Commissioning Hydronic Systems
The consistency of the process is part of commissioning’s value, but each project includes different obstacles, installation issues, and client team backgrounds. To coordinate performance in the piping, expansion tanks, pumps, and other components of popular hydronics systems, it takes a sound strategy of documentation, discussion, and testing. From owner’s requirements to post-occupancy follow-up, review how to put all the pieces together.
As a long-time commissioning provider, I can’t help but start with a hydronic system war story. About 20 years ago, we were building three identical elementary schools equipped with water source heat pumps. Commissioning was not formally part of the project, but as the district’s project engineer, I was monitoring construction activities.
A Tale From The TrenchesDuring construction, we noted less than desirable practices in terms of piping cleanliness. We notified the contracting team of our concerns and were assured that every assembly was “ragged out” and cleaning/flushing would take care of any other contaminants.
The buildings came online and one of them had a problem: all the heat pumps in one wing regularly shut down on internal safety controls. We took readings, ran trends, and investigated until we concluded that low water flow due to blockage in the pipe was the culprit. We even identified the section of pipe we thought the blockage was in. The contractor resisted, and it took weeks to convince him to drain the system and pull apart the pipe assembly in the suspected area. We found a Korean soda can in one of the elbow fittings just as we predicted (Figure 1). I’ll give you one guess as to what country the pipe was manufactured in. It was clear the contractor had neither taken the proper steps to keep the pipe clean nor ragged out the lines as promised, as this pop can was obviously in the pipe prior to delivery on-site. Needless to say, the contracting team was a bit red-faced.
The Commissioning Process as a ConstantThe commissioning process, when properly applied, is basically the same regardless of the system. Each different system does, however, have unique elements that warrant further discussion. For the purposes of this article, we will consider hydronic systems to include components responsible for moving working fluid from generation sources to terminal devices, and not boilers, chillers, or air-handling devices since each of these is a significant subject alone. This discussion includes piping, pumps, expansion tanks, air separators, makeup systems, and other appurtenances.
Proper commissioning starts with full development of the owner’s project requirements (OPR). Owner’s and design teams are typically quite good at putting together the program for the building in terms of space requirements, architectural details, and so forth. Often, subjects like maintainability, access, labeling, control sequences, system preferences, and training requirements are not fully developed. Without proper definition of these issues, subsequent work such as the specifications tends to contain whatever was used last time or the designer’s preference. The commissioning authority (CxA) leads the development of, or reviews and comments on, the OPR.
StrategiesFor hydronic systems, the OPR should include a discussion of water treatment strategies for open and closed systems. Will water treatment be done using a a pot feeder or by chemical injection and monitoring? This is an important discussion to have with the maintenance staff. They often have strong preferences because of past experiences, existing installed systems, chemical stocking, or a current relationship with an outsourced chemical treatment provider.
In cold climates, freeze protection strategies are an important discussion. Using glycol results in lower heat transfer efficiencies and adds to first and maintenance costs due to the glycol and feed system. This is another key discussion point with the maintenance staff because they will have varying methods for dealing with freeze protection. One client of ours has a rigorous cooling tower winterization process built into its scheduled PM program, and is not interested in complex cooling tower freeze protection systems.
In warm and moist climates, insulating piping and pumps from condensation is a key point. On any pipe system, insulation cladding is an important discussion that is often ignored. Will it be fiber, plastic, or metal? What is the extent of insulating components? Will there be removable components and where? It is very impressive to walk into a well laid out central plant with clean painted floors and color-coded plastic clad piping. Pride of ownership shows, and you know the systems are being well maintained. We also see insulation systems a few years old, ripped apart, and not properly re-insulated where maintenance was performed and no removable insulation components were installed.
Control system integration is another important consideration. We like to sit down with the design and maintenance team and hold a design-phase controls integration meeting. Often specifications will read, “Provide sensors and components necessary to execute the sequence of operations.” The result is a system missing many sensors critical to ongoing O&M of the system. For hydronics, all sensor locations should be specifically identified. Integration with any pump VSD should also be determined. Choices run from simple on/off/speed command to integrated building automation controllers transferring all available VSD parameters.
A Time To ReviewOnce the hydronic-specific considerations are well documented in the OPR, the remaining steps for the commissioning process fall into place, starting with review of project documents by the CxA.
The goal of the project document review is to verify that the design is consistent with the OPR, document quality is appropriate for the document phase, systems are maintainable, and systems can be commissioned. A good review exercise for hydronics is to do a flow rate sum check on terminal devices and compare to pumps and line sizing. The review examines how the system will be balanced, valve placement for zone isolation, dielectric fittings on dissimilar metals, maintainability, general pipe layout, and pipe sizing.
A common issue we find on variable-speed pumping systems is either including all (no variance in flow) or too few (or even no) three-way valves in the system (incorrect minimum flow). Placing three-way valves at the end of hydronic runs is important so that the two-way control valves along the way have instant access to hot water, improving dynamic response and control.
