Tips and tricks for commissioning, balancing buildings: Mechanical and plumbing systems
Building commissioning is one of the most important (and complex) types of projects an engineer can be tasked with. Mechanical and plumbing engineering issues are covered in detail.
- Jerry Bauers, National director of commissioning, Sebesta Blomberg, Kansas City, Mo.
- Michael P. Feyler, Co-director, building solutions group, RDK Engineers, Andover, Mass.
- Robert J. Linder, PE, Senior project manager, Karges-Faulconbridge Inc., St. Paul, Minn.
- James Szel, Senior vice president, Syska Hennessy Group, New York City
- Geremy Wolff, Commissioning manager, McKinstry, Bellingham, Wash.
- Barney York, Project manager, RMF Engineering, Baltimore
CSE: What unique requirements do HVAC systems have, and how have they changed in the past 1 to 2 years?
Wolff: The complexity of the system to increase efficiency has changed the way HVAC systems operate. Commissioning providers have to know what’s driving the savings so they don’t recommend an operational enhancement that impacts the savings. The other big challenge is in regard to demand control ventilation and its impact on the size of the central equipment and the complexity of the controls system to respond to the changes in outside air levels, temperatures, and humidity.
Szel: The requirements for monitoring, alarming, data logging, and remote notification for building automation systems (BAS) and electrical power monitoring systems (EPMS) have changed significantly. The increasing trends for more points/operating parameters have caused the systems to be so large that to some extent they may become unmanageable. The BAS is typically the last system to be completed, tested, and commissioned, which prolongs the construction/commissioning schedule. The emphasis on energy conservation is constantly increasing. Different energy-conscious systems seem to be developed every day. There are different process cooling methods for energy conservation such an economizer cooling, conservation of water use (cooling tower make up), and use of air cooled condensers.
York: The sustainability and energy efficiency movements have dramatically affected HVAC system design over the past few years. Manufacturers are now designing their equipment to be more energy efficient to comply with tighter energy guidelines, and professional designers are designing more complex systems. Energy recovery units and demand controlled ventilation were cutting-edge technology a few years ago and installed only at select facilities. I would estimate today these systems and strategies are the norm. I would attribute much of the new strategies’ success to the proper implementation of commissioning, which verifies these systems are properly operating.
CSE: What systems or best practices do you suggest to test the building envelope?
Feyler: RDK works with clients that require the CxA carry the building envelope contractor. The practice of the building envelope team inserting requirements into the commissioning specification, implementing two design reviews of the architectural drawings with tracking of those comments prior to construction commencement, is one of the best practices. Basic building envelope commissioning includes window testing, infrared scans, and moisture scanning of the roof.
Szel: Common building envelope testing practices include:
- Air leakage testing
- Water penetration testing
- Thermal bridge testing.
The air-leakage testing uses a “blower door test”—for example, using the protocol of ASTM E779–10. The PassivHaus Standard has stringent air-leakage requirements and is driving this discussion with many clients. The simplest water penetration test sprays the façade using a calibrated nozzle, for example, following ASTM E1105. This helps identify possible problems for indoor environmental quality (IEQ) and durability, as well as thermal issues. To look for thermal bridges we use infrared scanning. There are also standards like ASTM C1060-11a to look at insulation in façade cavities.
Wolff: If you aren’t an expert in building enclosure, partner up with someone who is. This is something that takes expertise in planning and execution and cannot be taken lightly. If the envelope testing is done incorrectly, damage can occur.
York: The ASTM E1105 chamber testing and AAMA 501.2 handheld nozzle testing to verify watertight construction in the field should be conducted, at a minimum. Our Cx work in the United Kingdom has confirmed the European Union construction industry is ahead of the United States in envelope commissioning. EU projects are required to do full building tests where giant fans on truck beds are used to pressurize an entire building during testing. Based on the importance of the building envelope to a building’s functionality and energy efficiency, I believe we will see the U.S. construction market move in this direction as well.
CSE: What type of test-and-balance (TAB) or air balancing issues have you resolved?
Wolff: Our commissioning team includes test and balance professionals. This allows us to independently validate the reports and assist with troubleshooting of issues. Ventilation settings and demand control ventilation strategies are things we spend a lot of time on. Most systems we commission are variable volume, so setting the maximum damper position with the system at full flow doesn’t provide the proper ventilation when the unit slows down, typically during cooler weather. This results in needing multiple setpoints for minimum ventilation points that accommodate the variations in airflow. This is compounded by the fact that it’s difficult to get accurate measurements without airflow stations, which is challenging on most package equipment.
Feyler: On multiple projects, RDK has carried TAB under its commissioning umbrella to facilitate the service that is key to the commissioning process. The best case we had was a hospital that had a public health department deadline for the issuance of the TAB report. As we carried the TAB contractor, we were able to bring this service to the front of the project during the design phase. In most cases the TAB contractor is under the HVAC contractor and brought in during the last months of construction. By RDK facilitating this service, the TAB contractor works with the team by providing its flow diagrams and approach to the project. In the hospital project, we were also able to insert the level of hours required for balancing during a preconstruction meeting so that the construction team could see how their installation needed to be completed to accommodate the balancing for the health department reporting in the timeframe that was required.
York: I often find myself helping resolve static pressure setpoint balancing issues. It is not uncommon to begin functionally testing a hydronic system and find the system setpoint to be a 20 psig differential. The setpoint is not necessarily wrong, but it does usually result in the variable flow pumps operating at a higher than necessary speed for much of the time. A properly functioning system should have a setpoint somewhere between 5 and 10 psig differential depending on the balancing valve types installed. I will routinely work with the TAB contractor during functional testing to help walk it through and adjust the setpoint to optimize pump performance.
Szel: In a raised floor environment, the differential pressure between under-floor and the data hall is critical to maintaining the space temperatures and one of the most challenging to achieve. Working with the mechanical contractor, the TAB contractor, and the building management system (BMS) contractor is necessary to achieve the correct balance.