When this 1980’s building was vacated by it’s previous tenant it was no Angel. However, building owner Derwent London was keen to retain the building and embark on a major refurbishment project that would revitalize the building and delivered a BREEAM rating of ‘Very Good’. What they got was nothing short of ‘Excellent’. The design ethos behind the services engineering for the Angel building is one of “energy-efficient simplicity,” says Project Coordinator and Norman Disney & Young (NDY) Associate Director Danny Hall.
“The services brief from Derwent London was simple,” says Hall. “They wanted a highly efficient building with a greatly reduced carbon footprint, both in its construction and ongoing life cycle.”
Following design appraisals by structural engineers, Adams Kara Taylor, it was confirmed that the Client’s aspirations to refurbish the existing building rather than demolish and rebuild would be possible. This greatly reduced the construction period and also resulted in significant CO2 savings by re-using the existing concrete structure. The retention of this existing structure presented NDY with a number of opportunities as well as some challenging design constraints. “The slab to slab heights of the exsitng building were designed around a variable air volume air conditioning system and as such were relatively generous compared to many building refurbishments,” says Allen Williamson, Director at NDY’s London office. “This allowed us to consider displacement ventilation as the preferred comfort cooling solution thus benefiting from the improved energy efficiency this system offers compared to many other system options”.
The buildings thermal mass is also used to full extent through the exposed concrete structural slabs to help attenuate building loads and help reduce energy consumption further.The existing structure did however impose challenges for the displacement system due to the number and size of the existing concrete beams, not least of all from the large existing perimeter beams which became internal as the building perimeter was extended. “Through our work with the displacement diffuser manufacturers and the factory testing that was jointly carried out we were able to determine the maximum beam depths that could be accommodated by the displacement system. To cater for those existing beams larger than this we designed additional return air paths” Williamson says.
To maximize the available office space an additional floor was incorporated into the scheme. “In the existing building, the main plant was located within internal plant rooms on the top floor. With the addition of another floor, this plant area was relocated to the roof where the new replacement plant was installed in exposed locations,” Williamson says. The increased height of the building and the new external roof plantmeant that the design team needed to be sympathetic to Rights of Light and sight line issues associated with nearby residential properties. This meant the new plant needed to be centralised as much as possible away from the building perimeter. NDY’s use of 3D CAD proved to be invaluable in drawing these areas,ensuring the most efficient plant layout possible was achieved without compromising maintenance.
The buildings extensive flat roof and terrace areas provided the potential of harvesting large volumes of rainwater. “Rainwater is collected from the these areas and stored in rainwater
harvesting tanks in the ground floor plant areas” says Williamson. “ This water is then distributed through the building and used for toilet flushing and irrigation. The use of this system is actively encouraged under BREEAM and has significantly reduced the building’s reliance on mains water.” A cornerstone of the planning approval process was the incorporation of renewable energy technology.
The local authority requires that, wherever possible, developments of this scale achieve CO2 emission reductions through the use of renewable energy technologies. Following a detailed analysis of the available technologies, their initial cost and potential payback and also considering the building’s location and extremely efficient cooling system, the use of biomass boilers was the most appropriate solution for the project, resulting in approximately 15 per cent saving in CO2 emissions per annum. The innovative energy-efficient NDY designs including displacement ventilation, water-cooled chillers and variable speed pumps, were all key contributors to the BREEAM ‘Excellent’ rating of over 74 per cent. The displacement ventilation, in particular, delivers exceptional energy savings. The elevated supply air temperatures compared to other systems means that outside air can be used to deliver cooling directly for a greater proportion of the year, resulting in the chillers being called into operation for far less time. The system also offers greater flexibility for the tenants to open windows and therefore improve the sense of occupant satisfaction.
The passive building design has been an important contributor to the BREEAM Excellent rating. Careful consideration was given by AHMM and NDY to enhancing internal office thermal comfort by providing a façade with a very high level of solar control. According to Hall, “this was achieved by combining high performance glazing with fritting to reduce solar energy being transferred into the space. In addition to ensuring the necessary compliance with the Building Regulations thermal performance criteria, this has also enabled a cooling system to be installed that offers high occupancy comfort benefits combined with low energy demands.”As recognition of the outstanding merits of this pragmatic refurbishment, one of the UK’s leading and most active charities, Cancer Research UK, has taken a significant proportion of office space. The Client and design team are all proud of what was achieved through this landmark project – a testament to a well coordinated team works with common purpose and commitment to achieve an ‘Excellent’ result.
Services provided by Norman Disney & Young:
• Public Health
• Fire Protection
• Fire Strategy with NDY Fire
• BREEAM/EPC Assessor
Location: London, UK
Architect: AHMM Project name: Angel Building
Client: Derwent London
Date: May 2008