O&M Glossary
View a list of common terms used in building O&M practices.
At the heart of all operations and maintenance (O&M) lies the equipment. Across the federal sector, this equipment varies greatly in age, size, model, and condition. The Federal Energy Management Program (FEMP) focuses on some of the common and emerging types of equipment applied across the federal sector, including:
- Presenting general equipment descriptions and operating principles
- Highlighting important safety issues
- Providing recommended general O&M activities in the form of checklists
- Discussing the key maintenance components of that equipment.
FEMP offers the following summaries to provide agencies with explanations of challenges they may encounter and offer solutions on how they can approach new procedures, capabilities, and policies.
The term "economizer" is used to refer to several different devices within the field of heating, ventilation, air conditioning, and refrigeration. This O&M best practice focuses specifically on air-side economizers (also known as outside air economizers). These devices supplement compressor-based mechanical cooling with "free cooling" provided by fresh air when delivering this fresh air requires less energy than conditioning the building's return air. American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) 90.1-2019 defines an air-side economizer as:
A duct and damper arrangement and automatic control system that together allow a cooling system to supply outdoor air to reduce or eliminate the need for mechanical cooling during mild or cold weather.
In most climates, the cost of installing air-side economizers in both new and existing buildings is easily recovered in the resulting energy savings. Their cost effectiveness has made air-side economizers common throughout the United States. However, realizing the potential savings requires that these devices are operated correctly and maintained adequately. This best practice provides an overview of key concepts that will help building operators and managers maintain air-side economizing equipment.
This O&M best practice includes:
- Description of economizer technology and its key components
- Maintenance checklist and safety precautions
- O&M cost
- Additional support and informative resources.
Commissioning is a quality-assurance process used to verify that a building performs according to the original design and intent and meets the needs of the owners and occupants. Federal agencies are required to make sure building systems and equipment are commissioned in new construction and existing buildings. Commissioning types include the following.
- Commissioning in New Construction and Major Renovations: This is done to ensure that systems, subsystems, and equipment in new buildings operate properly. It includes performing design reviews, functional testing, system documentation, and operator training throughout the project to make sure the building meets the requirements as intended by each building owner and as designed by the building architects and engineers.
- Ongoing Commissioning in Existing Buildings: Ongoing commissioning (OCx) is a term that appears in the U.S. Green Building Council's (USGBC) Leadership in Energy and Environmental Design O+M: Existing Buildings. According to USGBC, it is a "process that includes planning, point monitoring, system testing, performance verification, corrective action response, ongoing measurement, and documentation to proactively address operating problems in the systems being commissioned." Several currently practiced OCx approaches are available, including continuous commissioning and monitoring-based commissioning/real-time commissioning. Each has its own approach and methodology. This ongoing process is designed to resolve operating problems, improve comfort, optimize energy use, and identify retrofits for existing buildings. Although it is ideal for large complex buildings with automation and advanced metering systems, ongoing commissioning is the costliest approach for existing buildings because of staff and equipment allocations. However, the process can identify equipment inefficiencies as they occur and allow for quick remediation and greater energy and cost savings.
- Recommissioning in Existing Buildings: As defined in 42 U.S.C. 8253(f)(1)(F), "recommissioning means a process – (i) of commissioning a facility or system beyond the project development and warranty phases of the facility or system; and (ii) the primary goal of which is to ensure optimum performance of a facility, in accordance with design or current operating needs, over the useful life of the facility, while meeting building occupancy requirements." In practice, recommissioning (ReCx) is accomplished through testing and adjusting the building systems to meet the original design intent or optimize systems to satisfy current operational needs. ReCx relies on building and equipment documentation, along with functional testing to optimize performance. ReCx is applied to buildings that have been previously commissioned—either as new or existing buildings. This is done to ensure that systems and equipment in existing buildings meet the original design intent. ReCx is used in buildings that were previously commissioned to fine-tune them to meet their original design intents and operational efficiencies. ReCx should be considered for new buildings that were commissioned during construction and in which energy needs have increased.
