Commissioning the BAS
Commissioning of building systems is a process that verifies whether the operational building that is delivered not only meets the requirements of the building owner, but also the intent of the design. Successfully demonstrating that a building’s HVAC and building automation system (BAS) is operating correctly is a key component of the process led by the commissioning authority (CxA) in the functional performance testing phase.
However, in order for testing to be successful, a number of activities must be performed with specific processes followed, verifying that all elements are in place and are working together to support a successful demonstration. During the construction phase, these activities and processes can include a review of in-progress equipment installation, verification that adequate air and water flows meet the required heating and cooling capacities, and documentation of complete equipment installation including all trades before final confirmation that the HVAC system and related controls are performing according to owner requirements and design intent.
The HVAC system, like many other building systems, is operated by a BAS that functions according to a combination of automatic and manual inputs. The BAS is responsible for controlling a number of individual elements so that they work in concert and function as a system. Modern controls systems are highly sophisticated and complex even if the intent of this complexity is internal—so that the net result to the operator is simplicity. The complexity is due to the hardware that makes up the components of the automation, the controls theory, the logic that monitors current conditions and predicts the most appropriate response, and the sequences of operation that are defined by the specifying engineer to provide functionality, comfort, and efficiency of design. The BAS is therefore a critical part of the building systems commissioning process.
The BAS affects the commissioning of many other building systems and is a system that, in itself, requires commissioning for successful operation. As noted, demonstration of successful operation is just one of the later stages of the commissioning process. To maximize the benefits of the commissioning process and have the highest positive impact on a building throughout its lifecycle, commissioning must be performed early on as well as throughout construction and design—even during the planning phases of a building project.
Fundamentally, the HVAC system is required to provide adequate temperature, humidity, filtration, air movement, and air quality to all spaces. The specific levels required of these metrics—during both occupied and unoccupied periods—should be documented in the owner’s project requirements (OPR). Documentation of these and other requirements is one of the earliest activities of the commissioning process. The mechanical equipment (boilers, chillers, fans, pumps, valves, dampers) that modulate and ensure that interior environmental conditions are met are controlled by the BAS. The BAS is required to sense the status of building operations based on the various sensors and other inputs that comprise the BAS, and produce the appropriate response based on pre-programmed logic that modulates and enables these mechanical components.
Because of the considerable amount of moving parts, the variety of conditions that the HVAC system will be subject to, and the varying ways in which the HVAC system can respond to any single condition, commissioning is a critical process that delivers a functioning controls system and, therefore, HVAC system. Commissioning will test the functionality of individual components, the operation of individual components working in tandem to achieve the desired result, and the integration of building systems, such as electrical/mechanical, emergency power and associated systems, and controls/mechanical.
Owner’s project requirements
As mentioned, one of the first steps in the commissioning process is review of the OPR. The OPR includes project goals and the owner’s measurable performance criteria. However, because the owner may not know the right questions to ask or understand specific technical requirements that will be important to the project, the owner will often require assistance from the design team or the CxA to help develop this information. Owners of multiple buildings, such as university campuses, will usually have a better collection of information on which to develop the OPR than an owner of a single building.
Examples of information in the OPR that will be used in the commissioning of the HVAC and BAS include temperature setpoints and occupancy schedules for different spaces. As mentioned, modern controls systems are highly sophisticated, and there is a wide variety of customization that may be available depending on the complexity of the buildings or the operational goals.
A BAS that requires an exceedingly high level of operator skill or time commitment from the facility staff reduces the functionality of the building system just as much as faulty equipment does. For this reason, it is critical to define the level of complexity in interfacing with the BAS that will operate the HVAC system early in the commissioning process, as well as to verify that it is appropriately matched with the facilities staff responsible for the operations of the building.
Factors to consider in this process on the user side are the experience and training of the current staff, and any planned investment in future facility staff additions or training. Using this information, the specified BAS should match the ability of the future user in terms of: navigating the graphical interface of the BAS, drilling down into individual components of the HVAC system, changing setpoints, modifying the sequences of operation, and setting up and downloading historical BAS trend data to analyze the operation.
Basis of design
The basis of design (BOD) is the design team’s response to the OPR. It is critical that the BAS have a well-developed BOD. It should present the environmental assumptions, such as climate data used to size the HVAC system, as well as summarize how the elements in the design meet the OPR. The BOD should be broken down by system for easy reference.
