Using DXRs and Central Functions for Duct Static Pressure Reset Building Technologies A6V11668992 2019-03-12 Restricted
Siemens Industry, Inc.
Table of Contents Scope and Purpose ........................................................................................................... 4 DXR Templates and Central Functions ............................................................................... 4 Terminology .......................................................................................................... 4 Duct Pressure Reset and VAV Saturation ....................................................................... 5 Overview .....
Scope and Purpose This document provides an overview of Duct Static Pressure Reset strategies and describes how to configure Central Functions to set up static pressure reset using DXR automation stations. Duct Static Pressure Reset is a common method for optimizing pressure in the ducts so that all zones are satisfied and none are starved for air. It is addressed in a number of BAS (building automation system) standards and guidelines - see Appendix.
Duct Pressure Reset and VAV Saturation Overview When the pressure in the duct system is too low, VAV boxes may open to maximum or near maximum and still not get enough air. If pressure is too high, boxes could be nearly closed and the AHU could be forcing air through them, wasting energy. An efficient way to counteract these issues is to change the static pressure setpoint based on demand from the zone. Duct static pressure should be just low enough that a single box is almost fully open.
Excluding a box from the pressure reset system It is possible to configure a Saturation signal (in ABT Site or online) to stay permanently false (i.e., “Satisfied”). This allows a user to exclude a particular terminal from the pressure reset system. This may be useful in situations where, for example, a certain box is almost fully saturated but there is no actual need for pressure reset. See Excluding_a_terminal_box for more information.
FLO SAT QTY NumVavSuStrtn (FLO SAT QTY) is a Central Function calculated value object that reports the number of starved supply air VAV controllers to the PXC/PXCM and is used to control the AHU. When a Central Function is used to collect this information, the PXC/PXCM can be set to communicate with the AHU fan controller to increase the static setpoint if necessary. The above graphic illustrates the communication of parameters between a Room level DXR, Central Function DXR, and Primary Plant controller.
Using Saturation Level in ABT Site and ABT Inside Title 24 Fault Detection for VAV and FPB Templates For compliance with Title 24, an FDD configured template must be used. FDD templates are located on StdApps under Apogee > Desigo_ABT > CustomApplications > FaultDetection. VAV and FPB templates include Saturation level parameters by default. To find and edit them in ABT Site, go to the Default values task and locate them under Supply air VAV.
4 Locate the parameters and edit / configure as needed: 9 Siemens Industry, Inc.
Configuring VAV Terminal with Default Values (Optional) Although this configuration example is the suggested way of setting up Duct Static Pressure Reset, it is not the only correct method. There are other ways to achieve the same result, for example by using the VavSu11 AF (instead of VavSu12) and Central Functions. VavSu11 uses an external air flow controller / actuator. Furthermore, job requirements might necessitate changes in this configuration.
5 Select the object parameters for EnStrtnCal, StrtnLvl, and DlyOnStrtn. 6 Click the Add button. 7 If SU FLO SATUR (Supply air VAV airflow saturation) is required by the commissioning agent, expand the list under SU FLO SATUR and select PrVal and click the Add button. 11 Siemens Industry, Inc.
8 The NumVavSuStrtn (Number of supply air VAV air volume flow starved) parameter may be added to Additional parameters (or may be already exposed). Note that this object does not need to be pulled out from Show/Hide Parameters; it will be visible / shown while online even if not selected here. 9 If necessary, select the Avail on AS option for the parameters. (Note that doing this will increase network traffic.) 10 Click OK. 11 Close the application.
Excluding VAV Terminal from Saturation Calculation When the Enable Saturation Calculation parameter is set to false, the VAV box is not included in the Duct Pressure Reset calculation, but it still remains part of the group. The following example shows how to exclude a box while online in the controller. It can also be done by changing the same setting in the Default values area in ABT Site. 1 Go Online with the device. 2 Navigate to Room segment - HVAC 3 Click the three dots next to Supply air VAV.
