Most CFOs meet their rooftop units twice.
The first time is on a depreciation schedule, where a fleet of packaged HVAC units sits as a single line with a 15-year assumption attached to it. The second time is when a facilities manager calls to say a unit failed in July and the quote came back at $24,000 with a crane charge on top.
Between those two moments, nothing about that asset appears to be under management. The depreciation schedule implies the units are consumed by time. They are not. They are consumed by runtime.
Here is the claim this article defends. Every hour those units run while the building is empty is billed twice. Once by the utility, at a rate you can see. Once against the replacement date of a $20,000 asset, at a rate that has never appeared on a statement anywhere. Across 100 locations and 350 rooftop units, that second charge is worth roughly $620,000.
The second charge is measured
Research funded by the Department of Energy through NREL, building on work by Li and Braun in
Energy and Buildings, found that the equipment cost per unit of run time is similar to, or higher than, the electricity cost per unit of run time.
Read that again with a capital budget in front of you.
An unnecessary hour of runtime does not cost you the kilowatt-hours. It costs the kilowatt-hours plus roughly an equal amount of consumed asset life. This is not a vendor claim. It is the standard economic model the national labs use to quantify what HVAC faults cost the country, and it means every schedule left on hold is quietly moving a capital expenditure forward in time.
The 15-year number is a forecast, not a spec
Nobody stamped 15 years on the side of that unit.
ASHRAE puts packaged HVAC equipment in a median range of 15 to 25 years, drawn from survival analysis across hundreds of buildings. In the field the same equipment lands anywhere from 10 to over 20. Disciplined maintenance beats the median by five years. Reactive programs fall three to five short.
The replacement date driving your capital plan is not a property of the fleet. It is an output of how the fleet is operated, and it has a ten-year range.
Wear is bought in hours
Rooftop components are rated in operating hours and start cycles, not calendar years. Compressors, the most expensive part and the most common terminal failure, accumulate wear per hour of duty.
Geography proves it at scale. Systems in hot climates run 2,500 or more cooling hours a year against 1,000 to 1,500 in moderate ones, and that gap alone cuts three to five years off service life. You cannot change the weather in Phoenix, and nobody should try. But the hours a building runs while it is empty are the same everywhere, and those are the hours in question.
The hours nobody asked for
An analysis of 5,706 air handling units found 27% had no scheduled shutdown at all during scheduled unoccupied hours. More than a quarter ran continuously through periods when the building was, by its own schedule, empty.
Our own data matches. One multi-site retail client's thermostats were almost universally locked on hold, meaning the equipment ran on a schedule nobody had chosen. After deploying a
facility thermostat monitoring system, runtime across the portfolio fell 20%, with utility bills down 8 to 11%.
That 20% is booked as an energy result. It is also a capital result, and the capital result is the one nobody has priced.
The model
350 RTUs, 20% runtime reduction, 12% lower annual asset consumption, 15-year life becomes 17 years.
$623,000 NPV benefit
