How Do You Get A Net Zero Energy Building?
Four ways in which net-zero energy may be defined:
Net Zero Site Energy
Net Zero Source Energy
Net Zero Energy Costs
Net Zero Energy Emissions
Site Energy: It refers to the energy that a site (e.g. a building) absorbs and produces, regardless of where or how that energy originated. In a net zero-site energy building, a unit of energy must be generated for every unit of energy that the building absorbs over a year.
Source Energy: It refers to the primary energy necessary for the extraction and delivery of energy to a site, including energy that may be lost or wasted during the generation , transmission and distribution process. A coal-fired power plant, for instance, will produce 1 Joule of electricity in the coal consumed for every 3 Joules of energy. If natural gas is used at the site, it will require 1 Joule to extract and deliver the gas to the site for every 20 Joules consumed. These factors are accounted for by metrics for net zero-source energy buildings, although exact metrics will differ based on site and utility factors.
Net Zero Energy Cost: Perhaps it is the easiest measure to use: it means that over the course of a year, the building has a $0 electricity utility bill. In certain situations, the sale of Renewable Energy Credits (RECs) from on-site renewable generation can benefit building owners or operators.
Many conventional energy sources result in emissions of carbon dioxide, nitrogen oxides, sulfur dioxide, etc. The construction of Net Zero Energy Emissions either uses no energy resulting in emissions or compensates for emissions through the export of emission-free energy (typically from renewable energy systems on site).
Grid Connection And Net Zero
Many Net Zero Energy buildings are still connected to the electricity grid, enabling electricity generated from conventional energy sources (natural gas, electricity, etc.) to be used when the energy load of the building can not be met by renewable energy generation. If on-site energy generation, on the other hand, exceeds the criteria for building energy, the excess energy should be exported back to the power grid, if approved by law. Later cycles of excess demand are offset by excess energy output, resulting in a net energy consumption of zero. The grid link is typically important to enable the Net Zero Energy balance due to current technologies and cost limitations associated with energy storage. Differences in how utilities and jurisdictions deal with electricity payments that are exported from the building to the grid may have an impact on project economics and should be carefully measured.
Notwithstanding the Net Zero Energy Building concept or metric, the minimization of energy use by efficient building design should be a fundamental design requirement and the highest priority of all NZEB projects. Energy efficiency is typically the most cost-effective approach with the highest return on investment and, prior to developing renewable energy strategies, optimizing efficiency opportunities would minimize the cost of needed renewable energy projects. Project teams are able to refine effective projects and technologies using sophisticated energy analysis methods.
Energy efficiency initiatives include construction techniques and features such as high-performance envelopes, air barrier systems, daylighting, sun protection and shading equipment, careful selection of windows and glazing, passive solar heating, natural ventilation and recycling of water to minimize demand-side loads.
When construction loads are reduced, reliable equipment and systems can be used to meet the loads. This can include energy-efficient lighting, electric lighting controls, geothermal heat pumps, and high-performance HVAC. Renewable energy is not produced by energy conversion devices such as combined heat and power systems, fuel cells, and microturbines. Instead, they turn energy from fossils into heat and electricity, and energy conservation measures can be considered.
ON-SITE RENEWABLE ENERGY
Using renewable energy technology, the remaining energy requirements can be met once efficiency steps have been implemented. Photovoltaics ( PV), solar water heating, and wind turbines include traditional on-site electricity generation strategies.
Often, the productive use of biomass may provide clean, on-site thermal energy. For space heating , water heating, etc., biomass, wood pellets, agricultural waste, and similar items can be burned on-site. In combination with conventional fossil fuels, biofuels, such as biodiesel, can also be used to satisfy thermal loads. There is more information on biomass on the Alternative Energy page.
Renewable methods that are readily accessible, replicable, and most cost-effective should be given priority. Maintenance of the device must also be considered over time. In order to measure the economic merits of different programs over their available lifetimes, life-cycle cost analysis should be used.
OFF-SITE RENEWABLE ENERGY
Buildings may be able to use energy generated off-site to offset energy used in a building, depending on the NZE metric and guidelines used. A facility owner can install dedicated wind turbines, solar collectors, etc, at a separate location if space is small. Quite frequently, however, credit is received by buying renewable energy credits (RECs) for off-site renewable generation.
RECs from many renewable energy technologies are available. Without using fossil fuels or primary oil, large, utility-scale wind turbines, solar plants, geothermal plants, and hydropower installations produce electricity. The costs of installing and running these generating facilities are also covered by the sale (as well as the sale of electricity itself) of the "credit" for the sustainable generation of energy. The structure and demand for RECs are changing and regionally varying.
Federal Net Zero Energy Building Goals
The Department of Energy (DOE) for residential and commercial buildings has also identified two milestones for NZEB. The priority is to develop solutions for the integration of systems that will allow:
Marketable Net Zero Energy Homes by the year 2020
Commercial Net Zero Energy Buildings at low incremental cost by the year 2025.
These targets are in line with the Energy Independence and Protection Act of 2007, which calls for a 100 percent reduction in the usage of fossil fuel energy for new federal buildings and significant renovations by 2030 (compared to 2003 levels).
Founded under the DOE's Energy Conservation and Renewable Energy Office, the Building Technologies Office (BTO) focuses on improving the efficiency of buildings and their related appliances, components and systems. The BTO supports R&D programs, instruments, guidance, training and technical tools to enhance the efficiency of new and existing buildings in both the commercial and residential sectors. The BTO's Multi-Year Program Plan details the BTO's planned activities and short-term priorities, including both commercial and residential construction studies based on achieving long-term Net Zero priorities.
The Net Zero Energy Commercial Building Initiative (CBI) aims to achieve marketable net zero energy buildings by 2025 through an array of public and private partnerships to advance the development and adoption of high-performance buildings.
Under the Building America Program, which has demonstrated market change through research conducted under the BTP, parallel residential projects are carried out.
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