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How a BMS Design Engineer Should Approach “Power Fail Restart” Specification (Division 23 – During Estimation & Control Submittals)

January 7, 2026


Specification Extract (Div 23 – BAS):
“In the event of the loss of normal power, there shall be an orderly shutdown of all stand-alone DDC panels to prevent the loss of database or operating system software. Non-volatile memory shall be incorporated for all critical controller configuration data, and battery back-up shall be provided to support the real-time clock and all volatile memory for a minimum of 72 hours. Upon restoration of normal power, the DDC panel shall automatically resume full operation without manual intervention.”

Break the Spec into Design Obligations
*Never read this as a paragraph. Read it as compliance items.
1. Orderly shutdown on power failure
2. Non-volatile memory for critical configuration data
3. Battery backup for RTC & volatile memory
4. Minimum 72 hours battery autonomy
5. Automatic restart without manual intervention

PART A - How to Handle This During ESTIMATION
1. Controller Selection (MOST CRITICAL STEP)
Before freezing any DDC controller, verify directly from OEM datasheets:
1. Flash / EEPROM / Non-volatile memory available
2. Internal or external battery backup supported
3. Battery autonomy ≥ 72 hours
4. Firmware supports auto-restart after power restore

If even one point is unclear -> reject the controller during estimation.
* Never assume “all controllers have batteries” - many do not.

2. Battery Cost MUST Be Included in BOQ
Ask these questions during take-off:
1. Is the battery factory-supplied or field add-on?
2. Is the battery replaceable?
3. Is it included in the base controller price?
If battery is optional -> add a separate BOQ line item

Example BOQ Description:
“DDC Controller with RTC battery backup – minimum 72 hours autonomy”
This avoids cost disputes during submittal stage.

3. Panel-Level Considerations (Very Important) - For stand-alone DDC panels:
1. UPS is NOT mandatory per Div 23 spec
2. Battery backup is mandatory

However, for hospitals, data centers, or mission-critical buildings:
You may propose UPS as a value-engineering option (not a compliance requirement, but a reliability upgrade)

4. Risk Pricing & Protection
If the specification is strict and OEM data is not crystal, clear:
1. Add engineering contingency, OR
2. Include a clarification note in the proposal
This protects you during:
1. Consultant review
2. Submittal rejection
3. Post-award technical audits

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