VAV box Pressure drop. Connect hose from return side of steering box to upper fitting on reservoir. Where VAV zone damper position is unknown, a pressure request is made when the ratio of the zone’s. 8mm (20 AWG) galvanized steel casing. These units are designed to control the airflow rate of conditioned air into an occupied space in response to a control signal from thermostat or Building Automation System (BAS). The sensing points collectively average the primary air velocity pressure across the entire inlet area. 0 inches or less at that point, the inlet of that furthest VAV box. 24 PSPV10 10" VAV BOX WITH PNEUMATIC CONTROLS 12" 2100 $572. 6 in WC to minimize life cycle costs. This is my attempt to explain air pressure in ductwork. procedure for converting a vav box to a static pressure station 1) Remove the low connection at the inlet pickup and let it hang and sense atmosphere. SOUND 1 OPTIONS Pressure Independent Variable Air Volume Terminal Unit Model: VAV - PID Cosmos VAV terminal, features a primary inlet with an integral damper and a discharge plenum. That means the the velocity of the fluid is increasing therefore dynamic pressure drop increases than that of static pressure drop. minimum required static pressure at the inlet of the VAV boxes. Convert the VAV box into a static pressure/pressure independence station by controlling it with a static pressure signal from the duct 2/3 to 3/4 between the takeoff for the first Therma-Fuser diffuser and the takeoff for the last Therma-Fuser diffuser. Cooling external duct static pressure loss (ESP C) downstream, not including coil 5. ing VAV terminals. INSTALLATION All KYODO VAV/CAV boxes are finished with standard hanger brackets for installation by either steel wire or steel rods.
Static pressure is the outward push of air against duct surfaces and is a measure of resistance when air moves through an object like duct work. The actual refurbishment is purely a matter of disabling the old damper or removing the old damper section. water) is equal to about 25 Pascals (Pa). The fan's discharge pressure requirement is calculated by adding the static pressure required by the VAV boxes to the pressure drop expected in the ductwork at full flow. Pressure dependent control does not use a device to measure inlet pressure as a means to determine flow. Subtracting the pressure drops for all the things that aren't ducts or fittings from the total external static pressure yields the available static pressure. Mount the wheel to the. VAV System pictured above. Inlet Guide Vanes. Supply Diffuser 4. Pressure drop allowances for fittings are based on “Equivalent Length” of straight ductwork for the various types and sizes. “The TRACE 700 Software models this. The goal of this strategy is to identify the critical zone— the zone that needs the most pressure— and reduce the duct pressure to the point. supply fan air flow x x x install in inlet cone where feasible supply fan start/stop x x x x interlock with fa system, if required supply fan speed command xx x supply fan downstream static pressure x x x x 10% deviation from setpoint x supply fan downstream static pressure setpoint x x x supply fan duct smoke detector status x x. 5 inch of water gauge (871. The reduction speed can cause a renewal speed.
Minimum Flow Rate – 8 L/Min (with a static inlet pressure of 0. When measuring static pressure, the unit of measurement. The calculation works by keeping the static pressure in the ductwork constant throughout the system. an inlet control device and unloading valve (UV). Pressure dependent control does not use a device to measure inlet pressure as a means to determine flow. The simulation results show that the responses of the terminal box inlet pressure and the air. 0 inches or less at that point, the inlet of that furthest VAV box. This parameter is sent to the fuel control for fuel scheduling. Working pressure will be used when choosing sprinkler heads and designing the system. from the AHU's supply fan, through the index run's diffuser, including VAV box losses - what I need to size the system's supply fan) I'm only getting the static pressure drop of each "Revit system" (i. The Preliminary Fan Static Pressure Calculations assume that ductwork will be sized by “Equal Friction” or “Enhanced Equal Friction” methods. 50 rather than an inlet and downstream pressure, you can enter an Inlet Pressure of 0. The minimum flow is determined when the pressure ratio reaches the pump limit and the machine reaches maximum pressure. The cowling inlets are 2 inches long and slightly forward of the stock configuration. Static pressure is the pressure when water is motionless. The static pressure of 0. The Exhaust Fan drawing below illustrates how static pressures are measured in ductwork with a manometer.
