Commissioning provides reliable, consistent building operation throughout the life of the structure. It does so by carrying the operations and maintenance theme throughout the project and identifying deficiencies during construction, not during occupancy. Here are seven mechanical/electrical problems frequently found and fixed while commissioning institutional building projects.
Why Commissioning?Recent variations of this process have attempted to improve it by combining the basic elements into different approaches. These methods concentrate on team-building and more effective methods of fixing responsibility. When applied and executed properly, they provide cost savings and improvements in schedule and quality.
However, in spite of innovative construction processes, building owners continue to experience the consequences of incompletely or incorrectly designed and installed mechanical and electrical building systems. Consistent customer satisfaction is not happening with the level of quality currently attainable with traditional design documents, component supply networks, and construction methods.
Design professionals have traditionally relied on their extensive first-hand experience of building systems to express a design intent on the printed pages of drawings and specifications. Construction tradesmen have relied on extensive experience to install and start-up these systems correctly. Unfortunately, these traditional methods are now falling short. This is because advanced technology has been applied to building construction at an unparalleled rate during the last several decades. It has been brought to bear on issues of increased energy cost, more stringent life safety requirements, and the rising costs of construction labor and materials … in theory.
But the use of new technology combined with little or no increase in profit margins has created an ever-widening gap between the responsibilities of the design professional, the construction tradesman, and the equipment vendor. These entities no longer have a cushion of experience with the systems they are specifying, providing, and installing. The system may be specified correctly, supplied correctly, and installed correctly, yet it doesn’t work as expected.
The goals of commissioning are that:
- The building works right in the installed condition; and
- The building operating staff be left with the knowledge they need to ensure continuing correct operation.
In the course of commissioning the mechanical and electrical portions of building projects, institutional facility owners such as the State of Montana have uncovered a wealth of information on why things don’t work. This increased visibility may, in fact, be the biggest benefit of commissioning.
Traditional building projects are based on the elements of planning, design, bidding, and construction.
Commissioning vs. the PunchlistOne of the most frequently voiced objections to commissioning is:
“As the owner, I paid architects, engineers, and contractors to build my facility. Why should I have to pay extra to make it work right?”
The answer to this question lies in the changing character of the construction process. The need to apply new technology to building projects as early as possible is becoming an imperative. The need to build and occupy new facilities as soon as possible is also an imperative. The combination of new technology and rigid schedules has led to a situation where the construction community is no longer able to completely predict interactive system operation on the basis of plans and specifications alone. Field testing has become part of the design process.
The contractor submittal process and the engineer’s punchlist confirm equipment and systems have been supplied and installed correctly. Commissioning ensures that they work correctly.
Commissioning and O&MCommissioning is important to the O&M staff. If new, complex systems are passed on to the staff in a non-working condition, they may stay that way for the life of the facility. The number of staff has already been reduced past the breaking point. They are funded to maintain and operate the building, not finish the construction process. The only solution is to bypass and short-circuit parts of the design so that the building will be livable. If this happens, the sophistication of the technology is lost.
As the project nears completion, the engineer, contractor, and vendors all begin to draw the lines where their responsibility ends. All too often, the O&M staff is left standing in the middle with a building that doesn’t work. Commissioning steps into this situation and fills the gap between traditional responsibilities.
Vfd’s: Start-Up is the IssueAs variable-frequency drives (vfd’s) have become commonplace, problems with them are shifting from design issues to start-up issues. Engineers are becoming less concerned about the make of drive and more concerned about the factory personnel who are going to start up and program the drive. This makes the verification of correct start-up and programming a primary target of the commissioning authority (CA). At a recent project at Montana State University in Bozeman, the contractor learned this the hard way. The Agriculture Bioscience Research (Ag-Bio) building is designed with duel exhaust fans serving manifolded lab fume hoods. Each exhaust fan is isolated with its own automatic damper that closes when the fan is off. The fans are each sized to carry about three-quarters of the maximum exhaust load, and one fan will carry the load most of the time.
So far, so good. But when the fans, ductwork, and isolation dampers were installed, the dampers didn’t seal completely tight. This resulted in two things: a slight backflow through the non-operating fan and through the operating fan that slightly decreases the actual exhaust flow from the fume hoods, and some infiltration of cold air (-30°F is possible in winter) down the exhaust stack and into the exhaust ductwork. Neither of these should have been significant problems.
But what happened was this: Although the vfd’s had the ability to be programmed to compensate and correct for the backward fan rotation caused by the backflow, this programming was not included in the start-up. As a consequence, in switching from one fan to the other, the vfd was forced to start the motor while it was turning backwards, damaging the drive. Two drives had to be repaired before the supplier was called in to get expert help in diagnosing the problem.
