When we do an energy audit on a commercial building, scheduling problems are almost always on the list. Scheduling is the lowest-cost energy savings strategy available because it requires no new hardware and no capital investment. It is purely a programming change. Yet the same mistakes show up in building after building, and they cost real money year after year. Here are the five we find most often.
1. No Holiday Schedule
Your building automation system has a holiday schedule feature. There is a very high probability it has never been used.
A building running full occupied operation on Christmas Day, New Year's Day, Thanksgiving, and the other major holidays is wasting a meaningful amount of energy every year. A typical commercial building in cooling season might spend $300-600 per day on HVAC energy during normal operation. Running that same profile on a day when the building has five people in it instead of five hundred is straightforward waste.
The fix is five minutes of programming. Every major BAS platform has a holiday calendar feature that overrides the normal occupied schedule with an unoccupied or reduced-occupancy schedule on specified dates. Set it once a year, and it runs automatically. Some platforms allow you to set recurring holidays (the last Thursday in November, for example) so you do not have to update the calendar manually every year.
2. Start Times Set Too Early
We pull up a building's schedule and find that the HVAC system starts at 4:00 AM for a building that opens at 8:00 AM. When we ask why, the answer is almost always some version of "we wanted to make sure it was comfortable when people arrived." That is a reasonable goal with an unreasonable implementation.
A four-hour head start made sense in the era of pneumatic controls with slow-responding systems. A modern BAS with optimal start capability (which I will cover in a moment) can calculate the latest possible start time to reach setpoint by occupancy time, accounting for outdoor temperature, space temperature, and the building's thermal mass. That calculation typically produces a start time one to two hours before occupancy in mild weather and two to three hours in extreme conditions. Four hours is almost always too early.
The waste compounds because morning hours in Louisiana are often the most energy-intensive part of the day: the building is near its overnight setpoint (higher than occupied setpoint in cooling season), the sun is rising, and the system is pulling against maximum temperature differential. Running this period longer than necessary has a meaningful cost.
3. Optimal Start Enabled But Never Configured
This one is particularly frustrating because the feature exists and someone paid for it but it is sitting idle.
Optimal start is a standard feature on Niagara N4, most Siemens and Johnson Controls platforms, and many standalone thermostats in the commercial range. It works by learning how long your building takes to reach setpoint under various outdoor temperature conditions and adjusting the start time accordingly. The algorithm improves over time as it accumulates data.
Enabling optimal start requires a few configuration steps: enabling the feature in the controller, setting the earliest allowable start time, setting the occupancy time it is optimizing toward, and in some implementations, connecting it to the outdoor air temperature input. None of this is complex. It takes less than an hour per air handling system. But it is also the kind of task that gets deferred during commissioning when schedules get tight, and then never comes back around.
4. Exhaust Fans Running 24 Hours a Day
Exhaust fans in restrooms, mechanical rooms, and kitchen areas are some of the most commonly overlooked items in schedule management. They are often wired to a constant-power circuit, controlled by nothing, running every hour of every day regardless of occupancy.
An exhaust fan motor pulling 500 watts running 8,760 hours per year consumes approximately 4,380 kilowatt-hours annually. At Louisiana commercial electric rates in the range of $0.09-0.11 per kilowatt-hour, that is $390-480 per year for a single small fan motor. Multiply by the number of exhaust fans in a typical commercial building (often 10-20 or more), and the cumulative waste is significant.
Connecting exhaust fans to the BAS schedule, or even to simple time clocks tied to the occupied schedule, is a low-cost modification. In most cases, restroom and general exhaust fans need only run during occupied hours, with perhaps a brief purge cycle before the building opens in the morning.
5. Weekend Schedule Identical to Weekday
A lot of commercial buildings have identical HVAC schedules seven days a week. The building opens at 7:00 AM and the system starts at 5:00 AM, Monday through Sunday, regardless of the fact that Saturday occupancy might be 20% of weekday occupancy and Sunday occupancy is near zero.
The appropriate approach depends on how the building is actually used on weekends. For a medical office that closes on weekends, the weekend schedule should match the after-hours profile: setpoint setback, minimum ventilation, no occupied cooling or heating. For a retail building with weekend hours, the schedule should reflect actual operating hours rather than defaulting to the weekday template.
Reviewing and correcting weekend schedules is part of any scheduling audit we do. The question we ask is simple: does the schedule reflect how the building is actually used, or does it reflect a default template that nobody has ever adjusted? In most buildings, the honest answer is the latter.
The combined impact of correcting all five of these scheduling issues in a typical commercial building can be a 15-25% reduction in HVAC energy consumption, with no capital cost. That is the kind of return that pays for a scheduling audit in the first month.