- Retro-Commissioning in Existing Buildings: 42 U.S.C. 8253(f)(1)(G) defines retro-commissioning (RCx) as "a process of commissioning a facility or system that was not commissioned at the time of construction of the facility or system." Like new building commissioning, RCx is concerned with how equipment, systems, and subsystems function together, but it does not generally take a whole-building approach to efficiency. The process can identify and solve problems that occurred at construction but also addresses problems that have developed to this stage in the building's life. While the goal of RCx may be to bring the building, its systems, and equipment back to its original design intent, that is not a requirement. Depending on the building's age, RCx can often resolve problems that occurred during design or construction (for buildings that did not undergo the commissioning process during the design and construction process), or address problems that have developed throughout the building's life. In all, RCx improves a building's operations and maintenance procedures to enhance overall building performance. RCx is done to optimize systems to meet new operational needs through testing and adjusting. RCx is used in older buildings that have never been through the commissioning process and should be considered if building systems are old, expensive to operate, and have frequent equipment failures.
For more information, see Commissioning in Federal Buildings.
- Commissioning in New Construction and Major Renovations: This is done to ensure that systems, subsystems, and equipment in new buildings operate properly. It includes performing design reviews, functional testing, system documentation, and operator training throughout the project to make sure the building meets the requirements as intended by each building owner and as designed by the building architects and engineers.
A ground source heat pump (GSHP) system is a heating, ventilation, and air-conditioning (HVAC) technology that can provide space and/or water conditioning (heating and/or cooling) for buildings. They use either the earth (ground) or water—either groundwater or open bodies of water—as a heat source and sink for heat transfer. GSHPs can significantly improve the efficiency of heating and cooling systems and are considered a renewable energy technology.
Regular O&M of GSHP systems ensure they continue to operate effectively. In addition, tracking performance helps identify potential issues with the system and achieve maximum savings. Unfortunately, most GSHP systems do not include performance monitoring equipment.
The purpose of this best practice is to provide general information about the key components of GSHP systems, and to familiarize the designated staff member with the types and frequency of maintenance typically performed to keep a GSHP system in good working order. Support organizations should budget and plan for routine maintenance of GSHPs to ensure continuous operation.
This O&M best practice includes:
- Description of GSHP technology and its key components
- Potential safety issues and precautions
- Maintenance checklist and performance monitoring
- O&M cost
- Additional support and resources.
FEMP's mission is directly related to achieving the requirements set forth in the Energy Policy Acts of 1992 and 2005 and the Energy Independence and Security Act of 2007 as well as with practices that are inherent in the sound management of federal financial and personnel resources.
To that extent, FEMP published Metering Best Practices: A Guide to Achieving Utility Resource Efficiency in March 2015. This document provides energy managers and practitioners with useful information about energy and resource metering, the relevant metering technologies, communications, applications for data, and ideas for developing and implementing effective metering programs.
The learning objectives of the metering best practices guide are to:
- Highlight the benefits of using metered data to identify opportunities and drive cost-effective energy management and investment practices
- Understand and be able to outline the key elements of a metering plan, including prioritization
- Illustrate ways to use metered data to identify energy and cost saving opportunities
- Achieve a high-level understanding of metering technologies, equipment, and applications
- Describe the methods and approaches for building-level, distribution-level, and end-use metering
- Explain the data communication options for metered data.
The metering best practices guide focuses on providing energy, water, and facility managers and practitioners with information that facilitates using metering to achieve potential savings and benefits.
For more information, see Metering Best Practices: A Guide to Achieving Utility Resource Efficiency.
Modular boilers can improve the efficiency of heating and steam systems compared to large conventional boilers sized to meet large loads. Regular O&M of modular boiler systems will ensure that they continue to operate effectively. In addition, performance monitoring will help identify potential issues with the system and achieve maximum savings.
Fortunately, most modular boiler systems include performance monitoring information in the system controllers that can facilitate system diagnostics. Energy production can typically be reviewed from system controllers, and therefore ensuring the proper programming and continued function of the system controller is an essential part of O&M.
The purpose of this equipment O&M best practice is to provide general information about the key components of modular boiler systems, and to familiarize the designated staff member with the types and frequency of maintenance typically performed to keep a modular boiler system in good working order.
This O&M best practice includes:
- Description of modular boiler technology and system components
- Performance monitoring and potential safety issues
- Maintenance checklist and O&M costs
- Additional support and informative resources.
