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Be Aware Of Factors That Cause HVAC Performance To Slip Over Time
February 15, 2013 - Contact FacilitiesNet Editorial Staff »
Today's tip from Building Operating Managementcomes from David P. Callan and Kyle Hendricks of Environmental Systems Design: Be aware of factors that cause HVAC performance to slip over time.
Over time, building performance drifts out of tolerance from the original design intent. When tenant occupancy changes, equipment wears and temporary set point adjustments aren't restored, a building will perform very different operationally than it did at move-in. For these reasons, even a fairly new building that was commissioned and aligned with design intent before occupancy, may not be meeting its owner's operational expectations.
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 dictate 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 of the system are complex, the 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. Considering that building occupants are customers, and the customer is always right, this happens frequently.
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.
For more on this topic, click here.
This has been a Building Operating Management Tip of the Day. Thanks for listening.