Specifics to include in the BOD, with regard to controls, include the specified manufacturer, the other building systems to be integrated into the BAS, capabilities for remote connectivity, communication protocol such as BACnet or LON, integration requirements, type of sensors included in the design (as well as the required accuracy), trending capability, and other criteria for selection of various control components. Requirements for remote alarming may also be specified, including the details of who should be given remote access and if connection by mobile devices is desirable.
Once the OPR and BOD have been documented and the design progresses, the CxA will perform a design review against the OPR and BOD to verify that the progression of the design is consistent with this information. Toward the end of the design phase, controls diagrams are developed and will be subject to focused review by the CxA to confirm not only that the specified components are adequate to meet the OPR and BOD, but also that the controls points necessary to successfully and efficiently operate the building are provided and integrated into the BAS.
Review will also include sequences of operation and alarm inputs. Many of the problems encountered by the design engineer, owner, and integrator that cause many of the shortcomings after installation, even though it conforms to original design intent, can be eliminated during the design process.
Specifications are critical components of the documents that will be included in the design review. The controls section of the specifications will be reviewed along with the sequences of operation for consistency with the OPR and BOD. Issues to be identified throughout the review of BAS specifications include adequate capacity for control points, memory and appropriate timeframes and frequency for storing trends, and any desired remote access interface for the owner or any consultants the owner may wish to provide access to (including the CxA). Server performance is also an area that will certainly impact the performance of the BAS. In addition, any issues regarding integration and protocol for various control components and subsystems that will be required to work in tandem will be identified.
The submittal review phase is a necessary part of any commissioning scope. The automatic temperature controls (ATC) submittal is, in many cases, reviewed at a higher level of detail than any other by the design engineer and CxA. The submittal process allows the design engineer to verify that any substitutions are at least equal to that specified. The CxA does not review with this specifically in mind, because the CxA’s scope with regard to design review is typically to conduct an assessment against the OPR and BOD. The ATC submittal is highly relevant to the CxA because many controls-related details aren’t fully developed until the submittal phase. Design specifications may provide an overview of how the system is intended to function, but it is the ATC submittal that fully develops the sequence of operation to be programmed into the BAS, and provides all of the necessary specific hardware components.
The final approved submittals are also the basis for developing the commissioning prefunctional checklists (PFC) and functional performance test (FPT) plans. Other control elements, such as control valves, will receive focused review during the submittal process from the CxA. For instance, a valve working at above rated pressure might function for a short period of time, but will fail prematurely. Too high of a pressure drop for control valves is often ignored as long as the flow is reached. Cavitation will be an issue with upper limit pressure drops across the valve.
A difficult characteristic about BAS commissioning is that this system is one of the last systems to be installed and finalized. This means that progress occurs slowly, if at all, early in construction and rapidly toward the end, when all other systems and the building as a whole is preparing for turnover. It is, therefore, very important that an elevated level of communication occurs between the controls contractor, CxA, and the entire construction team.
It is also important that the controls contractor attend and participate in regularly scheduled commissioning meetings, even in the early stages of the controls installation. This encourages communication and often leads to the identification and resolution of particular issues before they become significant.
Another key point is that between the time of original design and equipment delivery, there may be desirable enhanced features that have been incorporated into the controls components to be delivered. During these commissioning meetings is an excellent time to review such cases and determine whether to incorporate new features into the system configuration with minimal effort.
PFCs are a fundamental component of the commissioning process and its documentation. All equipment in the commissioning scope is required to have an associated PFC. The PFC verifies that the equipment has been fully installed by all trades. Once the PFC is complete, the component is ready for final verification testing. Each PFC with a controls component will have controls items on the checklists. And the BAS itself may have a dedicated PFC, documenting that head-end graphics are complete, applicable systems being controlled are fully integrated, and trends have been enabled.
Point-to-point verification is a critical task to be completed and verified. Control points include the conversion from volts, amps, or pressure measurements into other variables used by the BAS. There is, of course, opportunity for error in these conversions and formulas and they must be verified so that the actual temperature, pressure, position, etc., matches the conversion as recognized at the BAS.
