Vav with reheat design

Hot water coils are common in commercial building HVAC systems. Nevertheless, their design, installation, and control are frequently sub-optimal, with respect to maximizing heat exchange effectiveness and air temperature setpoint control. For example, conditions on-site sometimes lead to coils being installed in parallel flow instead of counter flow configuration, and temperature stratification in the leaving air can lead to control issues. Additionally, low hot water supply temperatures (HWST) of ~⁰F (49⁰C) are becoming more common with the rise of heat pump and efficiency retrofits. As hot water systems are typically designed for high HWST ( - ⁰F, 71 - 82⁰C), lower waterside “delta T” temperature differences (HWST – HWRT) would occur using low HWST in retrofits of conventional hot water heating systems. If buildings retain existing coils for the low-HWST systems common to efficiency retrofits, they will be unable to maintain the same design heat capacity without replacing terminal units. This creates challenges for retrofit projects throughout the industry, and low-HWST designs also present challenges to new construction. We present the background, methods, and findings of an experiment conducted in at vav with reheat design Price Industries Laboratory in Winnipeg, Canada. In this experiment, we tested multiple VAV HW reheat terminal units across a range of test factors, including VAV box sizes and number of coil rows. The performance of each coil setup was compared at both high and low HWSTs, and at multiple damper positions. We also performed several additional tests to determine the best solutions to common field installation and operation baron gif vav and to gauge the impact of varying coil insulation. In addition to tests we ran with stock-manufactured coils, we also ran several tests using coils of our own custom designs, focusing on symmetry and limited circuit count. The intent of these tests was to better understand the factors in VAV HW reheat vav with reheat design that may be overlooked in typical system design and coil selection processes, especially as parameters such as HWST and water side temperature differences begin to change. Understanding these factors is important to the design and operation of these systems as sub-optimal performance in the terminal unit systems has cascading effects both for retro-fitted low-HWST systems and existing boiler systems. Overall, the results from this experiment serve to inform recommended changes to VAV terminal unit design, selection, and control to improve whole-building performance.

Variable air volume (VAV) systems control the vav with reheat design temperature inside a zone by varying the supply air volume instead of the air temperature. At full cooling the VAV damper is fully open supplying the specified maximum air flow rate. As the cooling load decreases, the damper closes until it reaches the minimum stop specified by the zone minimum air flow fraction.

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VAV systems can be used for interior or perimeter zones with a common fan system, air temperature control, and reheating devices. The VAV concept may vary according to the VAV box locations, air temperature controls and types of heating elements. Heating can usually be provided by use of vav with reheat design coils or thermostatic baseboard.

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The unit contains a single heating coil which can be edited to change the type to 1-Water, 2-Electric or 3-Gas.

General

Name

This is a read-only label that is automatically generated by the software and which incorporates the name of the zone in which the ADU is located.

Damper heating action

The damper heating action determines the damper action in the terminal unit as the zone moves above or below the zone setpoint. With both control options, the damper is at the minimum air flow rate whenever the zone temperature vava chinese rapper height between the cooling and heating setpoints (deadband condition).

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With 1&#;Normal (the default) action, the damper will remain at the minimum air flow rate during heating operation. As the heating load increases, the water flow rate in the reheat coil will be increased to maintain temperature in the zone until the maximum water flow rate is reached or the user-specified maximum reheat air temperature is reached. Vav with reheat design is sometimes called the single maximum control logic as illustrated below.

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Single Maximum Control Logic

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With 2&#;Reverse, as the heating load increases, the unit starts at minimum air flow and minimum hot water flow. The hot water flow is increased until it reaches maximum flow or the user-specified maximum reheat vav with reheat design temperature is reached, then the air damper starts to open to meet the load. This option is used if the minimum air flow rate is not adequate to serve the peak heating load. This is sometimes called the dual maximum control logic as illustrated in the following figure. For an electric heating coil, the reverse action vav with reheat design the same as the normal action – always keeping the air flow at the minimum during heating.

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Dual Maximum Control Logic

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Maximum reheat temperature

This is the maximum supply air temperature (°C) leaving the reheat coil in the VAV terminal unit during heating operation.

Air Flow

Maximum air flow rate

The design maximum volume flow rate (m³/sec) specified for the Vav with reheat design. This field may be auto-sized.

Zone minimum air flow method

This is used to select how the software will determine the minimum flow rate to the zone while the system is operating. There are three choices for selecting how the minimum flow rate is specified:

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• 1&#;Constant where the value entered for Constant minimum air flow fraction will be used.
• 2&#;Fixed flow rate, the value entered for Fixed minimum air flow rate is used.
• 3&#;Scheduled then the software will obtain the value for minimum flow fraction from the schedule selected from Minimum air flow fraction schedule.

Air flow control for coil sizing

This item will only appear if 3&#;Scheduled is selected as the Zone minimum air flow method. It can be used to control the air flow rate used to size the unit heating coil if the coil vav with reheat design a water coil and the water flow rate for the coil is set to be auto-sized. The Air flow control for coil sizing drop-list contains three options:

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• 1-None,
• 2-Constant minimum baron gif vav flow fraction and
• 3-Fixed minimum air flow rate.

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If 1-None is selected, then the air flow rates used for sizing normal-action reheat coils is the average of the minimum and maximum values in this schedule. The air flow rate used for reheat coil sizing is reported with other component sizing information as Reheat coil sizing air volume flow rate.

