July 2011

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Two Decades of Advancements in HVAC Control
Twenty years doesn’t seem that long

Steven R Calabrese

Steven R. Calabrese
Control Engineering Corp.

Contributing Editor

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Celebrating my twenty+ years in this business, I got to thinking about all of the major advancements that I’ve witnessed in my time. The subtitle above is a lyric from a song about a man reflecting back on his life, in amazement of how quickly time got behind him. Hmmmmmm...could that man be me???

Anyway, back in the early 1990s, we got along just fine without all of the technological advances that have transpired since. Anyone have a cell phone in 1990? Maybe a pager, right? Email? Internet? Just how did we manage to get by without all of this? I sometimes wonder. So back to the purpose of this writing: industry-specific advances since the early ‘90s. Bear in mind that these are taken from my personal experience, and I’m sure there are many more that we can think of if we all put our heads together!

Damper actuators

When I first entered this industry, control dampers were driven by “foot-mounted” motors that connected to the dampers with a hodge-podge of linkage hardware (rods, ball joints, etc.). To properly set up a linkage assembly was a real challenge, and often a time-consuming one at that. Then along came the direct-mount damper actuator. What a concept! What took them so long? The actuator has a hole in it that fits over the damper control shaft, and imposes radial force to turn the shaft and operate the damper. Brilliant! Life-changing to say the least, right? Well, maybe not, but certainly the first notable advance in practical technology in my experience in this business.

Control Valves

Back in that day, I purchased a lot of globe valves. These were the control valves of choice, as there wasn’t much of an alternative to them for the ” to 6” size range. Had a big old motor on top of it. Heck, even the ” globe valve assemby weighed a ton! Then came along the “genetically altered” ball valve and the direct-mount operator. See, they took a standard manual ball valve, engineered the port to have a more linear response to the rotation of the ball, and designed a suitably sized actuator to go on top of it. And the controls world was turned upside down! Hey, I remember when they came out, and they weren’t instantly accepted as the successor to the globe valve. But look around now, and you’ll be hard-pressed to find a globe valve used in a hot or chilled water control application, on any recently constructed project, say in the last ten years or so. No, the ball valve has taken over, and righly so.

Variable Frequency Drives

Was a time, certainly going back a couple of decades, that variable frequency drives (VFDs) were more of a luxury than a necessity. I remember seeing one for the first time. It was operating a fan motor on a VAV air handling unit. Maybe the motor was 10 HP, if that. Not that big. The VFD, however, was monstrous! Stood against a wall, must’ve been the size of a vending machine. At least that’s the vision that sticks in my mind to this day. I recall as well that these dinosaurs were notoriously unreliable, generated a lot of heat, and were in frequent need of service. Nowadays, a VFD for the same sized motor is what, the size of a payphone (I know…what’s a payphone?). Seriously, VFDs are ubiquitous, and required equipment for many (most?) motor applications in HVAC. And their reliability has risen to a point of inconsequence. The VFD is truly a technological advancement to be recognized in our industry.


In a recent column I wrote about wireless and shared an early experience I had with the technology. Early meaning ten years ago, maybe less. Certainly twenty years ago there wasn’t much on the market, if any, with regard to HVAC applications. Again, I can’t even remember owning a cell phone till around the mid ‘90s or so. Even then, it was a bulky thing with a big old antenna and fair-to-poor reception. Now the technology is rampant, in our busniess as well. The applications include wireless temperature sensing, wireless CO detection systems (for enclosed parking garages), even wireless routing of network communications. And the technology continues to propogate throughout our industry. It’s interesting to watch it grow, and to anticipate or guess at what’s coming next!

CO2-based Control

Who’d of thought twenty years ago that we’d be figuring occupancy in any given space by measuring the level of carbon dioxide in the space? So it’s not the most accurate means of doing so, but perhaps the only method more accurate would be to actually count bodies! Outside air CO2 levels are typically stable at around 400 parts per million (ppm). Now, if the “prescribed” amount of ventilation (outside) air was being delivered into the occupied space, the CO2 level would stabilize at a value somewhat higher than the outside CO2 level. If the prescribed amount of ventilation air is 15 CFM per person, then the indoor CO2 level would stabilize at around 700 ppm above the outside CO2 level, or around 1,100 ppm. If you do the math, you can determine the number of people in the space by knowing the indoor CO2 level and the amount of outside air being delivered into the space. More importantly is the ability to maintain the CO2 level at 1,100 ppm, as this more or less ensures that the occupants are getting their prescribed amount of ventilation air. Not an exact science, but a handy improvement over the way we used to guarantee ventilation air twenty years ago!

Electronic BTU Monitoring & Airflow Measuring

These two forms of monitoring have come a long way in a few short years. Ask anyone about BTU monitoring ten years ago, and they would say that it’s a BAS function. Same goes for airflow measuring. Take the appropriate measurements, and perform the calculations within the BAS. Not to say that it’s no longer done that way. However new methods have come to market, in the form of “self-contained” systems for both BTU monitoring and airflow measuring. For the BTU monitoring, the system consists of a flow meter, a pair of immersion temperature sensors, and a wall-mount control panel that the assorted measuring devices are wired back to. In the case of airflow measuring, a similar system of components, and a similar result: the desired value, be it the BTU value or the CFM value, is calculated “in the box” (i.e. manufacturer’s wall-mount control panel), and the value is manifested as an analog output that in turn can feed an input at the BAS. The control panel typically has a local display, and if you require it, an option for a communications connection to it. Of course if all you need is the single value, then you don’t need the data connection option, and you could argue that you don’t need the manufactured system at all. Hey, the old-fashioned way of doing it through the BAS may be the most economical alternative even still!

contemporary Data Connection to Packaged HVAC Equipment

Speaking of data connections, and thinking about what that means and how that has evolved over the past two decades, I can say with a fair amount of certainty that the only thing capable of being connected to via a data connection twenty years ago was large packaged equipment such as VAV rooftop units and chillers. And it wasn’t a slam-dunk, either. Over the years we’ve seen it get easier and more common, as the communication standards have developed and the equipment manufacturers have adopted those standards. Nowadays it’s not uncommon to see the option for data connection on many types of packaged HVAC equipment, such as boilers, chillers, and rooftop units of all sizes, and on other types of equipment as well, including variable frequency drives, generators, intelligent lighting systems, and electrical switchgear.

Remote Access via the World Wide Web

My first experience with the internet was somewhere bewteen ten and twenty years ago. I can’t pinpoint it any more accurately than that, but I will say that it was some years following that I was actually able to access a BAS remotely via the web. Even today, when asked about remote access by a prospective recipient of a BAS that I’m quoting, the client seems surprised with my answer that, in providing remote access to their system, they’ll be able to enter in a url in their standard web browser and “surf” their system just as easily as any other website that they would visit, from any computer anywhere in the world! That, my friends, is technology!

Tip of the Month

No tip today, just an invitation to anyone wanting to add to the list and share their experiences with the advancement in technology over the past twenty years (or more!). Maybe food for thought for a future column, if I get enough replies. You can drop me a line at steve@pcs-engineering.com. I look forward to anything you have to add!


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