TECHNICAL FEATURE
©ASHRAE www.ashrae.org. Used with permission from ASHRAE Journal, June 2014 at www.atkinsglobal.com. This article may not be copied
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Technical vs. Process Commissioning
Final Exam: Functional
Performance Testing
BY DAVE MCFARLANE, MEMBER ASHRAE
So far in this series on technical commissioning, we have examined commissioning functions and practices associated with the planning, design, and
construction phases of a new building project. We have outlined the owner’s
expectations in the Owner’s Project Requirements (OPR) document, and we
have reviewed and approved the Basis of Design (BOD) document, which
shows how the design meets the requirements of the OPR.
In addition, we have created a plan that outlines the
tasks everyone involved in the project must complete
to ensure the project meets its OPR. We have also monitored the construction process to ensure that all equipment and systems were properly installed, and we have
verified that all equipment and systems can be properly
started and run.
The next phase of technical commissioning—functional performance testing (FPT)—is the “final exam” a
new building must pass before it can “graduate” and be
turned over to a satisfied owner.
This is the seventh in a series of bimonthly articles that explain the technical commissioning process for
new buildings. Some of these articles’ content is based on ASHRAE Guideline 0-2005, The Commissioning
Process (published 2005) and the National Environmental Balancing Bureau (NEBB) publication Procedural Standards for Whole Building Systems Technical Commissioning for New Construction (revised April
2013). In addition, some of the information in this article series has been adapted from an unpublished
NEBB standard titled NEBB Standard Owner’s Project Requirements (OPR) Guideline (draft dated June 20,
2011); and from NEBB’s Procedural Standards for Building Enclosure Testing (March 2013).
Dave McFarlane is principal project director at Atkins in Fort Myers, Fla.
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Importance of the Issue Log
Up ’til now, at each step in the commissioning process
either the commissioning authority (CxA) or the contractor has carefully documented issues of concern in
the project issue log (which we have not discussed previously due to space limitations).
But the issue log is more than just a chronicle of problems. It also should include the date the issue was first
identified (and by whom), a description of possible solutions, who is responsible to correct the issue, and the
date the issue was corrected (and by whom).
The CxA must maintain the issue log, and a significant
part of all commissioning-related meetings should be
devoted to discussing possible resolutions, assignments,
costs, and completion dates for the items in the log. These
discussions are vital, because the CxA should resolve
TECHNICAL FEATURE issues as they come up, during any phase of the construction process, before moving to the next phase.
For example, FPT cannot begin until all equipment
and systems are verified to start up and function properly during pre-functional testing. So when key startuprelated items are entered into the issue log but not corrected, FPT will probably fail and need to be repeated
after the issues are corrected.
So pay careful attention to the issue log, and make sure
all issues are resolved before FPT begins.
Role of Functional Performance Testing
It’s important to note that ASHRAE Guideline 0-2005
requires functional performance testing. But the
Guideline does not describe the number or type of tests to
perform, nor does it define how stringent the tests must
be or even who should conduct them. This article is an
attempt to “flesh out” the Guideline in a practical manner,
and from a technical commissioning perspective.
This article also assumes that every issue in the issue
log has been corrected, all pre-functional tests have been
verified complete and successful, all building systems and
components are properly installed and functional, and all
valves and dampers open and close as required.
At this point, you may ask, “OK, if everything is well
designed, installed correctly, and fully functional—and
all known issues have been corrected—what else is there
to do?”
This is an important question, as my experience indicates that a traditional process-commissioning CxA
would give a very different answer than would a technical-commissioning CxA. I’ve found that a traditional
process-commissioning CxA would likely answer:
“You’re right. We’ve prepared the FPT forms, and the
contractors have informed us that all of their testing was
successful. We’ve verified that all of the commissioning forms have been completed, and we’ve randomly
sampled the building’s equipment and systems to verify
correct installation and proper operation.”
If our project employed traditional process commissioning, it would be complete; and we would be ready to
turn over the new building to its owner.
