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Operational Carbon

Because energy generation, delivery, management and use interact with everything we do in buildings, the most effective approaches to decarbonization target building systems holistically and strategically.

Building Operational Decarbonization Strategies

Building operational decarbonization strategies include a combination of the following approaches:

  • Energy Efficiency: reducing energy use through greater efficiency and conservation.
    • Use energy audits to identify facility-specific needs and opportunities. Factor in evolving energy needs, such as projected increases in electricity use for electric vehicle charging. Consider the service life, replacement cycle and embodied carbon of systems and equipment. Purchase and install efficient, ENERGY STAR certified equipment.
    • Prioritize energy efficiency opportunities before applying other strategies. Reducing energy use allows less energy to be purchased or produced. It can also save money upfront, for example, by capitalizing on daylight to reduce electric light and by allowing right-sized HVAC equipment.
  • Carbon Pollution-Free Electricity (CFE): transitioning to onsite or offsite energy sources that do not produce GHG emissions, including renewables.
    • Seek opportunities to buy CFE, e.g. from green tariffs or power purchase agreements.
  • Building Electrification: replacing onsite fossil fuel-burning equipment with electric systems.
    • Use electrification strategically to reduce reliance on fossil fuel consumption, especially in areas with relatively low-cost electricity (to reduce cost impacts) and low-GHG-emitting grids (to maximize carbon reduction).
  • Building and Grid Integration: improving the integration of buildings with the electric grid to manage energy loads and facilitate the transition of the grid to CFE sources.
    • Consider building control and grid interaction opportunities as building systems are designed or retooled, to promote additional energy, GHG and cost reductions. For example, participate in load-management activities such as peak shaving and demand-response that can shed loads on peak demand days with benefits to the electricity grid, air quality, and cost savings. For more information, see SFTool’s Grid-Interactive Efficient Buildings page.

See GSA’s Center for Emerging Building Technologiesopens in new window for information on building technologies, including numerous decarbonization technologies, that have been evaluated under the Green Proving Groundopens in new window program.

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Operational Carbon Components

  • Whole Building

Basic Action Plan Process Diagram
Key Strategies for the Transformation to Net Zero Energy Buildings

Energy Efficiency

The first step a building professional should take toward decarbonization is maximizing the building’s energy efficiency, since doing so saves money and reduces the amount of onsite renewable equipment or purchased CFE that is needed. Some of the most effective efficiency measures are passive, i.e., a product of the building’s siting and structure, including constructing a building envelope that is air-tight and has thermal mass capable of absorbing heat from sunlight during the heating season and heat from warm air during the cooling season. Properly orienting the building to make optimal use of the sun’s warmth, light and energy-producing capability has a big impact on how much energy is consumed.

Active efficiency measures are those that involve designing and operating building systems and equipment to perform more efficiently. Among those systems, space heating accounted for close to one-third of end-use consumption in U.S. commercial buildings in 2018.1 Other energy-intensive building systems include ventilation, lighting, cooling and water heating. There arean ever-increasing number of technologies and strategies to optimize the efficiency of all of these systems, as well as building controls and energy management systems to ensure they all work together as efficiently as possible.

In addition to building systems, a building professional must be aware of plug loads, the often increasing amount of energy used by plugged-in equipment, from computers to video screens, and process loads, the energy used by systems hardwired into a building structure, such as elevators, enterprise servers, and commercial kitchen equipment. Plug loads are projectedopens in new window to be one of the fastest-growing uses of energy in buildings in the coming decades.

Pie diagram of end uses of energy consumption by U.S. commercial buildings (2018) in British thermal units (Btu). The total is 6,787 trillion Btu. Space heating is 32%, or 2,167 trillion Btu. This means that 32% of the energy consumed by commercial buildings was used for space heating. Ventilation is 11%, or 728 trillion Btu. Lighting is 10%, or 709 trillion Btu. Cooling is 9%, or 589 trillion Btu. Cooking is 7% or 485 trillion Btu. Refrigeration is 5%, or 369 trillion Btu. Water heating was 5%, or 343 trillion Btu. Computing is 4%, or 270 trillion Btu. And other was 17%, or 1,127 trillion Btu.
Energy consumption by end use in U.S. commercial buildings.
Source: U.S. Energy Information Associationopens in new window
Energy Efficiency in Building Systems

For all building equipment and fixtures, opt for ENERGY STAR certified productsopens in new window and/or FEMP designated productsopens in new window wherever possible. In addition, SFTool's Cost-Effective Upgrades tool provides specific building efficiency opportunities geared to building size and climate zone.

