CIBSE Case Study: The First LEED Platinum & BREEAM Outstanding Building
CIBSE Case Study: The First LEED Platinum & BREEAM Outstanding Building
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Article from the October 2013 edition of the CIBSE Journal written by ARUP's Mark Plummer.
The Crystal in east London was designed to host events on sustainability. But the real star of the show is the building itself - which is the first in the world to achieve the highest possible ratings in BREEAM and LEED.
From the start, we knew that something spectacular would be required. The idea behind the Crystal, as agreed by Siemens and London mayor Boris Johnson in 2010, was to showcase London as global leader in the lowcarbon economy. The 6,900m2 building was to include high-spec offices, conferencing facilities, a 270-seat auditorium and the world's largest interactive public exhibition dedicated to the future of cities.
Less than three years later, the £30m Crystal was complete. The team, which included architects Wilkinson Eyre and Pringle Brandon, and engineer Arup, had created a building that was at the pinnacle of sustainable development: it is predicted to emit 85% less carbon dioxide than Part L target requirements; to consume between 189 and 234kWh/m /year, which averages out as a 42% improvement on other buildings of its type; to use 52% less electricity; and to use mains water for only 10% of its needs.
The Crystal is the fi rst building in the world to receive design and construction stage certification for LEED Platinum and BREEAM Outstanding (see page 28 for more on energy rating schemes). Here are some of the key systems and technologies we used to achieve this.
Of course, the project was not all about the integration of the latest technology. Great emphasis was placed on developing a highperformance façade that could minimise heating and cooling demand.
We were initially concerned that the architectural vision did not have the traits of a typical sustainable building. The concept mostly comprised transparent glass, which is excellent for natural light, but performs poorly from a thermal and solar gain point of view.
Throughout the early design stages, multiple computer analysis models were used to play with to optimise daylighting, reduce solar gain and maximise thermal effi ciency and natural ventilation. The process was intense, but the results are truly remarkable.
The curtain walling system allowed Wilkinson Eyre tremendous fl exibility when it came to the striking building shape. Arup experimented with the glazing facets, tilting clear glazing towards the sun where the rooms behind were predominantly heated, and away from the sun where the rooms were mainly cooled.
Six types of glass have been used, each different in opacity and transparency, so that the need for daylighting and reduction in solar gain could be balanced depending on the location. The engineering team settled on 39% strategically placed transparent glazing, with the rest made up of highly insulated panels.
It is worth noting that daylighting was one of the occasional aspects of the design where we had to choose whether to target the LEED or BREEAM credits, as BREEAM uses the overcast sky while LEED uses direct sunlight.
It was calculated that a maximum average U-value of 1W/m2K was achievable with the facade system, without jeopardising the budget. The curtain walling has also achieved excellent airtightness of 2.4m3/hr/m2@ 50Pa.
The crystalline roof created the challenge of where to put the HVAC plant. There was nowhere obvious to place the large airhandling plant required for the exhibition and auditorium.
Once the engineers reduced the air volume requirement to a minimum using computational fl uid dynamics (CFD), the chosen solution was to break down the large air-handling units (AHUs) into modular units, and mount these vertically to work as giant exposed down-flow units.
This approach minimised the amount of floor space to 4m2 per AHU while taking full advantage of the triple-height exhibition space.
The exhibition hall incorporates eight 11m-high, vertically mounted exposed ventilation units, three of which are supply and extract units, with thermal wheel heat recovery for minimum fresh air use. The other five supply-only units are coupled with the roof-mounted extract fans - to be used during the summer months. The modular nature of the units means that they only operate when they are needed and no energy is wasted during times of low occupancy.
A 1m-deep floor plenum supplies low- level air to the exhibition hall at 20° C. It uses air displacement to take advantage of the triple-height hall and only conditions the occupied zone. The same space-saving vertically mounted AHU and displacement air system approach has been used in the auditorium.
The Crystal's mixed-mode system provides occupants with the choice either to mechanically cool or naturally ventilate. The decision to use a mixed-mode system was driven by the flight-path for nearby City Airport. Although Siemens aspired to a fully naturally ventilated building, it was equally important to have very high-spec conference facilities that were not affected by outside noise.
The facade provides natural ventilation through high- and low-level parallel openings that maximise the amount of air intake and exhaust without compromising the architecture. Openable rooflights ventilate deeper spaces.
The building management system (BMS) will decide the optimum time to ventilate naturally or mechanically, with some local override. The roof-mounted weather station uses wind speed and direction to inform how far windows open on each facade. Rain sensors on the weather station close the openings during rain.