Commissioning personnel should perform a sensor-to-controller-readout calibration accuracy check sampling to confirm that the correct temperature is displayed. Actual measurements should be done. A commonly observed issue is the interpretation of an analog signal to a graphical value. For instance, a variable frequency drive for a fan or pump is displaying one speed on the graphics, but the actual speed at the drive panel is different. The way in which points are bound to the user interface—whether directly or through some sort of conversion—impacts the risk of this error.
Functional performance testing
FPTs are the most demanding part of the commissioning effort. FPT plans are developed by the CxA based upon design documents, submittals, the OPR, and the BOD. FPTs are then executed by the contractor and witnessed by the CxA for acceptance. Like PFCs, FPTs will have strong controls components for most equipment and systems. The FPT generally includes a demonstration of the expected sequence of operation as specified, alarms and safeties, schedules, and setpoints for variables to be maintained such as temperature, flow, and pressure.
Final FPTs are performed through the BAS with complete graphics. It is essential that all work, including balancing of air and water systems, is complete before final FPTs are performed. The CxA also should determine a list of points to be trended. The trends should be made available before any functional performance testing occurs. Any anomalies observed should be resolved before testing.
The commissioning issues log is maintained through design, construction, acceptance, and even the post-occupancy period. Controls-related issues, which are likely identified during acceptance and post-occupancy, often include installation work not being complete, an operational sequence not occurring as expected, or graphical representations not matching what is physically occurring in the controlled system. As with other items on the commissioning issues log, items are tracked until resolution.
Operations and maintenance (O&M) raining on the BAS is a major effort that must be scheduled prior to turnover for the operator to effectively control the building. The training should include a demonstration of the system through the BAS, but also allow the operator being trained to take control and navigate the system in order to validate the capability for operation after the contractor and CxA have completed their scope. A comprehensive agenda should be developed for training, and it is not intended to be an open question and answer session.
Post-occupancy, seasonal testing and warranty
While the goal is that all issues be resolved before project turnover, often problems are identified only after a building has been occupied for a period of time, and when the seasonal environment has altered the load on the building. Post-occupancy commissioning activities include monitoring the building operation, occupant and operator interview, and analysis of short-term trend data that is available through the BAS. This analysis of trends, created during the acceptance phase, is especially useful during the first heating and cooling seasons when the HVAC system is first tested with the full force of the natural environment. Any issues that arise can typically be addressed under the system warranty, and should be back-checked prior to the commissioning end-of-warranty review.
Sensor location is critical to successful HVAC and control system operation. A sensor takes a measurement at a specific point that is intended to be representative of a larger condition. For instance, the outside air sensor provides a critical measurement that may drive a large number of subsystems within the HVAC system. If this sensor is providing a measurement that is not true, the HVAC system will perform inefficiently and inconsistently with the design intent. Reasons for inaccurate readings may include locating a sensor near a false load such as an exhaust outlet, locating a sensor in a place that receives varying amounts of sun throughout the day, or simply that the sensor has not been properly calibrated.
Other sensors that can have significant impact are the air and water differential pressure sensors in the ductwork and piping systems. These sensors are representative of the system as a whole, and meeting pressure setpoint is intended to confirm that all air and water flow capacities are met at each load. Typically, the design engineer will specify a general location for such sensors, such as two-thirds of the distance down the duct or piping system. The contractor then determines the specific location. For critical locations, it may be more desirable to specifically locate such sensors in the design documents, or hold an on-site meeting with the contractor and engineer to locate them.
Control points need to be verified to control the appropriate equipment. For example, room temperature that is specified to control the discharge air temperature of its associated air handling unit may be programmed to the wrong unit. These issues will not always show on the BAS graphics as they may be buried in the control programming, but they may have a significant effect on system functionality and energy consumption. The CxA should determine a list of points that might be susceptible to such errors and need verification.
Control loop adjustment
Tuning of control loops is a process in the controls checkout and commissioning process that may require a period of operation, monitoring, and trial and error adjustment. This tuning process should be performed prior to project turnover and not during the post-occupancy period. Any controls system generally requires input, decision, action, and feedback. For a given set of inputs and outputs, the tuning process changes the proportional, integral, derivative (PID) variables of the control loop to achieve the most effective system response. By “effective,” we mean that we want the system to react quickly to any deviation in setpoint (whether that setpoint is temperature, flow, pressure, etc.). It is also desirable for the system not to overshoot and not to hunt back and forth excessively in trying to reach the desired target.
