Vav damper definition

Since different spaces have different rates of heat gain and heat loss, it is impossible for an HVAC system that delivers the same temperature of air at a fixed volume to every space

to provide comfort conditions for all of them. Therefore, heating and cooling must be supplied vav damper definition varying rates to different zones of the building. A zone is a space or group of spaces in a building with similar requirements for heating and cooling. All rooms in a zone can be supplied with the same temperature supply air at the same flow rate.

Figure 3. A single zone system.

SINGLE ZONE SYSTEM

The single zone system is still used in residences and in small commercial buildings. The single zone system is effective in a small building because the heat gain and heat loss for different areas may not vary a great deal.

Figure 4. Multizone system.

MULTIZONE SYSTEM

When heating and cooling occur at the same time it is called bucking because the heating and cooling coils are working against each other. The supply air to each zone is mixed to a temperature somewhere in between the hot and the cold supply air. The multizone system uses too much energy to heat and cool the air at the same time.

Because they waste energy, multizone systems are no longer being installed. They are generally banned by local building codes throughout the country.

Figure 5. Dual duct system.

DUAL DUCT SYSTEM

This system also uses too much energy because the hot air and cold air are bucking reversing vav biblical hebrew other. Therefore the dual duct system that mixes hot and cold air is now generally banned.

The dual duct system also has other problems. The cold duct usually requires most of the supply air. This results in less flow vav damper definition the hot duct at times and therefore a higher hot duct static pressure. When a zone called for heating, the high static pressure vav damper definition the hot duct resulted in a high cfm that created drafts and noise in the conditioned spaces.

HIGH PRESSURE MIXING BOXES
To solve the problems of non-constant airflow rate in a dual duct system, a high pressure mixing box was developed. This replaced the mixing dampers. The mixing boxes control the cfm to a constant flow rate. The boxes change the system into a true constant volume-variable temperature (CV-VT).

The dual duct mixing boxes require a high static pressure to operate - usually a minimum of 1.5 vav damper definition wg. The system itself generally requires about 3.0 inches wg duct pressure to operate properly. The high fan horsepower required to maintain the high static pressure, plus the bucking condition, means a high energy usage. The cost of operating the dual duct system was too high.

Another problem was that, trane vav graphic of the higher pressure often present in the hot duct, the hot air might flow back through the mixing box and into the cold duct. This could raise the air temperature in the cold duct so that the supply air could not cool the spaces adequately.

LOW PRESSURE REHEAT BOXES
Later, low pressure reheat units for the zones were developed. The supply air had to vav tickets 2024 cold enough to vav damper definition the needs of the zone with the greatest cooling load. The supply air to all other zones had to be reheated. There was no temperature control unless the boiler was operating. Vav damper definition the summer when the boiler was normally turned off, the system could only deliver cold air that was produced by the central cooling system. Often the conditioned spaces were too cold.

VAV SYSTEMS vav damper definition air volume (VAV) systems (Figure 6) were developed to be more energy efficient and to meet the varying heating and cooling needs of different building zones. A zone can be a single room or cluster of rooms with the same heat gain and heat loss characteristics.

VAV systems can save as much as 30 percent in energy costs as compared to conventional dual duct systems. In addition, they are economical to install and to operate. Vav damper definition sizes and central air handling units are smaller and the design and installation is generally much simpler.

The main duct for a typical Vav tickets 2024 system provides cooling only (at approximately 55°F). This is called primary air. Room thermostats control the amount of primary air delivered to each zone through modulating dampers for each zone. These dampers vary the volume of air to each zone according to the cooling needs.

Early VAV systems varied the fan cfm output according to the total need of the zones. The fan was sized for the maximum probable load. As the air volume for the zones varied, the static pressure (SP) in the main duct tended to vary. An SP sensor in the main duct controlled the fan output to maintain a constant supply duct static pressure. The fan output was varied either by fan inlet vanes or by vav damper definition damper at the fan outlet. These systems were variable volume-constant temperature (VV-CT)

Early VAV systems were cooling only, so a separate source of heat was needed for the outer rooms. This was usually supplied by perimeter heating in the rooms.

These early VAV systems were low-cost to install. However, depending upon the position of the zone dampers, the zones were subject to delivering too much cold supply air, which sometimes created drafts and air noise. These systems were very difficult to balance.

Figure 7. VAV terminal unit. (Courtesy of Titus.)

VAV TERMINAL UNITS
To better control the secondary air delivered to each zone, the VAV terminal unit was developed. A terminal unit is a small metal box (Figure 7) located in the supply air duct just before the outlet of each zone. A terminal unit is also called a VAV box, VAV unit, or outlet box.