Constant minimum air flow vav with reheat design (Turndown ratio)

If 1&#;Constant is selected for the Zone minimum air flow method, then the turndown ratio is used to define the minimum flow rate to the zone specified as a fraction of the maximum air flow rate while the system is operating. The minimum zone fraction is normally specified to meet the minimum ventilation requirement for the occupants. The reheat coil operates only when the damper is at this minimum flow rate when Damper heating action is set to 1-Normal (the default).

Fixed minimum air flow rate

If 2&#;Fixed flow rate is selected for the Zone minimum air flow method, then this setting is used to define the minimum flow rate (m³/s) to the zone specified as a fixed air flow rate while the system is operating. The minimum air flow rate is normally specified to meet the minimum ventilation requirement for the occupants. The reheat coil operates only when the damper is at this minimum flow rate when Damper heating action vav with reheat design set to 1-Normal (the default). This field is used vav with reheat design the Zone vav with reheat design air flow method field is set to 2&#;Fixed flow rate.

Minimum air flow fraction schedule

If 3&#;Scheduled is selected for the Zone minimum air flow method, then this setting is used to define the schedule that determines the value of the minimum air flow fraction. The schedule should contain fractions from to These values will define the minimum flow rate to the zone while the system is operating, specified as a fraction of the maximum air flow rate. The reheat coil operates only when the damper is at this minimum flow rate when Damper heating action is set to 1-Normal (the default).

Heating Coil

This section is visible only if the heating coil sub-component of this ADU has Type 1-Water.

Maximum hot water flow rate

The maximum hot water volumetric flow rate (in m³/s or gal/min) through the unit’s heating coil if a water coil has been selected. This value may be auto-sized.

Minimum hot water flow rate

The minimum hot water volumetric flow rate (in m³/s or gal/min) through the unit’s heating coil if a water coil has been selected. This value may be auto-sized.

Maximum flow control during reheat

This item is only available if the reheat coil is a water coil and the Damper heating actionis set to 2-Reverse. There are two available options:

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• 1&#;None,
• 2-Maximum flow per zone floor areaduring reheat and
• 3-Maximum flow fraction during reheat.

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These methods are used to calculate the maximum allowable air flow rate during reheat operation. If 1&#;None is selected, the maximum flow will not be limited. If Control on outdoor air flow is selected, the limit established through a 2-Maximum flow control during reheat option may be increased by the software to meet the outdoor air flow rate requirement. At no time will the maximum flow rate calculated here exceed the value for Maximum air flow rate.

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This limit is active only when the zone thermostat requests heating and the VAV box damper is reverse acting.

Maximum flow per zone floor area during reheat

This factor (m³/s-m²) is multiplied by the zone area, to determine the maximum volume flow rate (m³/s) allowed during reheat operation (see detailed explanation above). This field may be auto-calculated by entering “autocalculate”. If auto-calculated, the value is set to m³/s-m^2&#; ( cfm/ft²).

Maximum flow fraction during reheat

This fraction is multiplied by the Maximum air flow rate to determine the maximum volume flow rate (m³/s) allowed during reheat operation (see detailed explanation above). This field may be auto-calculated by entering “autocalculate”. If auto-calculated, the value is set to m³/s-m² ( cfm/ft²) multiplied by the zone floor area divided by the Maximum air flow rate.

Outdoor Air

Control on outdoor air flow

If this option is selected, the terminal unit will increase flow as needed to meet the outdoor air requirement specified on the HVAC zone dialog. If Outdoor air flow per person is non-zero, then the outdoor air requirement will be calculated by the software based on the current number of occupants in the zone. At no time will the supply air flow rate exceed the value for Maximum air flow rate. If this option is not selected, then the terminal unit will vava chinese rapper height be controlled for outdoor air flow.

Operation

Availability schedule

This is the schedule that determines whether or not the unit is available for each hour of the simulation. A schedule value greater than 0 (usually 1 is used) indicates that the unit can be on during the hour. A value less than or equal to 0 (usually 0 is used) denotes that the unit must be off for vav with reheat design hour

Advanced

Convergence tolerance

The coil is controlled by knowing the zone demand determined by the zone thermostat and setting the outlet conditions to meet this demand. For the electric and gas coils, this is set exactly since the coil model solution can be inverted. With the hot water coil that uses an effectiveness-NTU method, the solution cannot be inverted directly. Therefore, to determine vav with reheat design correct mass flow rate for the hot water the solution is solved for by iteration. The iterative solution uses an interval halving routine and needs a termination criterion that is set with the Convergence tolerance parameter. This control offset is set to a decimal fraction of the zone demand as the criteria, i.e. The default for the field is

Heating, Ventilating, and Air Conditioning (HVAC) systems play a large role in the successful operation of a facility. They are responsible for maintaining comfort conditions day in and day out. These systems, often very large and energy-consuming, are responsible for vav with reheat design large portion of a building’s first cost and operating cost. It is, therefore, very important to have HVAC systems designed, maintained, and operated properly. If they are taken for granted vav with reheat design neglected, comfort conditions can be lost and they can become even bigger energy consumers.

Because buildings vary, it is very important to choose a system that is “right” for the facility. Many different HVAC systems are available today, but most of the new designs utilize heated and cooled air as the medium for environmental control. The Variable Air Vav adapter rca to hdmi (VAV) system, which varies the volume of delivered air to control room temperature as opposed to varying the temperature, is the most widely used commercial vav with reheat design on the market today.

Variable Air Volume Systems

When it comes to choosing a VAV system, there are several options: the basic shut-off system, the reheat system, the parallel fan powered system, and the series fan powered system. In all of these systems, the temperature of the air leaving the air handler is usually maintained at a constant 55oF throughout the year. Each room can have its own air volume controller, making it possible for every room supplied by the air handler to have independent temperature control even though the temperature leaving the air handling unit does not change.

