CIBSE Case Study: Gold standard - Worcester's Hive Library
CIBSE Case Study: Gold standard - Worcester's Hive Library
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Article from the March 2013 edition of the CIBSE Journal written by Andy Pearson.
It is official: 72% of the public are impressed by The Hive. This ringing endorsement is for the UK's first, fully integrated public and university library. The statistics were compiled from an exit survey of visitors to the newly opened facility, which is situated in the heart of historic Worcester.
The public are not the only ones to have been wowed by this innovative new building. The judges at the CIBSE Building Performance Awards were won over by The Hive's impressive low-carbon, energy efficient credentials. It was awarded the accolade of Best New Build Project of the Year (above £5m). The judges described it as: "an excellent example of good practice engineering delivering BREEAM Outstanding energy performance".
It was 2004 when the concept for a low energy, integrated public and university library was put forward as a pragmatic solution to meeting the needs of both Worcester County Council and the University of Worcester. The council's existing library was no longer fi t for purpose and the university was seeking to improve its learning resources in the city. They formed a partnership and the idea for The Hive was born.
This pioneering concept needed an innovative new home, so in 2007 a PFI competition was launched. The partners put together a challenging brief for the project, which included the requirement that the new building should achieve a 50% reduction in carbon emissions (based on Part L of the Building Regulations 2006), and that 50% of the building's energy would come from renewable sources.
That was not all: the brief also called for the building to have a minimum environmental rating of BREEAM "Excellent", and it was to be, as far as practical, naturally ventilated. In addition, the scheme had to be suffi ciently robust to be able to maintain comfort conditions under the impact of climate change in 2020, and the building had to be capable ofbeing adapted to cope with the more extreme environmental conditions expected in 2050.
The competition was won by contractor Galliford Try, working with engineer Max Fordham and architect Feilden Clegg Bradley Studios. Their design was based on a fourstorey, open plan, irregular pentagonal-shaped building. Construction of the 13,253m2 building was completed early last year, and the scheme opened its doors to the public in July 2012.
Visitors enter the building on the ground floor where the council's customer service centre and the children's library are located. The spaces get progressively quieter as visitors make their way up through the bright, daylit interior of the building. Slotted beneath the entrance floor is the basement. This is home to the council's archive, a social space and cafe.
In contrast to the restrained colours of the library's interior, the exterior shouts "look at me!". The Hive's distinctive pentagonal shape is given further prominence by a covering of shiny golden scales, giving it the appearance of part Cheshire footballer's home, part Sikh temple. The scales are actually copper alloy shingles selected to enable the same material to be used to clad both the building's walls and roof. The scheme's idiosyncratic appearance is crowned, literally, by a roof formed of seven gold pyramidal cones, which Guy Nevill, senior partner at the scheme's M&E engineers Max Fordham, shamelessly describes as "emblematic of the distant Malvern Hills."
Emblematic or not, these seven golden cones are the key to the building's passive, low-energy environmental design. The environmental engineer's strategy from the outset has been to minimise base loads in order to meet the project's emissions target. "A big design driver was daylight because we needed to get as much light into the building as possible to minimise the electrical lighting load," Nevill explains. As a result, the golden cones enclose large glazed rooflights, which introduce daylight deep into the heart of the building through the central atrium and a series of voids strategically positioned in the building's various floor plates.
Light from overhead is supplemented by daylight introduced through vertical glazing set into the building's golden facade. These large areas of glazing ensure an average daylight factor of 3% is achieved across the main library floor. Shading devices and solar control glass help limit solar gains.
The natural light is complemented by a low-energy electric lighting scheme. This is based on high-frequency fluorescent fittings integrated within the building's finishes to provide background light. Light levels in the spaces are enhanced by manual task lights in the reading areas and through supplementary lighting fixed to bookshelves under daylight and PIR control. Daylight and PIR lighting controls also control lighting in the separate administration and office areas.
In addition to allowing daylight to enter, the other main purpose of the roof's distinctive golden cones is to allow exhaust air out under the building's natural ventilation strategy. In summer, a combination of large openable windows and smaller, linear openings at floor levels allow fresh air to pass through the facade and into the concrete-framed interior. Driven by the stack effect, the warmed air rises up through the floor voids to exit through a row of clerestory actuator-controlled openings in the roof cones, angled side walls.
Additional fresh air is delivered to the heart of the building through a concrete builders work duct that runs from an intake west of the building, beneath the basement social space to deliver fresh air to the base of the central atrium. "We set out to maximise the natural ventilation," Nevill explains.
Baffles, visible externally, form ventilation troughs to ensure negative pressure is always present in the cones. The engineer justified the need for the additional cost of the baffles after wind tunnel tests on a scale model at the University of Cardiff showed that their addition would ensure the cones were able to exhaust air regardless of the prevailing wind direction. A night-time natural ventilation strategy pre-cools the expanse of exposed concrete soffits that provide the majority of the building's thermal mass.
In very hot weather, when the natural ventilation can no longer maintain comfort conditions, the River Severn provides an additional source of cooling for the building. "Our strategy is to use the River Severn as a heat sink for the cooling system," explains Nevill. Cooling is needed to maintain comfort conditions at peak summer temperatures and to ensure the building remains comfortable under the UKCIP climate projections for warmer temperatures in 2020 and 2050. Water is drawn from the Severn and passes through a heat exchanger before being returned back to the river. For much of the year, when the Severn's temperature is below 14° C, direct heat exchange with the chilled water circuit provides sufficient cooling for the building. The cooled water is pumped through pipework embedded in the underside of the pre-stressed concrete floor plates, helping to cool the structure while at the same time increasing the radiant cooling output. The designers were fortunate in that the large expanse of concrete soffits meant that the cooling water need only be slightly cooler than ambient temperatures to have a significant impact. "The huge surface area of the soffits meant that the water only needed to be 2-3° C cooler than room temperature," Nevill explains. On the top floor where there are no concrete soffits, passive chilled beams fed from the cool water circuit provide additional cooling.
