Formed 5O to 60 million years ago, the Giant's Causeway is a promontory of basalt columns along four miles of the northern coast of the Antrim plateau between Causeway Head and Benbane Head, jutting out of the cliff faces as if they were steps creeping into the sea. The Giant's Causeway and its coastal environs were bequeathed to the National Trust in 1961, and it was subsequently designated a UNESCO World Heritage Site in 1986, the only such site in Northern Ireland. The site plays a major part of Ireland's heritage and tourism, attracting visitors from around the world each year. It is Northern Ireland's most visited tourist attraction, with 500,000 to 700,000 visitors per year - and over 5,000 visitors on peak days. Background to the Project Upgraded visitor facilities were opened by Moyle District Council in 1984, but as the Peace Process in Northern Ireland took hold and tourism increased, it became clear that larger facilities were required. The situation was exacerbated in May 2000 when a fire caused by an electrical fault engulfed the visitor centre. Due to the sea breeze, 80% of the building was damaged before the Fire Service arrived. By July, the site was cleared and temporary facilities installed.
In 2003, a Management Plan for the World Heritage Site was developed and an international competition was held to design new visitor facilities. The design competition called for financially sustainable entries that could cater for an increasing number of visitors to the Causeway, deliver a world-class visitor experience and be highly regarded for the quality of its architecture and exhibition design.
The winning design, selected from over 200 entries, was by Heneghan Peng Architects, of Dublin. Utilising the large difference in level across the site, the design creates two folds in the landscape. One, extending the line of the ridge, accommodates the building. The second, extending the level of the road, screens the car park from view. The Centre is designed as a partially underground facility to integrate with the landscape and to avoid interrupting the ridge line. The Visitor Centre building and landscape therefore become integrated and the visual focus shifts from the man-made elements to the landscape and stones. Following appointment of the remaining members of the Design Team in 2006, work commenced on the design and Environmental Statement for the new Centre. However, funding, political and planning issues dogged the project in the early stages and it was only in November 2007 that the impasse was resolved when Moyle District Council agreed in principle to lease its holdings at the Giant's Causeway to the National Trust to allow the Trust to take the lead in development of new facilities. Design was able to recommence and the planning application for new visitor facilities was finally approved on 27 January 2009. Construction of temporary visitor facilities was undertaken in 2010 to allow the old facilities to be demolished and the new centre constructed. The success of this temporary scheme was demonstrated by reduced traffic problems which had been evident on their previous visit had disappeared and the improved management of the site. The main Visitor Centre building project was tendered in March 2010 and Gilbert Ash were subsequently appointed as the Contractor for the works, with possession of the site granted in December 2010.
The building design has already achieved a BREEAM 'Excellent' award, which measures overall sustainability in design, materials, energy, construction management and ecology. Incorporated within the design of the Centre are a number of sustainable ecological, social and economic elements: • The design life of the building is 100 years, with minimal services intervention required during subsequent refurbishments • Income generation has been factored into the design to ensure ongoing economic sustainability of the Visitor Centre • The concrete used has a high recycled aggregate content to give a 'Green Guide' A rating • The basalt is locally quarried in Northern Ireland • Local specialist stonemasons (S McConnell & Sons) employed to achieve the high quality polished stone finish required • The green roof assists with insulation and minimises impact on the landscape • Indigenous grasses and wild flower seed collected from the surrounding area are used for the green roof planting to maintain the sensitive ecology of the site • The 'Park and Ride' system based in Bushmills reduces traffic congestion at the Causeway site and provides sustainable economic links with the town • The site car parks all feature Sustainable Urban Drainage Systems (SUDS) to avoid increasing the load on the local storm drainage infrastructure
Building Services and Low Carbon Design
The unique design of the building and the sensitivity of the site have resulted in a servicing strategy never before contemplated for a major public building. Boilers, flue and AC condensers were not permitted under Planning conditions and the visual impact of Solar thermal, wind turbines and photovoltaic panels precluded their use on the site. The architectural aesthetic also required that the interior of the public areas was exposed concrete and no ductwork, conduits, pipe¬work or other services were to be visible. The low carbon target set by the M&E consultant from the outset was to achieve an 'A' Energy Rating on the EPC and to make the design as passive as possible. This also reduces the size and complexity of the services installation.
