Beaufort court renewable energy centre zero emissions building Studio E Architects

Where possible the reuse of existing buildings is the best way to meet the sustainability agenda. An excellent example of this strategy is the headquarters of an energy company near London. The description of the development by David Lloyd Jones of Studio E Architects is quoted at length as being the most appropriate explanation of the design strategy.

Solar design aspects of the renewable energy centre and interim findings

David Lloyd Jones, Studio E Architects

The Renewable Energy Centre at Kings Langley in the UK is the new headquarters and visitors' centre for Renewable Energy Systems Ltd, a company whose business is developing wind farms on a global basis. The original buildings on the site housed chickens to provide eggs for the nearby Ovaltine malt drink plant. These buildings, derelict for 10 years, have now been converted and extended to provide for the office and visitors' centre accommodation. A sustainable approach was taken, particularly in respect to energy supply and use. The design was based on the comprehensive application of passive and active solar measures and is believed to be the first commercial net zero carbon dioxide emissions building in the UK. The project was completed in December 2003 and the energy systems, weather and internal comfort are being monitored over a 2 year period. An EC Framework 5 grant contributed to the cost of a hybrid PV thermal array, a seasonal heat store, the space heating and the associated mechanical and electrical systems (Figure 18.14).

Design principles

The Renewable Energy Centre is the first commercially developed building to be carbon neutral and entirely self-sufficient in energy. Indeed the various integrated renewable energy systems will, over any year, generate a surplus. This will be fed into the electricity grid for the use of the community.

No attempt was made to replicate the arts and crafts style of the original buildings in the new building works. The editions and replacements are expressed in a clean, modern, albeit sympathetic, idiom reflecting the contemporary concerns of Renewable Energy Systems and the leading edge energy technologies deployed over the site and concealed within the buildings.

The project brief was the conversion and extension of the former Ovaltine egg farm to provide 2665 m2 of headquarters office accommodation for RES. This was to be carried out using, so far as economically practical, a range of renewable energy measures and employing 'best practice' sustainable strategies. RES was assisted in this objective by the contribution from the EC Framework 5 Programme. This funding was conditional on the adoption of a radically innovative approach to resolving sustainable issues and the involvement of a pan-European design and development team. On the basis of this innovative content, RES requested that additional facilities for visitors and parties

Beaufort Court Wind Turbine

a. 225 kW Wind turbine b. Hybrid PVT array c. Crop store d. PV invertors e. 1500 m3 water heat sink f. Biomass crop (miscanthus)

g. Renewble energy centre h. Crop shredder i. Biomass boilers and gas fired backup boilers j. Electrical import/export meters k. 80 m deep borehole in chalk aquifer l. 2 no. air handling installations m. Fresh air n. Exhaust air o. Irrigation

Figure 18.14

Energy strategy who might wish to see and learn about the building and its energy systems.

Accordingly, the design principles upon which the development is based were to:

provide a fully operational head office which meets the commercial needs and conditions of the property market; provide exhibition, conference and facilities for the use of RES and visitors to the building;

• deliver a building that minimises energy consumption and the use of scarce resources and that contributes positively to local economic and community needs;

• deliver a building whose energy consumption is provided entirely from on-site renewable energy sources;

• integrate seamlessly the social, technical and aesthetic aspects of the project.

The new buildings

In order to provide for the new uses, the existing buildings had to be radically altered and extended. However, the local planning authority required that the views of the outside of the building must remain largely unchanged. Both the 'coach house' and 'horseshoe' buildings had to be converted for modern office use with, in addition, exhibition, catering, conference, meeting, and main plant spaces.

The conversion of the coach house was relatively straightforward: the building fabric was upgraded to meet contemporary office use and the courtyard was enclosed by inserting a new steel structure. The conversion of the horseshoe was more complex. The construction between the two towers, except for the timber roof structure, was entirely demolished, the ground floor was lowered, the upper level floor and the roof reinforced, and the outer external wall rebuilt. The ground floor was extended into the courtyard by 5 m and a new single-storey link, incorporating the main entrance, was placed between, and connecting, the two wings of the horseshoe. Turf was planted on the roof of the new office space.

A third entirely new building was introduced close to the northern perimeter of the site. So as not to intrude in the landscape, this building was partly sunk into the ground and the excavated earth banked up against the north wall. This building provides storage for the harvested biomass crop. Its roof comprises the hybrid photovoltaic/thermal array.

