Why you need commissioning in today's buildings
I sometimes get asked the following question from potential clients: “Why do we need a commissioning agent when I have a good Design Team and good Contractors on my project?” This is a valid question and one worth addressing here.
First off, having a good Design Team and good Contractors on a project is great! And the Owner’s careful selection of those teams is of utmost importance towards having a successful project! Unfortunately, due to the increasing complexity of building systems, it is no longer enough to have great Contractors and Design Teams. Setting aside, for now, any code, LEED, or other requirements mandating that a project is commissioned I will present my case to the answer to the question at hand: why you should include commissioning into your project, even if you have the best Design Team and best Contractors.
The reason that a good Design Team and Contractors aren’t enough to come out of a construction project with a well-functioning building lies in the concept of emergent behavior as a result of how much more complex mechanical systems are now than they were 40 years ago. Emergent behavior is defined as “behavior of a system that does not depend on its individual parts but on their relationships to one another.” In other words an emergent behavior or emergent property is a condition that appears when a number of simple parts or entities operate in an environment, forming more complex behaviors as a whole. The system is more than the sum of its parts. As this relates to buildings and building systems, it can be thought of as the expected, or unexpected, behaviors that stem from the interactions between parts or components of a system.
With that definition in mind, let’s look at how buildings have changed over time, then I’ll come back to emergent behavior.
Facilities built 20+ years ago:
Buildings 20 or 30 years old or older were much less complex in nature than buildings designed and built today.
Their HVAC systems included components such as:
Large boilers that produced steam or hot water
Constant volume air handling units, maybe with multiple zones
Pneumatic control valves and t-states controlling space temperatures via radiators which later gave rise to line-voltage thermostats and electric actuators
Heating and cooling units that were typically two separate systems which had to be manually switched from heating to cooling mode
Constant volume pumps
Commissioning as we know it today was not necessary on systems of this level of complexity because each system was much more stand-alone and had fewer interactions with other mechanical systems compared to today. Contractors could much more easily check the operation of each system individually due to the lack of interaction. For example, either heat was being provided, or it wasn’t.
Facilities built today:
Fast forward to commercial buildings erected or remodeled in the past 20 years:
Their HVAC systems include components such as:
Building Automation System
Electric valve/damper actuators (modulating and 2-position)
Digital sensors (thousands! occupancy sensors, temperature sensors, pressure sensors, daylight sensors, AFMS, etc.)
BACNET/MODBUS integration
Variable Frequency Drives (VFDs)
Individual zone heating/cooling terminal units such as VAV boxes, fan coil units, etc.
Smaller boilers working in unison
Numerous flavors of heating/cooling equipment design and combinations (i.e., geothermal, heat recovery, variable refrigerant, variable volume air handling units, etc.)
There are literally hundreds of thousands of these components in a modern building. Within these many parts that make up the building system are numerous interactions: such as between heating and cooling, sensors and VFD’s, occupancy sensors and HVAC, building static and relief dampers or exhaust fans, etc. Buildings are more complex every year as more and more systems inter-connect (i.e., internet of things) and new technologies emerge. All of this new technology has the potential to keep occupants comfortable and save large amounts of energy (and money!)...IF they are all set up and functioning correctly.
With this additional complexity, there is more and more interaction between systems; we are finding that one cannot simply look at each component individually, you need to look at the system as a whole. That is where the concept of commissioning process comes from.
Today’s Building System
A building system is comprised of many sub-systems, and each sub-system consists of parts. Individual parts include building envelope and structural pieces such as steel columns, beams, windows, air/water barrier, and insulation. Mechanical HVAC pieces such as valves, actuators, pumps, VAV boxes, air handling units, boilers, heat exchangers, sensors, and so on. Electrical pieces such as panels, breakers, emergency power generators, occupancy sensors, lighting fixtures, and such.
An example of this concept would be as follows:
Looking at this diagram, you can see how the individual parts come together and how they might influence other parts within the system.
Emergent Behavior
Ok, back to how emergent behavior comes into play with modern buildings. As I already indicated, we are seeing thousands of individual parts within a building, which make up numerous sub-systems. These then come together into the main system which is your building. With all these components, we see emergent behavior, both good and bad, as well as feedback loops which can be positive or negative.
Examples that we have seen of this are things like:
Building envelope (air/water barrier system) is non-continuous. Couple this with a building that is under a negative state because the outside air and exhaust systems are not functioning together properly. This negative condition, coupled with a non-continuous air/water barrier in the building envelope is drawing in excessive moisture from the outside during the summer or cold drafts during the winter. This excess moisture during the summer makes its way to the air conditioning systems making them work harder to handle the humidity levels and produces more condensate from the cooling coils. During the winter, with cold drafts, the heating system will have to work harder to keep up, or occupants will get cold when sitting next to exterior walls and run space heaters under their desks which will work against the main heating systems.
