Demystifying zero net energy design

A zero net energy (ZNE) building is typically highly energy efficient and produces as much renewable energy as it consumes on an annualized basis and is a powerful framework for new and existing buildings.

By Martin Howell May 13, 2020

On the back of the Paris Agreement on climate change and subsequent increased global action toward climate change mitigation and adaptation, countries, cities, and organizations — many of which are our clients — are setting their own stringent greenhouse gas reduction targets.

Many of our collaborators identify zero net energy (ZNE) building design as one approach to help progress the built environment towards these targets. A ZNE building is typically highly energy efficient and produces as much renewable energy as it consumes on an annualized basis. Sometimes mandated and in other cases a goal or aspiration, ZNE is a powerful framework for energy-efficient new-building design and existing building retrofits.

So why aren’t we seeing a mad dash to decarbonize through ZNE design?

For one thing, ZNE is in such an early stage of development that there’s some ambiguity about its definition. For another, regional variances in the way ZNE is interpreted as a concept have led to some confusion. It’s a complex subject with numerous variations across different building typologies and climate zones — not the one-size-fits-all some might think.

Breaking it down to the basics

Based on internal research already underway at Arup, my team and I saw the opportunity to develop an easy-to-use manual: a five-minute guide describing the options and opportunities for ZNE. In it we map out beneficial applications, existing policies, and various designations for both ZNE and zero net carbon. This guide helps us create a shared understanding and language with our clients as we partner with them as sustainability advocates and experts.

For example, one of our education sector clients wants to implement aggressive ZNE and carbon policies but isn’t quite sure how to do it. Using this guide, we’re able to start that process with them, working through the various classifications and application details at the building, campus, and organization levels with start-to-finish knowledge. My hope is that the guide raises awareness about ZNE — both its challenges and its opportunities — enough to make these conversations a little bit easier, and more plentiful, in the future.

Ease of electrification

One major opportunity linked to ZNE is electrification. Given that the electrical grid is greening through the implantation of large-scale solar and wind energy plants and distributed renewable sources, organizations can often effectively reduce their carbon emissions by relying more on electricity over natural gas. While typical buildings use both, it’s currently much easier to decarbonize electricity generation than it is to decarbonize natural gas.

But the compounding factor with electrification is the electrical infrastructure of our cities. It’s not just buildings that we’re electrifying, it’s also transit. We’re seeing a lot more electrification of personal vehicles and a shift toward zero emission buses (ZEB), all of which is going to put significant demand on the grid.

We’re going to need holistic changes to our current centralized infrastructure to be able to accommodate these additional loads, a process that has already started. Decentralized systems like distributed energy, renewable energy within urban environments, and vehicle-to-grid concepts, where you can actually start using the battery in your car as a storage device for the grid itself, are already influencing our existing grid infrastructure.

With electrification, there’s a portfolio of options available for building heating, including heat pumps, solar water heating, and heat-recovery chillers — heating presents probably the largest challenge that needs to be tackled for an electrification future. Not all solutions fit every building type, but that’s exactly the sort of issue we’re helping our clients resolve.

End-user experience

Despite this shift in infrastructure, the end-user experience should remain relatively unchanged, if not substantially improved by ZNE and electrification. If you’re no longer burning natural gas within your building, local emissions will reduce, improving air quality and reducing potential safety impacts. Plus, buildings that are greener, using more renewable energy, are generally healthier for occupants.

Beyond these immediate benefits, ZNE can be a fundamental first step toward individual and community resilience. ZNE is essentially implementing energy efficiency within a building and combining that with on-site renewable energy generation. Once you’ve gone through those two evaluation processes, it’s a much smaller step to start thinking about energy storage. Batteries can give you relative normalcy across utility interruptions and major events, and provide overall flexibility in interacting with the grid.

Here in wildfire-prone California, for instance, utility companies are actually cutting power to certain areas during times of high temperature, high wind, and low humidity because failed utility infrastructure can spark fires. If you live in a zone where there’s a high probability of fire, where you could potentially have your power cut to avoid a greater catastrophe, then being able to rely on additional resiliency within your building, through batteries and renewable energy, seems like a win-win.

California at the forefront

It’s an exciting time to be practicing in California. In 2006, California passed Assembly Bill 32, one of the first pieces of climate policy in the US, which required a significant reduction in greenhouse gas emissions. Since then, requirements have become even more stringent at the state level. The California energy code is becoming more and more aggressive, requiring higher and higher levels of efficiency from buildings. We’ve also started to see requirements for renewable energy infrastructure, as well as space and planning requirements for renewable energy in buildings.

Certain cities are taking the lead with additional reach codes moving toward a ZNE approach. In 2019, Berkeley became the first US city to mandate this move to electrification by prohibiting natural gas in new homes. Other Cities are following this move.

It is exciting to be in a position to help our clients work through the implications of these policies and help them move towards a decarbonized future.

Innovation cross-pollination

California certainly has a whole suite of environmental policies and regulations that are pushing us to decarbonize transportation and the built environment, but many of these measures wouldn’t necessarily be the best fit across the rest of the country or in other countries. California has a very mild climate, but other environments have significant heating and cooling needs that require a different approach.

In some parts of the world, there’s more of a focus on renewable hydrogen as a transitional fuel to effectively replace and decarbonize natural gas networks. That may also be a more viable approach for parts of the United States that experience colder climates.

And that’s really one of the best parts of my job: looking for opportunities to cross-pollinate what’s going on here with some of the innovative work going on in other parts of the world. Our aim, starting with tools like this new ZNE guide, is to share the benefits, best practices, and possible portfolio options of ZNE locally while providing that connective tissue for progressive energy-efficient work throughout the world.

This article originally appeared on Arup’s websiteArup is a CFE Media content partner. 

Author Bio: Martin Howell, associate principal, Arup