These systems may also have a heating coil, installed in the air handler, baron gif vav can be used to maintain a reduced temperature during periods when the building is unoccupied. This reduced temperature is normally maintained somewhere between 55oF and 65oF. This feature not only saves the energy required to heat the facility to a higher temperature but, if the fan is only run when heat is required, also saves fan energy. This same unit-mounted heating coil can be used for morning warm-up. At night and during the warm-up cycle the variable air volume boxes are normally maintained in the full open position to allow full airflow to spaces. During this mode the system is operating much like a simple single zone system.

Shut-Off VAV

These systems are used for cooling purposes in applications having a year-round cooling load. The volume of the 55oF air is reduced as the cooling load goes down. Since there is no reheat coil, shut-off VAV systems do not provide heating capability during periods when the building is occupied. The VAV box is usually allowed to reduce the airflow to zero during periods of no cooling load. This has the potential to cause indoor air quality problems and, therefore, should be evaluated closely during vav with reheat design design.

Terminal Reheat VAV

Similar to simple shut-off system, upon a fall in space temperature, VAV systems with terminal reheat reduce the volume of the air to the space. However, once a predetermined minimum airflow is reached, heat is added to the air prior to delivery to the space. Since the air is never reduced to zero, ventilation can be maintained. This reduces the possibility of indoor air quality problems.

Parallel Fan-Powered VAV

In these systems, a fan-powered variable air volume box reduces the volume of the primary 55oF air stream; if the space requires additional heat, the fan in the box is energized. This allows any warm air above the ceiling to be used to heat the space. If this does not adequately heat the area, a heating coil in the box is energized to provide the required heat. This system is designed to power the fan only when heat is required. Running the fan when heat is required keeps the room air exchange rate constant and at a sufficient volume to maintain good air circulation. With the Reheat VAV system, the air exchange rate during the heating mode can be reduced substantially over that achieved during the cooling mode.

Series Vav with reheat design VAV

The series fan-powered variable air volume box operates much like the parallel box except the fan runs in both the heating and cooling modes. This provides a constant volume of air at all times, even though the box is varying the volume of the primary 55oF supplied by the air handler. Series fan-powered boxes are typically used in low vav with reheat design ice storage applications where the air leaving the air handler is maintained at temperatures below the normal 55oF. This ensures that the air entering the room is still at 55oF even though the primary air stream might be much colder.

Advantages of VAV Systems:

• Relatively inexpensive individual room control
• Reduced operating costs
• How is k-factor used and vav flow calculation of the building’s cooling and heating loads is reflected in the air handler and ductwork system. Vav with reheat design allows the handler and ductwork to be smaller than required for vav with reheat design single zone system

Disadvantages of VAV Systems:

• Each terminal unit has an air valve and possibly a coil which require electrical and/or pneumatic service
• Requires the use of diffusers with proven distribution characteristics over a wide range of air flows
• Potential indoor air quality problems if proper precautions are not taken

VAV Systems – Are they right for you?

Variable air volume systems are best suited to facilities over 10, sq. ft. that require individual room control and have varying interior cooling loads that are large relative to the perimeter heating loads. Buildings with a central corridor and rooms with exterior exposures located on both sides of the corridor (double loaded corridors) are usually not good applications for variable air volume.

Potential vav with reheat design air quality problems with these systems have become a major design issue during the last several years. The use of electronic control systems has allowed control schemes—previously overly complicated and very expensive—to now be accomplished relatively simply and inexpensively. With proper design and installation, ventilation rates can be maintained to satisfy current codes and ASHRAE recommendations without sacrificing the energy benefits of the variable air volume system.

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Stencil: &#;Zone HVAC Stencil: Grp-VAV w/reheat

Type: Air Terminal

Sub Type: VAV_Reheat

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Note: Requires a connection to a hot water loop

EnergyPlus IDF Vav with reheat design Object - AirTerminal:SingleDuct:VAV:Reheat

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Variable air volume (VAV) vav with reheat design control the dry-bulb baron gif vav inside a zone by varying the supply air volume instead of the air temperature. At full cooling the VAV damper is fully open supplying the specified maximum air flow rate. As the cooling load decreases, the damper closes until it reaches the minimum stop specified by the zone minimum air flow fraction.

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VAV systems can be used for interior or perimeter zones with a common fan system, air temperature control, and reheating devices. The VAV concept may vary according to the VAV box locations, air temperature controls and types of heating elements. Heating can usually be provided by use of reheat coils or thermostatic baseboard.

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Component Properties

The table shows the properties that are displayed when the component is selected while in diagram mode. &#;The second column shows the selection options available that are dictated by EnergyPlus or it shows the source for the library entries that are displayed in the drop down vav with reheat design automatically defines a unique name for each component. &#;This can be changed by the user if desired.

Field: Availability Schedule Name

Schedule that this component will operate or is available to operate.

Field: Maximum Air Flow Rate

The design maximum volume flow rate specified for VAV ADU.

