Net-zero carbon school buildings

The UK has passed into law a target to cut greenhouse gas emissions to net zero by 2050. So is it possible to have a net zero carbon school building?

A framework for achieving net zero carbon buildings has been developed by the UK Green Building Council. It incorporates both the emissions from construction as well as the emissions from operational use.

This will help the UK with its goal to become net zero by 2050, as announced by the Prime Minister Theresa May in June.

A net zero carbon building is a building that is highly energy efficient and fully powered from on-site and/ or off-site renewable energy sources.

Schools can strive to be net zero from their new build projects. Existing schools can also aim to be net zero in their operational energy use.

In the UK, the operation of buildings accounts for around 30 per cent of emissions, mainly from heating, cooling and electricity use. For new buildings, the embodied emissions from construction can account for up to half of the carbon impacts associated with the building over its lifecycle.

The new framework from the UK Green Building Council offers guidance for developers, owners and occupiers targeting net zero carbon buildings, setting out key principles to follow and outlining how such a claim should be measured and evidenced.

Measure, reduce and offset

Regarding construction of new school buildings, the embodied emissions associated with products and construction should be measured, reduced and offset to achieve net zero carbon.

Regarding operational energy, the energy used by the building in operation should be reduced and where possible, any demand met through renewable energy. Any remaining emissions from operational energy use should be offset to achieve net zero carbon.

In the long term, a broader approach for net zero whole life carbon will cover all of the emissions associated with the construction, operation, maintenance and demolition of a building.

Richard Twinn, senior policy advisor at UKGBC said: “The urgency of tackling climate change means that businesses must work together to drive down emissions as fast as possible. But this requires a shared vision for what needs to be achieved and the action that needs to be taken. This framework is intended as a catalyst for the construction and property industry to build consensus on the transition to net zero carbon buildings and start to work towards consistent and ambitious outcomes. It is the first step on a journey towards ensuring all of our buildings are fit for the future.”

Construction considerations

To reduce the impact from construction, a whole life carbon assessment should be undertaken and disclosed for all construction projects to drive carbon reductions.

The embodied carbon impacts from the product and construction stages should be measured and offset at practical completion.

To reduce operational energy use, reductions in energy demand and consumption should be prioritised over all other measures.

In-use energy consumption should be calculated and publicly disclosed on an annual basis.

On-site renewable energy sources should be prioritised and any remaining carbon should be offset using a recognised offsetting framework.

The amount of offsets used should be publicly disclosed. Commenting on the framework, Rob Perrins, chief executive at Berkeley Group said: “This framework is an important step towards defining net zero carbon buildings and helping the industry understand how they can be delivered. We want to help lead this work, which is so important to decarbonising the built environment and protecting our planet for future generations.

Sustainability runs through everything we do at Berkeley Group. We have already become a carbon positive business and have committed to creating new homes that can operate at net zero carbon by 2030.”

Reducing operational energy

To reduce energy demand and consumption, the overall energy demand required to operate the building should be looked at. Improvements include efficient fabric and shading design to reduce heating and cooling demand, natural daylighting to reduce artificial lighting demand, and natural ventilation to reduce HVAC demand. Building systems should be appropriately sized to limit over-engineering.

Energy efficient building systems should be looked at, such as HVAC, lighting, and vertical transport.

For energy management, smart energy/ building management systems should be introduced. Improvements include conducting an energy audit, managing occupant behaviour, managing ‘peak loads’, adjusting HVAC temperature set points, and achieving ISO 50001 accreditation.

The physical wellbeing of building occupants should also be considered alongside energy reductions. These include considerations around indoor air quality, daylight and overheating. The building should be designed and operated in line with best practice guidance on overheating, however this assessment is not part of the scope

Speaking about the net zero framework, James Wimpenny, chief executive at BAM Construct UK said: “Contractors, clients, supply chains need to work together – and quickly – to radically change the way we procure, design and deliver buildings. Smart use of renewable technologies and efficient use of low carbon materials are a priority. Reducing carbon makes financial sense over the lifecycle of buildings and that means we should not focus solely on capital costs when procuring a building.”

Net zero in use

Ashmount Primary School in Islington, London, is the UK’s first zero carbon in use school. The scheme is zero carbon thanks to combined use of Combined Heat and Power (CHP) plant and a 495kW biomass boiler, housed in the Energy Centre. Base heating is provided by CHP and biomass with CHP also meeting electrical demands of the park lighting.

Excess heat from CHP (70kWe, 104kWth) is delivered off site to neighbouring dwellings thus offsetting the site’s own carbon footprint.

An E-Stack system uses low velocity fans to mix incoming and outgoing air in winter and a path for secure night-time cooling in the summer. Energy savings will be significant over a standard naturally-ventilated solution, saving £1,000 in costs per year.

The school building achieved a BREEAM Outstanding rating of 90.49 per cent, and won a BREEAM award for innovative approach to community energy distribution and approach to energy efficiency. It is the first school building to achieve BREEAM Outstanding.

During construction, virtually no waste was created.

Willmott Dixon MD Chris Tredget: “The constrained nature of the site meant meeting the zero-carbon brief was a challenge, and one way we achieved it was to export energy offsite to a nearby housing estate, just one feature that made it BREEAM outstanding.”

Striving for net zero

Hackbridge Primary School in the London Borough of Sutton is being built as a net zero school.

Designed by Architype, the project involves the creation of a new build primary school which will provide space for 420 pupils aged 5-11.

The school is being designed to be net zero carbon, zero primary energy and Passivhaus certified. It will be a highly sustainable environment to learn in and an environment to learn from. Careful consideration has been taken to select materials that are healthy, have low embodied energy and be easy to construct and maintain. The internal environment is developed to maximise natural day lighting and fresh air provision.

To achieve zero carbon and Passivhaus standards, a rigorous approach has been adopted first to reducing energy consumption through very high insulation levels, low air permeability and well considered junctions to minimise thermal bridging. Thereafter, a robust strategy for implementing enough Zero carbon technologies (LZCs) to provide a net zero carbon school will be devised.

Once energy consumption is reduced using PassivHaus methods, achieving a net zero carbon building becomes more realistic through the use of on site renewables.

The aim is to achieve this through an extensive array of high efficiency solar PVs and a reverse cycle ground source heat pump system with the potential for inter-seasonal thermal storage to boost the systems ‘coefficient of performance’. Off site renewables are not required.

The school will have no fossil fuel gas supply (using induction hobs in the kitchen) to avoid any combustion flue products from the site. The building will have a single high efficiency central air handling unit to provide mechanical ventilation to classrooms in winter. In mid season the windows are openable by staff for controlled ventilation and then in peak summer, to avoid potential issues with global warming in future years, the mechanical system can operate in conjunction with cooling from the reverse cycle heat pump (which through the thermal storage increases the winter time performance).