But when faced with the same question, a technical
commissioning CxA will likely answer:
“Our commissioning team has done a great job so far!
We’ve verified that the design satisfies the OPR. We’ve corrected every issue in the issue log, and we’ve personally
confirmed that all equipment and systems have been
properly installed and are fully functional. We’re now
ready for the project’s final exam: real-world, functional
performance testing of every building system. Our goal
is to ensure that the building itself (not just the design)
satisfies the OPR, so we must ensure that the occupants
find the internal environment to be efficient, healthy, and
comfortable. We’ve given all relevant contractors their
FPT forms, and we’ll now work with them during FPT,
observing and assisting as they perform every test.”
This “test-and-verify-everything” perspective is a big
difference between process commissioning and technical commissioning. Process commissioning permits
contractors to serve as their own SMEs, and allows them
to perform their own tests. However, technical commissioning requires the CxA to serve as the SME—and
as such the CXA either performs or supervises all functional performance testing.
Test Example: A Variable Air Volume Box
To illustrate how the FPT process works, this article uses
the example of a single variable air volume (VAV) box
serving a single space. But note: Proper technical commissioning requires that the CxA measure and verify the
correct operation of all control loops—not just a sample.
It is true that the CxA is permitted to perform limited
sampling during pre-functional testing (refer to the previous article in this series). But no sampling is allowed
during FPT. Instead, all systems and equipment must be
actively verified for real-world operation.
You may ask, “What’s wrong with sampling? It can save
time and potentially reduce overall costs.” The problem
is sampling can work well for “homogenous” systems—
such as a batch of well-mixed concrete: Every sample
taken has a high probability of having the same chemical
composition as any other sample. So if one sample meets
specifications, the rest of the batch should also meet the
specs.
But mechanical systems are never homogenous. Why?
Every system has probably been touched by multiple contracting firms and multiple technicians. Our sample VAV
box, for example, has had electrical, piping, sheet metal,
control, test-and-balance, and chemical-treatment contractors involved in its installation. Also, different employees of the same firm may build or install each of their components and systems differently. So it is likely that every
VAV box will respond differently to control inputs.
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TECHNICAL FEATURE Temperature (°F)
Temperature (°F)
Temperature (°F)
During the “final exam,” each control loop
FIGURE 1 VAV box control sequence is too tight.
of every system is checked to make sure its
80
control sequence actually does what it is
76
supposed to do. This is much more than
simply testing to see if a valve opens in
72
response to a call for heat, or a reheat valve
68
closes in response to a call for cooling. In
fact, from a technical commissioning perspective, those tests would have already
102030405060708090100110120
been performed during the operational perTime (Minutes)
formance testing (OPT) phase.
FIGURE 2 VAV box control sequence is too loose.
Instead, the FPT phase calls for hands-on
verification that every controlled device
80
performs all of the functions it is required to
76
perform, including:
•• The performance of all required steps it
72
is supposed to perform.
68
•• A controller/actuator response speed that
is appropriate for the application.
1020 3040 506070 8090100110120
•• A stable response.
Time (Minutes)
•• All events are controllable to the setpoint.
•• All adjustments take place automatically
FIGURE 3 Properly adjusted VAV box control sequence.
through the building automation system.
Figure 1 illustrates a control sequence that
80
is too tight. The figure shows a tempera76
ture that fluctuates hourly between 76°F
and 68°F (24°C to 20°C). The problem is
72
that when the temperature drifts from its
68
setpoint, the controller causes the temperature to cycle unacceptably. If a thermostat
controls this VAV box, the air flow damper
1020 3040 506070 8090100110120
Time (Minutes)
and heating control valve responses are too
rapid, which causes the cycling—and I can
practically guarantee that the occupants will complain
quickly enough—nor does the airflow increase at a rate
that it’s too hot or too cold.
sufficient to maintain the setpoint.
