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Building Manager Green Tip

December 2011

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Identifying BAS Savings Opportunities


Building Automation Systems (BAS) are capable of managing HVAC, lighting, and other facility devices from a central controller. While older buildings are less likely to feature BAS controls, almost all new construction and many renovated facilities feature these integration systems that enable building managers to optimize the environmental performance of their facility through occupancy, schedule, and related setbacks that ensure no more energy is being used than required.

This month's Green Building Tip examines five common improvements that can be applied to many BAS control programs. While the potential savings from automation systems are large, they rely on complex programming and algorithms to function properly.  Over time the BAS programming may not reflect the most efficient means of running a building.    

1 - Outdated Occupancy Schedules

Buildings, and more importantly the occupants within them, have a tendency to change over time.  Nighttime and weekend setbacks programmed when the building originally opened may no longer reflect the reality of how the facility is used today.  

TIP: Work with building occupants to determine realistic schedules and adjust these setbacks to ensure occupancy savings are maximized.

2 - Unrealistic VFD Setpoints

In air handling units, Variable Frequency Drives (VFDs) modulate the speed at which fan motors operate, and they are often set up to respond to changes in static pressure in the ducts that they are supplying.  If the static pressure setpoints are too high, the VFD will never reduce power to the motor, which wastes electricity and potentially causes comfort problems by oversupplying air to spaces that do not need it.  

TIP: Check to see that the VFD is modulating properly by trending the operation of the drive.  If it is consistently operating at full capacity, consider changing the pressure setpoint to a lower range.

3 - FCU Valves/Fans not Integrated

Fan coil units (FCUs) are heating and cooling devices that use a fan to push air over a coil that is filled with either hot or cold water.  If the fan is on but water is not flowing through the coil, energy is being consumed without providing heating or cooling to the space being served.  

TIP: Check to see if fan and valve operations are tied together. More detailed information about this and related FCU savings opportunities can be found in our October 2011 Green Building Tip.

4 - Occupant Overrides

Local devices such as thermostats, light switches, and fan speed knobs are often provided to allow occupants some measure of control over the conditions in the space, though in some instances  these overrides may result in inefficient operation.  Using a thermostat as an example, occupants may be provided with a range of temperatures they can adjust (e.g. ±2 degrees from the BAS setpoint) to suit their individual needs, but allowing full control over temperature settings may result in undesirable consumption patterns.

TIP: Examine the extent to which occupants are provided with the ability to deviate from BAS setpoints, and ensure that these are reasonable. Nighttime overrides should be limited to 1-2 hours to ensure overrides are not left in place once occupants leave.

5 - Operator Overrides

While BAS controls are generally designed to follow the sequence of operations set forth by the BAS program algorithms, it is possible to override this programming for specific equipment.  Such overrides are often enabled as a short term problem, but if left in place they may lead to larger problems from inefficient integration of building systems.

TIP: Review the list of operator overrides once a month, examining whether these setpoints still reflect the most efficient means of operating the building.

Green Building Services provides consulting services to ensure that the design, construction and operation of Harvard's built environment has minimal environmental and human health impacts, maximizes occupant comfort and generates an awareness of sustainable design and building operations. To learn more about our work and services, visit http://green.harvard.edu/gbs.