Central Functions Central Functions Basics The Central Function Application or Coordinator is implemented through the use of a DXR2E/M.18 controller. Central Functions coordinate the actions of the room controller to the primary plant. A DXR running the Central Function Application facilitates group data exchange between room applications or DXRs and the primary plant controller or Field Panel.
Central Functions can also be bundled together in order to collect and distribute Group Member data to / from multiple other Central Function DXRs. All central functions have “bundled” variants that are used as subordinate central functions to one master. If one central function may not be enough to control all of the data from the room controllers, a higher-level Central Function DXR can be used to communicate between the lower level central functions to the AHU/primary plant.
Commonly Used Outputs of SplyAir11 Point Database Description BACnet Name (Abbreviated name) Type Comment Direction of Data Flow Condition Value of air handling unit mode AhuModCndVal BCalcVal Used with Fault Detection: faults will not activate, when the AHU serving the Zones is not turnedon, and this parameter signals the AHU operational state (On/Off).
Adding a Central Function 1. Choose the Building component. 2. Choose the Building Structure task. 3. Choose the Add application template button from the Add Device dropdown. 4. 5. 6. 7. 8. Choose the Types in Library tab. Choose the CentFnct11_A type. Select the AS Type required. Choose the Add template to project button. Use the default name, version, and description and click OK. 9. Click the Template Properties button. 17 Siemens Industry, Inc.
10.Click the Unlock button. 11. Enter an Application Number. 12. Click OK. 18 Siemens Industry, Inc.
Configure Central Function for Supply Air VAV Saturation Evaluation 1. Choose the Central HVAC Function. 2. Choose Supply chain for air. 3. Click the drop down and change None to Supply chain air 11. 4. Choose Supply air VAV saturation evaluation. 5. Click the drop down and change the setting from None to Active. 19 Siemens Industry, Inc.
6. Choose the Default Values task. 7. Change Infrastructure Priority Objects IMPORTANT: When configuring a Central Function app type for the first time, the Infrastructure Objects must be changed. If they are kept as defaults, they can cause alarms to come in at a Life Safety priority, regardless of whether they are high priority. They should be as shown here: 8. Choose the Show/hide parameters button. 9.
10. Expand the displayed list to show the object parameters for FLO SAT QTY. 11. Select PrVal and click the Add button. 12.The parameter Num of supply air VAV airflow starved is added to Additional Parameters. 13. En able the Avail on AS option for FLO SAT QTY. 14. Click OK. 15. Close the application. 16. Add the Central Function Automation Station to the Building Hierarchy. 21 Siemens Industry, Inc.
Configuring Group Members and Masters Group master/member communication is how all central functions read and write to other applications. The high-level central function controls a single Group Master object. This Master object is then what writes to the Group Member objects in the lower level application functions.
6. Expand the Central function. Modify the Group Number to 1. (It may already be set to 1) 7. With the Group Master selected, the VAV Automation Stations should be displayed in the Group Members tab. All Automation Stations used in the Duct Pressure Reset calculations must have an Assigned selection in this tab. All Central Functions can be grouped hierarchically, which is used for separating Group Member and Master functions.
8. Use Assign Selected or Remove Selected buttons may be used to assign or remove the VAV Automation Stations from the group. Once the Terminal application is connected as shown, the data from the VAV box should be collected and read by the Central Function. This will allow the Central Function DXR to communicate with the AHU and perform Duct Pressure Reset correctly.
App Configuration Supply Chain Air 11 Appendix Duct Static Pressure Reset – Standards and Guidelines ASHRAE 90.1-2018 6.5.3.2.3 VAV Setpoint Reset “For multiple-zone VAV systems having a total fan system motor nameplate horsepower exceeding 5 hp with DDC of individual zones reporting to the central control panel, static pressure set point shall be reset based on the zone requiring the most pressure; i.e., the set point is reset lower until one damper is nearly wide open.
Issued by Siemens Industry, Inc. Building Technologies Division 1000 Deerfield Pkwy Buffalo Grove IL 60089 Tel. +1 847-215-1000 Document ID A6V11668992 Edition 2019-03-12 © Siemens Industry, Inc., 2019 Technical specifications and availability subject to change without notice.