A heating water loop differential pressure sensor which is 2/3rds of the way in the piping system is installed right next to a bypass valve. This pressure sensor is supposed to control pump speeds via the VFD. However, the sequence of operations also has the bypass valve referencing another sensor in the system, say near a heat recovery chiller. The pump speed changes affect the differential pressure sensor at the heat recovery chiller, which then causes the bypass valve to open. When this happens, it immediately causes a seen “pressure drop” at the 2/3 differential pressure sensor, so it speeds up the pumps and the cycle continues.
A modulating NG boiler is referencing the factory provided temperature sensor. This sensor was installed in the primary loop. The building secondary heating water loop temperature steadily drops as heat is pulled out of the system. However, the boilers never fire to maintain the setpoint in the secondary loop because it is looking at the sensor installed in the primary water header directly over the boilers. That water temperature is maintaining because nothing is pulling heat out of that system.
At another site, a NG, modulating boiler system kept tripping out on high limits. Upon investigation, we found that the system minimum flow bypass was installed in close proximity to the pump differential pressure sensor. Again, pump speeds were affected by the opening and closing of the bypass leg, this affected flow to the boilers causing them to short-cycle flow via the boiler feed pumps, we also found that the boiler rep had the boiler controller referencing the wrong temperature sensor for maintaining setpoint, made them trip out on high limits.
As you can see in the examples above, when you look at individual parts or components, they function “properly” per the design intent. That is, the differential pressure sensors worked, the pump VFD’s modulated, the bypass valves opened/closed, the boilers fired, etc. When you look at the system as a whole, when these individual parts start to interact with each other, you then begin to see how one component can influence another component and cause unwanted behavior. This is an emergent property or behavior.
Commissioning Addresses Emergent Phenomena
Tying all this back to the original question at hand, why do we need commissioning when we have good designers and/or Contractors? Note: before I continue with what I have to say, I want to clarify something. I do not want to understate or take anything away from the hard work and knowledge of Design Professionals and Contractors, that is NOT my intent. In each profession related to getting a facility designed, built, and running your team members are also dealing with more complexity due to advances in technology, and in my experience are doing really well keeping up with the changes in their trades! So what I am saying here is that advances in BAS involving all components of the building leads to countless issues that really don’t fall under one trade or another, but are a manifestation of the interaction AMONG the systems installed.
When you have a good Design Team, who did proper coordination amongst trades during the design, had an appropriate amount of detail and clarification in the construction documents, and had carefully thought-out and detailed sequence of operations, then the Contractors will have higher quality documents to build against. When a project gets into the tail-end of construction and into the acceptance and testing phases is when the most critical inspections and testing occur. Typically, the Design Professional has a very limited involvement at this point of the project. The Design Team puts the bulk of their hours into the design of the project and will do limited construction administration work, mainly dealing with answering RFI’s, issuing PR’s, doing above ceiling punch lists, etc. They certainly do not fully test their systems.
When you have a solid Construction Team, who have the experience in the equipment and systems which they are installing, have adequate labor forces, coordinate amongst the other trades, ask questions of the Design Team, etc., then the Design Team and Owner have a higher probability that the building will function as intended. Once members of the Construction Team install their components, they are supposed to check that they work.
Where things start to break down is during the testing and operations phase of the project. You see, the quality of the Design Team sets the stage during the early parts of a project’s life and only gets you a portion of the way along the road to a fully functional building. The Contractors are highly trained in their individual fields, whether it be mechanical, electrical, general, controls, etc., however, they may not be as skilled in the intricacies of other trades and how that could affect their components. These individual trades will test their components at the end of the project to make sure they work, i.e., boilers fire, pumps operate and are balanced to design flow, air handling units meet set point for air and water flows, pressure sensors give a reading, doors and windows are installed, insulation is installed, permanent power is in place, etc. That’s great, but as we’ve already discussed, the system as a whole is greater than the sum of its parts. The sub-systems and building as a whole need to be tested. It is in these interactions, where a building either functions properly or it doesn’t. The problem is that there really isn’t one single Contractor or group who is responsible for the interactions between systems, let alone have the knowledge and experience to test various systems. Individual trades are not paid to look at other trades work, nor do they have the knowledge to do so. In the examples of things we have seen listed above, when the individual Contractors each inspected their parts of the system while trying to troubleshoot, each of their pieces “worked” so they deferred the problem onto someone else.
This is why commissioning is SO important. It is the role of the Commissioning Firm to check, test, and ensure that each individual part, sub-system, and system-as-a-whole works per the design intent to meet the Owners needs and to document this process. The Commissioning Agent has the unique experience and knowledge to look at a building through different lenses. We start at individual parts, then move onto sub-systems, then look at the building as a whole to make sure everything is working properly and efficiently. Taking this one step further, this is why technical commissioning is so important! You need a Commissioning Firm who is actively involved in your project, is on-site during all checks and testing and has the hands-on experience to be able to vet out and identify issues that can hide within component interactions.
So when asked why a building needs to be commissioned, that is my answer.
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