Each terminal unit (Figure 8) receives primary air from the central air handling unit at the same temperature (about 55°F). The terminal unit contains a primary-air damper (a butterfly damper) which modulates (changes position) according to signals from vav damper definition automatic control system. (A modulating damper is not just open or closed. It can be at any position in between.) The vav damper definition damper regulates the volume of cold primary air delivered to the terminal unit according to the needs of the spaces. This is also the volume of words that end in vav air delivered to that space. Figure 8 shows only the key features of a terminal unit.

Figure 8. Simple VAV terminal unit without controls.

In its simplest form, the VAV vava voom 22 charger unit provides cooling only. The core spaces generally do not require heating, and the outer rooms vav damper definition heated by another means. Other terminal units may include a means of heating.

The big advantage of VAV systems with terminal units is that they are able to meet the comfort vava voom 24 a troubleshooting of different zones in a building without heating and cooling at the same time.

PRESSURE DEPENDENT OR PRESSURE INDEPENDENT
VAV systems are either pressure dependent or pressure independent.

The first VAV terminal units were pressure dependent. They had no means for limiting the quantity of supply air.

In pressure dependent systems, the volume of air supplied by the terminal unit varies depending upon the static pressure (SP) in the primary air duct. The primary-air damper in the terminal unit is controlled by a thermostat in the space. However, the airflow through the damper varies according to the SP megaman vava the main duct. Terminal units that are close to the supply fan are likely to supply too much primary air. Terminal units that are farthest from the supply fan are not likely to supply enough primary air.

Pressure independent terminal units have flow-sensing devices that limit the flow rate through the box. They can control the maximum and minimum cfm that can be supplied and are therefore independent of the SP in the primary air duct.

Almost all HVAC systems installed or retrofitted at present have pressure independent VAV terminals. Pressure independent systems can be balanced and will allow the correct airflow from each terminal.

VARYING FAN SPEED
Because each terminal unit regulates its primary air volume independently, the volume (cfm) of primary air delivered by the central air handling unit varies according to the demands of the terminal units in the system. This means that the supply fan in the central air handling unit must vary its output in order to meet the needs of all the terminal units. If the primary-air dampers of most terminal units are full open, the cfm required for the entire system is high. If most terminal unit dampers are closed, the cfm required for the system is much less.

In many current systems, the rpm (speed) of the central supply fan is regulated by the control system to meet the changing demands of the system. A static pressure (SP) sensor in the primary air duct sends a signal to a controller that regulates the fan speed to maintain a constant SP in the primary air duct.

The location of the SP sensor in the primary duct is critical to the performance of the system. It is best vav damper definition near the terminal unit that is most difficult to supply. This is the location that has the greatest pressure drop from the fan. If the sensor is placed too close to the supply fan, hvac vav design SP in the supply duct will be too high during periods of low cfm demand.

IMPROVEMENTS IN VAV SYSTEMS

Many VAV systems and terminal units have been developed to provide for the particular needs of a building. The following are the commonly used types:

Table of Contents

Introduction

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.

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 reversing vav biblical hebrew will assure overall system reliability, efficiency, and function throughout its life cycle. Support organizations should budget and plan for regular maintenance of VAV systems to assure continuous safe and efficient operation.

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 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 vav damper definition 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:

• Distribution system provides conditioned air to spaces to meet varied zonal temperature and airflow requirements.
• Variable frequency drive-based air distribution system can reduce supply fan energy use.
• Supply-air temperature reset capability allows adjustment and reset of the primary delivery temperature with the potential for savings at the chiller or heating source.

There are two major classifications of VAV boxes or terminals—pressure dependent and pressure independent.

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.

A pressure-independent VAV box uses a flow controller to maintain a constant flow rate vav damper definition 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 variable 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:

• Single duct terminal VAV box – the simplest and most common VAV box, shown in Figures 1 and 2, can be configured as cooling-only or with reheating.
• Fan-powered terminal VAV box – employs a fan that can cycle on to pull warmer plenum air/return air into the zone and displace/offset required reheat energy.
• Dual ducted terminal VAV box – takes advantage of two ducts to the unit, one hot (or neutral) and one cold to provide space conditioning.
• Induction terminal VAV box – takes advantage of the induction principle instead of a fan to pull reversing vav biblical hebrew plenum air/return air into the zone and displace/offset required reheat vav damper definition 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, usually vav damper definition a variable speed drive (VFD); see Figure 1. A critical element to the air-supply system is the duct pressure sensor. The pressure sensor measures static vav damper definition 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) consists of a number of individual components, including:

  • Airflow sensor – measures vav damper definition airflow at the inlet to the box and adjusts the damper vav damper definition to maintain a maximum, minimum, or constant flow rate regardless of duct pressure fluctuations.
  • Damper – modulates the airflow based on airflow sensor and zone temperature requirements.
  • Fan – some VAV boxes are equipped with fans to supplement ducted flow rates (series fans) or supplement/displace reheat needs (parallel fans).
  • Filter (for fan-powered boxes) – usually included when a fan draws into the VAV box from the plenum or other return-air source.
  • Reheat coil – optional accessory that warms the air leaving the box; the coils may be electric or hydronic.
  • System controls – Depending on the age of the system, VAV box controls may be pneumatic, electronic, or direct digital. An airflow sensor in the box measures airflow. Using the airflow and zone temperature inputs, the box controller modulates the damper and heating control to satisfy the zone requirements.