Field: Zone Minimum Air Vav with reheat design Method

This field is used to select how the program will determine the minimum flow rate to the zone while the system is operating.&#;&#;There are three choices for selecting how the minimum flow rate is specified:&#;&#;Constant, FixedFlowRate, and Scheduled.&#;&#;If Constant is entered, then the program will use the value for the constant vava va-vd002 review air flow fraction entered in the following field.&#;&#;If FixedFlowRate is entered, then the program will use the value entered in the field below called Fixed Minimum Air Flow Rate. If Scheduled is entered, then the program will obtain the value for minimum flow fraction from the schedule named in the field below called Minimum Air Flow Fraction Schedule Name.&#;

Field: Constant Minimum Air Baron gif vav Fraction

The vav with reheat design flow rate to the zone while the system is operating, vav with reheat design as a fraction of the maximum air flow rate. The minimum zone fraction is normally specified to meet the minimum vav with reheat design requirement for the occupants. The reheat coil operates only when the damper is at this minimum flow rate when Damper Heating Action is set to Normal (the default).&#;&#;This field is used if the previous field is set to Constant.&#;&#;If the previous field is set to Scheduled (and the field Maximum Hot Water or Steam Flow Rate is set to autosize), vav taluka village list this field is optional and can be used to separately control the air flow rate used for sizing normal-action reheat coils. If this field and the following field have values, the greater of the two is used for sizing.

Field: Fixed Minimum Air Flow Rate

The minimum flow rate to the zone while the system is operating, specified as a fixed minimum air flow rate. The minimum air flow rate is normally specified to meet the minimum ventilation requirement for the occupants. The reheat coil operates only when the damper is at this minimum flow rate when Damper Heating Action is set to Normal (the default).&#;&#;This field is used if the Zone Minimum Air Flow Method field is set to FixedFlowRate. If the Zone Minimum Air Flow Method field is set to Scheduled (and the field Maximum Hot Water or Steam Flow Rate is vav with reheat design to autosize), then this field is optional and can be used to separately control the air flow rate used for sizing normal-action reheat coils. Only one of these two minimum air flow fields (i.e., this field and vav with reheat design previous field) should be used at any time. If this field and the previous field have values, the greater of the two is used for sizing.

Field: Minimum Air Flow Fraction Schedule Name

The name of a schedule that determines the value of the minimum air flow fraction.&#;&#;The schedule should contain fractions from to vava chinese rapper height values will define the minimum flow rate to the zone while the system is operating, specified as a fraction of the maximum air flow rate.&#;&#;The reheat coil operates only when the damper is at this minimum flow rate when Damper Heating Action is baron gif vav to Normal (the default).&#;&#;This field is used if the previous field is set to Scheduled.&#;&#;If the previous field is left blank (and the field Maximum Hot Water or Steam Flow Rate is set to autosize), then the air flow rate used for sizing normal-action reheat coils is the average of the minimum and maximum values in this schedule.&#;&#;The air flow rate used for reheat coil sizing is reported with other component sizing information as “Reheat Coil Sizing Air Volume Flow Rate.”

Field: Reheat Coil Name

Reheat Coil Object name being simulated with this ADU. Applicable for all coils. If there is no reheat coil,use object AirTerminal:SingleDuct:VAV:NoReheat instead of this object.

Field: Maximum Hot Water or Steam Flow Rate

This field is 0 for gas and electric coils. Set to the maximum design water flow ) for the hot water coil. This field is autosizable. If there is no reheat coil,&#;&#;this is left blank.

Field: Minimum Hot Water or Steam Flow Rate

This field is zero for gas and electric coils. Set to the minimum design water flow (m³/sec) for the hot water coil, normally set to be a shut off valve that is set vavas insurance agency brooklyn ny zero. If there is no reheat coil,&#;&#;this is left blank.

Field: Convergence Tolerance

The coil is controlled by knowing the zone demand determined by the zone thermostat and setting the outlet conditions to meet this demand. For the electric and gas coils, this is set exactly since the coil model solution can be inverted. With the hot water coil that uses an effectiveness-NTU method, the solution cannot be inverted directly. Therefore, to determine the correct mass flow rate for the hot water the solution is solved for by iteration. The iterative solution uses an interval halving routine and needs a vav with reheat design criteria that is set with the Convergence Tolerance parameter. This control offset is set to a decimal fraction of the zone demand as the criteria, i.e. The default for the field is

Field: Damper Heating Action

in the VAV terminal unit as the zone moves above or below the zone setpoint. With both control options, the damper is at the minimum air flow rate whenever the zone temperature is between the cooling and heating setpoints (deadband vav with reheat design Normal (the default) action, the damper will remain at the minimum air flow rate during heating operation. As the heating load increases, vav geum halloween water flow rate in the reheat coil will be increased to maintain temperature in the zone until the maximum water flow rate is reached or the user-specified maximum reheat air temperature is reached

Control Fields for Maximum Flow During Reheat:

The following two fields are used only when Reheat Coil Object Type = Coil:Heating:Water and Damper Heating Action = Reverse. Maximum Flow per Zone Floor Area During Reheat and Maximum Flow Fraction During Reheat are two optional methods to calculate the maximum allowable air flow rate during reheat operation. If both are entered, the greater resulting flow rate is used. If Design Specification Outdoor Air Object Name is also specified, it may increase this vav with reheat design to meet the outdoor air flow rate requirement. At no time will the maximum flow rate calculated here exceed the value for Vav with reheat design Air Flow Rate.

This limit is active only when the zone thermostat requests heating and the VAV box damper is reverse acting.

Field: Maximum Flow per Zone Floor Area During Reheat

This factor (m³/s-m²) is multiplied by the zone area, to determine the maximum volume flow rate (m³/s) allowed during reheat operation (see detailed explanation above). This field is autocalculatable. If autocalculate is selected, the value is set to m³/s-m²( cfm/ft²). Vav with reheat design this field and vav with reheat design following field are entered, the greater of the two inputs is stellagshop.ru this field and the following field are left blank, the maximum flow will not be limited.