The site layout

The triangular site comprises 7.5 ha of farmland located in the metropolitan green belt. The boundary of the site is formed, to the south, by the M25 orbital motorway; to the west, by the mainline London to Glasgow railway; and, to the north east, by a private road. The egg farm is set out on an axis, which, if extended northwards, aligns with the Ovaltine factory - the destination of all the eggs laid on the old farm. The layout of the various elements comprising the development is shown on the site plan. Its location adjacent to one of Europe's busiest motorways brings sustainability in action closer to the millions of people using the road.

The energy strategy

It is intended that all energy used at the Renewable Energy Centre be provided by renewable sources located on the site. The project demonstrates the integration of passive solar techniques with a range of inter-related renewable energy systems. The energy provision derives from:

• optimising the use of natural ventilation, daylight, high insulation, low air infiltration, solar control, materials that derive from the minimum use of energy in their manufacture and transport (low embodied energy materials), recycled materials, the minimisation of resource depletion, low use of water, car sharing and the encouragement of the use of public transport;

• a hybrid photovoltaic/thermal (PVT) array providing both electricity and hot water installed as the roof to a biomass crop store, the heat of which is passed to:

- a seasonal heat store, comprising a 1100 m2 body of water concealed beneath the ground, used to assist heating of the buildings in winter (Figure 18.15);

- a biomass crop (miscanthus or 'elephant grass') cultivated on the surrounding land, harvested annually, dried and stored in the earth-sheltered space beneath the pVt array;

• future biomass plant which shreds the miscanthus and burns it to provide heating for the building (and, possibly, in a forthcoming adaptation, combined heat and power (CHP));

• ground water cooling pumped from an 80 m deep bore hole to cool the buildings in summer (and then passed out of the building to irrigate the biomass crop);

• a 225 kW wind turbine supplying, with the PVT installation, all the electrical power required by the building and a significant surplus fed into the national grid.

Clean and green

Bringing back to life a derelict building rather than building new is a considerable benefit in terms of land utilisation, use of resources and improving the amenity of the area. The construction work was undertaken on the basis of minimising waste and using materials and components with low embodied energy from readily available resources.

In order to minimise the need for energy, a judicious combination of active systems (mechanical ventilation, artificial cooling, heating and lighting, building management systems) and passive systems (solar heating, natural ventilation and lighting, solar shading, a well-insulated building envelope incorporating thermal mass) was developed.

The buildings are exposed to considerable external noise from passing trains to the west and the motorway to the south. To cut out the disturbance from noise inside the buildings, the outward facing facades had to be sealed. This, together with the relatively high levels of heat generated by modern office use, requires the building to be artificially cooled in summer months. The cooling source is water drawn from aquifers located in the chalk below the building. This strategy avoids the heavy energy consumption and potential polluting effects of refrigeration

Figure 18.15

PVT/heat store/space heating plant normally used for air conditioning. The cool water is used to drop the temperature of air being fed into the building and/or is circulated through convectors within the office space, cooling the air within it.

Heat is supplied from the biomass boiler (or gas boiler until such time the biomass plant is installed) and from the PVT array, either direct or via the seasonal ground heat store. Hot water from these sources is used in a similar way as the chilled water for cooling. Electricity is generated from the PVT array and the wind turbine.

Windows can be opened in facades and roofs facing away, or sheltered from, the motorway and the railway, to ventilate the building in y

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FRESH AIR

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COMBINED PV + SOLAR THERMAL ARRAY

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HEAT EXCHANGER

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temperate conditions. Exposed windows are shaded from the sun by fixed glass or aluminium screens and by deciduous tree planting, thereby reducing unwanted solar gains and the need for cooling. The building is well insulated and sealed.

Predicted energy use and energy supply is shown in the table below. The current monitoring programme will show whether these predictions are borne out in reality.

Estimated energy balance for the site:

Electrical

Space heating

Building annual loads

115 MWh

85 MWh

(2500 m2 building gross area)

PV/T direct contribution

3.2 MWh*

15 MWh

Heat collected into storage

24 MWh

Pumping load/heat lost from storage

-4.5 MWh

-12 MWh

Wind turbine

250 MWh

Miscanthus: peak expected

160 MWh

production (60 odt/year)

Net contribution

248.7 MWh

187 MWh

Potential electrical export

133.7 MWh

Potential surplus miscanthus for

102 MWh

heat export * With 48 m2 of PV.

heat export * With 48 m2 of PV.

