Accurex Model Xrv Dedicated Outdoor Air Systems User Guide

Model XRV Dedicated Outdoor Air Systems
User Guide

BACnet Quick Start Guide

3 – Command Unit Operation

1. Enable Unit
2. Control Occupancy
3. Reset Alarms
4. Global Alarm Notification
5. Control Temperature Setpoint (optional)

Document 485940
BACnet Integration Guide for
Dedicated Outdoor Air Systems

Reference Guide for BACnet Integration
Please read and save these instructions for future reference. The information in this guide assumes the controller was already configured with BACnet based on the original sales configuration. If the controller does not have BACnet enabled, please contact the equipment representative to get the necessary licensing and configuration files to allow BACnet communication to be used.

DOAS_08.000 Rev 2
Document Date: 01/2023

Basic Unit Integration

Below are the basic integration functions available on all equipment regardless of control mode. Some features are unit configuration dependent (heating type, cooling type, etc.). The controller’s BMS points list is static regardless of configuration to accommodate field configuration changes, however, not all points are applicable to every unit. Once the required sensors are installed in the equipment, the only mandatory requirements to make the unit operational are to enable the unit, if it hasn’t been enabled manually at the controller, and to command occupancy as desired.

Unpacking Integer Words to Binary Values

Binary values can be combined to create an integer word. By doing this, more information is available to the BMS in a smaller number of points and less network traffic. These integer words need to be “unpacked” once the BMS receives the value.
To unpack the integer word into the binary values, the integer needs to be converted to a binary number. The integers in the program are 32-bit, meaning up to 32 binary values are packed into the integer. Each bit can either be a 0 (Inactive) or a 1 (Active).

The BMS front end may have a solution already intact to pull individual bits from an integer. A “read bit” function looks to return what value a certain bit is in an integer. Bit number are 0-31 in a 32-bit integer with 0 being the lowest bit and the furthest to the right in the binary notation of the number. Bit 31 would be the largest bit and the furthest to the left in binary notation.
If the front end does not have a “read bit” or “bit extract” function, the binary value of individual bits can be determined by continually dividing the quotient of the integer by 2, the remainder of the division is the value of the bit (0 or 1). A function called Modulo or “mod” is commonly used to return the remainder of integer division.

Equation: x = (round down(a/2b ) )mod 2

• x is Boolean value for bit b, where 0 is inactive and 1 is active.
• a is the integer word value
• b is the bit of the binary number used as an exponent
•  The result of a/2b should round down to a whole number, truncating the decimal. For example, 5/21 is 2.5, however, only the 2 is used.

Example:
If the Device_Offline_Word (IV-8) is a decimal value of 11, the binary value would be 1011. This binary value would mean that Space Thermostats 1, 2, and 4 are offline. The rest of the bits in the binary number would be a Boolean value of 0. (Please see Binary Tables.)

• Bit 0 = 11/2° mod 2… this results in a Boolean of 1 or Active for bit 0.
• Bit 1 = 11/2¹ mod 2… this results in a Boolean of 1 or Active for bit 1.
• Bit 2 = 11/2² mod 2… this results in a Boolean of 0 or Inactive for bit 2.
• Bit 3 = 11/2³ mod 2… this results in a Boolean of 1 or Active for bit 3.

Modifying Equipment Operation

In addition to commanding unit occupancy, some system level sequences may require feedback from the BMS.
Common BMS adjusted sequences include items like supply air temperature reset control, demand control ventilation for multiple zones, and duct static pressure reset.

HEATING AND COOLING OPERATION SETPOINTS

* Typical range for standard configuration unit, please verify at point min and max properties.

DEHUMIDIFICATION OPERATION SETPOINTS

* Typical range for standard configuration unit, please verify at point min and max properties.

AIRFLOW OPERATION SETPOINTS

BMS Watchdog Enabled Control

BMS WATCHDOG
When directly commanding fans speeds, damper positions, or sending sensor values, the unit controller requires the BMS Watchdog point to be written to on a recurring basis. This tells the unit controller that the BMS is still actively communicating.

CONTROLLING AIRFLOW DEVICES
If desired, the speeds and positions of airflow devices can be controlled directly using BACnet commandable points. To control the devices via the BMS, the BMS Watchdog requirements must be satisfied.

* Typical range for standard configuration unit, please verify at point min and max properties.

SENDING SENSOR VALUES
Sensor values required for sequence operation can be sent to the controller over dedicated BMS points in place of a sensor wired to the controller (local sensor). When values are communicated to the controller over BMS, the BMS Watchdog must be satisfied. If the watchdog isn’t satisfied, the controller reverts to the local sensor (if installed and
valid) to control the unit or falls back to local control until the BMS watchdog is satisfied.

Advanced BACnet Settings

Additional settings can be accessed in the BACnet Advanced Settings menu including BACnet Broadcast Management Device (BBMD) configuration, relinquish default settings, Change of Value (COV) increments and restoring binary text values.

BBMD CONFIGURATION

To configure the controller to operate with a BACnet Broadcast Management Device (BBMD) on IP networks, go to the advanced BACnet settings menu and enter the IP address of the BBMD, foreign device configuration, and time to live settings.

COV INCREMENTS

BACnet COV is an optional portion of BACnet that supports providing new values/information only after an increase or decrease of the value is at least the listed COV increment. The controller’s COV increments are based on the unit of measure. All variables with the same unit of measure share the same COV increment value. Values can be adjusted on this screen, or by writing to the COV increment property of any BACnet object.

RELINQUISH DEFAULT SETTINGS

When the Return to Default function is enabled, the present value will not overwrite the relinquish default value and on a loss of power the controller will boot with last saved default values instead of last written values. This must also be enabled for the BACnet Comm Loss relinquish default to work.

When the Enable Relinquish Default function is enabled any value in the priority array for binary values or analog values will be cleared if a communication loss is detected.
All commandable points will revert to the relinquish default value.
Communication loss is determined based on the BMS Watchdog. The watchdog function must be enabled. The function will execute 5 minutes after the watchdog status goes inactive.

This may be desired if the BMS is running a reset routine on the setpoints and would like to revert to a default state if communication is lost. It is recommended to be used with return to default enabled, and a known relinquish default is saved.
When this box is checked by a user, the controller will write the present value of variables to the relinquish default for all binary and analog value BACnet objects that are commandable. The function operates in the background and takes approximately 30 seconds to complete.
This is desired to save any Test and Balance settings adjusted locally on the controller to be the BACnet relinquish default values. Alternatively, these values could be read and written to the relinquish default variables by the BMS system.

BINARY TEXT

If for any reason, the state text is missing from binary objects, checking this box will cause the controller to re-write the active and inactive text values.

DOAS Reference Tables

STATUS MODE TABLE
The following analog values can appear in the point to tell the building automation the current mode of operation of the unit. Values may rotate every three seconds.

ALARM TABLE
This table displays the latest alarm that is active in the unit controller.

BIT-PACKED INTEGER WORD TABLES
The following tables are used to unpack integer words into Boolean values.