Energy Efficiency Strategies

Energy efficiency is a complex topic because it involves optimization and interaction among multiple building systems. Upgrades and replacements must also be planned and conducted thoughtfully to avoid negative impacts on occupant health, comfort or job performance.

For all buildings systems and equipment, regular maintenance is essential. For more information, see SFTool's HVAC System Impacts O&M page.

Energy modeling is the process of using computer-generated calculations or simulations to estimate a project’s anticipated energy use impact. Energy modeling can enable the comparison of a building’s projected energy use to a baseline performance case and inform energy efficient building and system design decisions.

NREL.gov Buildings | Commercial Researchopens in new window

Energy.gov | EnergyPlusopens in new window

Building Commissioning is a process of verifying and documenting that the facility and all of its systems and assemblies are planned, designed, installed, tested, operated, and maintained to meet the owner's project requirements. This means testing all systems (HVAC, lighting, domestic water heating systems, etc.) to ensure they function as intended. Proper commissioning saves energy, reduces risk, and creates value for building operators. It also serves as a quality assurance process for enhancing the delivery of the project.

Energy.gov | Commissioning in Federal Buildingsopens in new window

Building Commissioning Association (BCxA)non government site opens in new window

Retro-commissioning is commissioning of a building that has never been or was not fully commissioned at its completion. It includes developing a building operation plan that identifies current operating requirements and needs, conducting tests to determine whether building systems are performing optimally in accordance with the plan, and making any necessary repairs or changes.

Short of full retro-commissioning, building re-tuning is a systematic process to identify operational problems by leveraging data collected from a building automation system (BAS) and correcting those problems at no-cost or low-cost. See the Pacific Northwest National Lab (PNNL) Building Re-tuning pageopens in new window for more information.

Monitoring-based commissioning (MBCx), when implemented with an energy management information system (EMIS) that monitors, analyzes, and controls building energy use, enables building engineers and facility/energy managers to continuously track whether energy savings have persisted and to find additional opportunities for improved system performance.

Energy.gov | Better Buildings EMIS Primer Second Editionopens in new window

  • Building Automation Systems: A building automation system (BAS) automation system (BAS) is used to monitor and control building components and systems. A BAS can integrate the operation of fans, pumps, heating/cooling equipment, dampers, mixing boxes, thermostats, and other devices. Monitoring and optimizing temperature, pressure, humidity, and flow rates are key functions of a BAS. A BAS also enables facility managers to balance energy use during times of peak demand and/or plentiful renewable generation, an important component of Grid-Interactive Efficient Buildings (GEBs).
  • Submetering: Energy and water submeters can measure resource use for different buildings in a multi-building campus, different floors of the same building, different tenants in a multi-tenant office or facility, individual building systems, electrical circuits, or even specific devices. Data from well-designed submetering systems can inform management strategies to significantly reduce energy and GHG emissions across building portfolios. For more information, see SFTool’s Submetering System Overview page.

Deep energy retrofitsopens in new window renovate buildings to reduce site energy use by at least 40% using an integrative and whole-systems approach that combines bundles of energy conservation measures rather than considering individual technologies in isolation. Though often more expensive upfront, deep energy retrofits tend to deliver substantially greater value than piecemeal solutions. For several years, GSA has demonstrated the value of using energy savings performance contracts (ESPCs) and utility energy service contracts (UESCs) to achieve deep energy retrofits.

Carbon Pollution-Free Electricity (CFE)

Executive Order 14057opens in new window defines CFE as “electrical energy produced from resources that generate no carbon emissions, including marine energy, solar, wind, hydrokinetic (including tidal, wave, current, and thermal), geothermal, hydroelectric, nuclear, renewably sourced hydrogen, and electrical energy generation from fossil resources to the extent there is active capture and storage of carbon dioxide emissions that meets EPA requirements.”

