Variable Air Volume (VAV) Basics
- One of the efficient ones that help in practical ways is the VAV system.
- Variable Air Volume system is the core advancement that is equipped with all the core advantages.
- VAV is a ventilating, air conditioning, or heating system that provides adequate protection from changing weather conditions.
How does a variable air volume system work?
Variable Air Volume system is the core advancement that is equipped with all the core advantages. VAV is a ventilating, air conditioning, or heating system that provides adequate protection from changing weather conditions. VAV system has additional equipment called VAV boxes, which helps to work differently from CAV (constant air volume) system.
What is a variable air volume and temperature system (VVT)?
Variable Air Volume (VAV) systems are a new technology used for heating, ventilating, and air conditioning. How Does a Variable Air Volume System Work? The primary variable air volume system comprises a supply duct, which distributes air that is about 550 degrees Fahrenheit when in cooling mode. Since the air supply in these units is constant, the flow rate varies to attain the …
What is a variable volume and temperature system?
How VAV systems work?
How does a variable air volume system work?
VAV stands for Variable Air Volume. In its simplest form, VAV systems use varying airflow at a constant temperature to heat and cool buildings. This is opposite of a CAV (or Constant Air Volume) system, which supplies consistent air flow at varying temperatures to heat or cool a space.Aug 22, 2018
When would you use a VAV system?
0:1011:49Variable Air Volume - VAV system HVAC - YouTubeYouTubeStart of suggested clipEnd of suggested clipBut with a Vav system you'll be able to control the amount of cooling possibly heating into each ofMoreBut with a Vav system you'll be able to control the amount of cooling possibly heating into each of the rooms. Individually. From the same main ductwork. And main ahu system.
What is the difference between constant air volume and variable air volume systems?
HVAC engineers can choose between CAV and VAV systems depending on the application. While a CAV system uses variable air temperature and constant airflow, a VAV system keeps constant temperature and variable airflow.Feb 7, 2021
Which is better CAV or VAV?
In general, CAV systems are less expensive and simpler to design and install, while VAV systems offer superior performance and energy savings for a higher upfront cost. In most cases, VAV ventilation the best option because long-term energy savings far outweigh the additional system cost.Feb 7, 2021
Do Vavs Have filters?
Each VAV terminal box is connected to a supply air source. This is a ducted connection that provides air from an AHU. Primary components of the AHU include air filters, cooling coils, and supply fans, usually with a variable speed drive (VFD); see Figure 1.
What do VAV boxes do?
The VAV regulates the volume of the air to the zone by opening or closing the damper, thus controlling the amount of conditioned air directed to the zone. Each zone in a building has a thermostat that controls the VAV, telling it when to open or shut the damper based upon the needs of the zone.Sep 13, 2021
What are the advantages of variable air volume air conditioning system?
The advantages of VAV systems over constant-volume systems include more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional passive dehumidification.
Do VAV systems use water?
VAV system generally have lower maintenance requirements as compared to the other systems. This is because there is no chilled water coil at the VAV terminal and, where non-fan powered VAV terminal are used, there is no filter at the unit.Nov 15, 2017
Why is VAV more energy efficient?
Most buildings operate the majority of time in turndown and it is during turndown that VAV systems save energy because they match the reduced loads – both the exterior loads, such as temperature and solar, and the interior loads of occupancy, plugs, and lighting. Also the energy penalty of reheat is during turndown.
Where are CAV systems used?
CAV systems are usually used in spaces with large open areas, few windows and uniform loads. Examples of theses types of spaces include lobbies, department stores, theaters, auditoriums and exhibition halls.May 4, 2005
What is the difference between VAV and VRV?
VRV and VRF are both same and are tpy of cooling system and having the beauty of cooling and heating the different spaces of a building with the same system. VAV is the method/device used to control the air quantity so as to attain the desired temperature in different rooms.Dec 18, 2014
What does CAV stand for HVAC?
constant air volumeTwenty to thirty years ago it was common practice to install a CAV (constant air volume) system in commercial buildings for ventilation and air-conditioning. These types of HVAC systems require high airflow rates and higher amounts of energy for heating and cooling.Sep 8, 2016
What is a Variable Air Volume System?