But when called to resolve the problem, the building
In this case, when occupants complain, the maintemaintenance staff may not be able to properly diagnose
nance staff may simply see the temperature as too high
it because the temperature is fairly close to the setpoint
or too low. So to resolve overcooling, they reduce air
much of the time. So the maintenance staff leaves, havflow; to resolve overheating, they throttle back valves.
ing done nothing—except to accuse the occupants of
But neither of those solutions is the proper fix.
being oversensitive.
Figure 3 reflects proper system calibration, adjustment,
Figure 2 illustrates a different challenge: A controller
and tuning: When the setpoint is adjusted, the VAV airflow
that does not respond quickly enough. The problem is
damper and the reheat control valve respond correctly, the
when the room temperature is below its setpoint, the
temperature reaches the control setpoint within a reasonreheat valve or air flow damper does not change quickly able time interval, and afterward the temperature is stable.
enough to meet the setpoint; and when the temperature
In this case, most occupants would feel comfortable, as
is above its setpoint, the heating valve does not close
OPRs often call for a temperature of 72°F (22°C), ±2°F (1°C).
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TECHNICAL FEATURE So for the “final exam” for our sample VAV box involves
verifying that:
•• Control sequences generate the appropriate temperature control responses;
•• Control sequences adjust the temperature to the setpoint;
•• All sequences yield stable results;
•• All sequences occur automatically through the control system;
•• The box reacts properly to a
power failure; and
•• Room occupancy/CO2 sensors
are properly set to open the air inlets
in order to maintain proper CO2 levels and room temperature.
Under the process commissioning
model, I have seen a contractor simply
set a thermostat to full heat and then
to full cool; and that was submitted as
the FPT. But this kind of test does not
measure response time or stability,
which is why such “tests” are unacceptable for technical commissioning.
Space limitations do not permit me
to describe the FPT requirements
and processes for all of the systems
and components for an entire project. Suffice it to say that the CxA
must perform functional performance tests on every control loop in
the project, which encompasses all
of a building’s major systems and
equipment, including boilers, chillers, air handlers, cooling towers,
pressurization systems, and so forth.
controllers with pneumatic differential-pressure sensors,
thermostats, and control valves.
In one of the processes I oversaw, an explosion could
result if the chemical mixture got too hot. If the temperature were too cold, the proper reaction would not
occur. In another process, the final result was a material
that could be either too brittle or too soft, depending on
chemical flow rates.
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Importance of Control Loop
Adjustments
In the 1970s, I worked as a chemical
process engineer. Part of my job was
to ensure pumps started and valves
opened and closed as required. We
used tuned control loops to maintain chemical flows, pressures, and
temperatures within tight constraints. This was before the advent
of computerized controls, so we used
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TECHNICAL FEATURE My coworkers and I became adept at checking and tuning control loops, which measured and controlled three
parameters, together known as PID:
1. The proportional (P) parameter, which measures
present error;
2.The integral (I) parameter, representing the accumulation of past errors; and
3.The derivative (D) parameter, predicting future errors.
We were required to maintain our control loops within
specific ranges; and our PID tuning resulted in quick
adjustments. We controlled temperatures, pressures,
and flow rates to the appropriate setpoints and stability requirements—thus yielding materials that met the
quality standards.
Today, computerized controls are commonplace in
HVAC systems, but the same tuning of control loops is
still essential. That’s because technical commissioning is about minimizing energy consumption as well as
improving occupant comfort.
However, the tuning of control loops is normally not
performed during traditional process commissioning.
It is common for the manufacturer’s “standard” control
loops to be left in place until there’s a complaint. I would
be a rich man if I had a dollar for every time I heard a
control technician say, “We don’t need to adjust the PID
loops; they’re preset at the factory.”
PID Loop Testing Process
It is important to ensure that a system’s control loops
are properly tuned. But because PID loop tuning is done
so infrequently, it may be necessary for the CxA to brush
up on how it’s done, in order to help the controls contractor properly test the equipment and systems they’ve
installed.