CFE is a critical consideration for building decarbonization due to the importance of ensuring that the electricity used to power building systems comes from generation sources that don’t produce GHG emissions. Furthermore, because CFE generation may vary by season, weather, or time of day, buildings designed or adapted to shift electrical demand to when CFE is available can help align CFE supply and demand. This can happen through load-shifting (e.g., demand response and grid-interactive efficient buildings) or energy storage. This hourly load-matching of electricity demand to CFE availability is referred to as 24/7 CFE, which EO 14057 defines as carbon pollution-free electricity procured to match actual electricity consumption on an hourly basis and produced within the same regional grid where the energy is consumed.

CFE Strategies

There are multiple avenues to procure CFE, depending on factors such as electricity market, regional availability, agency resources, and agency procurement authority. Some of these options are:

The General Services Administration (GSA) provides CFE procurement assistanceopens in new window to Federal agencies. Agencies may contact the GSA CFE Division at CFESupport@gsa.gov.

Other resources for CFE include:

Renewable Energy

Renewable energy is a very important subset of CFE, but not all CFE energy sources may be considered renewable - nuclear, for example - and not all renewable energy produces electricity - solar thermal water heating, for example, heats water directly from the heat of the sun. Renewable energy comes from sources that are either inexhaustible or can be replaced very rapidly through natural processes. Examples include the sun, wind, geothermal energy, small (river-turbine) hydropower, and other hydrokinetic energy (waves and tides).

Replacing energy generated from fossil fuel sources with energy generated from renewable sources is critical to building decarbonization and has a range of benefits. It mitigates GHG emissions, reduces U.S. dependence on foreign energy sources, and onsite renewable energy increases Federal energy security by reducing facility reliance on an electricity grid. Renewable energy tends to provide long-term price stability, as it doesn’t depend on costly and/or price-variable fuel sources. At the same time, some renewable energy sources, such as sun and wind, are ‘variable’ or ‘intermittent’, meaning the supply is not consistent. There also may be a mismatch between when and where renewable energy is most efficiently produced vs. where and when it is needed most. These challenges can be addressed through Energy Storage/Batteries and Building and Grid Integration.

For more information, see SFTool's Renewable Energy page, under "Procure".

Building Electrification

A common strategy in the drive toward net zero GHG emissions is building electrification: the elimination of onsite fossil fuel combustion by replacing fossil fuel-burning appliances and equipment with electric-powered technologies.

HVAC systems are typically the biggest users of onsite fossil fuels in public and commercial buildings. According to the DOE’s Commercial Building Energy Consumption Survey (CBECs)opens in new window, in 2018, space heating constituted at least two-thirds of commercial building consumption for natural gas, district heat, and fuel oil. The next most common uses, depending on building type, are domestic water heating and cooking.

Building electrification will generally increase the demand for electricity from the electric grid, in some cases requiring electrical infrastructure upgrades. To achieve GHG emission reduction goals, it will be critical to increase CFE generation while also pursuing Energy Efficiency and Building and Grid Integration.

Building Electrification Strategies

HVAC Systems

For the electrification of HVAC systems, heat pumpsopens in new window are a popular solution. These systems use electricity to transfer heat rather than generate it and are classified by their heat source. Air-source heat pumps work by drawing thermal energy from the air, while geothermal or ground-source heat pumps rely on the relatively constant temperature underground (tapped by geothermal wells), and water-source heat pumps employ a water source. Heat pumps are also characterized by their thermal distribution method, e.g., air-to-air heat pumps use air to circulate heat throughout a building, while air-to-water (hydronic) heat pumps use water for circulation purposes. Variable refrigerant flow (VRF) systems use refrigerants as the circulating medium.

While air-source heat pump performance has traditionally diminished in the coldest climates, cold climate heat pump performance continues to improve. HVAC systems typical for large buildings, including those relying on boilers and distributed heating systems, can make cost-effective electrification challenging. More feasible electrification options are currently available for smaller and medium-sized buildings with packaged rooftop units. Manufacturers and system designers continue to develop new strategies for electrification of space heating and domestic water heating systems.

For more information, see DOE’s Better Buildings report Decarbonizing HVAC and Water Heating in Commercial Buildingsopens in new window. For a short-form training focused on air-source heat pumps, see DOE’s Energy-Efficient Product Procurement Training for Federal Agenciesopens in new window.