The first stage was to get the building thermal envelope as efficient and airtight as possible. The retaining walls and roof are externally insulated using HD polystyrene. The earth itself also provides an insulation value and in summer, evaporative cooling helps keeps roof temperatures down. The external walls are 150 cavity walls, with 100 thick PIR insulation. The glazing is frameless and is double glazed argon fill low-e glass with a glazing Uw of 1.1 W/m2K. The outer layer of glass is 10mm thick for robustness (the roof lights can be walked on) and is 'extra white' grade to allow more daylight through. Due to the dimensions of the glazing panes, it was not technically or economi¬cally possible to use triple glazing.
Although the building itself can operate passively once occupied, a heating system has to be provided to warm the building up and to temper the incoming fresh air to meet occupancy requirements. The building is designed to operate at -15°C external temperatures for a prolonged period - whether any visitors can get to it is another matter! A 72 kW ground source heat pump system has been chosen to meet the heating requirements for the Centre.
This comprises a horizontal collector mat under the main car park (boreholes were not permitted as the underlying basalt rock is protected). The total collector pipework length is 4.5km. To maximise system efficiency the LTHW circulation temperature is 35°C, which gives a favourable COP of 4.2 and a nett carbon factor of 0.10 kgC02/kWh, 48 % better than natural gas and 62% better than oil. Underfloor heating has been provided to the building perimeter. The AHU coils have been sized to deliver their design heating duty using 35/30°C LTHW. DHW requirements are met by a separate high temperature GSHP unit to avoid compromising the COP of the main heating system.
Ventilation & Comfort Cooling Strategy
The deep plan and underground configuration of the building necessitates the use of mechanical ventilation to meet occupancy fresh air requirements at 12 I/s/person (20% higher than Building Regulations). The ventilation also has to provide sufficient cooling in summer to meet internal and solar gains. Solar gain is minimised in the architectural design of the walls ¬the external basalt columns are deep and angled such that solar gain can only take place in the late afternoon on the front (South) elevation. The design strategy comprises a low-carbon displacement ventilation system, which delivers air at low velocity at 19-21°C directly to the occupied zone and warmed air rises by buoyancy to the extract points at high level.
The fact that supply air only has to be cooled to 19-21°C means that displacement ventilation can use fresh air directly from outside for most of the year without mechanical cooling and can save substantial energy compared with conventional systems. Extensive research has also indicated that displacement ventilation systems also give better internal air quality than conventional ventilation, due to the segregation of exhaust air by the stack effect.
Earth Pipe Ground-Coupled Heat Exchanger
A unique ground-coupled ventilation and cooling strategy has been incorporated which uses the coolth stored in the ground at a depth of 1.5m (ground temperatures normally between 8-14°C) to pre-heat or pre-cool the building supply air. The system comprises a groundair heat exchanger matrix (or 'earth pipes') using specialist Rehau Awadukt underground heat transfer pipe with an antimicrobial inner layer. Air is routed through a total of 1 km of underground heat transfer pipes before entering the plant-room. The minimum supply air temperature from the ground heat exchanger matrix in winter is 3°C and the maximum supply air in summer is 21°C. Higher summer and lower winter temperatures will result in greater heat transfer and therefore more cooling or heating performance. A cooling coil has been added to each of the two main air handling units to guarantee a supply air temperature of 19°C for summer cooling. These coils use low grade cooling directly from the primary (brine) GSHP circuit at 14-18°C on the ground source collector loop. As an added benefit this 'recharges' the GSHP collector during the summer months and therefore acts as a large seasonal heat recovery exchange mechanism. Thermal Mass & Night Cooling The building includes very high levels of thermal mass - 4,900 tonnes of concrete are exposed to the internal space and supply air plenum. This mass forms a key element of the comfort cooling strategy for the Centre, ensuring that temperature rises due to peak gains from solar or high occupancy are 'damped out' by the absorption of excess heat, particularly into the roof slab where the air temperatures are highest. The thermal mass effectively averages day and night temperatures within the building. Night cooling is a technique employed in passive and low carbon buildings to take advantage of thermal mass to pre-cool the thermal mass of the building using cool night or early morning air. The Building Energy Management System will compare internal and external temperatures at night and will activate the night cooling function as required using the main air handling systems.
