Retro-Commissioning vs Commissioning for Existing Buildings

Most of the buildings that will exist in 2050 are standing today, and a large share of them have never had their systems tested against what they were meant to do. Over the years, schedules get overridden, sensors drift, and operators inherit controls they did not design. Retro-commissioning tackles that backlog in occupied buildings, and it is a core part of our commissioning services.

We have already compared the two processes at a general level in our existing article on commissioning vs retro-commissioning. This guide takes a different path. It looks specifically at existing buildings: how an RCx project is run, what it usually finds, where the savings come from, how California rules and benchmarking shape the decision, and how an owner should choose. Budlong has served California owners since 1958, and the guidance below reflects how our building commissioning services team approaches older properties.

1. What Is Retro-Commissioning?

Retro-commissioning is a structured process that tests, adjusts and documents the systems of an existing building that was never formally commissioned. The aim is to restore or improve performance without major capital replacement. It treats the building as a working machine to be tuned, in contrast with new building commissioning, which verifies a design as it is constructed.

Why existing buildings drift

Even a well-commissioned building degrades. Occupants change, tenants rearrange partitions, operators add manual overrides to stop complaints, and equipment wears. Control logic written for one use is rarely rewritten when the use changes. After a decade, the building may be doing something quite different from its drawings.

The existing-building mindset

An RCx provider begins with evidence rather than with design intent. Utility bills, trend logs, work orders and operator interviews reveal where the building departs from sensible operation. The team then tests those suspicions and corrects what it finds.

A useful rule of thumb: if the operator says “we never touch that setting,” the setting has probably not been reviewed since the building opened. Those are the first places to look.

Also Read: Commissioning vs Retro-Commissioning

2. How an RCx Project Works

Industry practice, including guidance from ASHRAE on commissioning existing systems, divides the work into phases. The names vary, but the logic is consistent.

Planning phase

Success begins with a clear scope. The owner and provider agree which buildings and systems will be studied, what savings or comfort outcomes matter and who will implement fixes. Twelve months of utility data, building drawings, control sequences and maintenance records are collected. Operators are interviewed early because they know about hot spots, noisy fans and recurring alarms.

Investigation phase

Investigators analyze trend data from the building automation system and compare it with expected behavior. They then run functional tests, which means forcing equipment through its operating modes and checking responses. A cooling plant is staged on and off, an air handler is driven through economizer positions, and valves and dampers are commanded to confirm that they actually move.

Implementation phase

Fixes fall into three groups: quick corrections made on the spot, such as schedule changes; measures needing a repair or a contractor, such as replacing a failed actuator; and capital proposals for later budgets. Each fix is retested so that the claimed saving is real.

Hand-off and verification

The project closes with updated documentation, trained staff and a verification period. Because weather and occupancy affect results, savings are checked against metered data, ideally across a heating and cooling season.

Also Read: The Building Commissioning Process

3. Related Processes Compared

Owners often hear several terms used interchangeably. They describe different activities with different starting points.

How an audit and RCx differ

An energy audit identifies measures, often including equipment upgrades. RCx concentrates on operations and controls, and it tests rather than only inspects. The two work well in sequence. Our guide to the ASHRAE Level 2 energy audit describes the audit side.

Monitoring-based approaches

Where a building has submetering and a capable automation system, analytics can flag faults as they occur. This keeps the gains from fading and turns RCx from an event into a habit. Developments in AI and machine learning for MEP systems are expanding what continuous analysis can detect.

4. Requirements, Codes and Benchmarking

There is no single rule that obliges every owner to retro-commission, but several layers of regulation and programs make it increasingly relevant in California.

Title 24 and existing buildings

The California Energy Commission administers the energy code, and it describes the standards at energy.ca.gov. When an existing nonresidential building is altered or expanded, the changed systems generally have to meet the adopted edition of Title 24 Part 6, including its acceptance testing requirements. Those tests resemble commissioning for the altered scope. They do not examine the rest of the building, which is why an RCx project can find problems that code-triggered testing never touches. Our guides to what Title 24 is and the Title 24 compliance guide explain the structure of the code.

Benchmarking and disclosure

California requires owners of larger nonresidential buildings to benchmark energy use and disclose it in certain transactions, using the free ENERGY STAR Portfolio Manager tool offered by the U.S. Environmental Protection Agency. Benchmarking creates a score that reveals whether a building is an outlier compared with similar buildings, and that result often becomes the trigger for an RCx study.

Local ordinances

Some cities have programs that go further. Los Angeles, for example, has an existing buildings energy and water efficiency ordinance that calls for periodic audits and tune-ups for larger buildings. Thresholds and deadlines change, so confirm them with the city before planning.

Standards and federal resources

ASHRAE publishes guidelines on the commissioning process for existing systems and on measuring energy savings. The U.S. Department of Energy offers building technology resources and research summaries, and Lawrence Berkeley National Laboratory has long studied the cost and benefit of commissioning in existing buildings. Those studies generally find that operational measures pay back faster than equipment replacement.

Green building programs

Rating systems for existing buildings often reward commissioning activity. See LEED commissioning requirements for how credit pathways interact with these processes.

5. Applications by Building Type

Retro-commissioning pays off where operating hours are long, systems are complex and controls are partly automated. The pattern of findings differs by building type.

Office buildings

Offices often run on schedules set before work-from-home patterns changed. Air handlers may run at full occupancy settings for half-empty floors. Our commercial practice has seen schedule and reset corrections deliver much of the benefit in such buildings, and the Wells Fargo project illustrates the scale of tenant spaces involved.

