Interested in getting to zero? How do you know when you have a “zero energy” or “zero (operational) carbon” building? A new ANSI/ASHRAE consensus standard has recently been published with the answer.
ANSI/ASHRAE Standard 228-2023, “Standard Method of Evaluating Zero Net Energy and Zero Net Carbon Building Performance”, provides the calculation method and factors needed to determine whether a building is or is not zero net. It can also show how close a building, site, community or portfolio is to achieving zero net status. The calculation is based on source energy, a code word for looking at energy not only in terms of what is crossing the boundary of the building site but also counting what is used to produce that energy and get it to the building. Similarly, multipliers are used for carbon dioxide and other climate-change-producing chemicals to give the amount of carbon-dioxide equivalent (CO2e).
EVALUATING ENERGY
Let’s first look at energy and the critical role of the building’s site boundary in the standard. The “site” can be a building, group of buildings or even a portion of a building along with the surrounding area of land inside a boundary the user defines. Normally this would be the property line. Energy-containing fuel, like natural gas, and pure energy, like electricity, can be metered coming into the site or even sometimes flowing out of the site across the boundary and can come from a number of sources. It can also be generated within the site, such as from a renewable source, like photovoltaic (PV) panels.
There are other standards dealing with efficiency within a building. For the purposes of Standard 228, if energy, such as electricity, is created and used within the site and does not cross the site boundary it is not considered in the standard’s balancing equation for compliance. If electricity from renewable or another source is exported across the boundary and is put on the grid, all the other generators on the electric grid do not need to produce that power. Depending on the mix of generating assets, exporting electricity back to the grid can result in a credit from not having to generate it with grid-based non-renewable or carbon-based sources.
There are certain situations where renewable electricity is too plentiful during the day and non-renewable generation has to be added in the evening and overnight. Generating solar-powered electricity at noon and exporting it into a grid overflowing with renewable energy does not compensate for having to burn natural gas for power at night. Where more granular information is available on this issue, possibly even hourly, an adopting authority can require that the calculation be based on that more finely tuned and locally available data to avoid giving credit where it is not earned. Some California locations have this level of detail available now and it is likely to become more prevalent in the future.
What if there is no ability to generate renewable energy onsite to balance what is coming into the site? Renewable energy from outside the site can be counted toward a building’s renewable generation, but it must meet certain qualifications and is discounted in the calculation. The amount is also limited to encourage the installation of onsite generation. The limit on counted offsite renewable energy is based on a reasonably efficient building.
Transportation energy that comes into the site and then goes out of the site through car chargers or gasoline/diesel fueling is netted out.
CONCENTRATING ON CARBON
“Carbon” is shorthand for the carbon dioxide that is creating global warming. Additional chemicals are rolled in by using the term “carbon-dioxide equivalent”, or CO2e. For carbon, the standard takes an approach similar to energy, looking at what crosses the site boundary and multiplying by a factor for CO2e emissions. At the moment, only operationally generated carbon in the form of fuel and energy use is considered. There is one exception: Refrigerant leakage can be such an important part of the CO2e emissions during operation that it was included in the calculation.
Similar to contracting for off-site renewable energy, having “carbon offsets” counted in the equations is another question. While the path is available for very limited carbon-offset purchases, it may not result in a zero-carbon rating under the current standard. It will likely be much easier to avoid the need if alternative options, such as increased onsite renewable generation, are available.
IMAGES: courtesy ASHRAE