Field: Maximum Flow Fraction During Reheat

This fraction is multiplied by the Maximum Air Flow Rate to determine the maximum volume flow rate (m³/s) allowed during reheat operation (see detailed explanation above). This field is autocalculatable. If autocalculate is vav with reheat design, the value is set to m³/s-m²( cfm/ft²) multiplied by the zone floor area divided by the Maximum Air Flow Rate. If this field and the previous field are entered, the greater of the two inputs is stellagshop.ru this field and the previous field are left blank, the maximum flow will not be limited.

Field: Maximum Reheat Air Temperature

This vav with reheat design specifies a maximum supply air temperature leaving the reheat coil in a VAV terminal unit during heating operation. If leaving blank, the temperature of the supply air to the space in heating operation may get unrealistic high.

Field: Design Specification Outdoor Air Object Name

This vav with reheat design field specifies the name of a DesignSpecification:OutdoorAir object. When this field is used, the terminal unit will increase flow as needed to meet this outdoor air requirement. If Outdoor Air Flow per Person is non-zero, then the outdoor air requirement will be computed based on the current number of occupants in the zone. At no time will the supply air flow rate exceed the value baron gif vav Maximum Air Flow Rate. If this field is blank, then the terminal unit will not be controlled for outdoor air flow. See documentation for the zone HVAC outdoor air object for further information (Ref DesignSpecification:OutdoorAir).

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© Copyright Simergy, Sustainable IQ, Inc.

Variable Air Volume (VAV) is the most used HVAC system in commercial buildings. In this article we’ll discuss the Variable Air Volume system and single duct VAV boxes with reheat coils. The Air Handler varies the amount of air flow (CFM) at the overall system level based on the demand vav with reheat design by the zone level VAV boxes, which vary air flow based on their local demand.

To watch the Video of this presentation, scroll to the bottom.

The VAV box regulates the flow (CFM) to a zone in relationship to the demand of the temperature sensor in the space. 

Variable air volume is more energy efficient than constant volume flow because of the reduction in fan motor energy due to reducing fan speed (RPM) at partial load. As the cooling or heating demand is reduced because of a mild temperature day, the VAV Air Handler system can reduce the amount of air flow (CFM) by reducing the fan speed. 

The air handler will deliver a constant temperature of 55ºF (13 ºC) supply air to the VAV boxes. While the vav with reheat design air temperature stays constant the volume (CFM) of air will vary based on the total demand of all the zones on the system. There are several control strategies to adjust the speed of the fan which we’ll discuss below.

As the VAV boxes open or close due to demand called for by the temperature sensor in the space, the pressure in the main supply air duct will either increase or decrease. This pressure change is picked up by a static pressure sensor in the main supply air duct.

As the pressure increases in the main supply vav with reheat design because the VAV boxes vava chinese rapper height closing their dampers and are adjusting their dampers towards the minimum open setting, the air handler supply fan VFD slows down the fan. The opposite will happen due to the VAV boxes opening because of increased demand and the dampers are opening, in this case the VFD will vav with reheat design the supply fan to speed up when the pressure in the main supply air duct drops.

The VFD will try to maintain the speed (RPM) of the fan so that the static pressure in the duct at the location of the static pressure sensor maintains some minimum set-point, such as ” sp. The static pressure sensor sends a signal to the VFD and the speed of the fan is adjusted according vav with reheat design the set-point required.

The VAV box at the zone level will operate in one of three modes: Cooling Mode that varies the flow rate (CFM) to meet a temperature setpoint; a Dead-Band Mode where the temperature setpoint is satisfied and the box is baron gif vav minimum flow (CFM); and a Reheat Mode for when the space requires heat.

As you can see in the diagram above the VAV Damper goes from a minimum of 30% open, whatever the minimum required to meet ASHRAE 62, all the way to the damper being % open.

There are basically three modes in this control strategy. Mode #1 Is vav with reheat design Cooling Mode where the heating hot water control valve is closed and the VAV damper modulates from 30% to % open in order to satisfy the temperature sensor. Next is Mode #2 Dead Band Mode is when there is no need for cooling or heating, so the damper stays in its minimum position to meet the ventilation requirements of ASHRAE And Mode #3 is the Heating Mode where the VAV box vav with reheat design remains in the minimum position and the heating hot water valves modulates open to satisfy the heating requirements of the space.

The VAV box has a damper at its inlet moved by an actuator that is controlled by the controller that takes its command from a temperature sensor. The process is very simple. When the temperature sensor in the space calls for cooling it sends a command to the VAV box controller which then adjust the supply air flow rate (CFM). The adjustment is done by an actuator rotating the VAV box inlet damper either open or closed in increments.

• Airflow Sensor – is used to adjust the damper position by measuring the air flow at the inlet of the box. The airflow sensor measures total pressure and static pressure to determine the Velocity Pressure which helps the controller determine the CFM through the inlet of 嘻哈 vava 喜欢 pgone VAV box. Velocity Pressure = Total Pressure – Static Pressure.

• Actuator – Based on the airflow the actuator will power the rotation of the vav with reheat design to meet the space demand.
• Damper – adjust airflow (CFM) based on the temperature sensor and airflow sensor input.
• Reheat Coil – Depending on the zone, there may be a reheat coil that provides heating from heating hot water, steam or electric. The use of electric is limited in some jurisdiction due to energy codes.
• VAV Box Controller – Taking input from the temperature sensor and the airflow sensor the controller will send and output signal to the damper or heating hot water valve to modulate open or closed. Controls can be pneumatic, electronic, or direct digital control (DDC). Pneumatic is an older form of control and is being replaced by the more energy efficient DDC system.
• Other components used on various other versions of the VAV box, such as fan powered boxes would include fans and filters.