The modern construction industry demands extreme comfort and energy efficiency. That is why engineers are continually developing new HVAC units to combat the disadvantages of older models. Variable Air Volume (VAV) systems are a new technology used for heating, ventilating, and air conditioning.
How Does a Variable Air Volume System Work?
The primary variable air volume system comprises a supply duct, which distributes air that is about 550 degrees Fahrenheit when in cooling mode. Since the air supply in these units is constant, the flow rate varies to attain the desired temperatures. VAV boxes have a few simple parts, including the damper and a coil for heating and cooling.
Benefits of Using Variable Air Volume Systems
Every variable air volume system controls the airflow depending on the individual zones. Therefore, it can easily accommodate a low demand in one part of the house and a high demand in another region. By doing so, the unit ensures the comfort of all users simultaneously. That is why VAVs are popular in offices and commercial buildings.
What is a VAV system?
VAV systems supply air at a variable temperature and airflow rate from an air handling unit (AHU). Because VAV systems can meet varying heating and cooling needs of different building zones, these systems are found in many commercial buildings. Unlike most other air distribution systems, VAV systems use flow control to efficiently condition each building zone while maintaining required minimum flow rates.
Why is a VAV box pressure dependent?
A VAV box is considered pressure dependent when the flow rate passing through the box varies with the inlet pressure in the supply duct. This form of control is less desirable because the damper in the box is controlled in response to temperature only and can lead to temperature swings and excessive noise.
Why do commercial buildings use VAV systems?
Because VAV systems can meet varying heating and cooling needs of different building zones, these systems are found in many commercial buildings. Unlike most other air distribution systems, VAV systems use flow control to efficiently condition each building zone while maintaining required minimum flow rates.
What is the most common option for VAV performance monitoring?
The most common option for VAV performance monitoring is using the structure’s building automation system (BAS). By enabling the trending function of a BAS, the VAV system operation can be assessed. Key points to trend include:
What is the primary goal of a HVAC system?
The primary goal of any heating, ventilation, and air conditioning (HVAC) system is to provide comfort to building occupants and maintain healthy and safe air quality and space temperatures. Variable air volume (VAV) systems enable energy-efficient HVAC system distribution by optimizing the amount and temperature of distributed air. Appropriate operations and maintenance (O&M) of VAV systems is necessary to optimize system performance and achieve high efficiency.
How does a VAV box work?
Control of the system's fan capacity is critical in VAV systems. Without proper and rapid flow rate control, the system's ductwork, or its sealing, can easily be damaged by overpressurization. In the cooling mode of operation, as the temperature in the space is satisfied, a VAV box closes to limit the flow of cool air into the space. As the temperature increases in the space, the box opens to bring the temperature back down. The fan maintains a constant static pressure in the discharge duct regardless of the position of the VAV box. Therefore, as the box closes, the fan slows down or restricts the amount of air going into the supply duct. As the box opens, the fan speeds up and allows more air flow into the duct, maintaining a constant static pressure.
What are the advantages of VAV fan control?
Another advantage is energy savings and reduced wear. VAV fan control, especially with modern electronic variable-speed drives, reduces the energy consumed by fans , which can be a substantial part of the total cooling energy requirements of a building.
What is the benefit of modulating control of a compressor?
Modulating control of the compressor also reduces wear and delivers further energy savings. A final advantage is increased dehumidification. Because VAV air flow is reduced under part-load conditions, air is exposed to cooling coils for a longer time. More moisture condenses on the coils, dehumidifying the air.