The River Severn also provides cooling for the chillers, in what Nevill terms "a high grade cooling system". The water-cooled chillers deliver water at a flow temperature of 6° C. This system is primarily used to cool IT and meeting rooms as well as the archive. In summer, when the river temperature rises, cooling from the high grade circuit is "blended" with the river circuit to lower its temperature to ensure it can still cool the floor plates.
River abstraction was not without its challenges. In addition to ensuring the system could cope with water levels in both flood and drought conditions, the system also had to be designed to ensure that return water was never more than 3° C above ambient to comply with the Environment Agency's Freshwater Fish Directive. The designers also had to satisfy British Waterways that removal and replacement of the water would not affect the river traffic. On the plus side, however, the engineers calculated that the river cooling solution should cost less than a third of that of conventional chillers to run, and would take up much less space in the building.
Cooling is not needed in winter. Instead, heat is provided by a 550kW biomass boiler, situated in the building's basement. This is powered by local woodchip. Biomass made sense because Worcester Council already has several biomass installations. "The council has a well-developed local supply chain and an established source of supply from local woodlands," says Nevill.
The biomass boiler provides the primary source of the heat for the naturally ventilated building. Heat loads are minimised by the building's airtight construction; the building has an air leakage rate measured at 4.3m3/m2 facade at 50Pa. Nevertheless, the biomass boiler is supported by three 250kW gas boilers to meet peak heating load and to provide backup.
Heat from the boiler is circulated through the embedded pipework in the concrete soffits and the chilled beams. The heating circuit also includes perimeter trench heaters beneath the glazing and concealed at the edge of the floor slabs. The units serve two functions: they prevent cold downdrafts from the glazed areas and secondly they warm the incoming fresh air that enters the building through the floor-level linear openings. "The trench heaters preheat the incoming fresh air," says Nevill.
While the large areas of exposed concrete soffit are helpful in maintaining a stable, thermal environment within the library, they are less helpful at controlling the spread of noise. As a result, acoustic absorption has been added to the numerous balustrades and to the underside of the roof.
The basement archive, which houses more than 26,000 records, is the one area of the building serviced independently from the rest of the library. This thermally massive concrete box comprises 300mm thick waterproof concrete walls surrounded by 200mm of insulation. The archive is designed to meet the strict requirements of BS5454 to obtain national archive certification. As a result, its roof-mounted air handling plant has been designed for strict environmental control of plus or minus 1° C temperature and plus or minus 5% relative humidity. The plant includes a full back-up system.
In addition to its low energy credentials, the scheme also includes a rainwater harvesting tank for water collected from the building's golden roof. Rainwater is used by the low-flush WCs and by the archaeology department for washing archaeological finds. Local area shutoff valves and mains supply leak detection help reduce risk from damaged pipes.
The building opened to the public in July 2012. Initial feedback has been positive with the users valuing the feeling of freshness in the air and appreciating the quantity of daylight. The PFI contract includes a commitment for the scheme to meet thermal comfort and energy targets. "Feedback so far has been qualitative rather than quantitative," saysNevill. The public can, however, monitor the building's performance using the display screen in the entrance foyer. Max Fordham has, however, been appointed to carry out additional post-occupancy monitoring and to work with facilities contractor SGP to improve the building performance. Nevill says this work is "due to begin shortly".
The innovative design for The Hive exceeded the BREEAM Excellent requirement in the brief by securing a BREEAM Outstanding rating with a score of 86.40% at the final post construction review. According to Nevill, "it is the highest ever score for a public library". The scheme also exceeds the 50% carbon reduction target, with renewables contributing almost 35% to the reduction. To cap it all, it also achieved an Energy Performance Certificate A rating. No wonder the CIBSE judges were impressed.
- Gross floor area: 13,253 m2
- Building Emissions Rate: 17.4/kg CO2/m2/yr
- Predicted electricity consumption: 105 kWh/m2/yr (includes small power and IT which are not included in Part L fi gures, but is based on longer opening hours than Part L). Part L estimate of electricity consumption is 32 kWh/m2/yr
- Predicted fossil fuel consumption: 5 kWh/m2/yr, not including biomass fuel, assumes gas usage for peak loads and backup only
- Predicted renewable energy generation: 38 kWh/m2/yr biomass generated heat
- Predicted water use: 2.5 m3/occupant/year. 1.5m3 potable water per occupant per year. 1m3 harvested rainwater per occupant per year
- % Predicted water use to be provided by rainwater or greywater: 40% as above
- Basic building cost: 1842 £/m2
- Services costs: 804 £/m2
- External works: 424 £/m2
- Total area of site: 1.3442 ha
Project partner /client: Worcestershire County Council
Project partner / client: University of Worcester
PFI consortium lead: Galliford Try Investments Ltd
Architectural design: Feilden Clegg Bradley Studios
Landscape architects: Grant Associates
M&E sustainable engineers: Max Fordham
Structural engineers: Hyder Consulting
M&E subcontractor: Briggs and Forester
Main contractor: Galliford Try Construction
Facilities management: SGP