The good news is that this information is contained in the commissioning report, and the situation was thoroughly reviewed during the commissioning debriefing meeting at the acceptance of the building. The maintenance staff, campus engineers, and project manager all discussed the situation and now know this critical portion of the vfd programming. The contractor paid for the first two incidents, and the owner doesn’t want to have to pay for any more.
Outside Air Temperature Sensor LocationIt would seem to be common sense to install the energy management and control system (EMCS) outside air sensor in a location out of the sun and away from warm air exhausts, but it doesn’t always happen that way. The verification and confirmation of a sensor location that yields an accurate outdoor air reading should be a prime commissioning target. The CA should also keep in mind that multiple buildings connected into an EMCS may each need their own outside air temperature sensor to operate on a “stand-alone” basis in the event of a network shutdown.
In the course of a retrofit at the National Guard Headquarters in Helena, the sensor was mounted on the side of the main rooftop air-handling unit (AHU). As a result, its temperature indication was accurate when the unit was not running (during unoccupied times), and was close to being right during moderate outdoor temperatures, but was thrown off by the AHU relief when the unit was running, especially in cold outdoor conditions. Also, the sensor’s eastern exposure caused high morning readings.
As a result, the system was started up and checked out correctly, but it failed to signal the hydronic boilers for heating water of sufficiently high temperature to heat the building during cold winter conditions (30°F to -30°F is typical). The eastern exposure aggravated early morning start-up problems. After the sensor was tried in alternate locations, a shaded location on the opposite site of the building away from the rooftop units was found to give consistently accurate readings.
At a small college in northern Montana, the EMCS shared the existing campus data exchange network. This should have worked fine, but the system was plagued with EMCS network panel shutdowns. The system vendor has replaced network communication cards with upgraded models but problems persist. Fortunately, each building was equipped with its own sensor, and so has reliable standalone operation even if the network goes down.
Freeze Protection Thermostats: Balance and LocationSometimes even simple applications can yield surprises. The Ag-Bio building’s main outside air intake was equipped with two large hot water coils to temper outside air for distribution throughout the building. The coils were piped in parallel and operated off a common supply manifold and common control valve. Although there were no balancing valves initially installed, the situation appeared to be “self-balancing,” and all the air went into the same plenum anyway so precise air control off each separate coil was not required.
But it wasn’t quite that simple. Each coil had been provided with its own freeze protection thermostat. When the AHUs started up in cold weather, the control valve opened and the majority of the initial water flow was through one of the coils. This was not a problem with regard to temperature control, because the flows and/or the coil exiting air temperatures averaged out eventually. But before the flows could average out, the freeze thermostat on the low-flow coil tripped and shut off the AHU. After balance valves were added to the coils, the problem appeared to go away. But only testing during the cold weather this winter will confirm the solution.
Other freeze thermostat problems include:
- Air stratification causing nuisance trips when coil damage is unlikely;
- Air stratification allowing coil damage when the freeze thermostat fails to trip;
- Freeze thermostat incorrectly located in the AHU failing to protect the coil; and
- Freeze thermostat located too far downstream in ductwork and incapable of being warmed fast enough to prevent nuisance AHU tripping.
Ductwork Plumbing and Air QualityAs concerns increase over indoor air quality (IAQ), drainage from cooling coils, humidifiers, spray dehumidifiers, outside air intakes, and evaporative coolers must get increased scrutiny from the CA. One of the most frequently encountered installation failures is the lack of sufficient slope in drain lines as installed. This particular design detail is almost never worked out in the construction drawings. In fairness to the designers, without knowing the exact equipment to be supplied, such design detail is hard to define before installation.
As a result, many drains from ductwork-mounted plumbing appliances are installed with whatever slope the installation allows. The end result is they either fail to drain the intended assembly, allow water to pool in the drain piping, or flow the liquid so slowly that the pipe is soon clogged with dirt, scale, and microbiological growth. Whether water pools in the ductwork or in the pipe, the growth of microorganisms in the hvac system is a recipe for bad IAQ.
In any climate of blowing, powdery snow, the best approach in designing outdoor air intakes is to choose the most weatherproof unit available and then assume it won’t work. This means that all of the intake air plenum ductwork needs to be sealed tight and sloped to a drain. The best method of sealing tight is soldering. Mastic duct sealant is not intended to be waterproof and will leak over time when submerged. The CA should check for the required straight length of ductwork downstream of any humidifier and also ensure that plenty of access is available for cleaning and inspecting any water sources in the ductwork. All drains from ductwork should be indirect drains with traps and, if directly connected to the sanitary sewer, must be equipped with traps and trap primers to ensure the most reliable operation.
Access and AccessoriesThe heart of the acceptance phase of commissioning is the functional performance tests (FPTs). These are the tests that certify and document the operation of systems consistent with the design intent. They also verify that the equipment is accessible for testing and has the necessary test connections. The CA’s verification of access and testing ports is an important part of the commissioning peer review as well as the functional performance testing phase itself.