The zone controller has an allowable control set point range from 40 to 90 F (4 to 32 C) for heating and 45 to 99 F (7 to 37 C) for cooling. The required alpha name of the performance curve that parameterizes the variation of the duct static pressure set point (P sm, Pa) as a function of volumetric flow through the fan (Q fan, m 3 /s), which is used so that the resistance associated with VAV box damper operation is reduced. The big issue is keep the noise down and maintain control with resonable velocity at reduced cooling load with the damper closing off. 7 MPa, 7 bar) Maximum Air Inlet Pressure Important Safety Instructions Read all warnings and instructions in this manual and in the PD2K Proportioner manuals. Reset E-O-L set point and re-measure flow at each terminal. TEC Terminal Box (VAV) Controller The TEC Terminal Box Controller provides high performance Direct Digital Control (DDC) of pressure-independent, variable-air-volume zone-level routines. length, starting at the VAV box inlet. Thus, the VAV box flow is independent of duct static pressure. After 4 min, pressure drops across each cyclone and the total system static pressure were measured with airflow directed across the filters to check that cyclone inlet velocities were maintained. Nailor Industries, Inc. STATIC PRESSURE CATALOG FAN CURVE FAN WITH ELBOW ON INLET FAN WITH ELBOW ON INLET AND NO OUTLET DUCT Figure 9. The sinusoidal pressure boundary condition defined by the UDF can now be hooked to the outlet zone. Pressure independent over a 150 Pa-750 Pa (0. the same static pressure throughout the duct run. Air Flow and Static Pressure Airflow: This is the maximum amount of air moved by a fan when there is no resistance, such as open air.
A zone can be a single room or cluster of rooms with the same heat gain and heat loss characteristics. Morning Cool-Down is also available. It is lined with insulation to provide sound absorption and thermal resistance, it is designed to meet the needs of today's VAV systems. operating pressure re erence Leakage flow: estimated from leakage area operating pressure and average pressure OR no standard ASHRAE Handbook: and average pressure measured directly Referenceflow: unsealed ducts 2. Model RME - Room Variable Air Volume Boxes Installation, Balancing, Maintenance The Anemostat Model RME single duct Relief Box provides energy-saving low pressure variable volume (VAV) temperature control at the lowest prime cost for the popular low and medium pressure packaged air handling, air conditioning units. Cooling external duct static pressure loss (ESP C) downstream, not including coil 5. multi-port pressure sensing ring - provides both accurate airflow sensing and control in response to duct static pressure. Airflow in this case is in CFM at 1" w. Static pressure in fan systems is typically less than 2” SP, or 0. The fitted equation allows sound power to be calculated with satisfactory accuracy. heating is not required. SINRO VAV BOX Web: www. Inlet Dampers. location maximum air flow (cfm) minimum air flow (cfm) air pressure drop (in. Model TSS terminals provide variable air volume (VAV) control beyond the typical single duct box.
Based on an input from a duct pressure sensor located in the duct system, the pressure controller modulates the inlet guide vanes or fan speed to maintain a constant pressure at the sensor. The manufacturer's published data provides the static pressure operating range and the minimum static pressure drop across each terminal u nit for a given airflow. Pneumatic Building Controls Overview and Conversion to Direct Digital Controls (DDC) Pneumatic Building Controls How Does It Work A pneumatic control system uses compressed air as a medium of control for HVAC systems. Environmental pollution control. The actual airflow delivered to the space depends on the duct system static pressure at the inlet of the terminal unit. 20 inches, your VAV box itself might impose 0. Details about box installation and room, for acoustically-critical cases B. Inlet connection is rectangular. sensor, and damper. The dampers or inlet guide vanes for the fan are commonly controlled by a controller maintaining a fixed pressure in the supply ductwork downstream of the AHU. They may be field-mounted and can be configured for use in non-hazardous as well as hazardous locations. In a previous paper, it was shown that sound power level for a variable air volume (VAV) terminal device ("box") could be related to mass flow rate and upstream static pressure. BETA Pressure Independent VAV SDV & SDV/E are AHRI BETA products at JORDAN BUILD 2017, AMMAN – JORDAN BETA INDUSTRIAL LLC AT WEST AFRICA HVAC EXPO – LAGOS Build Expo Ethiopia, held in Millenium Hall Addis Ababa Meet us at BATIMATEC 2017 – ALGERIA Stand G2-44, BETA Volume Control Dampers and Back Draft Dampers. increases the static pressure at the outlet. inlet outlet with inlet box pelican diffusor 875 rpm 8 its own Rotating speed Fan total efficiency accessories CUSTOMER DATA Inlet pressure (STATIC) Outlet pressure (STATIC) -76. Fechheimer Pitot airflow stations and traverse probes measure in the same manner and magnitude as the Pitot tube, via separate signals of airstream total pressure and static pressure, in inches water column (IN w. VAV box ODO AI ation hardw ING CONT low is held pressure flu l directly to amper actu eam duct pr the tempe l to the flow the air flow ct amount o roportiona ace tempe e maintain ermostat s um setting ATION O VAV/C or threaded YODO reserves awings are not ctuator rec ntroller. The ﬁeld test of ASH-RAE RP-1353 shows that the leakage between the VAV box and the.
