What is Zero Energy Building ?
Zero energy buildings combine energy efficiency and renewable energy generation to consume only as much energy as can be produced onsite (or offsite) through renewable resources over a specified time period. Achieving zero energy is an ambitious yet increasingly achievable goal that is gaining momentum across geographic regions and markets. Private commercial property owners have a growing interest in developing zero energy buildings to meet their corporate goals, and in response to regulatory mandates, and many local governments are beginning to move toward zero energy building targets.
The Zero Energy Building is a building that is highly energy efficient and fully powered from on-site and/or off-site renewable energy sources. And the WorldGBC defines Net Zero Carbon as when the amount of carbon dioxide emissions released on an annual basis is zero or negative.
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WorldGBC recognises that, in most situations, net zero energy buildings (i.e. buildings that generate 100% of their energy needs on-site) are not feasible. However, buildings which are energy efficient, and which supply energy needs from renewable sources, are a more appropriate target for the emissions reductions required to achieve the Paris Agreement.
By using energy as the only source of measurement, the full impact of emissions on the environment cannot be determined. Carbon (measured in Carbon Equivalence CO2e) is the ultimate metric and a universal language to track the impact of greenhouse gas emissions of buildings.
The Net Zero Carbon Buildings Commitment of WorldGBC focuses on operational carbon emissions of buildings over which the entity has direct control. This determines a universally viable baseline in scope that can be applied to any type of entity, across all sectors and in any context.
Including any additional emissions scope beyond this – e.g. embodied carbon, refrigerant emissions, industrial and manufacturing process loads or construction related activities – is strongly encouraged. An entity may determine, based on its carbon emissions profile, that one or more of the above list offer significant potential to reduce the carbon footprint for their business operations.
Industrial and manufacturing process loads are often independent of the building itself. For example, processing of aluminium is an activity that happens within a building, but does not serve building occupants, or relate to how the building operates. As a result, industrial and manufacturing process loads are not currently included in the Commitment. While addressing operational energy-related carbon emissions through the Commitment, WorldGBC acknowledges that emissions from building and construction also comprise 11% of energy related emissions from the extraction and manufacturing of materials (known as embodied carbon) and construction processes.
Due to the complex nature of standards related to embodied carbon (for existing assets in particular), WorldGBC does not currently require these to be included within the Commitment.
Although embodied carbon is not included in the Commitment at this stage, it remains a priority. WorldGBC aims to include embodied carbon emissions in future iterations of the Commitment, and actively encourages entities to plan how they can incorporate this challenge going forward.
Net Zero Carbon Buildings Commitment
WorldGBC’s Net Zero Carbon Buildings Commitment calls on businesses, organisations, cities, states and regions to reach net zero carbon operating emissions within their portfolios by 2030, and to advocate for all buildings to be net zero carbon in operation by 2050.
The Commitment seeks to recognise and promote advanced climate leadership in decarbonising the built environment, to inspire others to take similar action, and to remove barriers to implementation.
It aims to maximise the chances of limiting global warming to below 2 °C and reduce operating emissions from buildings (currently 39% of energy-related CO2 emissions) through the five components of the Commitment framework:
Through this framework, the Commitment ensures that all signatories can deliver against their targets, while driving real and tangible reductions.
A zero energy building (ZEB) produces enough renewable energy to meet its own annual energy consumption requirements, thereby reducing the use of non-renewable energy in the building sector. ZEBs use all cost-effective measures to reduce energy usage through energy efficiency and include renewable energy systems that produce enough energy to meet remaining energy needs.
There are a number of long-term advantages of moving toward ZEBs, including lower environmental impacts, lower operating and maintenance costs, better resiliency to power outages and natural disasters, and improved energy security. Reducing building energy consumption in new building construction or renovation can be accomplished through various means, including integrated design, energy efficiency retrofits, reduced plug loads and energy conservation programs.
Reduced energy consumption makes it simpler and less expensive to meet the building’s energy needs with renewable sources of energy. ZEBs have a tremendous potential to transform the way buildings use energy and there are an increasing number of building owners who want to meet this target. Private commercial property owners are interested in developing ZEBs to meet their corporate goals, and some have already constructed buildings designed to be zero energy.
Grid Connection and Net Zero
Most Net Zero Energy Buildings are still connected to the grid, allowing for the energy produced from traditional sources (natural gas, electric, etc.) to be used when renewable energy generation cannot meet the building's energy load.
When, conversely, on-site energy generation exceeds the building energy requirements, the surplus energy should be exported back to the utility grid, where allowed by law. The excess energy production offsets later periods of excess demand, resulting in a net energy consumption of zero.
Due to current technology and cost limitations associated with energy storage, grid connection is usually necessary to enable the Net Zero Energy balance. Differences in how utilities and jurisdictions address payment for energy that is exported from the building into the grid can impact project economics and should be carefully evaluated.
Regardless of the definition or metric used for a Net Zero Energy Building, minimizing the energy use through efficient building design should be a fundamental design criterion and the highest priority of all NZEB projects. Energy efficiency is generally the most cost-effective strategy with the highest return on investment, and maximizing efficiency opportunities before developing renewable energy plans will minimize the cost of the renewable energy projects needed.
Using advanced energy analysis tools, design teams can optimize efficient designs and technologies. Energy efficiency measures include design strategies and features that reduce the demand-side loads such as high performance envelopes, air barrier systems, daylighting, sun control and shading devices, careful selection of windows and glazing, passive solar heating, natural ventilation and water conservation.
Once building loads are reduced, the loads should be met with efficient equipment and systems. This may include energy efficient lighting, electric lighting controls, high-performance HVAC and heat pumps.
Once efficiency measures have been incorporated, the remaining energy needs can be met using renewable energy technologies. Common on-site electricity generation strategies include photovoltaics (PV), solar water heating, and wind turbines.
Renewable, on-site thermal energy can sometimes be provided by effective use of biomass. Wood, wood pellets, agricultural waste, and similar products can be burned on-site to provide space heating, service water heating, etc. Biofuels, such as biodiesel, may also be used in conjunction with conventional fossil fuels to meet thermal loads.
Priority should be given to renewable approaches that are readily-available, replicable, and most cost-effective. System maintenance must also be given consideration to over time. Life-cycle cost analysis should be used to evaluate the economic merits of various systems over their usable lifetimes.
Depending on the metric and guidelines used, buildings may be permitted to use energy generated off-site to offset energy used in a building. If space is limited, a facility owner may install dedicated wind turbines, solar collectors, etc. at a separate location. Most often, however, credit for off-site renewable generation is gained by purchasing renewable energy credits (RECs).
RECs are available from many renewable energy technologies. Large, utility-scale wind farms, solar plants, geothermal plants, and hydropower facilities generate electricity without using fossil fuels or primary energy. The costs of constructing and operating these generation facilities are often paid for by selling the "credit" for generating energy renewably (as well as selling the energy itself). The structure and market for RECs is evolving and it varies regionally.
Net Zero Energy Building principles can be applied to most types of projects, including residential, industrial, and commercial buildings in both new construction and existing buildings. A growing number of projects have been designed and constructed across the various market sectors and climate zones.