The Invisible Air Curtain
Any visitors to the Giant's Causeway will be immediately aware that the Visitor Centre is on top of a ridge and the site is very exposed. Draughts are a potentially serious problem. The required capacity of conventional heated air curtains to protect the door sizes used exceeds the entire heating system capacity and using electrically heated air curtains was out of the question. The building has therefore no air curtains on the entrance doors to deal with draughts in winter and is instead protected against draughts by a combination of external facade treatment at the entrances and innovative ventilation design. A revolving entrance door has been provided on the main entrance - this ensures that the 'wind tunnel' effect, which is evident on buildings even where draught lobbies are used (due to simultaneous open doors at either end of the building) is negated. The rear tunnel entrance which has conventional sliding doors is protected partly by the topography of the landscape and the external tunnel entrance design encourages wind to be directed through the vehicle access road tunnel instead of the pedestrian entrance tunnel. The final door 'air curtain' protection is provided by positive pressurisation of the main concourse space to 15-20 Pa. This is similar to the pressure control regime employed in surgical operating theatres and clean rooms to keep dust and bacteria out. When the doors are opened, the pressurised air is released out through the door and helps protect against draughts. This is achieved with no additional heating or fan power ¬in fact, less fan power is used as there is no powered general extract system. Pressure relief louvres are controlled via the BEMS to ensure the building is not over-pressurised.
The Centre has been designed with a good natural daylighting via rooflights integrated into the green roof design to help reduce the use of artificial lighting. Lighting and conduits have been cast into the concrete using proprietary boxes which contain bespoke recessed or spot fittings. For flexibility and future proofing additional boxes have been provided on a grid based system throughout the building so the light fittings can be moved around to suit future internal layout changes as required. The lighting is generally a mix of high efficacy metal halide fittings and LED feature lighting. Within the interpretive exhibition area fittings are fast-response low voltage IRC tungsten display lighting fittings linked to a Dali lighting control system to allow scene changing for the dynamic multi-media displays. Emergency lighting is via a central static inverter system. The emergency luminaires are also used for quick-response pilot lighting for safe access when the building is not open. Back of house lighting is via T5 high frequency fluorescent luminaires and PIR automatic lighting controls are fitted to the back of house areas and public WCs.
The Centre incorporates the following heat recovery systems: • Back of house ventilation ¬mechanical ventilation with heat recovery • Catering refrigeration - all major refrigeration equipment is cooled by the primary (brine) GSHP circuit which contributes to Centre heating in winter. • IT I Comms racks are cooled by the cooled by the primary (brine) GSHP circuit which contributes to Centre heating in winter. • Use of the primary (brine) GSHP for comfort cooling purposes during summer recharges the GSHP collector for winter use by seasonal heat recovery I storage • Heat is extracted from the grey water recovery system from washbasins and used to generate DHW primary LTHW at the same time as cooling the recovery water to prevent microbiological growth. The warm water also increases the COP and efficiency of the DHW heat pump.
The main supply intake is rated at 145 kVA to include for the electrical heat pump load and electrical catering equipment. An emergency generator connection point has been provided. Planning restrictions preclude the installation of a fixed stand-by generator and the National Trust will hire a generator as required. Comprehensive sub-metering has been provided, including separate metering for the catering which is franchised. Electrical floor boxes with power and IT/comms outlets have been provided in a 3m x 3m grid in the floor to allow for flexibility and future internal layout changes. 50% of these electrical points are concealed under the stainless linear floor grilles in non-active sections and the main electrical distribution routes follow the line of the grilles for maintenance access. Fire alarm and PA points have been cast into a grid in the roof slab using proprietary boxes and conduit in a similar fashion to the lighting. Incoming IT cabling and links between the adjacent Causeway Hotel and Innisfree (overflow car parking) are fibre-optic. The IT system also interfaces with the radio system covering the car parks, pathways and stones. A twin electric vehicle charging station has been provided in the main car park - one of a number of designated key locations in NI. Even the hand dryers have been carefully selected for optimum performance and efficiency, with the lowest drying time available (10-12 secs) and a heated high velocity air jet at 224 mph, giving a high green rating of 3.8.
Water Conservation and Management
The Centre has the highest standards of water conservation and recovery. With over 5,000 visitors on a peak day and virtually all of them using the toilet facilities at least once, the load on the local water infrastructure and annual water consumption is potentially very high. The following water conservation and management features have been incorporated by the M&E Consultants: • Low water dual flush WCs - 4 litre I 2.8 litre • Waterless urinals - downdraught type specified as the frequency of use is too high for the standard cartridge type • Rainwater recovery from green roof and rooflights used for toilet flushing • Automatic taps with quick response shut-off •Grey water recovery from washbasins in the toilets used for toilet flushing and roof irrigation • Condensed water from earth pipes in summer is recovered and recycled.