As previously noted, proper technical commissioning calls for the CxA to oversee the measurement and
verification of all control loops. This objective is accomplished by making minor system setpoint changes and
then data-logging the controlled event. For the VAV box
example, the controlled event is the space temperature,
so the CxA must ensure these five data points are logged:
•• Space temperature;
•• Damper position;
•• Reheat valve position;
•• Discharge air temperature; and
•• Airflow volume from the box.
For each loop, the tests involve subjecting the
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controller to small but definitive changes from the wall
thermostat setpoint and measuring the results. In our
VAV box example, the system is started and run at a setpoint of 72°F (22°C) until stable.
Next, the setpoint is adjusted to 75°F (24°C), which
should cause the box to begin heating, and the system’s
response is measured by readings taken every minute.
In a typical VAV box, the damper position should throttle
back, the airflow should be reduced to the heating (or
minimum) setpoint, and the reheat valve should open.
The CxA then makes sure the required data points are
logged, ensures that the temperature has adjusted to
75°F (24°C), and verifies that the system’s response time
conforms to either the OPR or to acceptable responses as
described in the Commissioning Plan.
Finally, the setpoint is lowered to 69°F (20°C), which
should cause the box to begin cooling. As before, the
system’s response is measured via readings taken every
minute. In a typical VAV box, the damper position should
open to the maximum or cooling airflow, the airflow
should increase, and the reheat valve should close. As previously, the CxA also makes sure the required data points
are logged, ensures that the temperature has adjusted to
69°F (20°C), and verifies that the response time conforms
to either OPR or Commissioning Plan standards.
If performance is unsatisfactory in any way, the CxA
collaborates with the contractor to investigate the problem, determine the cause, and adjust the control loops
as needed.
Testing all control loops is another difference between
FPT in technical and process commissioning. A typical
process commissioning approach calls for the CxA to
sample 10% to 15% of a building’s control loops and by
extrapolation conclude that all systems work properly. In
contrast, under technical commissioning the CxA verifies
that 100% of a building’s control loops work properly.
Identifying and Resolving Problems
As noted in the previous article in this series, project
contractors have the ultimate responsibility for their
own quality control. Therefore, all contractors need to
perform their own tests before the CxA either conducts
or witnesses FPT.
For our sample VAV box, multiple contractors would be
involved in a successful testing process. It’s worth noting
that each contractor should have verified their work during
pre-functional testing. However, that is an insufficient level
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TECHNICAL FEATURE of testing in the world of technical commissioning—if for
no other reason than the amount of time that often elapses
(weeks or months) between pre-functional testing and FPT.
While our sample VAV box may have passed prefunctional testing, conditions can change in the weeks or
months before FPT. For example, the box will fail FPT if
there is an insufficient flow of hot water to the reheat coil;
and there are many reasons why the flow might be reduced
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during the time that passes since pre-functional testing,
including:
•• A plugged strainer (responsibility: chemical treatment contractor);
•• A manual valve having been closed (mechanical piping contractor);
•• Improper testing and balancing (testing, adjusting,
and balancing contractor);
•• The control valve failing to open
(controls contractor); or
•• The VAV box fan failing to start
properly (electrical contractor).
In a previous article, I noted how a
project’s contract documents should
permit the owner to financially
penalize a contractor for testing
beyond a specified limit; and retests
required during FPT would fall under
the financial-penalty stipulations.
But contractors can avoid those penalties by ensuring their systems work
properly before the CxA shows up on
site to oversee the final tests.
Fully Tested = Fully Confident
Functional performance testing is the
“final exam” that verifies all of a building’s systems work in the real world.
After all project issues are resolved
and functional performance testing
is complete, the technical-commissioning CxA can look the owner in
the eye and confidently state:
“Your building works as you’ve
intended. We’ve verified that your
project requirements have been
fully satisfied. Through careful and
detailed hands-on testing, we’ve made
certain that the building functions as
designed. All known issues have been
corrected, and we’ve personally verified that 100% of the building’s equipment has passed every test.
“Congratulations! Your building has
been through a comprehensive technical commissioning process. And we
know this because we’ve overseen or
conducted all of the tests in person.”
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