About our building

In 2014 / 2015 City Hall emitted 1,985 tonnes of carbon dioxide. This is better than the average amount for similar buildings.

City Hall has been designed to keep our carbon dioxide emissions as low as possible. We are continuing to work on ways to improve this. For example:

• in 2007, solar photovoltaic panels (solar panels) were installed, generating energy with zero carbon emissions
• ‘voltage optimisation’ technology has been installed to reduce the voltage we use to the minimum required
• lighting improvements continue to be carried out: we are changing from 75 watt bulbs to 16 watt LEDs where possible
• movement sensors on all floors help ensure lights are switched off when areas aren’t occupied
• 'boiler optimisation' makes sure that we don't generate more heat than the building needs
• smart meters allow our energy use to be measured on a floor-by-floor basis. This will help us target further energy efficiency improvements

An unusual shape

Controlling the heat build up that comes from exposure to sunlight is very important in a glass building. City Hall is designed to do this in a number of ways:

• in conventional terms, the building has no front or back – it’s a geometrically modified sphere. This minimises the surface area of the roof exposed to direct sunlight, which reduces the amount of heat build up inside the building
• the building's spherical shape means it has around 25 per cent less surface area than a cube of the same volume. This means that less heat escapes during the winter, and the building doesn't get too hot in the summer
• the building leans back away from the river, to present as little surface area to the sun as possible. This also means that the building does not leave the river walking in shadow.
• the floor plates at the back of the building are staggered inwards, providing natural shading for the floor beneath

Reusing ground water

We use cold ground water to cool City Hall, which is very energy efficient.

• the actually cold water is brought up to the building through bore holes, where it flows through beams on each floor to chill the office spaces
• this reduces electricity consumption as we don’t need to refrigerate water or use air conditioning systems
• after being used to cool the building this water is then used for flushing the toilets

Energy saving

The building runs its cooling on a quarter of the energy used by a typical modern office building. We manage this every day, for example:

• the building is naturally ventilated, with user operated vents beneath every window
• heat generated by computers and lights is recycled
• recycled materials have been used to fit out the building, including recycledfloor tiles in the public areas.