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The primary goal of any heating, ventilation, and air vav out (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.
The purpose of this equipment O&M Best Practice is to provide an overview of system components and maintenance activities to keep VAV systems operating safely and efficiently. Regular O&M of a VAV system will assure overall system reliability, efficiency, and function throughout its life cycle. Support organizations should budget and plan for regular maintenance of VAV vav out to assure continuous safe and efficient operation.
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 vav out of different vav out zones, these systems are found in many commercial buildings. Unlike most other air distribution systems, VAV systems use flow control to efficiently vav out each building zone while maintaining required minimum flow rates.
Figure 1 presents a typical VAV-based air distribution system that consists of an AHU and VAV boxes, typically with one VAV box per zone. Each VAV box can open or close an integral damper to modulate airflow to satisfy each zone’s temperature setpoints. In some cases, VAV boxes have auxiliary heat/reheat (electric or hot water) where the zone may require more heat, e.g., a perimeter zone with windows.
Some features of a VAV system include the following:
There are two major classifications of VAV boxes or terminals—pressure dependent and pressure independent.
A VAV box is considered pressure dependent when the vav out rate passing through the box varies with the inlet pressure in the vav out 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.
A pressure-independent VAV box uses a flow controller to maintain a constant flow rate regardless of variations in system inlet pressure. This type of box is more common and allows for more even and comfortable space conditioning. The balance of this guide will focus on pressure-independent VAV boxes.
Figure 2 presents a schematic of a typical pressure-independent VAV box; in this case, the box also has a reheat coil. This VAV box has three modes of operation: a cooling mode with vav out flow rates designed to meet a temperature setpoint; a dead-band mode whereby the setpoint is satisfied and flow is at a minimum value to meet ventilation requirements; and a reheating mode when the zone requires heat.
There are several different types of VAV and terminal boxes. The most common include:
This O&M Best Practice focuses on the pressure-independent VAV terminal box and relevant connections vav out 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, usually with a variable speed drive (VFD); see Figure 1. A critical element to vav out air-supply system is the duct pressure sensor. The pressure sensor vav titus desv-10 controller static pressure in the supply duct that is used to control the VFD fan output, thereby saving energy.
VAV terminal box. The VAV terminal box (see Figure 2) 1200 cfm vav shippig weight of a number of individual components, including:
Zone temperature control. The primary control point for any VAV system is the zone temperature. Either a zone sensor or thermostat provides a signal to the VAV controller.
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 systems.
Keeping VAV systems properly maintained through preventive maintenance will minimize overall O&M requirements, improve system performance, vav out protect the asset. Follow vav titus desv-10 controller guidelines in the equipment manufacturer’s maintenance manuals.
VAV systems are designed to be relatively maintenance free; however, because they vav out (depending on the VAV box type) a variety of sensors, fan motors, filters, and actuators, they 1200 cfm vav shippig weight periodic attention. While some of the maintenance activities are time-based preventive actions (e.g., verifying actuator function or checking, cleaning, and changing filters), some can fall into the predictive maintenance category, whereby tending temperature data can be used to identify miscalibrated sensors. A sample checklist of suggested maintenance activities is provided below.
It is important to keep a written log, preferably in electronic form in a Computerized Maintenance Management System (CMMS), of all services performed. This record should include identifying features of the VAV box (e.g., box number, location, vav titus desv-10 controller type), functions and diagnostics performed, findings, and corrective actions taken.
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 vav out and frequency by VAV component type. This checklist does not supersede maintenance recommendations from the equipment manufacturer, nor is it a replacement for contracted O&M or warranty services.
Component | Action | Maintenance Frequency | ||
---|---|---|---|---|
Semi-Annually | Annually | As Needed | ||
VAV Box – Duct Connections | Check VAV box duct connections for leakage or movement. Verify that hangers and mountings are secure. | X | ||
VAV Box Zone Temperature Sensor (Thermostat) | Verify function and accuracy (compared to calibrated vav out. Check vava screen review to controller to verify corresponding control, damper action, and minimum setting. | X | ||
VAV Box – Airflow Sensor | Verify function of flow sensor (compared to calibrated value) and corresponding control of box damper. Clean sensor per manufacturer’s recommendations. | X | ||
VAV Box – Controls | Verify function 1200 cfm vav shippig weight technology type and per manufacturer’s recommendations: Pneumatic – check for air leaks in hoses and fittings. Electronic – check for proper electrical connections. Direct Digital Control (DDC) – check for proper connections corresponding to damper action. All – Check for proper operation and correct corresponding damper and valve actions. | X | ||
VAV Box – Damper | Check seals and alignment in duct. | X | ||
VAV Box – Damper Linkage and Control | Check linkage for tension and position relative to control point. Lubricate per manufacturer’s recommendation. Verify minimum and maximum positions are correct. | X | ||
VAV Box – Filter (if present) | Check, clean, and/or replace filters on all fan-powered VAV boxes. Change per manufacturer’s recommendations. | X | X | |
VAV Box – Hydronic Reheat (if present) | Check and clean reheat coil. Check control valve and fittings for water leaks, and check coil for cleanliness and fin condition. | X | X | |
VAV Box – Electric Reheat (if present) | Check vav out clean reheat coil. Check for secure electrical connections and signs of overheating in connectors or conductors. | X | X | |
Building Automation System (if applicable) | Perform VAV system re-tuning. | X | ||
Other Components and Systems | Perform appropriate inspections and maintenance of other components and systems including, but not limited to, AHU, return fan, and VFDs. | X | ||
VAV System Documentation | Document all maintenance activities in logbook or electronic CMMS. | Upon Activity Completion |
The most common option for VAV 1200 cfm vav shippig weight monitoring is using vav out 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:
Modern VAV systems vav out designed to be more efficient and have less overall wear due to reduced system fan speed and pressure vav out 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 is very little reliable data published on the actual cost variance of VAV maintenance compared to a constant volume system.
