Retro-commissioning existing buildings

Most existing buildings do not run the way they were designed to, and many were never fully commissioned in the first place. Over the years, schedules are extended for one tenant and never reset, sensors drift, dampers seize, setpoints are overridden to silence complaints and sequences are modified by successive contractors. The result is a building that uses more energy than it should and still generates comfort complaints.

Retro-commissioning (RCx) is a systematic process for finding and correcting these problems in a building that was not previously commissioned. When the building was commissioned originally, the same process is often called re-commissioning. Either way, the focus is on making existing systems work properly through operational changes, repairs and controls adjustments, rather than replacing equipment.

What makes retro-commissioning different

ASHRAE Guideline 0.2 addresses the commissioning process for existing systems and assemblies and is a useful reference for structuring the work.

The retro-commissioning process

1. Planning

The project begins by defining goals: energy savings, comfort, equipment life, preparing for a certification, or meeting a building performance requirement. The team gathers utility bills, drawings, previous TAB and commissioning reports, maintenance records and occupant complaint logs, and develops the current facility requirements, which describe how the building is used today and the conditions it must maintain.

Utility data analysis at this stage, such as comparing energy use intensity with similar buildings and examining monthly patterns against weather, helps identify where to look.

2. Investigation

This is the core of retro-commissioning. Typical activities include:

• Interviews with operators, who often know exactly where the problems are.
• Review of BAS programming, schedules, setpoints and overrides.
• Trend data collection and analysis, often over several weeks. See trend logging and using BAS data.
• Short-term data loggers where the BAS lacks points.
• Site inspections of equipment, dampers, valves, sensors and controls.
• Functional testing of selected sequences to confirm actual behaviour.
• Spot measurements of airflows, water flows and temperatures.

3. Analysis and reporting

Findings are compiled into a master list of deficiencies and improvement opportunities. Each measure is described with its estimated cost, estimated savings, simple payback and non-energy benefits such as comfort or reduced maintenance. Measures are usually grouped into those that can be implemented immediately at low cost and those that need further engineering or capital funding.

4. Implementation

The owner selects measures to implement. Many are carried out by in-house staff or the existing controls and service contractors. The retro-commissioning provider supports the work and clarifies the required changes.

5. Verification and hand-off

Implemented measures are verified through testing and trend review to confirm they work and have not created new problems. The final report documents changes, updated sequences and recommendations for keeping performance in place. Operator training on the changes is essential.

Typical findings

The same issues appear in building after building:

1. Equipment running when not needed: air handlers, exhaust fans and pumps operating nights and weekends, often due to extended or overridden schedules.
2. Simultaneous heating and cooling: reheat coils fighting cold supply air, or heating and cooling valves leaking through.
3. Economizer problems: dampers stuck, linkages broken, sensors inaccurate or control logic disabled.
4. Excess outdoor air: minimum outdoor air set far above requirements, increasing heating cost in Canadian winters.
5. Fixed setpoints: supply air temperature, duct static pressure and chilled or hot water temperatures held constant instead of reset with load.
6. Sensor errors: drifted or poorly located sensors causing incorrect control.
7. Valves and dampers that do not work: failed actuators, disconnected linkages and valves stuck open.
8. Poorly tuned loops: hunting valves and dampers that waste energy and wear equipment.
9. Disabled or bypassed sequences: features turned off years ago to solve a short-term problem.
10. Overridden points: values manually locked at the BAS and forgotten.

Most of these can be corrected with programming changes, recalibration and modest repairs.

Costs, savings and incentives

Retro-commissioning is often among the most cost-effective energy measures available because it uses existing equipment. Savings and payback vary widely with building type, condition and the scope of measures implemented, so estimates should come from the investigation rather than general rules.

Several Canadian utilities and provincial programs have offered incentives for retro-commissioning studies and implementation, though program availability and rules change frequently. See utility incentives for HVAC upgrades in Canada and check current programs before starting.

Retro-commissioning also pairs well with an energy audit. An ASHRAE Level 2 audit identifies capital upgrades, while retro-commissioning makes sure existing systems operate well before money is spent on replacements.

Keeping the benefits

Without follow-up, many of the improvements from retro-commissioning drift away within a few years as overrides and schedule changes creep back. Ways to protect the investment include:

• Training operators on what was changed and why.
• Updating sequences of operation and BAS documentation.
• Implementing ongoing or monitoring-based commissioning with fault detection.
• Reviewing schedules, overrides and key trends on a regular cycle.
• Tracking energy use monthly against a weather-normalized baseline.

Frequently asked questions

How long does retro-commissioning take?

For a mid-size commercial building, the investigation phase typically spans several weeks to a few months, partly to collect trend data across varied conditions. Implementation time depends on the measures chosen.

Does retro-commissioning require new equipment?

Usually not. The emphasis is on operational and low-cost improvements. Where equipment is found to be at end of life, the report will note it for capital planning.

Key takeaways

• Retro-commissioning systematically finds and fixes operating problems in existing buildings.
• Investigation relies on operator interviews, BAS review, trend analysis and targeted testing.
• Common findings include excess run time, simultaneous heating and cooling, economizer faults and fixed setpoints.
• Most measures are low-cost changes to controls, schedules and maintenance.
• Ongoing commissioning and operator training keep savings from drifting away. See our retro-commissioning service for how we approach existing buildings.