The building uses two 300kWT electric ground-source heat pumps for 100% of the heating and most of the cooling. This system involves some 17km of pipework that loops around 160 21m-deep structural piles and 36 150m-deep bores. The pump system enables heat rejected from the server room cooling system or exhibition space to be recycled and reused for heating other areas of the building. Unused rejected heat is stored in the ground until it is needed.
The heat pumps are located in the energy centre, which also houses the back-up air-cooled chiller, all the primary and secondary pumps, the transformer and switch room. The 400kW air-cooled chiller can be used for peak cooling loads should there be a large event or as a back-up cooling source. The ground-source heat pumps raise the water temperature to 45° C. Energy from 19m2 of roof-mounted solar thermal panels further heats the water to 65° C for kitchen use and legionella prevention.
Only 10% of the water used in the building will be supplied by the public mains. The rainwater harvesting and 100% blackwater recycling systems are designed to meet the non-potable demand for WC flushing and irrigation, while water treatment technology treats stored rainwater to achieve potable quality.
The Crystal showcases Siemens' latest technology for BMSs, lighting control, security and fire safety. KNX controllers were selected for the lighting control (interfacing with the Dali fittings), occupancy sensors, room HVAC controllers and blinds.
The BMS system uses the BACnet-based PX controllers and a Desigo head-end to control and monitor the HVAC systems.
There are BACnet links to the variable speed drives, ground-source heat pump control system, the chiller and blackwater and rainwater treatment systems. There are also extensive interfaces with the KNX control networks.
User panels located throughout the conference facilities control the audiovisual equipment, room booking, blinds, mood lighting, room temperature and natural ventilation.
All systems are metered. As part of the building's LEED certification, a measurement and verification plan is in place to collect this data and allow the building to be compared against its projected performance. In addition, the energy piles used in the ground-source heat pump system had sensors installed during construction, so that they can be monitored
for research purposes.
The monitoring enables the FM team to identify poorly performing systems and ensure that the building performs at its optimum level. Even with its final BREEAM and LEED ratings, the process of cutting, refining and chipping away at the Crystal goes on. CJ
The Crystal can be used as a single large space for conferences or divided into separate meeting spaces, and the building services are designed to reflect this inherent flexibility. The meeting rooms benefit from a regular grid of noise-free passive chilled beams with underfloor fresh air supply.
Removable partitions are used to separate the space and alert the BMS of a change in use. With the partitions closed, temperature and fresh air automatically adjust to save energy and ensure user comfort.
The multi-service chilled beam cooling system in the second-floor open-plan office space takes full advantage of the variable roof height and irregular geometry to conceal services, providing lighting, passive cooling, associated sensors, audio and wi-fi.
The high-specification boardroom uses plasterboard chilled ceiling rafts, one of the first systems of its kind to be installed in the UK. These are supported from the irregular roof soffit and incorporate lighting, cooling, AV and acoustic treatment, without having a noticeable impact on the sense of height.
A mix of underfloor heating and perimeter trench heaters is employed throughout the building; these use the 50/40° C low temperature hot water (LTHW) supply and return temperatures.
A key requirement of the brief was to ensure the building would operate exclusively on electricity. The "all electric" operation anticipates the increasing decarbonisation of electricity generated by a grid network.
The elegant Crystal roof, which is a prominent sight on the east London skyline, is an integral part of this strategy, integrating a 300kWp 1,580m2 photovoltaic (PV) array. This generates 156Mwh of power, which adds up to 17.5% of the building's annual needs.
The PV panels clip onto a frame fixed to the standing seam, and can easily be changed for more efficient arrays as technology advances.
The roof is relatively flat, with angles ranging between 5° and 10°. The PVs face south, east and west, so different arrays will yield higher outputs throughout the day.
The building also demonstrates smart operation, reducing reliance on the grid during times of peak demand. The lighting is by LED, metal halide or fluorescent, and these are individually controlled via the Dali lighting control system.
This provides maximum flexibility to suit individual room settings, dimming depending on daylight levels and switching on or off by presence detection.
The continuing advancement of LED technology provided the opportunity to work closely with OSRAM and produce innovative lighting and fixture designs. There are some spaces in the building, such as the cafe and auditorium, that are lit solely with LEDs.
There are also six AC electric car charging points - which take between one and five hours to charge a car - and one DC fast charging point, which typicallly takes about 30mins.