Pressure plates can be provided to insure uniform airflow, when the heater must be installed adjacent to the fan. Temperature sensor Zone damper VAV box VAV box pressure VAV flow Inlet dampers Inlet Guide Vane (IGV) Discharge Damper VAV box Minimum flow, Al-IU damper Duct stato pressure damper IGV Static pressure VSD VSD inlet damper Inlet Guide Vane (IGV) VSD Energy savings Da mper Control Guide Vane Hydraulic/eddy current coupling. Reverse relief airflow prevention and building pressurization with a decoupled relief air damper in air-handling units. Applications: There are six popular VAV systems. The sensing points collectively average the primary air velocity pressure across the entire inlet area. VAV Terminals/Single Duct Required Minimum Inlet Static Pressure, Inches wg. Static pressure is the outward push of air against duct surfaces and is a measure of resistance when air moves through an object like duct work. Saccenti - BOLDROCCHI S. Asli Variable Air Volume (Vav) Terminal Units are volume flow rate controller for supply air on variable air volume system. Undersizing VAV terminals to accommodate typical airflow sensors results in higher pressure drops and sound levels, increased energy consumption and noise in the occupied space. Savings can be increased by controlling VFD fan speed to maintain static pressure near the most distant VAV boxes. As a rule, total pressure is a more important factor than static pressure since total pressure is what HVAC fans must overcome. To obtain velocity pressure (the force. mba mba kg/ m gr/m mbar Inlet flow Specific weight Dust concentration Inlet temperature Barometric pressure at inlet. dual duct VAV box system. These differential pressure switches are suited for low-to-high differential pressure process media or fluid power applications where high and varying static pressures, high overrange, proof, shock pressure or cycle rates are expected. zAvailable only when density is calculated using the ideal gas law. “The eQUEST v3. Bldwhisperer.
Total Pressure = Static Pressure + Velocity Pressure Velocity Pressure Q 2 =(A 4005) where A = cross sectional area at the flow point considered. l All Therma-Fuser diffusers within two feet of wall equipped with three way blow away from wall. Drop Box Figure 11. Field configured VAV algorithms; Built-in actuator 70in. The CVB Controllers are primarily intended for pressure independent, single duct VAV box control. Elbows cause non-uniform. of the air inlet. The use of an outlet cone enables more of the fan’s pressure capabil-ity to be available to overcome system static pressure. If one VAV box cannot meet noise criteria, consider using two. pressure-dependent and pressure-independent applications in duct systems with static pressures up to 3" wg. VAV boxes can also be classified as pressure independent and pressure dependent. If you're an HVAC contractor or technician interested in a free static pressure test procedure, contact Doc at robf@ncihvac. Hall is president and owner of Systems Management & Balancing. Environmental Protection Agency In the past, variable air volume (VAV) supply air systems have consisted of pneumatically actuated mechanical inlet vanes or discharge dampers which maintain constant duct static pressure. 5 inch of water gauge (871. The Neptronic VAV controllers have tailored curves also in the lower velocities which are more represen-. Illustration: Suction pressure. temperature setting allowing the VAV terminal outlet box to open to provide conditioned air As the VAV box opens, the VariCool automatically adjusts to maintain the systems static pressure set point Multiple VariCool Systems may be networked together for unit lead lag, back up/assist, and system rotation Options.