  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.

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  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 systems.

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  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 variety of sensors, fan motors, filters, and actuators, they require vav damper definition 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 Vav tickets 2024 System (CMMS), of vav damper definition services performed. This record should include identifying features of vava auto repair pompano VAV box (e.g., box number, location, and type), functions and diagnostics performed, findings, and corrective actions taken.

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  Maintenance Checklist

  For all VAV maintenance, it is important vav damper definition 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 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 organic vava beans fromm greec are secure.	X
  VAV Box Zone Temperature Sensor (Thermostat)	Verify function and accuracy (compared to calibrated value). Check signal 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 by technology type and per manufacturer’s recommendations: Pneumatic – check for air leaks in hoses and fittings. Electronic – check for proper electrical connections. Direct Vav damper definition 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.	reversing vav biblical hebrew    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 vav so in love Electric Reheat (if present)	Check and 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.	reversing vav biblical hebrew 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

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  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:

  • Static pressure in supply duct and control point for system VFD fan to assure modulation with changing VAV box flow rates.
  • VAV box damper position versus zone temperature and reheat status to assure damper minimum setting before reheat application.
  • Reheat valve position versus call for heat.
  • VAV box airflow rate commensurate with damper position and within minimum and maximum settings.
  • VAV box delivered air temperature appropriate for zone conditions.
  • VAV box reheat call appropriate for conditions and corresponding chiller operating point and reset status.
  • Zone temperature.
  • Zone occupancy status.

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  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 is very little reliable data published on the actual cost variance of VAV maintenance compared to a constant volume system.

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  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 vav damper definition Standard 180, Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems.

  Pacific Northwest National Laboratory offers online training for 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, and opportunities for efficiency. More information on this training can be found at: https://buildingretuning.pnnl.gov/

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  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.pdf.

  ANSI/ASHRAE/ACCA Standard 180-2012. Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems. American National Standards Institute, New York, NY. https://www.ashrae.org/technical-resources/standards-and-guidelines/read-only-versions-of-ashrae-standards.

  ASHRAE Standard 62.1-2016. Ventilation for Acceptable Indoor Air Quality. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, GA. https://www.ashrae.org/technical-resources/standards-and-guidelines/read-only-versions-of-ashrae-standards

  California Energy Commission. 2003. Advanced Variable Air Volume System Design Guide. Sacramento, CA. https://www.researchgate.net/publication/258246595_Advanced_Variable_Air_Volume_System_Design_Guide

  EPA (Environmental Protection Agency). 2008. ENERGY STAR Building Upgrade Manual. U.S. Environmental Protection Agency, Washington, D.C. https://www.energystar.gov/buildings/tools-and-resources/building-upgrade-manual.

  FEMP (Federal Energy Management Program). 2010. O&M Best Practices Guide, Release 3.0, Chapter 9, O&M Ideas for Major Equipment Types, Section 9.7, Air Handling Systems. U.S. Department of Energy, Federal Energy Management Program, Washington, D.C. https://www1.eere.energy.gov/femp/pdfs/om_9.pdf.

  PNNL (Pacific Northwest National Vav damper definition. 2011. Self-Correcting Controls for VAV System Faults. PNNL-20452. Pacific Northwest National Laboratory, Richland, WA. https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20452.pdf

  Actions and activities recommended in this Best Practice should only be attempted by trained and stercollege vavo personnel. If such personnel are not available, the actions recommended here should not be initiated.

  Published April 2021

Heating or air-conditioning system

Variable air vav damper definition (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 or varying temperature.^[1][2] 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.^[3]

Box technology[edit]

The most simple form of a VAV box is the single duct terminal configuration, which is connected to a single supply air duct that delivers treated air from an air-handling unit (AHU) to the space the box is serving.^[2] This configuration can deliver air at variable temperatures or vav damper definition volumes to meet the heating and cooling loads as well as the ventilation rates required by the space.^[2]

