“Performance drift is inevitable in large, complex commercial retail estates,” Harpham said. “As systems age and operating conditions evolve, they gradually move away from the standard defined during the commissioning process.” 

Component wear, sensor inaccuracies, fluctuating refrigerant charge, and changing operating conditions all contribute. Harpham said another factor is the accumulation of well-intentioned adjustments made to address comfort complaints and alarms. 

“While this may fix the immediate issue, it often masks the root cause, such as a failing door seal, blocked evaporator, or degraded refrigerant charge,” he said. 

Small Changes Add Up 

Contractors say performance drift begins much earlier than many operators realize. Property owners and business operators may assume things are humming along, but the equipment may tell another story. 

Brian Garry, field supervisor at Donnelly Mechanical in Queens, New York, said performance drift starts almost immediately after startup and is accelerated by environmental conditions, equipment cleanliness, and everyday operating changes. 

“Performance drift is extremely common with all HVAC equipment and begins immediately following initial startup," Garry said. “[Its] rate and extremities vary based on environmental factors such as poor air and water quality, construction or demolition projects, and even natural factors such as pollen.” 

Garry said aggressive thermostat adjustments made in search of immediate comfort often create unnecessary wear when left in place. 

Leonard Stupak, CEO of Los Angeles-based LA Construction, Heating and Air, said many business owners assume equipment is operating properly simply because it is still running. 

“Most business owners think that their system is fine as long as it is running and that nothing needs to be done,” Stupak said. “But dirt, debris, and other factors are causing their systems to perform worse and worse over time.” 

He said clogged blower assemblies, dirty evaporator coils, neglected filters, and debris-packed condenser coils are among the most common causes. 

Stupak recalled a retail customer at the Northridge Fashion Center who suffered from poor airflow. A previous contractor installed inline duct fans to push air farther through the ductwork, but the problem persisted. 

The actual cause was a severely fouled indoor coil and an old filter lodged inside the coil, restricting airflow. Once the coil was cleaned, the supplemental fans were no longer needed. 

Problems Often Hide in Plain Sight 

Unlike catastrophic failures, performance drift develops gradually and often without triggering alarms. 

Harpham said many operators first notice the problem through rising energy bills, increasing fault frequency, or growing numbers of reactive maintenance calls. In supermarkets, where refrigeration can account for 40% to 50% of total energy consumption, even small efficiency losses can translate into high costs. 

“Performance drift rarely reveals itself through a single fault or failure event,” Harpham said. “By its nature, it develops gradually and often goes unnoticed until operating costs become material.” 

Because systems continue running, underlying issues can remain hidden for months or years. Recurring temperature complaints, nuisance alarms, or repeated service calls for the same issue often indicate equipment has drifted away from its original operating conditions rather than suffered a discrete failure. 

Garry said owners often don't recognize the problem until utility bills begin climbing. 

“This is usually only discovered when you are making your monthly payment to your energy provider,” he said. 

He added that many customers assume a system is operating normally because it is still producing cooling or heating, even though pressures, amperage readings, and temperatures may indicate it is working much harder than necessary. 

Stupak said efficiency losses of 10% to 40% are not uncommon when maintenance issues accumulate. He cited one commercial customer whose filters were changed twice annually, even though they became dirty much sooner. Switching to quarterly filter replacements restored airflow and improved performance. 

Dirty filters restrict airflow, forcing blowers and compressors to work harder, while dirty indoor and outdoor coils reduce heat transfer and can eventually lead to premature component failures. 

“The system may still be running, but it’s not running the way it was designed to,” Stupak said. 

That, Harpham said, is what makes performance drift so difficult to identify. 

By the time increased energy consumption and recurring service calls become obvious, systems may be significantly out of alignment with their original design parameters, requiring more extensive repairs to restore performance. 

The Trap of Traditional Maintenance

Traditional preventive maintenance programs focus on scheduled inspections and service intervals. Harpham said those approaches often miss subtle changes that occur between visits.  

“Traditional maintenance programs can miss these changes because they are designed around scheduled tasks and fault response rather than ongoing performance optimization,” he said. 

Continuous commissioning takes a different approach, comparing actual operation against expected performance and identifying deviations early. Increasingly, that process incorporates IoT connectivity and artificial intelligence, he explained. 

“The most effective approaches combine operational data with AI models trained on refrigeration and HVAC behavior,” Harpham said. 

Garry said continuous commissioning gives contractors visibility that scheduled maintenance alone cannot provide. 

“Continuous commissioning allows for immediate discovery in real time,” he said. “Otherwise, these variables would only be discovered by the technician during a scheduled site visit.” 

Root Causes, Not Symptoms 

Traditional maintenance programs often address symptoms rather than underlying causes. 

Harpham pointed to a North American retailer with 1,800 stores that used continuous commissioning and automated health checks to improve reliability and reduce energy consumption. 

Stupak cited a multifamily project completed through the Los Angeles Department of Water and Power Tune-Up Program. After filters were replaced, condenser coils cleaned, and refrigerant charges adjusted across more than 600 units, the property manager reported approximately 60% fewer summertime service calls. 

For all three experts, the lesson is the same: Solve the root cause rather than repeatedly treating symptoms. 

By identifying performance drift early, contractors can help customers reduce energy costs, improve reliability, extend equipment life, and avoid unnecessary service calls long before equipment failure occurs. 

“The system may still be running, but it’s not running the way it was designed to,” Stupak said.