditional HVAC, UFAD systems introduce conditioned supply air at the floor level through diffusers, which is then exhausted through return vents in the ceiling to mitigate cross-contamination.

UFAD offers several advantages over the traditional HVAC, such as:

• Easier access to building services
• Improved ventilation & air quality
• Lower energy usage by 30%
• Lower lifecycle costs
• Plus much more

Building owners seeking even more modern and energy efficient HVAC infrastructure should consider newer options such as UFAD.

Consider the ongoing debates between VAV vs VRF vs radiant vs chilled beams, and you’ll see how different strategies can yield different benefits. This is why it’s critical to work with an experienced partner who can show you the most efficient way to set up your system.

AirFixture has successfully executed hundreds of UFAD projects in the last 20 years and will bring that expertise to work for your project. Contact the experts at AirFixture today to learn more about UFAD. Let us design the perfect UFAD solution for your commercial building.