Wind turbines are a widely implemented renewable energy technology in the United States. Although much of the capacity is in utility-scale wind farms, wind turbines are also deployed as on-site distributed energy resources to power schools, businesses, government sites, and other facilities.
Wind as a distributed energy resource is often called distributed wind. Distributed wind projects are interconnected behind a customer’s meter to offset on-site electricity use or to the distribution grid to support local loads and grid operations.
Distributed wind can also electrify or provide backup power to remote, off-grid assets not connected to a distribution grid. These best practices focus on on-site distributed wind turbines.
A broad range of wind turbine sizes can be used in on-site distributed wind projects. Effective O&M of wind turbines, regardless of size, is necessary to maximize system production and help achieve energy reduction, decarbonization, and resilience goals.
The purpose of this best practice is to provide an overview of wind turbine components, maintenance requirements, and reporting considerations to ensure safe and efficient operation of on-site wind turbines.
Regular O&M of wind turbines will ensure that systems continue to operate effectively, and tracking operating conditions and performance will also help identify potential issues, maximize savings, and inform future designs and standards. Owners should budget and plan for regular maintenance to ensure continuous operation.
This O&M best practice for on-site wind turbines includes:
- A description of on-site wind turbines and its key components
- Identification of potential safety issues
- Maintenance checklist and other considerations
- Performance monitoring (measurement and verification) and costs
- Additional resources and references.
Read more about this best practice.
Read FEMP's 10 considerations when drafting an O&M agreement with a third-party wind turbine maintenance contractor. Solar photovoltaic (PV) systems are among the most commonly used renewable energy technologies on federal sites. Solar PV cells convert light directly into electricity. As light enters a PV cell, photons impart energy to electrons, producing an electrical current. Effective O&M of these systems is necessary to maximize system production.
The purpose of this best practice is to provide an overview of the system components, maintenance requirements, and reporting requirements to keep solar PV systems operating safely and efficiently. Regular O&M of solar PV arrays will ensure that systems continue to operate effectively. Tracking system performance will help identify potential issues and maximize savings. Support organizations should budget and plan for regular maintenance to ensure continuous operation.
This O&M best practice includes:
- Description of solar PV technology and system components
- Performance monitoring (measurement and verification) and potential safety issues
- Maintenance checklist and O&M cost
- Additional support and informative resources.
Solar water heating (SWH) systems use energy from the sun to generate heat that can then be used to heat water for domestic hot water needs, space heating, industrial processes, or pool heating. They are a reliable and cost-effective technology that can help reduce utility bills for homes and businesses.
Operation and maintenance of solar water heating systems is almost identical to other types of hydronic heating systems and involve the same types of components. Systems are designed with automatic controls to operate without intervention, but it is important to keep an eye on the performance of systems, to provide preventative maintenance, and to quickly repair failures in order to avoid lost production.
The purpose of this best practice is to provide an overview of the system components as well as maintenance requirements to keep SWH systems operating safely and efficiently. Regular O&M of SWH systems will ensure that issues are identified early and systems continue to operate effectively. Organizations should budget and plan for regular maintenance to ensure continuous operation.
This O&M best practice includes:
- Description of solar water heating technology and system components
- Maintenance checklist and potential safety issues
- Performance monitoring and O&M cost
- Additional support and informative resources.
Standby generators are self-contained systems that provide electricity when power from the primary source, usually the local electric grid, is unavailable. When the grid experiences an outage, an automatic transfer switch (ATS) signals the standby generator to start and begin providing power. When the grid is again available, the load, and power is transferred back to the grid, and the ATS signals the generator to stop.
Standby generators are usually internal combustion engines coupled with an electric generator and can be powered by diesel fuel, propane, natural gas, or other liquid fuels. These generators typically operate for a limited amount of time and are not meant for extended use. Executing the necessary O&M on this system is crucial for optimized efficiency and preparation for power outages.
The purpose of this equipment O&M best practice is to provide an overview of system components, maintenance requirements, and best practices to ensure the safe and efficient operation of standby generators. Neglecting proper maintenance of standby generators could result in premature system failure and lack of power during an outage. Support organizations should budget and plan for routine maintenance of standby generators to ensure continuous operation.