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 1200 cfm vav shippig weight America (ASHRAE/ACCA) StandardStandard Practice for Inspection and Maintenance of Commercial Building HVAC Systems.
Pacific Northwest National Laboratory offers online training 1200 cfm vav shippig weight building and HVAC system operation and Re-Tuning™ to assist facility managers and practitioners. This training covers many system types but specifically addresses VAV systems, how they work, vav titus desv-10 controller opportunities for efficiency. More information on this training can be found at: stellagshop.ru
AHRI Standard Standard for Performance Rating of Air Terminals. Air Conditioning, Heating, and Refrigeration Institute, Vav out, stellagshop.ru://stellagshop.ru
ANSI/ASHRAE/ACCA Standard Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems. American National Standards Institute, New York, NY. stellagshop.ru
ASHRAE Standard Ventilation for Acceptable Indoor Air Quality. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, GA. stellagshop.ru
California Energy Commission. Advanced Variable Air Volume System Design Guide. Sacramento, CA. stellagshop.ru
EPA (Environmental Protection Agency). ENERGY STAR Building Upgrade Manual. U.S. Environmental Protection Agency, Vav out, D.C. stellagshop.ru
FEMP (Federal Energy Management Program). O&M Best Practices Guide, Release , Chapter 9, O&M Ideas for Major Equipment Types, SectionAir Handling Systems. U.S. Department of Energy, Federal Energy Management Program, Washington, D.C. stellagshop.ru
PNNL (Pacific Northwest National Laboratory). Self-Correcting Controls for Vav out System Vav out. PNNL Pacific Northwest National Laboratory, Richland, WA. stellagshop.ru
Actions and vav titus desv-10 controller recommended in this Best Practice should only be attempted by trained and certified personnel. If such personnel are not available, the actions recommended vav out should not be initiated.
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ASHRAE. “Guideline 36, High-Performance Sequences of Operation for HVAC Systems”
Hwakong Cheng. “Guideline Best in class hvac control sequences”. stellagshop.ru
ASHRAE. “ASHRAE Standard Ventilation for Acceptable Indoor Air Quality”.
ASHRAE. “StandardEnergy Standard for Buildings Except Low-Rise Residential Buildings”
Steve Taylor. “VAV System Design Tips”. stellagshop.ru%20VAV%20Design%stellagshop.ru
Jerry Sipes, PH. D., P.E. Price Industries. “Terminal Unit Sizing: Inlet Valves”. stellagshop.ru?utm_content=&utm_medium=social&utm_source=linkedin&hss_channel=lcp
Automated Logic. “ZNA VAV Controllers” stellagshop.ru
Ruskin. “Modulating Fire/Smoke Dampers – Three Dampers in ONE!” stellagshop.ru
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Automated Logic,ZS IAQ ZONE SENSORS stellagshop.ru
As we previously discussed in one of our building technology basics videos, VAV (Variable Air Volume) controllers are integral to HVAC systems that require varying cooling and heating loads in different zones. In this article, we will explore some of the most common types of VAV boxes and their specific applications. Of course, there are many one-offs and iterations of these applications, but these are the ones you’ll see most frequently.
Standard, cooling-only VAV boxes consist of a VAV controller with an actuator that controls a damper. The VAV controller is also usually wired to sensors that measure pressure, temperature, and humidity at the inlet of the box and to a wall sensor in the zone that is being heated or cooled.
VAV boxes are commonly equipped with reheat coils that heat the vav out going through the box when conditions call for vav out. These reheat coils can be either electric or hydronic. Regardless, they 1200 cfm vav shippig weight the same purpose of heating the air in the box before it is pushed into the space.
Fan-Powered Boxes (FPB) consist of the same components as standard VAV boxes and also include a small fan. Where this fan is placed in the box determines whether it is a parallel FPB or a series FPB.
The term “parallel” for these units comes from the fan being placed outside of the primary airflow so that it is blowing in a parallel direction with the air coming in through the inlet. The fan in a parallel FPB pulls air from the plenum above the ceiling which is warmer than the air coming from the central unit (usually an air handler). Because of this, the fan typically runs during heating or deadband modes only.
The term “series” for these units comes from the fan being placed in series (or inline) with the primary airflow. These fans are located near the outlet of the VAV box and are responsible for delivering air to the space, so they are usually always running.
With parallel FPBs in cooling mode, in particular, the central unit is required to provide enough airflow to reach the space whereas, with series Vav out, the central unit can be downsized because the terminal unit will be delivering the airflow to the space. To learn more about pressure control in VAV systems and the air handler’s role in efficient VAV operations, check out the articles below:
Static Pressure Control and VAV Operation
AHU Supply Temp Sets the Stage
The Vav out series boxes are an acoustic insulated, round in, square out damper terminal designed for Variable Air Volume (VAV) or Variable Volume and Temperature (VVT) zoning applications. You may also choose to have Prolons PL-FSD flow vav titus desv-10 controller pre-installed from the factory for pressure independent applications.
From Controllers to VAV Boxes, we carry a large variety of products to complete your HVAC projects.
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