BCI-R™ / BCI2-R™ VAV Controls Staged Heat Issues (Max Heat Morning Warmup, Daytime Warmup) – Trane Commercial HVAC Help Center

BCI-R / BCI2-R VAV Controls Staged Heat Issues (Max Heat Morning Warmup, Daytime Warmup)

Summary:

If you are experiencing issues with VAV controls and staged heat, specifically related to MAX heat morning warm-up and daytime warm-up, there are a few possible causes and solutions to consider

Overview / Troubleshooting:

Follow Steps 1 & 2 below to ensure your BCI-R VAV unit (controller and comm interface) is configured for heating and the appropriate space conditions have been met for it to initiate. If you have not done so already, refer back to BCI-R / BCI2-R Point Configuration for Control with (non-Trane) Automation System to ensure all base settings are configured correctly (done automatically on installation into Trane BACnet Automation System)

Step 1. BACnet Point Configuration (1-time setup):

For proper heat operation, you MUST configure the 1. "Out of Service" and 2. "Present Value" BACnet properties as show below for the following points.

You can use a generic BACnet tool, non-Trane BACnet front end or the free Trane BACnet Setup Tool

	Point Type / Instance	Point Name	1. "Out of Service" BACnet Property	2. Present Value (BACnet Property)	Notes
1	BO/1	System Control Command	FALSE (aka "In Service")	ACTIVE (BAS Control)
2	BO/20	Morning Warmup Enable Command	FALSE	ACTIVE (Enable)
3	BO/21	Daytime Warmup Enable Command	FALSE	ACTIVE (Enable)
4	AO/4	Morning Warmup Setpoint BAS	FALSE	70 degF (typical)	Temperature at which MWU (heating) sequence will be satisfied. The sequence will be initiated at 1.5 degF below this value - this is a hard-coded offset. MWU will also terminate after 1-hour of running, whichever happens first.
5	AO/5	Daytime Warmup Terminate Temperature Setpoint BAS	FALSE	70 degF (typical)	Temperature at which DWU (heating) sequence will be satisfied and terminate. This value MUST be less than the Active Heating Setpoint (AI/50)
6	AO/43	Daytime Warmup Initiate Temperature Setpoint BAS	FALSE	67 degF (typical)	Temperature at which DWU (heating) sequence is initiated. *this point was added to v7 firmware and newer
7	AO/2	Space Temperature Setpoint BAS	FALSE	72 degF (typical)	Heating will be allowed if Space Temperature < Active Heat Setpoint Active Heat Setpoint = AI/50 (AO/2 minus AO/29)
8	AO/29	Occupied Offset	FALSE	1.5 degF (typical)
9	AO/11	Space Temperature BAS	FALSE	Communicated from BAS (15 minute heartbeat)	OPTIONAL - if used, a value must be sent at least once/15 minutes (aka heartbeat) If you'd prefer, use hardwired sensor and leave Out of Service = True Check AI/15 to confirm correct setting
10	MO/7	Occupancy Request (BAS)	FALSE	1-Occupied (typical)
11	MO/8	Heat Cool Mode Request	FALSE	1 - Auto (typical) 4-Cool	See below for when to use 3-Morning Warmup Not recommended to use 2-Heat for VAV units with staged heat as not all RTRMs support it.

Step 2. Operational Conditions Required for Heat (DWU / MWU):

At this point, the RTU will now be set up for proper heat operation in a Building Automation System and monitoring the operating conditions for the need to warm up the space(s), and turn on heat in the conditions below.

For modulating heat, also see BCI-R / BCI2-R RTU Modulating Heat (VAV, SZVAV, CV) - Occupied Heat, Supply Air Tempering

Again, Tracer BAS Applications (VAS & Area) manage these for you automatically in conjunction with your occupancy schedule (per SC BAS-APG007 / SC+ BAS-APG036 Appendix E

DWU/MWU Operation

Condition	MO/8 (Heat Cool Mode Request) "Present Value"	MO/7 (Occupancy Request) "Present Value"	AI/15 (Active Space Temperature)	AI/50 (Active Setpoint)	MI/19 Status	MI/20 Status	Resultant Mode
DWU Initiate	1-Auto	1-Occupied	Transitions below AO/43 (DWU Initiate)	---	13-Max Heat*	1-Occupied	Daytime Warmup
MWU Initiate	1-Auto	Transition from 2-Unoccupied to 1-Occupied	Is 1.5 degF below AO/4 (MWU Setpoint	---	13-Max Heat*	1-Occupied	Morning Warmup (OAD = Closed)
Heat Command	use option 1 above (Auto), do not command MO/8 = 2-Heat	---	---	---	N/A	N/A	Fan only mode

*Fan/Heat Time Delays: In both modes, the fan will stay at 1% for 6-7 minutes and heat 1-2 minutes after that (up to 9 minutes total). This is done to ensure VAV boxes have time to drive open before 100% fan operation since neither mode controls or monitors Duct Static Pressure or DAT, which needs to be handled by the BAS (Trane BAS performs automatically)

Optional Heat Limiting

The following points can be used to limit heating capacity of the unit

Point Type / Instance

Point Name

1. Service

("Out of Service" BACnet Property)

2. Present Value

(BACnet Property)

Notes

BO/5

Heat Lockout Command

IN SERVICE

ACTIVE (Disabled)

Active will disable heating

AO/20

Heat Capacity Enable Setpoint

IN SERVICE

0% (no heat) to 100% (full heat)

Heat will be limited based on # of stages available / modulating heat

Troubleshooting / FAQs:

Unit will not heat
- Verify no diagnostics are locking out heating/fan operation
AI/15 is the Active Space Temperature the RTU is using
- will only use communicated value if AO/11 is "In Service"
AI/50 is the Active Space Temp Setpoint the RTU is using
- will only use communicated if AO/2 is "In Service"
MI/19 stuck = 3-Morning Warmup
- This occurs if you sent Morning Warmup at the Unocc-->Occ transition, but the RTU does not think it needs to heat. Increase AO/4 or lower AO/11 (both must be in service)
MI/19 = 13-Max Heat, fan @ 100%, no Heat firing
- This happens when AI/15 (Active Space Temp) > AI/50 (Active Setpoint)
- Adjust AO/2 (BAS Setpoint) higher or AO/11 lower
AO/43 does not exist
- Make sure you are on v7 firmware or higher
- If upgrading from older, you will need to rebuild points
What happens if MO/7 = Unoccupied and MO/8 = Morning Warmup?
The unit will do nothing when M/O8 is in MWU. MWU is a unit function and not a system function so for MWU or DWU to work the MO/8 needs to be in Auto
MI/19 never shows 2-Heat
- A VAV unit with Staged Heat will never enter an occupied Heat mode
- For mod heat, see BCI-R / BCI2-R RTU Modulating Heat (VAV, SZVAV, CV) - Occupied Heat, Supply Air Tempering

WARNING:

Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.