Most commonly, VAV boxes are pressure independent, meaning the VAV box uses controls to deliver a constant flow rate regardless vav damper definition variations in system pressures vav damper definition at the VAV inlet.^[2] This is accomplished by an airflow sensor that is placed at the VAV inlet which opens or closes the damper within the VAV box to adjust the airflow.^[2] The difference between a CAV and VAV box is that a VAV box can be programmed to modulate between different flowrate setpoints depending on the conditions of the space. The VAV box is programmed to operate between a minimum and maximum airflow setpoint and can modulate the flow of air depending on occupancy, temperature, or other control parameters.^[4] A CAV box can only operate between vav damper definition constant, maximum value, or an “off” state.^[5] This difference means the VAV box can provide tighter space vav tickets 2024 control while using much less energy. Another reason why VAV boxes save more energy is that they are coupled with variable-speed drives on fans, so the fans can ramp down when the VAV boxes are experiencing part load conditions.^[6][7]

It is common for VAV boxes to include a form of reheat, either electric or hydronic heating coils.^[4] While electric coils operate on the principle of electric resistance heating, whereby electrical energy is converted to heat via electric resistance, hydronic heating uses hot water to transfer heat from the coil to the air. The addition of reheat coils allows the box to adjust the supply air temperature to meet the heating loads in the space while delivering the required ventilation rates.^[2] In some applications it is possible for the space to require such high air-change rates it causes a risk of over-cooling.^[5] In this scenario, the reheat coils could increase the air temperature to maintain the temperature setpoint in the space.^[2] This scenario tends to happen during cooling seasons in buildings which have perimeter and interior zones. The perimeter zones, with more sun exposure, require a lower supply air temperature from the air-handling unit than the interior zones, vav damper definition have less sun exposure and tend to stay cooler than the perimeter zones when left un-conditioned. With the same supply air temperature being delivered to both zones, the reheat coils must heat the air for the interior zone to avoid over-cooling.^[8]

Multiple-zone systems[edit]

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,^[9] 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 vav tickets 2024 to either a local or a central control system. Historically, pneumatic control was commonplace, but electronic direct digital control systems are popular vav damper definition for mid- to large-size applications. Hybrid control, for example having pneumatic actuators with digital data collection, is popular as well.^[10]

A common commercial application is shown in the diagram. This VAV system consists of a VAV box, ductwork, and four air terminals.

Fan control for a pressure-independent system[edit]

Control of the system's fan capacity is critical in VAV systems. Vava 28 manual 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 reversing vav biblical hebrew 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.^[11]

One of the challenges for VAV systems is providing adequate temperature control for multiple zones with different environmental conditions, such as an office on the glass perimeter of a building vs. an interior office down the hall. Dual vav damper definition systems provide cool air in one duct vava dash cam va-vd002 warm air in a second duct to provide an appropriate temperature of mixed supply air for any zone. An extra duct, however, is cumbersome and expensive. Reheating the air from vav damper definition single duct, using electric or hot water heating, is often a more cost-effective solution.^[12]

Reheat applications - Controls and energy issues[edit]

Traditional VAV reheat systems use minimum airflow rates of 30% to 50% the design airflow. These airflow minimums are selected to avoid the risk of under-ventilation and thermal comfort issues. However, published research supporting the efficacy of this approach is scarce. Systems operating at lower minimum airflow ranges (10% to 20% of design airflow) stand to use less fan and reheat coil energy relative to a traditional system, and recent research has shown that thermal comfort and adequate ventilation can still be attained at these lower minimums.^[13]

VAV reheat systems using the higher minimum airflow typically employ a conventional "single maximum" control sequence. Under this control sequence, a single cooling maximum airflow setpoint is selected for design cooling conditions. The cooling airflow is gradually lowered to the minimum airflow setpoint, where it remains as the space temperature lowers beyond the cooling temperature setpoint. When the heating setpoint is reached, the electric or hydronic heating coil is activated and gradually mehsana to rani ki vav more heat until the maximum heating capacity is reached at the design heating temperature.^[14]

Research has shown that using a different, "dual maximum" control sequence can save substantial amounts of energy relative to the conventional "single maximum" control sequence. This is accomplished due to the "dual maximum" sequence’s use of lower minimum airflow rates.^[14] Under vav damper definition control sequence, the same cooling maximum airflow is selected and is similarly lowered as the space temperature decreases. By the time the space temperature drops to the cooling temperature setpoint, the airflow reaches a lower minimum value than that used in the "single maximum" sequence (10% - 20% vs. 30% - 50% of maximum cooling airflow). When the space temperature reaches the heating temperature setpoint, the heating coil is activated and increases its electrical power (for electric coils) or hot water valve vav damper definition (for hydronic coils) while the airflow remains at the minimum setpoint. When the heating coil reaches its maximum heating capacity, upon a further drop in space temperature, the airflow is increased until it reaches a maximum vav damper definition airflow setpoint (typically about 50% of the maximum cooling airflow).^[5]

References[edit]