Civic and institutional buildings

City halls, courthouses and campus buildings tend to be older, with phased additions and mixed control generations. RCx can reconcile those systems. Examples in our portfolio include Pasadena City Hall and Los Angeles City Hall, and our institutional group supports owners in this sector.

Hospitals and laboratories

These facilities run around the clock with strict ventilation and pressure requirements. RCx here must protect safety first, then look for efficiency, for instance in air change rates and reheat. See our health facilities expertise.

Schools and campuses

Summer and holiday setback, shared systems across buildings and aging controls make schools strong candidates. Savings often depend on matching schedules to the actual academic calendar.

Hotels and multifamily

Common areas, central plants and guestroom controls drive findings. Hotels are sensitive to comfort complaints, so RCx should improve rather than disturb guest experience.

Is your building working as hard as it should?

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6. Deliverables and Project Management

Because RCx is done in a working building, project management matters as much as engineering.

Typical deliverables

• An RCx plan listing scope, roles, schedule and success measures.
• A systems inventory with controls information and known issues.
• A findings log that ranks each issue by savings, cost and difficulty.
• Functional test procedures and completed test results.
• Implementation records showing the before and after condition.
• A final report with verified savings and recommendations for capital work.
• Updated control sequences, setpoint schedules and operator training materials.

Team roles

An owner’s representative sets priorities. The RCx provider plans and directs the work. Facility staff supply knowledge and implement many fixes. Controls contractors reprogram logic, and mechanical contractors make repairs. Clear roles avoid the common stall where a finding is documented but nobody owns the fix.

Working without disruption

Tests are scheduled around tenant operations and critical processes. Where a cooling or ventilation system cannot be shut down, tests are staged or done with temporary measures. Tenant communication should be handled before any equipment is cycled.

Cost and benefit tracking

Each measure carries an estimated cost, expected savings and simple payback. Tracking these figures keeps decision makers focused on measures that matter and prevents long tails of low-value tasks. Our article on commercial building MEP upgrades that improve ROI shows how to rank projects by return.

7. Special Cases in Older Buildings

Older buildings raise challenges that new construction does not.

Missing or outdated documentation

Drawings may no longer match the building, and control sequences may exist only in the memory of a retiring operator. Investigation then begins with field verification, documenting what is installed and how it behaves. Capturing that knowledge is itself a major benefit.

Aging control systems

Legacy controls may lack trending ability or have lost vendor support. A first step may be adding data logging so that the investigation has evidence. Consider upgrades only after the value of better controls is clear.

Mixed equipment generations

Additions over time produce a patchwork of equipment with differing efficiency and control strategies. RCx can coordinate sequences so that old and new equipment cooperate. For central plants in tall buildings, the principles in our chilled water system design for high-rise buildings article help frame what good operation looks like.

Indoor environmental quality

Ventilation reductions can save energy but must not compromise air quality. Any change to outdoor air or fan speed should be checked against the applicable ventilation requirements and, where appropriate, indoor air quality testing.

Electrification and decarbonization plans

Owners planning to replace gas equipment with electric systems benefit from RCx first. Right-sizing loads and fixing waste can reduce the capacity of the new equipment, a point discussed in our piece on the impact of electrification on MEP engineering.

Tenant-controlled spaces

In multi-tenant buildings, the owner may control base building systems but not tenant systems. Scope should be drawn carefully and lease terms reviewed.

8. When to Choose Each Process

The right process follows the situation of the building rather than preference. The table summarizes common cases.

Cost drivers

Cost reflects building size, number and complexity of systems, quality of documentation, controls capability, and how much implementation the provider performs. Utility incentive programs may offset part of the cost, and eligibility rules differ by utility, so check before committing. Our guide to energy efficient MEP design for lower operating costs offers related budgeting context.

Savings drivers

Most savings come from a short list of mechanisms: shorter run hours, elimination of simultaneous heating and cooling, tighter and reset-based setpoints, improved economizer operation, lower fan static pressure, better equipment sequencing and reduced plug and lighting loads from controls. The exact result depends on the building, and savings claims should rest on verified metered data, not on rules of thumb.

Writing the scope of work

Define the systems, deliverables, testing depth, who performs repairs, the verification method, the reporting format and the expected role of the building staff. Ask for an independent provider where possible so that the party finding the faults is not the party who built or serviced the systems.

Choose by starting point, not by label. If there is a design to verify, commission. If there is an operating building to understand, retro-commission.

Also Read: Energy Efficient MEP Design for Lower Operating Costs

9. Best Practices, Verification and Persistence

Many projects achieve savings in the first year and lose them by the third. Persistence has to be designed in.

Typical findings to expect

Best practices

• Start with data analysis before touching equipment.
• Involve operators from day one and credit their knowledge.
• Fix and retest quickly, to maintain momentum and confidence.
• Document sequences in plain language and keep them with the building.
• Verify savings against weather-adjusted utility data.
• Schedule periodic reviews and track key indicators monthly.

Common mistakes

• Choosing the cheapest proposal with no testing depth.
• Finding faults but leaving implementation unassigned.
• Overriding controls again after the project because of a single complaint.
• Skipping operator training and documentation updates.
• Claiming savings without a measurement and verification plan.

Persistence is cheaper than repetition. A few dashboards, a quarterly review and a clear owner will keep most RCx gains in place for years.

10. Where Budlong Delivers This

Our commissioning engineers work from offices in Glendale, Downtown Los Angeles, Camarillo and Fremont, serving Los Angeles, Ventura, Orange, San Bernardino, Riverside and Santa Barbara counties.

11. Related Reading

12. Frequently Asked Questions