Table of Contents
The BCI-R and BCI2-R BACnet interfaces include points for adjusting the fan speeds on Precedent units equipped with variable speed supply fans.
These points are primarily intended for Test and Balance purposes and are generally set once and left alone. It is important to note that these points have limitations regarding their functionality and actual impact.
It is advisable that if these points are integrated into a Building Automation System (BAS), they should not be accessible to customers or displayed on graphical interfaces, as this will interfere with the unit's Test and Balance settings.
Analog Output 44 (AO-44) Supply Fan Minimum Speed BAS
As the name implies, AO-44 Supply Fan Minimum Speed BAS is a minimum speed adjustment, but it is limited in its operation. All Precedent units with direct drive fans have a defined/hard coded minimum that the fan will run down to and this can not be lowered. AO-44 is designed to adjust what the min value of AI-7 Supply Fan Speed Command will go down to, but not lower than the hard coded minimum set by the unit type:
- 3-5T w/ PWM controlled ECM fans, hard coded minimum is 54%
- 6-10T w/ Plenum fan, hard coded minimum is 68%
Example:
- If AO-44 were set to 35% on a 6-10T unit, ReliaTel would enforce 68% for the minimum value of AI-7
- If AO-44 were set to 75% on the same unit, ReliaTel would enforce 75% for the minimum value of AI-7
Analog Output 45 (AO-45) Supply Fan Maximum Speed BAS
Unlike AO-44, the name of AO-45 is not exactly what is implied. AO-45 Supply Fan Maximum Speed BAS mimics and overrides the operation of the DA COOL/FAN SPEED potentiometer (R136) on the RTOM of the unit. This setting adjusts the CFM/Ton of the unit in a similar way that an adjustable fan sheave would adjust the final drive speed of a belt driven fan. AO-45 & R136 are used as a multiplier to adjust what AI-7 means to the motor.
- AO-45 set to 0% = RTOM R136 set to full counter-clockwise
- AO-45 set to 50% = RTOM R136 set to full 12 o'clock
- AO-45 set to 100% = RTOM R136 set to full clockwise
AO-45 is a test and balance feature that was added to BCI firmware version 7.0.13 and is only available on RTRM version 20 or later.
It is also important to note that changing AO-45 will not change the value of AI-7 Supply Fan Speed Command. AO-45 is a multiplier:
- AI-7 x AO-45 = Actual Fan Speed Command (not visible through BAS)
Note: AO-45 Set to In Service (Out of Service = False) will override the function of RTOM R136. IF TAB was completed using RTOM R136 and AO-45 is set to In Service after the fact, it will change the airflow/balance of the unit.
Using AO-44 & AO-45 from the BAS
To utilize either AO-44 or AO-45, they need to be set In Service (Out of Service = False).
For 3rd party integration, the "Out of Service" point is actually a property of the AO point itself.
Some 3rd party vendors have access to the property through the normal point discovery others have to discover the point, expand it and the find the property to add to their database.