HVAC: Why Things Go Wrong
March 14, 2013
What happens when the engineers leave and move onto the next project? Simple: Things start to "drift."
There are a few simple explanations for drift. First, the complex controls used in new installations are reliant on sensors. Sensor technology has improved in the last five years; however, these devices still require periodic recalibration and replacement. Secondly, people, both occupants and operators, are not machines. People have minds of their own and are not inclined to mold themselves into the prescribed behavior dictated in the design conditions and sequences of operation. We say that "passive buildings require active occupants" to achieve outstanding performance. But, in most commercial buildings, the opposite logic is employed. Occupants and facility managers alike want buildings to actively control themselves, so that occupants can go about their business with little or no attention paid to the building systems.
Even when the components are complex, the HVAC system control logic should not be. If facility staff, in response to a building occupant complaint or a change in tenancy, cannot quickly find a simple or temporary adjustment to the system, they will be forced to override the controls and deviate from the intended, and presumably optimal, sequence of operations.
Some of the problems that routinely occur include: permanent temperature resets that may result in simultaneous heating and cooling or poor refrigeration performance, system static pressure increases to overcome isolated air distribution issues, automatic start/stop overrides, manual locking of outside air dampers, disabling energy conservation control features, non-functioning sensors, previously unknown control device and valve failure and improper installation of components.
The good news is, there are a few things facility managers can do to reveal operational deficiencies as well as to enhance performance, to varying degrees. Measures to optimize HVAC systems include energy audits and commissioning. Indeed, from a simple audit to retro- and ongoing commissioning, reexamining the building's HVAC systems is the first step to optimizing efficiency.
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