Domestic Water Heating Systems

Transitioning domestic water heating systems from fossil fuel energy sources to CFE sources is an effective first step to the decarbonization of a building. Heat pump hot water heaters use a third or less energy than traditional electric water heaters since they transfer heat instead of generating it.

A significantly less efficient means to decarbonize domestic water heating systems is through electric resistance heaters, often referred to as electric boilers. They use about the same energy as fossil fuel-powered systems but can be supplied with CFE generated onsite or CFE purchased from the electricity grid. Consider electrification of all domestic water heating systems at end of life, as an upgrade to aging equipment, or as part of larger building upgrade projects. Buildings with distributed water heaters serving kitchenettes, shower rooms, and concessions may provide opportunities to prioritize electrification of water heating in certain high-demand locations first.

Building Electrification Policies

An increasing number of local and state governments are starting to adopt building performance standards, which the White House Office of the Federal Chief Sustainability Officeropens in new window defines as “an outcome-based policy and law aimed at reducing the carbon impact of the built environment by requiring existing buildings to meet energy- or GHG emissions-based performance targets.”

The National Building Performance Standards Coalitionnon government site opens in new window brings these jurisdictions together to learn from each other. The Federal Building Performance Standardopens in new window requires federal agencies to eliminate Scope 1 emissions from onsite fossil fuel combustion from 30% of federal floorspace by 2030. Denver, Coloradonon government site opens in new window is one of the first jurisdictions to develop a program focused squarely on building electrification.

Energy.gov | Decarbonization Resource Hub | Better Buildings Initiativeopens in new window

Building and Grid Integration

DOE’s Building Technologies Office coined the term Grid-Interactive Efficient Buildings (GEBs)opens in new window, uniting the goals of building energy efficiency and building and grid integration into one suite of strategies. GEBs build on the well-established discipline of energy efficiency by adding strategies and technologies to also manage peak demand and coordinate buildings’ electrical loads, taking into account peak usage hours, renewable generation, storage options, and resiliency needs as appropriate. GEBs contribute to building decarbonization through cost-effective load management strategies. Efficient appliances, equipment, and whole building energy optimization reduce both overall energy consumption and peak demand.

For more information, see DOE’s Better Buildings Federal Smart Buildings Acceleratoropens in new window and SFTool’s Grid-Interactive Efficient Buildings page. For a case study showing GSA applying GEB concepts to a building project, see GSA Oklahoma City Federal Building: Smart Buildings Case Study (March 2023)opens in new window

Graphic shows four characteristics of GEBs:  Efficient, Connected, Smart, and Flexible
Characteristics of Grid-Interactive Efficient Buildings
Adapted from: Department of Energy EERE GEB Overviewopens in new window and Department of Energy EERE GEBsopens in new window


Many refrigerants currently in use in commercial office building cooling and refrigeration systems belong to a class of chemicals known as hydrofluorocarbons (HFCs). HFCs act as powerful GHGs that trap thousands of times more heat energy in Earth’s atmosphere than CO2. Substances like this are described as having high global warming potential (GWP). When these refrigerants accidently leak from our systems, they are known as fugitive emissions and documented as Scope 1 emissions. In October 2021, the EPA issued regulations to phase down the consumption and production of HFCs by 2037. Additionally, some States have enacted laws and regulations to reduce GHG emissions associated with HFCs. GHG emissions accounting includes estimated fugitive emissions of HFC refrigerants from refrigeration and air conditioning equipment. Federal agencies estimate and report fugitive HFC emissions in their Annual Energy Management Data Report to the DOE FEMP.

Strategies to Reduce the Impact of Refrigerants

Monitoring and managing refrigerant leaks in our systems helps reduce refrigerants’ potentially significant contribution to climate-changing GHG emissions. GSA has a Refrigerant Management Standard Operating Procedure (SOP) (coming soon!) that directs O&M vendors and the contracting officer’s representatives (CORs) that oversee them to repair leaking systems and document leaks when they occur in a National Computerized Maintenance Management System (NCMMS). This documentation is critical so that GSA can accurately report Scope 1 emissions and develop strategic plans to reduce leaks and phase out reliance on equipment that uses high-GWP refrigerants.