Introduction
Description of Technology
- VAV systems supply air at a variable temperature and airflow rate from an air handling unit (AHU). Because VAV systems can meet varying heating and cooling needs of different building zones, these systems are found in many commercial buildings. Unlike most other air distribution systems, VAV systems use flow control to efficiently condition each building zone while maintai…
Key Components
- This O&M Best Practice focuses on the pressure-independent VAV terminal box and relevant connections for source air, water, electricity, and controls. Supply ducting system.Each VAV terminal box is connected to a supply air source. This is a ducted connection that provides air from an AHU. Primary components of the AHU include air filters, cooling coils, and supply fans, …
Safety Issues
- As with any electromechanical device, all aspects should be powered down to a safety state before any maintenance or diagnostics are performed. As needed, and per manufacturer’s and electrical safety recommendations, VAV system functions can be enabled for testing and verification or performance. Standard electrical and mechanical safety practices apply to these …
Maintenance of Technology
- Keeping VAV systems properly maintained through preventive maintenance will minimize overall O&M requirements, improve system performance, and protect the asset. Follow the guidelines in the equipment manufacturer’s maintenance manuals. VAV systems are designed to be relatively maintenance free; however, because they encompass (depending on the VAV box type) a variet…
Maintenance Checklist
- For all VAV maintenance, it is important to follow the manufacturer’s recommendations. Proper maintenance should only be performed by trained and qualified personnel. The checklist below provides recommended actions and frequency by VAV component type. This checklist does not supersede maintenance recommendations from the equipment manufacturer, nor is it a replace…
Performance Monitoring
- The most common option for VAV performance monitoring is using the structure’s building automation system (BAS). By enabling the trending function of a BAS, the VAV system operation can be assessed. Key points to trend include: 1. Static pressure in supply duct and control point for system VFD fan to assure modulation with changing VAV box flow rates. 2. VAV box dampe…
O&M Cost
- Modern VAV systems are designed to be more efficient and have less overall wear due to reduced system fan speed and pressure versus the on/off cycling of a constant volume system. However, at the zone level, the VAV system can have greater maintenance intensity due to the additional components of dampers, sensors, actuators, and filters, depending on the VAV box type. There i…
Additional Support
- Because VAV systems are part of a larger HVAC system, specific support comes in the form of training opportunities for larger HVAC systems. To encourage quality O&M, building engineers can refer to the American Society of Heating, Refrigerating and Air-Conditioning Engineers/Air Conditioning Contractors of America (ASHRAE/ACCA) Standard 180, Standard Practice for Insp…
Sources of Information
- AHRI Standard 880-2017. Standard for Performance Rating of Air Terminals. Air Conditioning, Heating, and Refrigeration Institute, Arlington, VA. http://www.ahrinet.org/App_Content/ahri/files/STANDARDS/AHRI/AHRI_Standard_880_IP_2017.…
Overview
Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. Unlike constant air volume(CAV) systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow at a constant temperature. The advantages of VAV systems over constant-volume systems include more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional pass…
Simple VAV systems
The simplest VAV system incorporates one supply duct that, when in cooling mode, distributes supply air at a constant temperature of approximately 55 °F (13 °C). Because the supply air temperature is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served.
Even a simple VAV system has several advantages over a CAV system. One is more precise tem…
Multiple-zone VAV systems
The air blower's flow rate is variable. For a single VAV air handler that serves multiple thermal zones, the flow rate to each zone must be varied as well.
A VAV terminal unit, often called a VAV box, is the zone-level flow control device. It is basically a calibrated air damper with an automatic actuator. The VAV terminal unit is connected to either a local or a central control system. Historically, pneumaticcontrol was commonplace, but electroni…
Fan control
Control of the system's fan capacity is critical in VAV systems. Without proper and rapid flow rate control, the system's ductwork, or its sealing, can easily be damaged by overpressurization. In the cooling mode of operation, as the temperature in the space is satisfied, a VAV box closes to limit the flow of cool air into the space. As the temperature increases in the space, the box opens to bring the temperature back down. The fan maintains a constant static pressure in the discharge …