On a Saturday afternoon, an empty office building should look very different on the meter than it does on a Tuesday. In many commercial buildings it does not, because schedules were overridden years ago, dampers stick open, or pumps and fans never get the stop command. HVAC load profile analysis plots demand by hour and day to expose that gap. This guide explains how to build the profile, read the patterns, quantify the waste, and turn findings into tracked fixes using a maintenance management platform instead of a one-time report.
HVAC Load Profile Analysis: Weekend and Off-Hours Waste
Compare how your building actually runs after hours with how it should run, then fix the difference.
Weekly load heat strip: expected vs found
Expected
MonTueWedThuFriSatSun
Found
MonTueWedThuFriSatSun
Occupied loadUnexplained loadSetback load
What a Load Profile Actually Shows
A load profile is a plot of electricity, chilled water, or heating demand against time, built from interval meter or building automation data. It turns a monthly bill into a daily story.
Baseload
The minimum demand the building holds when nothing should be running.
Ramp
The climb at start-up. A long or early ramp means systems start too soon.
Shoulder and tail
The slow fade after closing. A tail that never drops signals equipment left on.
Data sources to combine
- Utility interval data or submeter readings, ideally 15-minute resolution.
- BAS trends for fan status, valve position, and supply temperatures.
- Occupancy schedules, badge data, or lease hours for context.
- Weather data, so weather-driven load is not mistaken for waste.
Benchmarking Context: ENERGY STAR and Portfolio Manager
The U.S. EPA's ENERGY STAR Portfolio Manager, supported by DOE programs, gives owners a way to track energy use over time and compare buildings on a weather-normalized basis.
Benchmarking tells you which buildings use more than expected. A load profile tells you when and why. Use the first to choose where to dig, and the second to find the fix.
Using both together
- Benchmark the portfolio and flag buildings with high or rising intensity.
- Pull interval data for those buildings first.
- Build weekday, Saturday, and Sunday profiles separately.
- Investigate the largest off-hours gaps before small daytime tuning.
Measuring the Off-Hours Gap
Weekend load ratio
Average weekend load / Average occupied weekday load
Compare this ratio to your own design intent. A large drop is often expected for an empty building, but the right target depends on tenants, data rooms, and ventilation needs, so set it per building.
Ratio close to target
Schedules, setbacks, and shutdowns are working. Look for smaller refinements.
Ratio well above target
Something runs when it should not. Move to pattern diagnosis.
Companion measures
- Night baseload as a share of peak weekday load.
- Start-up time compared with first occupancy.
- Shutdown time compared with last occupancy.
- Hours of operation per week for major fans and pumps.
Reading the Pattern: Symptom to Likely Cause
| Profile pattern | Likely cause | First check |
|---|---|---|
| Flat load all weekend | Schedule overridden to continuous or on hand | Review BAS schedules and override log |
| Early morning ramp before occupancy | Start time set far too early, or no optimal start | Compare ramp time with first arrivals |
| Load stays high long after closing | Late shutdown or cleaning-hour overrides | Check end times and zone overrides |
| High night baseload | Pumps, fans, or reheat running unnecessarily | Walk the plant after hours |
| Cooling load in winter nights | Economizer faults or simultaneous heating and cooling | Inspect dampers and valve positions |
| Weekend load jumps at fixed times | Unsynchronized equipment or tenant timers | Match jump times to equipment start logs |
Turn Every After-Hours Finding Into a Tracked Work Order
Assign, schedule, and verify HVAC fixes so savings are confirmed instead of assumed.
Common Causes of Off-Hours HVAC Waste
Schedule overrides
Temporary holds that were never released, often after a special event.
Hand mode points
Equipment forced on at the controller, ignoring the BAS schedule.
Setback not applied
Setpoints stay at occupied values overnight and on weekends.
Stuck dampers and valves
Outdoor air or water flow continues when it should close.
Simultaneous heating and cooling
Reheat fights cooling, driving up load in every hour.
Tenant and zone overrides
After-hours buttons or timers extend runtime beyond need.
Many of these are maintenance problems as much as controls problems. A stuck actuator or failed sensor needs a work order and a technician, not a new setpoint.
From Data to Fix: A Six-Step Analysis Flow
1
Collect
Gather interval data, BAS trends, and schedules for at least a few typical weeks.
2
Normalize
Account for weather and holidays so comparisons are fair.
3
Profile
Plot weekday, Saturday, and Sunday curves separately.
4
Diagnose
Match patterns to causes and rank by estimated energy impact.
5
Correct
Fix schedules or equipment through assigned work orders.
6
Verify
Re-plot after two weeks to confirm the profile changed.
Worked Example: Estimating the Waste
Annual off-hours waste
Excess kW x Hours per year x Energy rate
Excess weekend load found80 kW
Weekend hours per year2,496 h
Assumed rate$0.12 per kWh
Estimated annual wasteabout $23,960
These figures are illustrative to show the method. Use your own metered load, local rates, and actual run hours, and treat the result as an estimate to verify after the fix.
Turning Findings Into Maintenance Work
Controls fixes
- Correct schedules and release stale overrides.
- Restore setback setpoints.
- Enable optimal start and stop where supported.
Equipment fixes
- Repair stuck dampers and failed actuators.
- Replace drifting sensors.
- Service leaking valves causing simultaneous heating and cooling.
How Oxmaint supports the follow-through
- Work orders assign each finding with priority, due date, and technician.
- Preventive maintenance tasks can verify schedules and actuator operation on a recurring basis.
- Asset records link repeat HVAC problems to specific equipment.
- Mobile workflows let technicians document findings during after-hours walks.
- Reports track completion so savings projects do not stall.
Off-Hours Audit Checklist
- Weekday, Saturday, and Sunday profiles plotted separately.
- Weekend load ratio calculated and compared with a target.
- All BAS overrides and hand-mode points listed.
- Start and stop times compared with real occupancy.
- Night baseload source identified.
- Weather and holidays accounted for.
- Fixes assigned as work orders with owners.
- Profile re-checked after each fix.
Frequently Asked Questions
What is an HVAC load profile?
It is a time-based plot of HVAC demand that shows when equipment runs and how hard.
How much should weekend HVAC load drop?
It depends on tenants and ventilation needs. Set a per-building target from design intent and past data.
What data do I need?
Interval meter data, BAS trends, schedules, and weather. Track the fixes with work orders.
Is off-hours waste a controls or maintenance issue?
Both. Overrides are controls issues, while stuck dampers and failed sensors need maintenance.
How do I confirm savings after a fix?
Re-plot the profile after two weeks. A demo shows how to track it.
Stop Paying to Cool and Heat an Empty Building
Find after-hours load, assign the repair, and confirm the profile changed.
