BTL Mark: Resolve interoperability issues & increase buyer confidence
The challenge is that simply upgrading from pneumatic to DDC will not necessarily save energy.
& Angela Lewis
November Issue - BAS Column
of our work involves energy studies and retrofits to commercial
buildings. What we find on these projects are a variety of
control systems, from the original pneumatic systems installed years
ago to the latest DDC systems that are part of an integrated
system. Because of this we are often in a position to advise
owners about upgrading both pneumatic and older DDC systems. The cost
to upgrade these systems is significant, and owners demand to know the
benefits of upgrading in terms of reduced energy expense, improved
comfort, and better tools for operations.
The challenge is that simply upgrading from pneumatic to DDC will not necessarily save energy; in fact since DDC controls are more accurate, they can actually use more energy. The solution is to use the new control sequences for systems optimization that can readily result in significant energy efficiency. A few examples of these sequences include improved scheduling, economizer control, static pressure and discharge air reset. For VAV terminals, the use of DDC allows for better occupancy control; for reheat boxes it allows the ability to utilize different minimum flow settings for heating and cooling. In addition to saving energy, networked control systems are an essential tool for better building operations, allowing operators to see what is going on in the space from any place where there is an Internet connection.
Of course upgrading the controls on a mechanical system is a lot like renovating an old house. It isn’t so hard to tell when to start making changes, but often hard to know when to stop. While there is rarely a question about replacing pneumatic logic, receiver controllers, indicators and transmitters on many projects it is tempting to leave in existing pneumatic valve and damper actuators. We generally recommend replacing pneumatic actuators with new electronic actuators. These devices have become highly reliable and provide accurate feedback for improved control. For control valves we usually will retrofit butterfly valves with new actuators but it is generally better to replace older globe valves.
One of the biggest challenges is the decision about what to do with VAV boxes. Leaving the boxes with pneumatic controls makes it impossible to properly optimize systems and have good visibility into what is going on in the space. Retrofitting is expensive though since it requires new controllers, power, network connection, new thermostats, control valve, and re-balancing at least at the box. While some boxes can readily be converted to DDC, we find some older boxes are not able to accept new DDC controls due to the use of integrated actuators, no flow sensing or the use of mechanical volume regulators. Even boxes that can readily accept a new DDC controller are often in such poor condition that they are problematic. When doing a retrofit, it is recommended to either have an allowance to repair boxes, or ideally plan to replace the boxes when upgrading the controls.
A new control system is likely to provide numerous benefits for improved operations of an existing building, but a new control system, coupled with systems that are re-designed for efficient operations can result in better comfort, operability, and energy savings that can rapidly pay for the investment.
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 www.buildingintelligencegroup.com We also invite you to contact us directly at Paul@buildingintelligencegroup.com or firstname.lastname@example.org
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