Retrocommissioning

The energy use index (EUI), a basic measure of a building’s energy performance, is the amount of energy in Btu consumed annually per square foot of conditioned space. It is calculated by tabulating all the energy consumed annually in a building and dividing that Btu measurement by the square footage of floor area that is heated, cooled, or both. Good candidates for RCx include buildings that have an unaccountably high EUI, an unexplained increase in energy consumption, or persistent occupant-comfort complaints. The US Environmental Protection Agency (EPA) publishes energy performance target ratings (PDF), a table of nationally averaged EUI values by building type (updated in 2014). This table provides a quick initial assessment by which you can benchmark a building’s energy performance. A more comprehensive approach is to use the EPA’s free online energy-performance rating tool, Portfolio Manager, which takes in to account source energy and the impact of weather variations as well as changes in the key physical and operating characteristics of each building. High utility costs and the availability of utility incentives, an experienced in-house staff, and high-quality building documentation are additional factors that can contribute to a successful and cost-effective RCx project.

Buildings with a majority of older equipment that will need to be replaced in two or three years are not good candidates for RCx—it’s often more cost-effective to allocate RCx project funds to the future purchase of more-efficient new equipment. Buildings with major design problems also make poor RCx candidates because efficiency improvements are unlikely to ever compensate for a serious system-design flaw.

The RCx process typically begins with selecting a commissioning provider who will guide the project through the planning, investigation, implementation, and hand-off phases. A qualified provider will have excellent communication skills, be adept at cultivating a team approach to problem-solving, and be skilled at providing operations and maintenance (O&M) training. The provider will also need to have significant experience in building energy systems design, operations, and troubleshooting and to be well-versed in diagnostic testing, monitoring, and analysis techniques.

Certification of commissioning providers is currently offered by five independent organizations, each with its own unique standards, which can be viewed in detail on the company websites (see sidebar). Building owners may or may not consider certification to be an important qualification for their commissioning provider. As or more important are the provider’s technical knowledge, relevant experience, and communication skills. Some building owners with significant in-house expertise—at the level of an energy manager or energy engineer—may not choose to involve a commissioning provider at the beginning of the project but will bring one in later for specific diagnostic, monitoring, and analysis tasks. Once the commissioning provider has been selected, they will work closely with the building staff and follow a four-phase process.

Planning phase. In the planning phase, the building walk-through is an intensive information-gathering session that gives the commissioning provider the opportunity to talk with the operations staff, become familiar with the major energy-consuming systems, and begin to identify potential energy-saving measures (see sidebar). Prior to the walk-through, the building’s operations staff should prepare a prioritized list of existing problems and necessary improvements, along with insights on current building conditions. The owner should provide utility bills for the past three years, preventive maintenance records, and any active service contracts. All this information gives the commissioning provider an in-depth understanding of the building’s energy usage and O&M practices so that they can develop an accurate and realistic RCx plan that defines the project objectives, scope, schedule of procedures, and documentation requirements.

Investigation phase. The goals of the investigation phase are to understand how the building systems are working and to identify and prioritize energy-saving opportunities and system improvements. Start by assembling critical staff, both employees and outside contractors; their knowledge of the building and its operations will be essential to conducting a successful RCx effort. A thorough review of building documentation and current O&M practices should then be undertaken by the commissioning provider, including the owner’s specific operating requirements, such as temperature and humidity setpoints, outside air requirements, and occupancy schedules.

Diagnostic monitoring comes next, through measuring whole-building and end-use energy consumption, operating parameters such as actuator and damper positions, outside air-temperature and humidity levels, and equipment run times. Short-term diagnostic monitoring can be conducted using a building automation system’s trend-logging capability or with portable dataloggers. The measurements provide an understanding of the system’s performance under various operating conditions, which allows the provider to calculate potential savings opportunities and to identify problems that may require further investigation through functional testing of individual equipment. This diagnostic monitoring forms the energy-use baseline against which all future energy-saving measures will be calculated.

The commissioning provider will discuss a list of findings with the owner, including identifying the most cost-effective energy-saving opportunities and the system improvements that are within the scope and budget of the project. Together the owner and the provider decide which strategies to implement, and the provider summarizes the recommendations in a report to the building owner.

Implementation phase. Depending on in-house resources and time constraints, there are several approaches the building owner can take to implement the recommendations:

Regardless of the approach taken, the commissioning provider will develop an appropriate implementation plan that incorporates milestones for documentation and verification of results as the project progresses. This plan organizes and defines the work needed to complete the savings and improvement measures. Upon completion of each measure, the system is tested and the data compared to the energy baseline. Calculations are performed to confirm that the expected improvements and resulting energy savings have been realized and that the measures are well integrated and are having the anticipated effect on the building.

Hand-off phase. The commissioning provider develops a comprehensive record of the entire RCx project that brings together all of the important information from project deliverables in a summary form. O&M manuals should be compiled for each energy-saving measure and system improvement as valuable resources for the building operations staff. The commissioning provider also conducts in-depth training to ensure that the staff has the skills to maintain the improvements and energy savings as well as to do any specific O&M functions required to sustain a high level of building performance. To achieve long-term persistence of the RCx effort, the commissioning provider recommends strategies, in the form of an ongoing commissioning plan, that the owner and operations staff can follow to confirm that savings are continuing into the future.

RCx is an extensive undertaking that requires a significant commitment in time, effort, and funding by the building owner and operations staff. This process results in a building whose energy systems and equipment are operating at optimal levels and meeting the needs of the building owner and occupants. You can expect substantial savings that will persist over time and quick payback periods. Many utilities offer incentives for RCx, including paying for part or all of an initial RCx feasibility study or paying for a portion of the cost of implementation.

In compiling the 2009 study, LBNL researchers found that commissioning is almost always cost-effective in both new and existing buildings, even in the case of smaller buildings (including those under 100,000 square feet). Projects with a comprehensive level of commissioning were found to achieve nearly twice the median level of savings and five times the savings of the least comprehensive projects. Perhaps predictably, given their high energy use, high-tech buildings were found to be particularly cost-effective for commissioning.

Energy savings from commissioning have been shown to persist for at least three to five years, but beyond that, longer-term data remains unavailable. For this reason, recommissioning every five years or so is recommended to maintain top levels of building performance. Alternatively, to help better manage the expenses involved in RCx and recommissioning, the industry is beginning to move toward a monitoring-based approach that will allow it to better confirm savings, improve persistence of benefits, and identify further opportunities for improvement on an ongoing basis.