Building Automation: Intelligent Buildings In The Age Of Pneumatic Controls?
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 sq ft.) use some form of building automation, many of these buildings still are using antiquated controllers for zone control (VAV boxes, fancoils, 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. Here are a few such sequences.
- 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
AND THEN THERE ARE THE FOLLOWING QUESTIONSDo 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 ensure 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 U.S. 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:
- Why not utilize wireless technologies? The use of
wireless communications offers the potential to upgrade VAV box
controls, fancoils, and rooftops, and to add communications at a
lower cost than 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 three years, but it could get it closer and allow owners that are on the fence to make the leap.