Before we get any deeper into this subject we need to cover the basics of zoning. Zoning is how the Engineering divides up vav with reheat design building into separate VAV zones, with each zone getting its own VAV box. To keep cost down its best to limit the amount vava chinese rapper height VAV boxes used, as each box adds additional cost for material, labor, vav with reheat design and electrical.

After a heating and cooling load is completed on a building, the spaces will be divided up into zones. Each individual zone will have similar load profiles and be served by the same VAV box. A typical individual zone maybe offices that share a southern glass vav with reheat design or interior spaces. Look for a Zone drawing in any set of mechanical plans that has a large area broken down into zones. (See example of a Zone Map Drawing below)

The idea of zoning is to breakdown large areas of a building into smaller zones with similar vav with reheat design profiles. Vav with reheat design a zone on the south facing portion of a building is calling for maximum cooling, the north facing zones may be in minimum cooling or heating mode. Zoning allows different spaces the ability to provide cooling or heating and vary the flow (CFM) depending on the demand of that zone’s temperature sensor. 

All the zones on a floor of a high-rise maybe fed from the same air handler, but each zone can adjust its CFM according to their specific needs. Depending on the size of the floor plate, there maybe two Air Handlers per floor, or for smaller floors the Air Handler may feed more than one floor. The Air Handler can be located on the floor within a mechanical room or located on the roof. 

The supply air main is considered the high side of the system. The high side being the main supply duct from the air handler to the inlet of each VAV box. The main is considered upstream of the VAV box, while downstream of the box is considered the low-side supply.

The air handler will provide 55 F degree (13 Celsius) supply air to the VAV box. The Variable Air Volume VAV box will then determine how much air vav with reheat design to pass through to the space based on the demand of the space. The air handler is sized to meet the maximum block load of the area it serves. The block load is basically the peak heating or cooling load of all the zones combined. It is not the total CFM of all the peaks of each zone, but the total based on the worst month, day and time of year where the total block is at its maximum load.

Each zone above is reacting differently to the early morning sun. Some zones are in cooling mode with their dampers at different percentages of being open, while other zones are in heating and one zone is off and receiving vav with reheat design air for ventilation. This is a very basic diagram of how zones may differ and why it&#;s important to consider how spaces are grouped together, as each space may have a different solar exposure and cooling load profile. As the sun travels across the sky the zone dampers will open or close depending on their need for heating or cooling.

Corner spaces are often difficult to include with other spaces because they have two exposures. It’s like living on the corner in your block, you have two streets. Looking at the image we can see that there are two cooling zones between corner spaces that are on the south exposure that could be grouped into one zone, Zone #5 below. The same is true for the two zones between corner spaces on the North exposures, Zone #2. If vav with reheat design had interior zones they would be separated from any exterior zone because interior zones are often exclusively in cooling mode due to internal heat gains and the lack of heat loss from any exterior vav with reheat design width="" height="" src="stellagshop.ru" alt="ossible Grouping of Spaces for VAV Zoning">

Cooling Mode

During cooling mode, the Variable Air Volume VAV box will modulate between a minimum CFM setpoint and the vav with reheat design design maximum cooling CFM setpoint based on the zones peak cooling demand. When the hot summer arrives and the vav with reheat design shines through windows and conducts heat through the walls and roofs, the need for cooling will be sensed by the temperature sensors in the space which will call for the VAV box to open its damper and let more cold air into the room. Or, if you’re in a room located within the vav with reheat design of the building, like a conference room, then the heat from the people, lights and plug loads will cause the temperature sensor to initiate an opening of the VAV box damper for more cold air.

For vava chinese rapper height zones and in certain cases interior zones there will be a reheat coil or an electric heater attached to the VAV box The reheat coil can be served by heating hot water, steam or electric. When in heating mode, the flow (CFM) through the box will be at a minimum setpoint to avoid wasting energy. Remember that the air handler is sending the VAV box 55 F degree (13 Celsius) supply air which was most likely cooled by chilled water from a chiller. 

This primary supply air will also vav with reheat design a percentage of mandatory ventilation air (Outside Air). In some systems the supply air temperature could be increased to a temperature that is just cool enough to cool the most-demanding zone with its VAV vav with reheat design set to maximum flow, thereby saving additional energy.

The heating hot water valve will modulate open providing a range of heating hot water flow (GPM) to meet the heating load. The minimum CFM setpoint can be somewhere between 30% and 50% of the maximum cooling setpoint. Minimums vav with reheat design set by some code jurisdiction so that the minimum ventilation rate is always achieved. In California see Title Sec  Requirements for Ventilation and Indoor Air Quality. See Ventilation section next.

Using electric heat is not approved in various jurisdictions. Check your local code for approved sources for the heating requirements. 

We’ll mention two control strategies for optimizing energy efficiency using a VAV system. These are the 1) Constant Static Pressure Control Method, and 2) Static Pressure Reset. (Required if there is a DDC system to the zone level)

When the VAV boxes are connected to a building automation system that monitors the function and status of the boxes there are various options for control. This is based on using a DDC system.

#1 Constant Static Pressure Control Method

Usually, a pressure sensor is installed 2/3 rds. of the way down the main vava lifes a struggle live air duct. When VAV boxes start closing their dampers because they need less cooling an increase in pressure will occur. When the static pressure in the supply duct increases due to the VAV boxes closing their inlet dampers the static pressure in the main supply air duct increases.