Installation and startup details should be fully developed at the design phase, including requirements for pressure testing, cleaning/flushing plan, water treatment, expansion tank pre-charge, system pressure setting, glycol feed start-up, pump start-up, and VSD start-up.
Once the construction phase starts, the contractor submittals are reviewed by the CxA for consistency with the project documents and OPR. There are no new hydronic-specific topics to focus on here. The review is made in the context of those key items outlined in the OPR and project documents. Any discrepancies noted are documented and submitted to the project team.
Ongoing EvaluationDuring construction, the CxA will make field observations to evaluate systems as they are being installed. The goal is to identify and correct issues as early as possible. Key areas to observe include pipe routing, correct installation of components, insulation, cleanliness, and capping of line ends. We want to be sure there are no pop cans left in the pipe.
On one project, we noted that the contractor was soldering the three-way valves in backwards. Needless to say, they were very happy this problem was found after only a few units were installed. Field observations are a prime opportunity to develop trust and appreciation between the CxA and contractor, an important element for success.
As construction and installation draw to completion, equipment start-up activities begin. The CxA will monitor and witness selected start-ups to include pressure testing, cleaning/flushing, makeup systems (including glycol feed), and pump start-up. One of the most important considerations at this point is the cleaning and flushing. We have seen many improperly cleaned systems with contaminants such as copper shavings, plastic shavings, and solder flux gobs blocking the strainers and damaging control valves.
When the contractor completes all installation and start-up activities, they will review his work and complete system readiness checklists and turn these over to the CxA, along with the completed manufacturer start-up documents. The CxA then conducts an installation verification of the commissioned systems. For hydronics, the CxA will verify pipe routing, installed components are correct, insulation is correctly installed/clad, systems are accessible, and labeling is correct. Issues noted are documented in the commissioning issues list and submitted to the project team for correction.
One useful technique during installation verification is doing what we call a “hand over hand” of the piping layout compared to the schematics. By following the pipe routes on the schematic and comparing them piece by piece to the field install, we find missing components and incorrect pipe routes. On a recent project, we found a 12 in. chiller bypass line routed to the wrong side of the loop. On another project, we found a fluid cooler three-way valve installed backwards making it impossible to cool the water source heat pump loop.
Obviously, these errors would be noted later in testing, but finding it earlier in the process saves time and improves the schedule. Of course, it would have been better if these issues had been noted during site observations, but no process is perfect, and each step has time constraints like anything else. The important thing is that the process seeks to identify and correct as many issues as possible along each step of the way.
TAB First, Then FPTTesting, adjusting, and balancing (TAB) should be verified prior to moving to functional testing. The CxA will review the TAB report to confirm compliance with the project documents. The TAB report is also spot-checked in the field by having the TAB contractor demonstrate a percentage (typically 10%) of reported values. For automatic flow devices, it is a simple matter of verifying the pressure drop is within range (typically 2 to 32 psi). For circuit setters, the differential pressure is measured across the device and used, along with the valve setting, valve size, and calculation wheel to determine flow and compare to the report. Pump curves are confirmed by checking differential pressure at operating conditions and at dead head. Issues noted are documented in the commissioning issues list and submitted to the project team for correction.
Once the contractor resolves issues with installation and TAB, functional testing can begin. The CxA will typically develop the functional tests and work with the contractor to witness and observe functional testing performed by the contractor. There is not too much hydronic-specific subject matter to focus on during functional testing, as the hydronic loop is a subset of a larger system controlled by the BAS (higher level testing). On a component level, the sensors should be checked for calibration, pump HOA switches verified, glycol pump operation tested, and glycol low-level alarm verified.
The CxA will review O&M manuals for consistency with project requirements and suitability for use by the maintenance staff. The O&M manuals are often a bit weak on useful information, only containing information about what was installed and not much on how to take care of it. Also, there is typically nothing that discusses maintenance of the system as a whole, just the components. The systems manual is a document intended to bridge that gap and is typically developed by the CxA. For hydronic systems, this manual might include valve tag schedules with shut-off locations, water treatment chemicals and procedures, sensor locations, seasonal procedures, control interactions with pumps, and overall system diagrams.
The CxA will review training agendas and verify training is completed. The training requirements should have been defined back in the OPR and transferred to the specifications, which are then used by the CxA to review the agenda. During training, key elements include demonstrating the water treatment, makeup systems, pump maintenance procedures, checking glycol levels, and pointing out the location of shut offs.
Depending on the work scope, the CxA may also perform seasonal testing and conduct a post occupancy review. Hydronics would be tested and reviewed in the context of the OPR, project design documents, and any subsequent information and issues gathered during the commissioning process.
Hydronic systems are utilized in many commercial buildings, including schools. Improperly designed and constructed hydronic systems can become huge liabilities for the owner. Improper care of the hydronic system can also lead to premature failure of boilers, chillers and coils. Properly designed, constructed, and maintained hydronic systems are energy efficient, have a long life, and provide superior temperature control. The commissioning process is an important tool to help ensure that the owner receives a properly working building that meets their operational needs and is maintainable. ES