These conditions are imposed on the furthest surface of two plenum, one for the inlet and one (bigger) for the outlet, that I've modelled before. Supply Duct Zone 1 Zone 2 Zone 3 Zone 4 Section 1 – Introduction. TEC Terminal Box (VAV) Controller The TEC Terminal Box Controller provides high performance Direct Digital Control (DDC) of pressure-independent, variable-air-volume zone-level routines. AND UP B All Transverse Joint and Longitudinal Seams 3"W. 00 00 563000. 1999 Air Conditioning Clinic TRG-TRC014-EN. 69 pa) of extra static to the return. I recently ran across a job where duct static was dropping to 0. 50 inches water gage, with the total flow through either inlet. This item is sold with out collar, if required please select it. energy management and occupant comfort. The blower design dictates the amount of CFM it can deliver at a given static pressure. This pressure is similar to that found by blowing up a balloon. 50) to achieve the same result. The result, under some conditions, will be chatter (the rapid opening and closing of the valve) but this can be overcome by using pilot pressure to regulate flow - it is a different kind of valve (pilot operated relief). 2" duct static for a setpoint then go to the furthest VAV box away and use your manometer and see if you are getting the VAV minumum static 1" at box inlet. 1 GENERAL A. The controller can be conﬁ gured to control the supply fan VFD to maintain a duct static pressure setpoint. velocity pressure (given by VAV box manufacturers) In order to avoid unnecessary calculations and simplify the process, Neptronic decided to merge some of the variables together (the K factor). Match static pressure supplied by the fan with the static pressure required by the system by adding static pressure loss to the system a little bit downstream of the fan Inlet Vanes Modulate the capacity of a fan by "pre-swirling" the air in the direction of the fan wheel rotation before it enters the wheel.
STATIC PRESSURE CATALOG FAN CURVE FAN WITH ELBOW ON INLET FAN WITH ELBOW ON INLET AND NO OUTLET DUCT Figure 9. The range of pipes nominal pressure generally used for the gravity fed system are given in table 1. What is a fan performance curve. 0 inches or less at that point, the inlet of that furthest VAV box. Therefore, as the boxes close, the fan slows down or restricts the amount of air going into the supply duct. to generate both the pressure and velocity at the box inlet. The primary air fan is then modulated to maintain duct static pressure either by discharge dampers (FC fans only), inlet guide vanes, or variable frequency drives (VFDs). Indeed, rooftop units are cheaper than central plants with boilers, chillers, pipping and controls. Pressure sensors are especially beneficial in cleanrooms by assessing and monitoring air pressure, quality and ventilation; all important considerations in a cleanroom environment. The static pressure equals to the summation of the duct pressure loss downstream of the sensor to the terminal box and box inlet static pressure. Staircase pressurization fan , what is the equation to calculate the air flow and static pressure for fan ? How to consider exhaust fan capacity and static pressure? If we use in room space split ac & fresh air fan in this situation how to balance outside air temp. Using the two air flow pressure taps at each unit, green (high pressure) and yellow (low pressure), read and record the air flow pressure to the zone (this value may be in excess of design flow requirements). Change the fan motor static pressure according to external duct static pressure. for longer lengths, increase the duct size and provide a duct transition to maintain the duct static pressure drop at or below 0. More specifically, it allows you to feel. The fan maintains a constant static pressure in the discharge duct regardless of the position of the VAV box.
VAV Inlet connection shall be either square or round and sized with an inlet velocity of not greater than 10m/s. variable air volume box schedule (vav) plan designation manufacturer model no. They also offer improved space com-fort and flexibilityfor a wide variety of HVAC applications. And typically the pressure sensor is 2/3 of the way down the duct from the air handler. ing VAV terminals. VAV and CAV boxes and 8 It is assumed that the primary air damper is located at the box inlet. For the sake of energy saving of variable air volume (VAV) system, this paper presents the a review of static pressure control around the optimization problem of static pressure reset in VAV air conditioning system. ), the pressure gauge will not be revolved even after the handle is operated. 1 and how they affect minimum VAV box setpoints Learn how fan arrays can reduce costs and improve performance Learn how best to measure and control minimum outdoor airflow 4. Match static pressure supplied by the fan with the static pressure required by the system by adding static pressure loss to the system a little bit downstream of the fan Inlet Vanes Modulate the capacity of a fan by "pre-swirling" the air in the direction of the fan wheel rotation before it enters the wheel. Include catalog performance ratings indicating airflow, static pressure, heating coil capacity and NC designation. DESIGN OF AN EFFETIVE LOW PRESSURE VAV AIR DISTRIUTION SYSTEM ABSTRACT The aim of this paper is to provide the air conditioning engineer with a clear set of guidelines for use in the design of the air distribution system for a low pressure Variable Air Volume system. The Digi-VAV ® resets the minimum airflow at each terminal box, optimizes both the AHU outside air intake and the supply air static pressure, and implements volumetric tracking return air fan control. Therma-Fuser diffusers are sized for the design or maximum air volume required using the published performance guide. That means the the velocity of the fluid is increasing therefore dynamic pressure drop increases than that of static pressure drop. air terminal units consist of a supply inlet duct connection, discharge outlet duct connection, and at least one damper assembly, located in between for volume control of primary airflow. The TEC Terminal Box Controller can operate stand-alone or can be networked to perform complex HVAC control, monitoring and energy management functions. Green Product. 05″wg/12 Pa or more) to obtain the required air volume. The rectangular inlet spigot is fitted with multi-point air flow sensor grids and motorized volume control dampers for greater airflow accuracy and reliability ranging from sensing point no.