This O&M best practice includes:
- A description of the standby generator technology and its key components
- Identification of potential safety issues
- Maintenance checklist identifying key actions and their frequency
- Additional resources and references.
An automatic transfer switch (ATS) is a device that allows safe transfer of electricity from a primary source, usually an electric-utility grid, to a backup source, e.g., emergency or standby generator. The purpose of an ATS is to reliably provide a load with electrical power from a standby generator to a facility without the possibility of backfeeding the utility grid. An ATS is often used with standby power systems that serve critical loads such as industrial processes, data networks, and other installations such as healthcare, financial, and military applications.
Executing the necessary O&M for an ATS is crucial for optimized reliability, resiliency, and utilization during power outages.
The objective of this equipment O&M best practice is to provide an overview of system components, maintenance requirements, and best practices to ensure the safe and efficient operation of ATSs. Support organizations should budget and plan for regular maintenance of all ATSs to ensure continuous operation.
This O&M best practice includes:
- Description of ATS technology and system components
- Potential safety issues
- Maintenance checklist and performance monitoring
- O&M cost
- Additional support and resources.
Unitary heating, ventilation, and air conditioning (HVAC) systems, which combine heating and cooling in one unit (packaged) or a few sections (split) are one of the most common technologies used for space conditioning in commercial buildings. They are designed to be flexible so that the equipment can be installed indoors (mechanical room, attics, ceilings, etc.) or outdoors (rooftops or on the ground). Effective O&M of these systems is necessary to maximize efficiency and production, provide occupancy comfort, and reduce failures.
The purpose of this equipment O&M best practice is to provide an overview of unitary HVAC equipment, maintenance requirements, and best practices in order to operate the systems safely and efficiently. Support organizations should budget and plan for regular maintenance to ensure continuous operation.
This O&M best practice includes:
- Description of the unitary HVAC unit technology and system components
- Maintenance checklist and performance monitoring
- Potential safety issues
- O&M cost
- Additional support and informative resources.
The primary goal of any HVAC system is to provide comfort to building occupants and maintain healthy and safe air quality and space temperatures. Variable air volume (VAV) systems enable energy-efficient HVAC system distribution by optimizing the amount and temperature of distributed air. Appropriate O&M of VAV systems is necessary to optimize system performance and achieve high efficiency.
The purpose of this equipment O&M best practice is to provide an overview of system components and maintenance activities to keep VAV systems operating safely and efficiently. Regular O&M of a VAV system will ensure overall system reliability, efficiency, and function throughout its life cycle. Support organizations should budget and plan for regular maintenance of VAV systems to ensure continuous safe and efficient operation.This O&M best practice includes:
- Description of variable air volume technology and system components
- Maintenance checklist and potential safety issues
- Performance monitoring and O&M cost
- Additional support and informative resources.
According to the U.S. Department of Energy, motor-driven equipment accounts for well over half of the electricity used by U.S. industry (DOE 2012). As such, many manufacturers, businesses, and industries have turned to energy savings equipment and strategies to reduce this staggering total. One of the most accepted and cost-effective energy reduction strategies is the installation of variable speed drives (VSDs).
The term VSD is a catch-all term related to devices that affect the output speed of a drive or motor system. Under this broad heading are devices that can control motor speed via electronics (alternating current (AC) and direct current (DC) electronic drives), clutching mechanisms (eddy current clutches), and mechanical devices (fluid couplings, magnetic couplings, and a variety of pulley, belt, chain, and gear-box devices). By far, the most common VSD is the variable frequency drive (VFD) due to its efficiency and ability to affect the most popular type of electric motor—the AC induction motor.
The purpose of the VSD best practice is to provide an overview of system components and maintenance activities to keep VFD systems operating safely and efficiently. Regular O&M of VFD systems will ensure overall system reliability, efficiency, and function throughout their life cycles. Support organizations should budget and plan for regular maintenance of VFD systems to ensure continuous safe and efficient operation.
This O&M best practice includes:
- Description of variable speed drive technology and system components
- Maintenance checklist and potential safety issues
- Performance monitoring and O&M cost
- Additional support and informative resources.