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Intelligent Buildings in the Age of Pneumatic Control?
How intelligent can a building be if most of the temperature control is provided by antiquated controls?
Paul Ehrlich & Ira Goldschmidt
The title of this column may seem like an oxymoron, but, upon further thought, it appears to be the harsh reality for the majority of our buildings. The fact is that pneumatic and electro-mechanical controls are still used in a significant portion of control in commercial buildings.
While the majority of large commercial buildings (i.e., over 100,000 s.f.) use some form of building automation, many of these buildings still are using antiquated controllers for zone control (i.e., VAV boxes, fan coils, etc.) and rooftop units. While no exact figures are available we find that a large percentage, if not a majority, of existing buildings appear to have at least some obsolete controls still in place.
The question then is how intelligent can a building be if most of the temperature control is provided by antiquated controls (e.g., a building with all pneumatic VAV box controls)? While the answer to this is open to opinion there is no question that it restricts the building’s ability to operate as if it were fully automated. In particular, consider that many of the optimized sequences that can be used in fully-automated buildings today are either tied to or more readily implemented through the use of networked DDC zone control including:
Duct Static Pressure Reset Based on VAV Box Demand
Supply Air Temperature Reset Based on the amount of Zone Heating vs. Cooling Demand
Reset of Chilled Water Based on Cooling Load (optimally determined by, say, the AHU’s chilled water valve reaction to above the supply air temperature reset)
Occupied/Unoccupied Control by Zone
Intermittent Occupied Control Based on Occupancy Sensing
Demand response and smart grid compliance
Then there are the following questions:
Do Pneumatic VAV Box Controls Really Work? – Proper testing and setup of a large number of VAV box volume regulators is a time-consuming effort that is probably not performed at intervals necessary to assure operators that the question to this answer is “yes”. However, without this maintenance there is no ready way to know otherwise especially when the VAV box has a reheat coil that could be using simultaneous heating and cooling to mask the improper operation.
How Does a Building Engineer Really Know If Acceptable Space Temperatures Are Being Maintained at all Times? I don’t think we need to provide an answer to this question….
So if the use of obsolete zone controls is the
figurative “last mile” in a building’s automation challenge when will the
conversion of all US buildings to full DDC finally be completed? While there is
no definitive answer to this question the evidence indicates that it could take
many more years. A recent DOE statistic indicated that the average life of a
commercial U.S. building is 73 years. Therefore, unless the owners of existing
buildings have a plan for upgrading the controls they could be in place for
decades to come or at least until a major renovation of the building occurs.
So why are pneumatic VAV box controls, for example, not being replaced in this age of automation and energy efficiency? Simply put, the typical payback estimated for the work involved is in the five to ten year range - not a compelling economic argument for most bottom-line oriented building owners. There are, however, a couple of ways that may help to turn this predicament around:
Wireless technologies. The use of wireless communications offers the potential to upgrade VAV box controls, fan coils and rooftops and to add communications at a lower cost then hardwired controls.
Why not incorporate the energy savings from the above list of optimum control strategies in the payback calculation. This may not bring the payback of a DDC upgrade to within 3 years, but it could get it closer and allow owners that are on the fence to make the leap.
Stand by while we ponder both of these possibilities – we hope to get back to you soon with some real project data.
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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