The standard reference for service life of building components such as HVAC systems, Plumbing, air handlers, Digital Controls, and elevators, etc. may come from many different reference books whose authors have deduced, observed, or tested a sample of similar components to produce a “mean” service life. It is unlikely that any single author has lived long enough to test each sample in service, so some assumptions need to be made when arriving at these estimates.
The “mean” is a similar number to an “average” and represents the number of years at which half of the sample will have failed. The assumption is that the failures occur on a perfect “bell curve”. A bell curve is a way to describe a symmetrical pattern where the first sample to fail and the last to fail are equal distance from the “mean”.
However, the likelihood of all components failing at the exact same time is very slim. On the other hand, the likelihood that you want to replace worn out components all at the same time is very high. Herein lies the dilemma for the building maintenance staff.
To make matters worse, there are many other factors that will impact service life of a system and its components including improper maintenance, variable duty loads, high-cycling, abuse, neglect, proper adjustment, etc.
For example; a college dormitory may have higher loads in the cooler months than in the warmer months when school is out. Commercial buildings are subject to internal heat loads from computers and machinery. Residences are subject to internal moisture from showers, dishwasher, and condensation, etc. Each condition has a different impact on the service life of the components.
Many facilities have highly capable maintenance staff. Only they can, and should, make a final determination when a component or system should be replaced. The owner is always in a better position to compare maintenance costs with replacement costs in determining when a component should be replaced.
From an engineering point of view, a major remodel of any building is best conducted simultaneously among several systems when the building is unoccupied. Workers generate disruption, dust, downtime, and operational hazards – it is always best to do as much remodeling as possible at the same time.
A major remodel is generally due in 20 years increments. 20 years coincides with mean mechanical limits of things like seals and bearings and fan blades and valves. The 20 year mark also coincides with technological advances for systems such as digital HVAC Control Systems, elevator switches and controls, lighting system or lighting technologies, etc.
In addition, 20 years also coincides with the time after which many manufacturers will no longer support older equipment with OEM spare parts or service agreements. Finally, after 20 years of service, depreciation schedules, insurance policies, and integration with new components further diminish the practical service life of the component.
For these reasons many Property Condition Assessments will recommend further analysis to mitigate immediate building needs, a sturdy maintenance plan to rebuild or replace sub-components of major systems, and a well-planned major remodel at 20 years, 40, years, 60 years, etc. We can debate service life of a HVAC compressor all day long, but the most practical way to own a building is with proactive maintenance and periodic major remodeling.