Control components that make up such systems include sensors, valves, dampers, system fluids, and heat transfer equipment. Each of these components responds differently, at different time delays, thermal capacities, sensitivities, ranges of motion, and rates of change. These elements are what lead to the complexity in control logic, and necessitate the process of loop tuning in the commissioning of a controls system. Monitoring of such systems often includes analyzing historical trend data. Plotting this data against time will demonstrate whether there is hunting, cycling, overshooting, and other undesirable elements of system inefficiency and instability. Varying loads and seasonal environmental changes will also impact BAS response. It is therefore critical that post-occupancy verification, seasonal testing, and warranty period review should be included in the commissioning scope.
Remote access to the BAS has been noted as something that may be desirable, either to the building operator to monitor or make revisions remotely, or to the CxA or energy consultant to remotely monitor building operation in an efficient manner. Most modern control systems are capable of this feature; the system can be accessed anywhere in the world that is connected to the Internet. However, there is a level of coordination required between the contractor, owner, information technology professionals, and the party requesting access. The cooperation on the part of the owner and information technology professionals has proven critical to success here. Security issues must be coordinated for access, and it is also important to consider the level of access that is desired. For instance, the operator may wish to make changes to schedules or temperature setpoints, while a CxA or energy consultant could typically only be given the rights to observe and download historical trend data. Regardless of the specifics of who should have access at what level, this requirement should be discussed early in the design and documented in the OPR. If not planned for, this desirable aspect of a BAS that can dramatically increase the effectiveness of the facility operations team can be difficult to realize.
An important factor of an extensive control network that is often overlooked is the quality of the network communication. Network bandwidth analysis and traffic variable configurations may need special attention depending on the project configuration. Error, collision of rates, and lost data are common aspects of the communication network, and will occur in a BAS more frequently on a network with a broadband that is used at a higher percentage for other uses. A common solution implemented is to increase the speed of the network or install fiber optics. However, simply controlling the network traffic and reducing or eliminating interference is a preferable alternative. Also the activity of the BAS as it relates to the HVAC system can be adjusted. For instance, is it necessary to repeatedly transmit the same variable that is used infrequently? Is it critical to see a 0.2 F change in temperature when the precision of a sensor is 2%? The answers to these questions might not only resolve communication issues but might be crucial for the future expansion of the network.
The CxA should be familiar enough with the control system limitations to foresee wiring issues that may cause problems, such as separating power and control wiring as much as possible. It may not be acceptable for a network cable and a power line to be in the same conduit. Verifying that the proper wiring gauge is used for communication and control is critical. Also, the process should verify the maximum wiring length between an actuator and a controller, or the acceptable maximum length of a communication wire. Like many aspects of commissioning, sampling may be acceptable for project goals and should be targeted where expected issues might arise. Network traffic is certainly a larger concern with existing buildings and networks rather than new or modern systems.
One aspect of commissioning and building controls that is not fully taken into consideration is the aspect of emergency power. Often emergency power is simply thought of as the systems and equipment that are on an emergency power circuit. While this is certainly important, it is also true that the associated controls must be part of the emergency power system. For instance, in the event of a power failure, an emergency generator will activate, energizing the appropriate circuits for the applicable HVAC equipment. However, if the controls associated with that equipment are not provided with power, the equipment will either not operate according to specified requirements or perhaps not operate at all.
Building automation components are also sensitive to disruption and electrical inconsistencies. Such criteria should be considered in the specification of controls components, and any requirement for full system response in the event of a power failure for critical areas should be considered.
Finally, the systems on emergency power should be tested by actually disconnecting power at the building. This will not only allow the testing of the emergency generator and automatic transfer switch—confirming that specified system voltage is achieved—but will also confirm that the required HVAC components and applicable controls respond correctly and in the required timeframe.
Mike Eardley is associate vice president and director of commissioning services at Cannon Design where he manages project execution and staff activity on commissioning and energy consulting projects across the firm’s 15 international offices. He is president of the Building Commissioning Certification Board of the BCA (Building Commissioning Assn.) and is a 2012 40 Under 40 award winner.