Problems with access and accessories that have been identified during the commissioning process include:
- AHU cabinet doors blocked by piping and structural columns;
- AHU’s ductwork lacks straight runs required to take accurate air-flow readings or straight sections are outside the machine room in sealed spaces;
- Ceiling spaces are too crowded for effective access to equipment;
- Terminal air distribution devices (vav boxes, reheat coils, fan terminal units, etc.) are installed too high above suspended ceiling grids, making safe ladder access impossible;
- Balance valves are not installed;
- Fluid flow fittings (“Pete’s Plugs”) and pressure gauges are not installed;
- Pump flow fittings and gauges are installed upstream of suction diffusers, piped off of casing drains, or located too close to pipe bends, making head measurement inaccurate;
- Electrical disconnects and panels have been relocated during construction and are difficult to find, or are no longer within “line of sight” of the equipment they control; and
- EMCS panels lack required computer interface connections and modem phone lines for remote monitoring and fault diagnosis.
EMCS Programming — A Valuable O&M ToolWhen so programmed, the building EMCS is a diagnostic and preventive maintenance tool as well as a control system. But all too often, the building owner is left with an EMCS central control station that is not programmed to be of the most benefit to the O&M staff. The system controls temperature but has not been set up to track equipment run time, perform trend logging, or provide remote monitoring.
Programming the EMCS “front end” to track equipment run time frequently falls through the crack between the engineer’s specifications, the control contractor’s programming, and O&M staff’s knowledge of the new system. The result is that the contractor doesn’t program the system, and the O&M staff isn’t trained to program it, either. Training is generally part of the CA’s job, and coordinating programming should be part of the job, too. When the project is accepted, the EMCS should have already logged equipment run time, and the O&M staff should be ready for the first preventive maintenance work that comes up.
Trend logging and off-season FPTs go hand-in-hand. The trend log is a vital diagnostic tool for confirming stable control during the initial months of operation. It will frequently reveal the most unexpected combinations of operations. Some recorded examples include:
- Boilers firing for brief, random periods during summer cooling periods for no apparent reason;
- Control dampers and valves hunting through complete cycles as frequently as every five or ten minutes;
- Heating zones that never make setpoint temperature after unoccupied night shutdown;
- Rooftop AHUs that short cycle dangerously during unoccupied periods in response to freeze-protection programming;
- AHUs that trip off and restart intermittently due to back-rotation of the return air fan; and
- Outside air temperature sensors that track the elevation of the sun more accurately than they track the actual outside air temperature.
Finally, all EMCS systems should be equipped with modems, a phone line, and programming to allow the system to be monitored from off-site locations. It is surprising how often this is not included in construction projects. The off-site monitoring should be provided automatically by responsible control contractors. After all, it is in their best interest to be able to diagnose problems and revise programming without travelling to the site. Nonetheless, remote access is frequently overlooked and the owner and contractor are both denied a valuable tool for working bugs out of the control system.
Test That Emergency GeneratorExperience has shown that testing the emergency generator during the warm weather of the construction season is almost useless in guaranteeing a cold start during winter months. Experience has also shown that emergency generators frequently fail to generate their full rated power. This is not necessarily a fatal flaw, but it needs to be documented during commissioning to provide a benchmark for future evaluation of maintenance procedures and the eventual replacement of the unit.
Reasons why emergency generators fail to work in emergencies include:
- Lower natural gas pressure in cold weather starves gas-fired units;
- Cold winds penetrate enclosures and neutralize the effectiveness of engine heaters;
- Moisture condenses in diesel fuel, freezes,and clogs fuel filters; and
- Loss of main power shuts off the local EMCS panel (EMCS system is not on the emergency power circuit), generator engine cooling dampers fail closed, and the generator shuts down on high temperature.
Off-season generator testing should be a part of every emergency power project. If the generator is available with automatic exercising programming, so much the better. If the generator can be connected to the EMCS to trend log a few key parameters during automatic testing (such as power output and fuel pressure), that is the best yet.
ConclusionAlthough many of the items listed above might have been identified by a thorough engineer’s punchlist procedure, experience has shown that many were not. The biggest problems are the ones that seem to fall between the traditional lines of responsibility of the engineer, the contractor, the equipment vendor, and the owner. Commissioning seeks to fill this gap.
A final reminder: Commissioning does not take the place of owner involvement, but it will improve construction quality and ongoing maintenance when applied as part of a team effort managed by an owner’s representative. It adds first cost to the project, but pays it back many times over in reduced warranty calls and improved occupant productivity. ES
The Seven Biggest CSX Problems
- Variable Frequency Drive Programming
- Outside Air Temperature Sensor Location
- AHU Freeze Protection Thermostats
- Ductwork Plumbing Drains
- Maintenance Access and Testing Accessories
- EMCS O&M Programming
- Emergency Generator Testing