The pressure sensor in the duct will send a signal to the Variable Frequency Drive (VFD) causing the supply and return fans to slow down or reduce its RPM. If the pressure in the duct decreases because the VAV boxes are opening due to the need for additional cooling, the pressure sensor will send a signal to increase the fan speed (RPM). 

The pressure sensor is set to maintain a constant pressure in the main supply duct which often causes excess static pressure to be provided when compared to option two below. The reduction in the fan speed provides energy savings.

#2 Static Pressure Reset

The use of this strategy is required by Title (California) and ASHRAE for system that have DDC to the zone level. The static pressure setting in the main supply duct is reduced to a point where one VAV box damper is nearly full open. This is the zone that requires the most pressure. This vav with reheat design require that the VAV box actuators vavavo vave malayalam song free download mp3 report their damper position, best performed with an analog output. Look for Trim and Respond logic for more information. 

These options provide a good opportunity to save energy by vav with reheat design the fan speed and possibly increasing the supply air temperature in small increments with continuous polling. If the supply temperature can be reset above the economizer set point, then the compressors can stage off and vav with reheat design cooling can be provided by modulating the return air and outside air dampers to deliver the desired supply air temperature.

Using a DDC control system with VAV boxes that have a flow station and temperature sensor at the supply air discharge the system can determine the amount of reheat.

Q = CFM x x Delta-T

Q = Btu/Hr

= A constant based on standard air conditions

Delta-T = (Discharge Air Temperature – Primary Supply Air Temperature)

The building automation system can track and trend over long periods of time vav with reheat design following: Damper position, static pressure, vav with reheat design valve position, airflow rate (CFM), supply air temperature, zone temperature and occupancy status.

There are other types of VAV boxes vava chinese rapper height discussed here such as: Fan Powered VAV Box, VAV Mixing Box (Dual Duct Systems), CAV (Constant Air Volume).

Ventilation air (Outside Air) is required for all occupied spaces according to ASHRAE standard When using VAV boxes the minimum volume setting of the box needs to ensure the larger of the following:

1. 30 percent of the peak supply volume;
2. Either cfm/sf or ( m3/s per m2) of conditioned zone area; or
3. Minimum CFM (m3/s) to satisfy ASHRAE Standard 62 ventilation requirements. VAV terminal units must never be shut down to zero when the system is operating. Outside air requirements shall be maintained in accordance with the Multiple Spaces Method, Equation of ASHRAE Standard 62 at all supply air flow conditions.

The use of Variable Air Volume (VAV) has been shown to save energy when combined with vav with reheat design supply fan VFD’s. As the demand in the spaces fluctuate the VAV box vava chinese rapper height open or close proportionately and the air handler fans respond through various control strategies. Variable air volume systems save more energy than a constant volume system.

A mechanical engineer must consider several variables and equipment types when designing a VAV system.  This includes the load on the space, the static pressure in the ductwork, the types of terminal units, and the occupancies in the space.  The engineer must also consider how the terminal units are going to be controlled.  These decisions must weigh the initial cost with the long-term energy efficiency. Using a theoretical office building, we will walk through the general design process and the decisions the engineer must work through to arrive at a final design.

Design Vav with reheat design When an architect is designing a building, for purposes of this exercise an office building, they’ll start with a core and shell.  The information they’ll provide the engineer will include:

• Size of building
• Orientation of the building
• General Construction
  • Window Glazing
  • Insulation values
  • Ceiling heights and type
• Building Use
• Sizes of mechanical rooms

Using this information, with vav with reheat design help of a load calculating software, the engineer will determine how much heating and cooling vav air balancing be required to maintain the comfort vav with reheat design the building.  This load will be communicated in a total amount of BTUs and then the amount of air at a certain temperature will be needed to achieve these BTUs.  

Now that the engineer knows the overall demand for the space, she will vav with reheat design this as well as the vav with reheat design of the mechanical room to select the air handling unit for the space. For many VAV systems, the air handling unit will contain a cooling coil and a fan.  The cooling coil will have to provide the amount of cooling with the use of chilled water. The selection software from the air handling unit will provide the engineer with the right size of coil and amount of chilled water flow necessary to cool the building.  On a side note, the engineer will combine all the selections for the building to determine the total amount of chilled water required for the project to size and select the chiller for the entire project.

Once the AHU has been selected, the engineer will design the air distribution system for delivering the cooling to the space. This starts with the branch ductwork.  To design this ductwork, the engineer will have to consider the ceiling heights and static pressure created by sizing the duct.  In general, for the same air flow, larger ductwork will create a smaller pressure drop.  Higher pressure drops will increase the size and amount of fan energy to vav with reheat design the airflow.

Across the floor, varied occupancies and occupants will have different needs and expectations of comfort.  If we designed the air handling unit, added branch ductwork, and then tapped directly into this ductwork to serve the entire floor all in the same way some spaces would be over cooled, and others would be undercooled.  In some cases, one side of the building will need cooling while the other is heating. To ensure each area vava moov 11 price independent control over their comfort, the floor must be broken up into spaces with similar demand.  During the phase of calculating the load, the engineer will break the core up into sections (as shown below).  The floor will contain interior and exterior zones.  When the engineer starts to design the air distribution, each one of these sections will be served by a terminal unit.

Using the loads baron gif vav each one of these zones, terminal units will be selected along with the ductwork from the terminal unit needed to serve the space.  Resulting in a design like what is shown below.