Two or more VAV boxes can be controlled with one temperature sensor. Reset E-O-L set point and re-measure flow at each terminal. The damper in the primary air section will do some throttling to hold the maximum air flow to 1400 cfm. Pressure oil cooler inlet 5. 25″wg / 62 Pa the sound level becomes noticeable (NC35) and around. (LEFT SIDE) 2. The measured (in the field) static pressure at the VAV system static pressure sensor with the index VAV box "floating" at the lowest VAV fan speed is the set point that should be entered and locked in. These sensor are normally used in conjunction with the VAV 1000, 2000 and 3000 series VAV terminal controllers for individual zone control in HVAC systems. Parallel boxes use the warm air in the plenum to heat the. ©2000 Twin City Fan Companies, Ltd. A cold air control damper and static pressure controller are used to reduce cold medium pressure supply air to low pressure. The wide-open static pressure and airflows are found in the performance data section of the catalog. ( total lift ) with foot valve and pump suction piping filled with water. Alfa PI VAV are connected with Nepcross cross flow differential sensor (Neptronic Make Canada) for measuring the air volume, which is located in the upstream section of the VAV chamber. 46 PSPV12 12" VAV BOX WITH PNEUMATIC CONTROLS 10" 1350 $593. With the formula we can calculate the maximum velocity pressure we will have to measure.
The supply fan keeps duct pressure constant. Duct velocities are systematically reduced over the length of the distribution layout, which allows the velocity pressure to convert to static pressure, offsetting friction losses in the succeeding section of duct. Relating reading Ventilation and Fan Pressure Optimization for VAV Systems Engineering Bulletin (Trane literature number SYS-EB-2) "VAV System Optimization," Engineers Newsletter (volume 20, number 2) Figure 5-4 Fan-pressure optimization speed or inlet-vane position of supply fan static pressure sensor damper. STATIC PRESSURE CONSTRUCTION CLASS A All transverse joints, longitudinal seams and duct wall penetrations 4" w. The zone controller has an allowable control set point range from 40 to 90 F (4 to 32 C) for heating and 45 to 99 F (7 to 37 C) for cooling. When more dampers close, the duct system static pressure increases. This unit is served by a central air handler and modulates the amount of ‘primary’ cooling air to the space between a minimum set point and the design airflow. Reverse relief airflow prevention and building pressurization with a decoupled relief air damper in air-handling units. Pump inlet. • Chilled beam technology is emerging in the U. The graphs below show the effects that blade actuation has on static pressure, Bhp, and cfm with inlet vane dampers and parallel bladed inlet box dampers. Design data required: 1. Relating reading Ventilation and Fan Pressure Optimization for VAV Systems Engineering Bulletin (Trane literature number SYS-EB-2) “VAV System Optimization,” Engineers Newsletter (volume 20, number 2) Figure 5–4 Fan-pressure optimization speed or inlet-vane position of supply fan static pressure sensor damper. In other words the air flowing into the room fluctuates depending on the duct static pressure which may lead to occupants discomfort if it is not balanced properly. Details about box installation and room, for acoustically-critical cases B.