When retrofitting or purchasing new equipment, GSA must refer to EPA’s Significant New Alternatives Policy (SNAP) Programopens in new window to specify acceptable refrigerants. GSA must purchase equipment with EPA-approved acceptable and safe substitutes that are non-ozone depleting and have a low GWP. Refrigerants listed as unacceptable may not be used in new air conditioning or heat pump equipment at GSA projects, even where EPA's "unacceptable as of" date is in the future. Requirements are listed in the Facility Standards for the Public Buildings Service (P-100)opens in new window and Federal Acquisition Regulation (FAR) Subpart 23.8, Ozone-Depleting Substances and Greenhouse Gasesopens in new window.

Operational Carbon Case Studies

The Wayne Aspinall Federal Building is a case study for minimizing operational carbon. Originally constructed in 1918, renovations successfully converted the building into a model of energy efficiency and sustainability, while preserving its original character. Net Zero Energy Building objectives are met through a combination of high-performance, energy efficient materials and systems, and on-site renewable energy generation. As a result of the upgrades, the building is now 50% more energy efficient than a typical office building. On-site renewable energy generation is intended to produce 100% of the facility’s energy needs throughout the year. Energy efficiency features include variable refrigerant flow (VRF) for the HVAC, a geo-exchange system, advanced metering and building controls, high-efficient lighting systems, a thermally enhanced building envelope, interior window systems which maintain the historic windows but increase thermal performance, and advanced power strips (APS) with desk mounted individual occupancy sensors. Renewable energy is provided by 385 photovoltaic roof panels that generate enough power to meet the electricity needs of 15 average American homes or 123 kw.

Picture of Kern Center
R.W. Kern Centernon government site opens in new window, Amherst, MA

The R.W. Kern Center is a case study for minimizing operational carbon. In addition to passive solar orientation, an air-tight envelope, and triple glazed windows to help mitigate against large swings in temperature and humidity, the double-stud cavity wall and roof are filled with low embodied carbon cellulose to achieve assembly values of R-40 and R-60, respectively. An inverter-driven heat pump system provides heating and cooling to the spaces, separate from the heat recovery ventilation system. By reducing the building’s design energy use, a 118 kilowatt rooftop solar array can generate more than enough energy on an annual basis. Wood is the major structural material and unnecessary finishes were rejected so the “carbon budget” could be spent on high-impact, high-performance components, like the triple-glazed windows and insulation.

The Phipps Center for Sustainable Landscapes is a case study for minimizing operational carbon. Passive-first strategies are coupled with high-performance technologies to permit the downsized mechanical system (a custom-built rooftop energy recovery unit) to operate as efficiently as possible. The long, relatively narrow building sits on an east-west axis, which allows for maximizing southern exposure. High-performance glazing on the north and south facades permits solar gain in the cold months, while louvers and strategic deciduous tree plantings prevent unwanted heat gain and glare in the warm months. Computational fluid dynamics studies determined placement for BAS- and occupant-controlled windows to maximize natural ventilation. Daylighting is maximized with light shelves and sloped ceilings to direct natural light into the interior and energy use is monitored by the individual plug, which permits any anomalies to be addressed. Occupants each have electricity meters at their desks to encourage energy-saving behaviors. Energy is produced onsite via a vertical-axis wind turbine and a 125kW photovoltaic array. The atrium, constructed of concrete with fly ash to reduce embodied carbon, acts as thermal mass, increasing energy efficiency.

The Chesapeake Bay Brook Environmental Center is a case study for minimizing operational carbon. Conservation strategies were organized into passive and active approaches. The building was designed to maximize diffused daylighting from the north while shielding the building interior from direct sunlight from the south and a photosensor dimming-control system was used in almost every space to reduce electric lighting when sufficient daylight is present. Windows and even walls were designed to open up and take advantage of the natural breezes prevalent near the Chesapeake Bay and the mechanical system uses a variable-refrigerant flow (VRF) system with geothermal wells. Two 10-kW wind turbines, each on a 70-ft pole, are located off the east and west ends of the building, as far away as possible from nearby trees, but close enough to limit site disturbances. A PV system, consisting of (141) 270-W modules for a total of 40 kWp (kilowatt peak), is located on the sloped roof and 6.5 kW of additional PV modules were added after the completion of construction.


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1. EIA.gov | 2018 Commercial Buildings Energy Consumption Survey, Consumption and Expenditures Highlights (eia.gov)opens in new window

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