What is Net-Zero Building?
Net-Zero or Zero Net Energy (ZNE) or Net-Zero Carbon are all terms for achieving zero greenhouse gas (GHG) emissions for buildings and their operations. This is achieved through a combination of energy efficiency and renewable energy.
A Net-Zero building is any building whose yearly energy consumption or load is equal to or less than the renewable energy it produces on-site or offsets through the purchase of RECs (See REC Factsheet), off-site generation, or a Power Purchase Agreement (PPA).
Net-Zero buildings are high performance, which means they implement various energy efficiency measures in order to reduce their energy consumption. Leadership in Energy and Environmental Design (LEED) is one the standards in the US used to judge a building's performance in terms of energy efficiency. However, LEED scored buildings are not guaranteed to be Net-Zero. The other building standard that does reach Net-Zero is Passive House (PHIUS).
Generally, buildings 5 stories or taller will consume more energy than they can limit with energy efficiency and produce with on-site renewables. They will need to offset their remaining consumption with renewable energy produced off-site.
(Below is a useful PowerPoint that summarizes what Net-Zero is, why it is important, and how to achieve legislation at the state level)
Why is Net-Zero Building Important?
In MA, the state has committed to the goal of reducing GHG emissions by at least 80% by 2050 (See 2008 Global Warming Solutions Act). In order to achieve that goal, the state must significantly reduce its energy consumption and transition to renewables. The state has already begun to do this by implementing the Renewable Portfolio Standard (RPS) (See REC Factsheet), which mandates that utilities source an increasing percentage of their portfolio from renewable sources each year.
Net-Zero is important because 67% of energy consumption and emissions in MA comes from buildings and their operations (2016 EIA Data). Buildings must transition to Net-Zero in order for the state to reach its 2050 goal of at least 80% GHG emissions reduction.
How to Achieve Net-Zero for All Buildings?
As stated in the first section, Net-Zero is achieved through building better buildings that are energy efficient and use renewable energy. Renewable energy generation is increasing and becoming cheaper to build but it is still far too expensive to build out enough renewables to completely offset the existing energy consumption of all buildings. Therefore, energy efficiency is the first and cheaper option for achieving Net-Zero.
For newer buildings, energy efficiency becomes easier as newer technologies are implemented and building standards improve. However, many buildings are older and far less efficient than newer ones built with energy efficiency in mind. For older buildings, audits and deep energy retrofits are needed to reduce energy consumption. Once energy consumption has been reduced enough, it becomes easier to offset the remainder with renewables.
Although it is easier to achieve energy efficiency with newer buildings, overall energy efficient building standards are driven by the building code. Net-Zero ins not required and energy efficiency standards are minimal with the current MA State Building Code and the 2016 Stretch Energy Code (780 CMR Chapter 115 AA). The Stretch Code requires that new building must have a Home Energy Rating System (HERS) index of 55. The HERS index ranges from 150 to 0, with 0 being the most energy efficient. In order to achieve Net-Zero for all buildings, a better code must be implemented.