Low-energy buildings

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This week, a look at low-energy buildings focuses on the world’s first zero carbon emissions office, with top tips on how to design your own – plus checklist, products, suppliers’ guide and how Arup is turning green.

The green HQ: Beaufort Court, Kings Langley, Hertfordshire

When wind farm developer and operator Renewable Energy Systems needed a headquarters, it naturally wanted a development reflecting the greenness of its business. Chief executive Ian Mays spotted the derelict Ovaltine egg farm that once produced the eggs for the famous malt drink near his home. He decided to buy it and convert it into what is now said to be the world’s first zero carbon emissions head office.

The building’s low-energy features include a unique hybrid solar panel that produces electricity and hot water. Water heated by the panel is passed through the coils in an air-handling unit to warm the air used for heating the building. In summer, excess heat produced by the 170 m2 of solar panels heats 1400 m3 of water stored in a tank. In the winter this is used to pre-warm the air that heats the building. Additional heat is produced by a biomass boiler burning elephant grass, which is grown on five acres of land on the site.

Natural ventilation was ruled out because the windows need to be closed in the summer as the egg farm is next to a noisy M25 and railway line. At night air is circulated through the building to cool the structure but additional cooling is still necessary. Water from a 75 m deep borehole is used to cool the building and is supplemented by chilled beams in the offices when necessary. The chillers supplying the chilled beams are powered by a wind turbine and electricity from the hybrid solar panels. Indeed, the building is a net exporter of power to the grid – the wind turbine produces 225 kW of electricity, enough to power 30 homes.

Project team

Client
Renewable Energy systems

Architect
Studio E Architects

Environmental and M&E engineer
Max Fordham

Structural engineer
Dewhurst McFarlane & Partners

Quantity surveyor
A&S Friend & Partners

Main contractor
Willmott Dixon

Tips for designing low-energy buildings

Studio E Architects and services engineer Max Fordham offer six tips for designing low-energy buildings used at Beaufort Court.

1. Push the envelope
The design of the building envelope is the best opportunity to minimise energy use. Select the form, orientation and materials to optimise natural lighting, cut solar gains and minimise the need for artificial cooling in summer, as well as retain heat in the winter. For example, ridge lights were introduced high up into the horseshoe roof at Beaufort Court to naturally light the heart of the building and ventilate the spaces below.

2. The light–heat balance
Creating naturally lit buildings that have low heating and cooling demands is difficult. This is because naturally lit buildings need to have a large envelope area in relation to the volume to get light into the building but the envelope surface area needs to be minimised to limit heat and cool losses. The trick is to find a satisfactory balance between the two.

3. Plant deciduous trees
Use deciduous trees for solar shading as they will provide effective shade in the summer and beneficial winter sun when the leaves fall off. At Beaufort Court, hornbeam trees were planted at regular intervals around the perimeter of the building. Any type of deciduous tree is suitable, but the faster growing varieties will give greater effect in a shorter time.

4. Take care at junctions
Consider the junctions carefully between different construction elements where air leakage is most likely to occur. These include openings such as windows, roof eaves and any wall or roof penetrations.

5. A material world
Consider the embodied energy of the materials to be used – the energy used to extract, produce or manufacture the materials. Natural materials such as timber generally have low embodied energy whereas manufactured materials such as steel, aluminium, plastics and glass are energy-intensive to produce. Note that energy consumption in use generally outweighs that consumed during production, so the use of building insulation saves more energy than it takes to produce it.

6. Use it wisely …
The way the building is used has a strong influence on its energy consumption. A workforce that is well-educated in how their building works will be in a better position to contribute towards its success.

Hot property: Beaufort Court’s unique solar panels

This is the first time a PVT (photovoltaic/thermal) module that converts sunlight into electricity and heat has been used outside a research facility. It was developed by Dutch energy research specialist ECN and incorporates Shell Solar’s PV cells fitted into Zen Solar’s thermal modules.

Most of the research concentrated on developing the adhesive to attach the PV cells to the copper absorber sheet. Because of the very high temperatures attained inside the panel, this was not an easy job. According to Bill Watts, the Max Fordham engineer who worked on the project, the panel generates as much power as a conventional PV panel and almost as much hot water as a conventional thermal panel. The panel generates far more power than conventional solar systems.