A building can meet its performance targets and work exactly as intended at turnover. A few years later, energy use rises, comfort complaints increase, or equipment runs constantly.
That does not necessarily mean the design failed. Buildings change after occupancy. The question is whether current operations still support the building performance that the design was intended to deliver.
Building Performance Changes as the Building Changes
Every design starts with assumptions about how the property will be used. These range from occupancy and schedules to loads and space use. However, those are just assumptions, and real operations rarely stay frozen. For example, an office designed around a typical workday may eventually operate several hours longer as tenant schedules evolve. That change alone affects how long HVAC, lighting, and ventilation systems need to run. Equipment also wears over time, and changes in maintenance can affect how efficiently systems operate.
Building energy use ultimately depends on both good design and how effectively the building is operated once occupied. Real-world data shows how significant those operational differences can become. A study of 51 high-performance office buildings found that measured energy use ranged from roughly 30 to 330 kWh/m² per year. This is an elevenfold difference despite similarly strong performance credentials. The researchers identified operations, maintenance, and occupant behavior as key factors influencing actual building energy performance.
The takeaway is not that the original design was wrong. It is that maintaining energy efficiency requires the building's operation to evolve along with the building itself.
Small Changes Can Undermine Energy Efficiency
As a building’s use and operating conditions change, the systems serving it do not always adjust in sync. Small changes to schedules, setpoints, controls, and equipment conditions can gradually alter how those systems interact, reducing the building's energy efficiency. Individual components may still function, but the building as a whole can begin using more energy than it should.
Consider a tenant space that is consistently too warm. Facility staff may lower the central supply-air temperature to solve the complaint. That can improve comfort in the problem area, but it also sends colder air to other parts of the building, where reheat systems may turn on to compensate. A relatively small adjustment can leave one system working harder to cool the air while another uses additional energy to warm it back up.
Even modest control changes can have a measurable impact. The U.S. Department of Energy estimates that adjusting temperature setpoints could reduce commercial-building energy use by about 8%, while limiting heating and cooling to periods when a building is likely occupied could reduce it by about 6%.
This kind of performance drift is significant across commercial building systems. A Lawrence Berkeley National Laboratory study using multi-year data from more than 60,000 pieces of HVAC equipment found that, on any given day, 40% of air-handling units and 30% of air-terminal units had a reported fault. Those faults included sensing, mechanical, and control-related issues that can affect both energy use and comfort.
For building optimization, the goal is to make sure the building's systems continue working together efficiently.
Building Energy Performance Usually Leaves Clues
As small operational changes compound over time, a gap in building performance often becomes visible before anyone knows exactly what is causing it. Rising energy use, hot and cold complaints, overnight equipment operation, long runtimes, short cycling, or recurring maintenance calls can all be signs that the building's systems are no longer operating as efficiently as intended.
This is where data becomes useful. Utility history can reveal long-term changes, interval data can expose after-hours loads or demand spikes, and building automation trends can show whether equipment is actually following schedules and sequences.
Benchmarking provides additional context by establishing a baseline for tracking energy use over time. ENERGY STAR reports that buildings that consistently benchmark energy use save an average of 2.4% per year. While benchmarking does not improve energy efficiency on its own, it can help owners identify performance changes earlier and provide a clearer starting point for building optimization.
Retro Commissioning and Building Optimization Start With Diagnosis
Once a performance gap is visible, the next step is to determine what is driving it. Rather than assuming the solution is new equipment, owners can use real building data to identify where performance has drifted.
Diagnose Before You Replace
Poor building performance does not automatically require a major capital project. A commercial energy audit can show how and when energy is being used, while building energy modeling can evaluate how changes in occupancy, schedules, equipment, or proposed improvements may affect performance. Retro commissioning goes a step further by testing how systems currently operate and identifying issues with controls, sensors, setpoints, sequences, and system interactions.
That process can produce meaningful savings without replacing major equipment. An analysis of nearly 1,500 buildings found median primary energy savings of 5% to 14% for existing-building commissioning projects, with a median simple payback of 1.7 years.
The goal is to identify which operational changes can improve energy efficiency using the systems already in place, and where deeper engineering or capital investment is warranted.
Building Energy Performance Should Be Verified, Not Assumed
Once the right improvements are identified and implemented, the next step is verifying that they deliver the expected results in real-world operation.
Emerald's work on ILA Hyde Park is a strong example. The multifamily project used early energy modeling to establish performance expectations, followed by on-site performance verification and testing to confirm that energy systems were operating as designed. Emerald then implemented measurement and verification during the first year of occupancy to track actual energy use.
The results validated the approach. Energy modeling projected savings up to 60%, while first-year measurement and verification showed actual energy savings of 53.7% compared with a baseline code-compliant building. Rather than assuming the building would meet its modeled targets, the project measured performance after occupancy and confirmed the savings in real-world operation.
That same principle applies to existing buildings. Whether the goal is improving energy efficiency, evaluating retro-commissioning measures, or planning future building optimization, measure and verify actual performance rather than assuming expected results were achieved.
Building Performance Is Something You Manage
Building performance is not something owners can set once and expect to hold indefinitely. As operating conditions change, maintaining energy efficiency requires ongoing attention to how the building is performing and whether systems still align with current needs.
Emerald Built Environments, A Crete United Company, helps owners manage that process through energy analysis, building energy modeling, and commissioning and retro-commissioning. These services can help identify where performance has drifted, determine which improvements are worth pursuing, and verify that changes deliver the expected results.
If your building is using more energy than expected or not performing as it should, Emerald can help determine why and define the right path forward.
