zEPI: The Zero Energy Performance Index

During the International Green Construction Code (IgCC) meetings in May, I was introduced to a new scale used to evaluate the energy usage in buildings. The method is called the Zero Energy Performance Index (zEPI). You may start hearing the term more in the future.

To understand zEPI, we have to first take a look at how our industry approaches energy efficiency in buildings. One approach is a prescriptive method, which uses building technics to reduce energy usage. For example, we know that insulation can help reduce energy usage in a building. The plumbing industry has followed this theme by insulating water heaters and hot water piping to also reduce energy usage. Manufacturers have followed as well by making more products with higher insulation values. The end result is more energy-efficient products at a lower price. Code and regulatory agencies have encouraged energy reductions by requiring higher standards in building designs to obtain building permits. More building owners and operators are requesting more energy-efficient building methods to reduce energy usage.

This approach has been a win-win for the industry—to a limit, as it can only go so far. What about payback? For example, at what point does adding more insulation on a water heater and piping add cost but minimal energy use reductions?

The next step was to develop a performance approach to reducing energy. This method incorporates an energy model to verify the amount of energy that one method would save when compared to another method. This method helps the design team know what approaches could be used and what ones should not be used in a building. The regulatory agencies have followed this lead and have added energy modeling requirements to their building codes. The end result is that buildings are more energy efficient than they were a few years ago.

The problem has been in real-world operations. Some buildings do not live up to their promise of using less energy, as the owners expected. Building designers know that adding energy-efficient systems does not guarantee an energy-efficient building. For example, low-flow showerheads may have been designed and installed in a building to reduce water and energy usage. But, what if the maintenance personnel unknowingly replaces them with higher flow showerheads? It is not unusual for owners to hold design teams responsible when energy savings are not met.

In the last few years, the building industry has taken a step back and looked at what we are doing. The industry is asking: What are our energy goals? What type of building do we want to build?

zEPI is relatively new to most designers. The intent of this article is to introduce the reader to zEPI. The intent is not to provide a step-by-step guide to design and build by the zEPI scale.

The 2030 Challenge

A growing segment of the building industry is concerned about using fossil fuels to generate energy and the greenhouse gases that are emitted when using fossil fuels. From a global, total energy usage perspective, buildings are one of the largest energy users. As a result, it makes sense to reduce the amount of fossil fuels that a building will use. However, it is important to remember that buildings use energy that is produced by a municipal system, which uses fossil fuels. As a result, decreasing the energy that is used on a particular building site also decreases the amount of fossil fuels that are used by the municipal utility.

This same segment of the building industry is concerned that making incremental improvements with energy efficiency is not enough to make a significant change in our building industry. Thus, the 2030 Challenge was initiated to encourage the development of net-zero energy buildings, or buildings that generate all of the energy used on-site. The technology to do this does exist, and many net-zero energy buildings are in operation. The concern is that they are expensive to build, and net-zero may not be practical for many building types. For example, it is practical for office buildings in moderate climate zones but not for hospitals in extreme climate zones.

The 2030 Challenge takes into account that technologies and methods need time to develop in order for net-zero buildings to be more common and make a real impact on global energy usage. This is one reason why the year 2030 was chosen as the target. Every year, building methods will improve until all buildings built in 2030 are net-zero buildings.

It is important to note that net-zero is not the same as a building that is off the grid. Most of the net-zero calculations are based on one year of energy usage. A building can generate, use, and supply energy to the grid. But, sometimes the building will not generate energy and will need to purchase energy from the grid. With net-zero, the energy supplied to the grid and the energy used from the grid should be equal.


Before you can understand zEPI, you have to understand this background context. We need a method to increase the energy efficiency of buildings every year so that by 2030 all buildings are net-zero. Unfortunately, current energy codes and standards that make incremental changes every few years will not meet the 2030 Challenge. To respond, zEPI was developed.

zEPI gives building designers, owners, and regulators a way to evaluate buildings with the goal of meeting the 2030 Challenge. A zEPI score of zero is a net-zero energy building. A score of 100 is a building with the average energy consumption of one built to the building standards of energy consumption at the year 2000 benchmark.

Most codes do not include the zEPI scale, but it is included in the 2012 IgCC. It is important to note that the IgCC is not incorporated as an enforceable code in many places. However, as more areas look for ways to meet the 2030 Challenge, they should consider adopting the IgCC. The 2012 IgCC sets a zEPI score goal of 51. The intent is to lower the score every year until it reaches zero in 2030.

The zEPI model is developed during the design phase of a project, but as we know, buildings can be operated very differently than they were designed. As a result, the actual energy usage may be different than the energy model. To deal with this, future editions of the IgCC may include an outcome-based approach that tracks actual energy usage in a building to develop the building’s energy rating.

At this point zEPI is not connected to Energy Star, ASHRAE’s Building Energy Quotient (bEQ), or LEED. These methods are very important and are used in many different areas. zEPI could be used as a complement to and basis for green building rating systems. Because net-zero energy is a clear goal, zEPI can be an important tool for the industry to meet this goal.

zEPI can be used for many different types of buildings, including office buildings, schools, and health care facilities. As more energy data is available from actual building energy use, it can be used to improve the quality of zEPI scores.

In conclusion, zEPI is expected to be used as a metric for setting energy requirements that will be used in codes and public policy initiatives that have net-zero goals. The method can reduce the confusion of current moving target energy codes. zEPI should help the manufacturing industry develop new products that will help designers and building operators install systems that will help reach the 2030 goal.

Winston Huff, CPD, LEED AP BD+C, is a senior project manager, plumbing fire protection designer, and sustainable coordinator with TRC Worldwide Engineering, Inc. He serves as an ASPE representative on the ICC Green Construction, Energy, and Water Code Development Committee and is on the U.S. Green Building Council’s Water Efficiency Technical Advisory Group. He was the founding editor of Life Support and Biosphere Science and has served as its editor-in-chief. He is also the editor of Me Green You Green, a LEED credit databank at www.megreenyougreen.com.

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