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Advanced Rooftop Controls
The concept of the ARC is to provide a retrofit controls package for existing packaged systems that offers a dramatic improvement in efficiency.
& Angela Lewis
February Issue - BAS Column
when we think about building automation systems (BAS), it is in the
context of large commercial buildings, those well over 25,000 square
feet. According to the latest government data though (from the 2012
Commercial Building Energy Consumption Survey), 88% of all commercial
buildings are 25,000 square feet or less. Most of these buildings
do not have any sort of BAS, but what they do have are millions of
packaged units including rooftops and split systems.
Traditionally, packaged units have fairly basic controls; the
manufacturer provides safety and economizer controls as part of the
unit and then the contractor furnishes a wall-mounted thermostat that
controls the operation of the fan and the stages of heating and
cooling. The use of a programmable thermostat allows for the
setpoints and fan operation to be scheduled. The controls
available for these packaged units are pretty basic, and in operation,
often not very effective.
Over the last few years, there has been an effort on the part of a number of suppliers, in cooperation with the Department of Energy and various utilities, to develop and market an “Advanced Rooftop Controller” (ARC). The concept of the ARC is to provide a retrofit controls package for existing packaged systems that offers a dramatic improvement in efficiency. These systems generally consist of a new controls package along with a variable frequency drive (VFD) for control of the evaporator fan. Most ARC packages offer the following capabilities:
The concept of the
ARC is great and there are several pilot studies showing very
impressive energy savings. For this reason, we would encourage looking
carefully at these solutions for retrofit projects.
There are, however, some economic challenges with utilizing ARC solutions. The cost to purchase the ARC product and do the installation is not trivial. While there is the possibility of good savings potential, the payback works out much better for larger units (7.5 tons and above) and in areas with higher energy costs. We would also encourage looking carefully at how units are currently being used and at their condition. For example, units where the fan only operates when the unit is in heating or cooling will not produce as much savings as those where the fan runs at all times during occupancy. Finally, you should carefully weigh the costs and benefits of retrofitting controls on an older unit against replacement of that unit with a new high SEER unit. Most packaged equipment is fairly inexpensive and has an anticipated service life of around 15 years. It may not make sense to replace the units then to invest in new controls. ARC suppliers such as Transformative Wave offer good tools to allow you to estimate costs and savings and we would recommend using these as well as your own calculations.
About the Authors
Paul and Ira first
worked together on a series of ASHRAE projects
including the BACnet committee and Guideline 13 – Specifying DDC
Controls. The formation of Building Intelligence Group provided them
the ability to work together professionally providing assistance to
owners with the planning, design and development of Intelligent
Building Systems. Building Intelligence Group provides services for
clients worldwide including leading Universities, Corporations, and
Developers. More information can be found at
We also invite you to contact
us directly at Paul@buildingintelligencegroup.com or
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