Progress Toward a Carbon Emission Standard

Buildings are a major cause of greenhouse gas emissions. But until now there has not been a standard to measure and manage emission reductions. RESNET has issued a new standard to measure a building’s emissions accurately. The standard accounts for the difference in cleanliness of different electric grid at different times of the day and the year. It can give credit for measures that avoid using energy when the grid is more polluting.

Credit: copyright 2022 David B. Goldstein

The buildings that we live, work, and spend time in account for some 40 percent of total U.S. climate-warming carbon emissions. (The number varies significantly depending on how emissions are counted, as elaborated below).  Since the U.S. is committed to reducing greenhouse gas emissions by 50 to 52 percent no later than  2030, carbon emission limits for buildings are a critical need. This is especially true when we consider that the high cumulative levels of U.S. emissions means that this country should do more than its committed level to embolden other countries to reduce the emissions driving the climate crisis.

We have multiple methods to decarbonize our buildings including:

  • increasing the energy efficiency of our buildings,
  • adding renewable energy to a facility or the grid,
  • changing the time at which electricity is consumed so that most, or all of it, can be supplied by renewables – like solar and wind power, and
  • changing from a fuel with higher emissions to electricity.

None of these goals can be achieved in practice without a metric for success at reducing emissions. My previous blog describes broadly how this is being done through the RESNET CO2 Rating Index, but this blog reports on new developments and an action agenda for near term policy and analytic work.


The motivation and technical choices that underlie the CO2 Rating Index are explained in a paper published as part of the ACEEE Summer Study on Energy Efficiency in Buildings in August 2022. The paper, co-authored by myself and RESNET’s Energy Modeling Director, Neal Kruis, provides detailed descriptions of what the RESNET CO2 Rating Index does, how it is planned to evolve, and what technical resources it draws upon.

The RESNET CO2 Rating Index provides an objective, science-based framework for encouraging all four of the choices introduced above: energy efficiency, on-site renewables, flexible demands that optimize the time of energy consumption, and fuel choice. The method is critically dependent on the timing of electricity consumption, and the paper describes how this dataset was derived.

In contrast, existing methods, which are not time-dependent, can give misdirected advice on how to reduce buildings’ carbon footprint. Virtually all the estimates of the carbon footprint of the sector overlook this important factor, which is why the estimate of sector-wide emissions with which this blog began is subject to caveats.

This description is more important than it seems because it is not just a question of demonstrating the credibility of the RESNET results. The importance is that the developers of the time-dependent emissions data have talked to their peers in other countries, and have not found a comparable data set anywhere in the world. This is a problem because the importance of time of use in planning emissions reductions is not just an American problem - but is a problem across the globe. We will next discuss how we are planning to solve it.

Encouraging Global Solutions

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has issued its “ASHRAE Position Document” on Building Decarbonization” that recommends that ASHRAE standards should meet seven specified goals. ASHRAE standards are used as the basis of energy codes in numerous countries around the world.

All four of the options listed in this blog are on their list.

ASHRAE is working on an update to its Standard 90.2 on energy and emission performance of residential buildings and Standard 189.1 on Green Buildings. Both of these standards are planned to use hourly CO2 calculations as part of their requirements. Standard 90.2 will likely use the RESNET CO2 Rating Index directly. The key methods and data underlying the RESNET CO2 Rating Index are being proposed in ASHRAE Standard 189.1. The developer of this ASHRAE proposal along with myself and RESNET project members are presenting a paper at an international meeting in Athens Greece this October that will help encourage harmonized action elsewhere.

Another approach to global harmonization on measuring the carbon impacts of buildings correctly is through the International Organization for Standardization (ISO). In this forum the author is working with the Korean leadership of a working group that is preparing a new standard for Net Zero Energy and Net Zero carbon that is projected to be published by mid-2023. The draft standard distinguishes between these two, and four other, definitions of Net Zero. It also accounts for the variability of the differing estimates of building sector emissions. Other ISO work on Net Zero can also support the value of calculating emissions based on time of use, which can help achieve all of the four options outlined in this blog’s introduction.

These new standards can offer new tools to manage the reduction of emissions to zero or beyond, and help us all reach our climate stabilization goals more rapidly and at lower cost.

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