A building management system (BMS) controls and optimises all the energy systems, including opening and closing the roof lights. It also records all monitored results from the various energy systems before passing the results to a site in Denmark for uploading onto the website.

RES actively encourages staff to use public transport, bicycles and car sharing for travel between home and office.

About 5 ha of the 7.5 ha site are given over to miscanthus cultivation. In addition there is a car park and a 5 aside football pitch. The remainder of the land is planted with indigenous species of trees, shrubs and grasses. Wildlife is encouraged by the re-creation of natural habitats.

The renewable energy sources

Wind Turbine

The 225 kW wind turbine has a hub height of 36 m and a rotor diameter of 29 m and is a Vestas V29 model previously in operation in the Netherlands. The turbine is connected to the buildings' electrical distribution network and to the national grid. It is expected to generate 250 MWh annually, which is greater than the anticipated building consumption, and excess power (equivalent to the needs of around 40 homes) will be exported to the grid.

Biomass

The buildings' heating needs will primarily be met by a biomass boiler fuelled by the energy crop: miscanthus or 'elephant grass', 5 hectares of which have been planted on the site. The crop is harvested annually in the late winter with conventional harvesting equipment and stored as bales until needed. The bales are shredded before being fed into the biomass boiler. The field is expected to yield 60 oven-dried-tonnes per year with a calorific value of 17 GJ/tonne. The 100 kW biomass boiler is provided by Talbott's heating. It is 80 to 85 per cent efficient and can modulate down to 25 per cent of full load. The shredded bales are fed into the boiler by a mechanical screw auger. Biomass is carbon neutral as the CO2 emitted during combustion is balanced by the CO2 absorbed by the crop, which is coppiced on short rotation. The emissions from the boiler comply with the Clean Air Act. The boiler is expected to be installed and operating in 2004-2005.

Ground water cooling

Ground water is used to cool the buildings during the summer. Water is extracted from the local aquifer at 12°C via a 75 m deep borehole. First, it is used to cool and dehumidify the incoming air to the buildings in the air handling units. The water is then circulated at 15°C through chilled beams (finned tubes) at high level in the offices. Finally, the water is used to irrigate the energy crop.

PVT array

The 170 m2 solar array comprises 54 m2 of hybrid PV/thermal (PVT) panels and 116 m2 of solar thermal panels. The PVT panels consist of a photovoltaic module, which converts light into electricity, and a copper

Water In

Water In

Figure 18.16

PV/thermal panels (Courtesy of Studio E Architects)

Thermal Pvt

Figure 18.16

PV/thermal panels (Courtesy of Studio E Architects)

heat exchanger on the back to capture the remaining solar energy. The panels have been developed by ECN in the Netherlands, incorporating Shell Solar PV elements and Zen Solar thermal elements. They produce electricity and hot water (Figure 18.16). The solar thermal panels are identical to the PVT panels, but without the photovoltaic element.

Seasonal underground heat store

The underground heat store is an 1100 m3 body of water that stores the heat generated by the PVT and solar thermal panels for use in the buildings during the colder months. The top of the store is insulated

Highland Laddie ShipBeaufort Court

with a floating lid of 500 mm expanded polystyrene. It is hinged around the perimeter to allow for the expansion and contraction of the water and the design also incorporates a suspension system to support the roof should the water level reduce. The sloping sides are uninsulated. As long as the ground around the store is kept dry, it will act as an insulator and additional thermal mass, increasing the capacity of the store. The high specific heat capacity of water (4.2 kJ/kg°C) makes it a good choice for storing heat.

During the summer there will be little or no demand for heat in the building, so the heat generated by the PVT array will be stored in the heat store. In the autumn some of the solar heat generated will be used directly in the buildings and the excess will be added to the heat store. The temperature of the water in the store will gradually rise over the summer and early autumn. During the winter the solar heat generated will be less than the buildings' heat load, and heat will be extracted from the heat store to heat the incoming air to the building. The temperature of the water in the store will drop as the heat is extracted. Some heat will also be lost to the surroundings. This is estimated to be about 50 per cent of the total heat put into the store over the summer. The relatively low-grade heat from the store can be used to preheat the incoming air to the building, as the outside air will be at a lower temperature than the water.

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