Drift Happens: How Optimized HVAC Sequences Degrade, and What Top Energy Managers Are Doing About It

This article is part of our Building Owner Signal series. We're highlighting patterns we see across conversations with building owners. These short insights focus on operational risks, emerging priorities, and what owner teams should pay attention to now.

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A 1-million-square-foot hospital opened in 2019 with full ASHRAE Guideline 36 sequences designed in. When Matt Gelnett, Director of Engineering at InSite, came in a few years later to look for additional savings, the energy manager warned him the audit would probably come up dry—the advanced sequences were already running.

Then InSite pulled the BAS data.

Air handler supply-air temperature resets were locked at extreme values across most of the building, disabled by a handful of failed VAV dampers and broken sensors. The hospital was burning the energy it had been engineered to avoid.

"One small fault—a broken damper actuator here, a failed sensor there—prevented the functioning of an entire advanced sequence, causing systemic energy loss and overriding any Guideline 36 planning and implementation work that was done during construction," Gelnett told us.

That building was 5 years old. Its designer's intent was already gone.

Every commercial building drifts. LBNL's Smart Energy Analytics Campaign tracked the same pattern of degradation across 104 organizations and 6,500 buildings over four years. The main message: You can expect performance to degrade by 15%, unless you have the technology, roles, and processes in place to prevent drift. The Energy Management role itself has changed, and the programs in our community have already restructured to reflect that.

Programs that used to treat the BAS as the sole energy management system have now built an analytics layer on top of it. Lincoln Property Company simplified its Guideline 36 sequences across the portfolio and built an FDD program to catch drift.

Programs that used to buy tools and hope have built shared accountability across owner, vendor, and contractor. Hudson Pacific Properties cycled through three FDD platforms before pairing Clockworks with mechanical contractor MacDonald-Miller and turning analytics into a managed function.

Programs that used to deliver static schedules at commissioning have moved to dynamic optimization. Microsoft replaced fixed schedules across roughly 50 buildings with machine-learning predictions refreshed every day.

When Nexus Labs began in 2020, the energy managers running drift prevention programs were the exception. Now, it's the mainstream—and this community is the one driving it. Monthly bills, periodic audits and RCx, and retrofit projects are still front and center for energy managers. But drift prevention, continuous monitoring, and advanced supervisory control are now just as important, if not more.

Five trends we see separating Connected Energy Management from the energy management of 20 years ago:

1. Define optimized sequence standards per equipment type—written specs for AHUs, VAVs, chillers, terminal units. Lincoln wrote simpler sequence standards when off-the-shelf G36 turned out to be too complex to maintain at scale. You can't maintain what you haven't defined.

2. Upgrade existing buildings to run those sequences. Capital projects program the standards into the BAS. This is ongoing—buildings get upgraded over years as renovations, controls retrofits, and capital cycles open up funding.

3. Drift prevention on whatever's been upgraded. FDD with a named owner and a regular cadence runs against whatever sequences are in place today—don't wait for portfolio-wide upgrade to start. Auburn University's super-user model—one technician working roughly 30 faults per month against three named KPIs—is one great example. Steps 2 and 3 reinforce each other.

4. Shared accountability when internal capacity is limited. Build a structure where someone owns each part—analytics, triage, field execution. Hudson Pacific's three-way model with Clockworks running the analytics and MacDonald-Miller running the triage is becoming commonplace where owners are short-staffed.

5. Advanced supervisory control on top. Once standards, upgrades, and drift prevention are in place, supervisory control tunes setpoints, schedules, and resets minute by minute within bounds the energy manager sets.

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Join us for NexusCast on June 17th, 2026, where we'll be diving deep into sequence drift and HVAC optimization.

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