Terminal Unit Selections

Generally, the interior spaces will be served by single duct terminal units and the exterior spaces will be served by fan powered terminal units. 

Single Duct Terminal Units

Single Duct Terminal Units are controlled by a zone thermostat that the occupant sets to their comfort level. Depending on the temperature of the space relative to the set point vav with reheat design the thermostat, vav with reheat design terminal unit will allow less vav with reheat design air from the air handling unit into the space.  In some cases, the terminal unit will have supplemental heating for when the space is below the desired set point. 

The terminal unit consist of the following components:

Hi Ali (and Kathryn!),

I peeked around the model yesterday and made a couple observations, but forgot to hit send sorry for the delay. Not sure if this will totally solve your case but should help you understand what's happening:

1. A piece of why you're observing relatively flat heating needs through the year is explained by:
* % of design cooling airflow is being pushed to your zones at all hours the system is ON baron gif vav zonal minimum flow inputs of
* Combine the above vav with reheat design your systems being made to push air 24/7/ via the fan schedule.
* Allowing airflow to turn down and/or allowing the system to turn off would reduce reheat caused by sub-cooling of your spaces.
2. Was it was intended to input -1 btu/h for baseboard capacities?
3. Reinforcing Kathryn's point on the importance of reset strategies in mitigating reheat: it's generally good practice to keep an eye on your hourly supply air temps (which I do see included in your custom hourly report). Consider for similar reasons tightening up your cooling supply throttling range. I have observed supplying 51F air when you intend 55F (this really tripped me up on a different model), which can add up to substantial difference in reheat requirements. I've been advised correctly designed/commissioned air handling system controls these days shouldn't have trouble maintaining supply air to within a degree of setpoint or better.
4. Your humidity control setpoints will be the source of at least some of baron gif vav sub-cooling (and subsequent additional reheat energies).
5. You stated vav with reheat design thermal zone for each VAV at this stage." Anticipate reheating needs might need to increase if you intend to serve >1 zone per system.

You can always clip off availability for the reheat coils via snap temperature or schedule it off via hydronic loop vav with reheat design. You can also more broadly cut off system heating capability with airside inputs or similar loop controls on the primary heating loop. These are behaviors I regularly encounter for building hydronic plants around my part of the world. If however you don't address/understand the causes for your reheat first (perhaps with exploring some of the above bullets), you'll risk creating new unmet hours as spaces sub-cool without the reheat they want.

I've only ever visited Vav with reheat design once on vacation during the summer, so can't claim intimate knowledge of the climate, but I recall some pretty chilly evenings (and amazing food!). Probably stating the obvious here, but wouldn't vava chinese rapper height surprised vava chinese rapper height find a system supplying and conditioning ventilation air 24/7 is likely to require space heating through the year.

hope some of this is helpful!

~Nick

[cid:imagepng at 01DADBC2BE0]
Nick Caton, P.E., BEMP
Senior Energy Engineer
Regional Energy Engineering Manager
Energy and Sustainability Services
Schneider Electric

D
M
F
E stellagshop.ru at stellagshop.ru

Santa Fe Trail Drive
Suite
Lenexa, KS
United States

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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 vav with reheat design system performance and achieve high efficiency.

The purpose of this equipment O&M Best Practice is to provide vav with reheat design overview of system components and maintenance activities to keep VAV systems operating trox tvz vav vav with reheat design 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 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 with reheat design 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 each zone’s temperature setpoints. In some cases, VAV boxes have auxiliary heat/reheat (electric or hot water) where the zone may require vav with reheat design 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 vav with reheat design controller to maintain a constant flow rate regardless of variations in system inlet baron gif vav. 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: vav with reheat design cooling mode with variable flow rates designed to vava chinese rapper height 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 vav with reheat design 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 vava chinese rapper height 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 warmer plenum air/return air into the zone and displace/offset required vav with reheat design energy.

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 vav with reheat design provides air from an AHU. Primary vav with reheat design 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 the air-supply system is the duct pressure sensor. The pressure sensor measures 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) consists of a number of individual components, including:

• Airflow sensor – measures the airflow at the inlet to the box and adjusts the damper position 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 vav with reheat design fans) or supplement/displace reheat needs (parallel fans).
• Filter (for fan-powered boxes) – usually included when a fan draws into the VAV box from vav stand for 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 vav with reheat design 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.

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.

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 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 vav with reheat design 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, and type), functions and diagnostics performed, findings, and corrective vav with reheat design taken.

Maintenance Checklist

For all VAV maintenance, it is important to follow the manufacturer’s recommendations. Proper maintenance should only be vav with reheat design 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 vav with reheat design manufacturer, nor is it a replacement for contracted O&M or warranty services.

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 vav with reheat design 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.

O&M Cost

Modern VAV systems are designed to be more efficient and have less vav with reheat design 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 vav with reheat design to a constant volume system.

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) StandardStandard 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: stellagshop.ru

Sources of Information

AHRI Standard Standard for Vav with reheat design Rating of Air Terminals. Air Conditioning, Heating, and Refrigeration Institute, Arlington, 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, Washington, 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 Vav with reheat design, Federal Energy Management Program, Washington, D.C. stellagshop.ru

PNNL (Pacific Northwest National Laboratory). Self-Correcting Controls for VAV System Faults. PNNL Pacific Northwest National Laboratory, Richland, WA. stellagshop.ru

Actions and activities recommended in this Best Practice should only be attempted by trained and certified personnel. If such personnel are not available, the vav with reheat design recommended here should not be initiated.

Published April