Most buildings around the world – residential, commercial or industrial – use a lot of energy during their lifetime, whether for lighting, heating, ventilation systems or plugged-in devices. In fact, buildings use about 40% of global energy, 25% of global water, 40% of global resources, and they emit approximately one third of greenhouse gases.

The energy required to run these buildings has risen precipitously over the last decades, putting more and more demand on national power grids. This in turn, has increased the pressure to generate power by (often) burning fossil fuels - contributing to the climate change we see today. This deadly cause and effect has forced many engineers and policy makers to question by what means we could reduce energy consumption in the buildings we construct and use.

What is a zero-energy building?

A zero-energy building (ZEB) is a building where the total energy used, over a year, is equivalent to the amount of the renewable energy created by it – in other words, it produces enough energy to meet its own annual requirement. This means it does not need to draw energy from the power grid, reducing greenhouse gas emissions in the process. Incidentally, for these homes, offices and manufacturing plants it is their utility bills that are one of the most expensive running costs (if not the single biggest cost) after any mortgage or bank repayments. So, not only are there environmental reasons for having ZEBs, but financial ones too.

One thing to note is that there are various definitions and names/acronyms which zero energy buildings go by around the world: nearly zero energy buildings; zero net energy; green buildings; net zero carbon buildings; or simple zero energy buildings. Although these terms may differ in scope and approach, the fundamental aim of reducing energy usage, improving the building’s energy performance and lowering greenhouse gas emissions apply to all definitions.

Another point to note is that zero-energy buildings refer just to the operation and maintenance of the building in question, and does not account for the greenhouse gas emissions associated with the non-operational phase of a building, i.e. the planning, design, construction and deconstruction phases, and, in particular, the environmental impact of souring, manufacturing and transporting the materials used in the build.

Components of a zero-energy building

There are two key components of a ZEB: reducing the energy consumption of the building itself, and creating renewable energy for its own use on-site. The first key element (of decreasing the total amount of energy used in a building) can be driven by employing energy efficient lighting systems, insulation, better water management, improved ventilation systems and smart meters. Even changing the behaviour of occupants can have an impact on the energy efficiency of a building. The second element (generating renewable energy on site) could include installing solar panels, small wind turbines, or micro combined heat and power systems which meet the electricity, heating or cooling needs of a building. Any excess energy that the building does not need can be transferred to the national grid, enabling the owners of the building to earn money from their own frugality.

Examples of zero energy buildings

There are various examples of zero energy buildings around the world, some have been newly constructed, and others have been achieved through retrofitting existing buildings. As the transition from energy intensive to energy efficient gathers pace, buildings across the world are proving that high performance can be combined with renewable energy generation. Let’s take a look at a few.

Indira Paryavaran Bhawan, New Delhi, India

Opened in 2014, this building was the first ever zero net energy multi-storeyed building in India. The engineers reduced energy demand by providing adequate natural lighting, shading and landscaping to lessen ambient temperatures, as well as producing 100% of its energy requirements via an on-site installed solar panel – located on its rooftop. When compared to conventional buildings, it has reduced electricity consumption by 40%, and water consumption by 55%.

Panorama St Paul’s (the former BT HQ) at 81 Newgate Street

This major commercial building in the heart of London aims to become the capital’s first existing building to transition to net zero carbon. The plan is to achieve this by 2050 through extensive retrofitted energy efficiency measures. These include photovoltaic panels (solar panels) on the roof, air source heat pumps and chillers, and passive design strategies such as high-performance fabric. The scheme has been designed to achieve a carbon reduction target of 51%.

energy+Home1.0, Muhltal, Germany

This was a 1970s built residential property, which in 2011 became one of the first in Europe to become a “surplus energy house”, meaning that it generated more energy than it needed. This was done by incorporating rock wool insulation, new windows and a heat recovery system. To generate renewable energy onsite, an air-to-water heat pump was installed, which absorbed heat from the outside air and transferred it to water, heating the rooms with low-temperature underfloor panels. Solar energy units were installed on the roof to supply 100% of its electricity requirements.

Walgreens, Evanston, USA

This pharmacy retail store was the first net zero energy retail building in America, producing more energy than it consumes. It does this by not only generating electricity through two wind turbines on site and 850 solar panels on its roof, but also reducing its energy consumption in store. They have installed LED lighting, daylight harvesting and use carbon dioxide refrigerant for heating, cooling, and refrigeration equipment. As a result, the building has reduced its energy consumption by more than 50%.

Future: Zero Energy Cities?

An engineered extension to zero energy buildings is zero energy cities. As more buildings become energy sufficient (and even sell energy back to the grid), it is conceivable that communities and cities will themselves become zero energy. This will mean that the total energy used by any given city’s infrastructure is equal to the amount of renewable energy it creates.

The design and construction of more sustainable buildings including the use of zero-carbon technologies/materials will help reduce carbon emissions in the long run. Obviously, for a whole city to become zero energy, it is not just the buildings that will have to change. Transportation, vehicles, street lighting, recycling plants, smart power grids, better designed public spaces and intelligent building management will all be needed to create a smart city ecosystem and reduce consumption.

Whether residential, commercial or industrial, engineering solutions that create zero energy buildings are the first steps to achieving zero energy cities – a transition that will be critical in slowing down rampant climate change and a transition we need now to accelerate.