The controller modulates the airflow into the. In an air conditioning system as the static pressure or resistance increases the horsepower. That being said usually start out at 1. 10 Minimum Operating Pressure. Therefore, as the boxes closes, the fan slows down or restricts the amount of air going into the supply duct. In a previous paper, it was shown that sound power level for a variable air volume (VAV) terminal device ("box") could be related to mass flow rate and upstream static pressure. O11 / Digital: See pg. Another way is to use two hoses with static pressure tips, and the manometer will subtract the two pressures for you. This diffuser is designed to maintain coanda effect (draft free) of discharge air along the ceiling, providing a sustained discharge velocity throughout the volume range. Inlet Guide Vanes. Target Mass Flow Rate option for pressure outlets (not available for the multiphase models). CF-10 Air Flow Cross sensor , Inlet Diameter 10 Inches , 2 outputs ( Total pressure and static pressure ) 300 to 3000 FPM Neptronic. This is a function of the control package. Coordinate the VAV box location and the inlet duct connection so that a minimum of three to five straight duct diameters to the inlet duct or the minimum duct diameters as required by the VAV box manufacturer are provided. ©2000 Twin City Fan Companies, Ltd.
Include electrical characteristics and connection requirements. As for a variable air volume (VAV) System, the air duct static pressure is a typical control variable maintained by modulating supply fan speed. Heating Requirements The supply air temperature of a VAV system is usually constant at 55°F and only cools a space. A Guide to the Design of an Effective Low Pressure VAV Air Distribution System The aim of this paper is to provide the air conditioning engineer with a clear set of guidelines for use in the design of the air distribution system for a low pressure Variable Air Volume system. Correct inlet sizing for available static pressure. The range of pipes nominal pressure generally used for the gravity fed system are given in table 1. Duct strength, deflection and leakage are more functions of pressure than of velocity. Due to our VAV diffuser's variable discharge area, Vari-Flow VAV diffusers will not dump under any load condition. are approximately 22 interior zone sensors and associated VAV boxes per floor where VAV boxes are supplied. The vanes are controlled through mechanical linkages and actuators based on a change in external static pressure. 50 rather than an inlet and downstream pressure, you can enter an Inlet Pressure of 0. This allows the VAV boxes to operate properly and distribute the proper air quantity to the controlled zone. Pressure-dependent control is where the terminal unit damper is. The following graphic attempts to give relative representation of the four major valve styles. RoundVAVSingleInlet "Single Inlet" Round VAV Single Inlet — The zone-level flow control device of HVAC system offers low-pressure drop, low sound levels, and valve characteristics, which create stable control conditions within the conditioned space.
The fan compensates as described above to maintain a minimum amount of pressure in the duct work. energy management and occupant comfort. Field: Duct Static Pressure Reset Curve Name. Rectangular VAV terminal units for standard applications regarding the supply air or extract air control in variable air volume systems where low-leakage shut-off is required. VAV with fan tracking positive pressure Application principle This Variable Air Volume system is a slightly simplified version of the Variable Air Volume system with VSD Fan Control (See Application Notes D3). Pressure independent boxes can maintain airflow at any point between maximum and minimum regardless of box inlet static pressure, as long as the pressure is within the design operating range. In addition, the VAV boxes must be of a make and model that can in the future be retrofitted for a possibly hydronic conversion project; the VAV boxes must be able to be converted from electric heat to hot water heat similar to the Johnson Controls Model TSS Single Duct VAV. 50 rather than an inlet and downstream pressure, you can enter an Inlet Pressure of 0. Pressure independent VAV boxes have the ability to maintain a constant maximum and minimum airflow as long as the box inlet static pressure is within the design range of the VAV box. That means the the velocity of the fluid is increasing therefore dynamic pressure drop increases than that of static pressure drop. ADVANTAGE: Energy Efficient and Environmentally Friendly WHERE THEY ARE USED:. The Siemens BACnet Terminal Box (VAV) Controller can operate stand-alone or can be networked to perform complex HVAC control,. If the installed box is too small, the zone may overheat and. The Magnum incorporates many of the same features found in our little blaster line and are suitable for either shop or industrial applications. The boxes are selected on the basis of acceptable noise level when the pressure at the entry of the boxes is of 3 In. Alternatively VAV terminals are ideal to be used for CO 2 control. Thermal Products Corporation, Mfg. • VAV systems typically use cooling only air handlers. Vav Box Inlet Static Pressure.