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Green Sky Thinking: Scott Brownrigg on 'carbon minus' design

King’s Troop Royal Horse Artillery, Woolwich

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One of the first events in this year’s Green Sky Thinking programme, last night’s talk Creating a Carbon Minus Scheme for King’s Troop Royal Horse Artillery gathered a small crowd of around 30 sustainability enthusiasts at the offices of Scott Brownrigg, who are one of the supporters of Green Sky Thinking 2012. Boldly subtitled Is carbon minus just a load of horse s**t?, the event promised to be both intriguing and entertaining.

Project director Ed Hayden, the host of the evening, started off with a short review of Scott Brownrigg’s key sustainable projects: The Red Kite building, featuring natural ventilation, The Kestrel House – using low energy systems (active chilled beams), Lilly office building, which has a mixed mode ventilation approach, and 3 Assembly Square in Cardiff.

He then went on to introduce the main features of the King’s Troop Royal Horse Artillery. The project was won in a limited competition, in a team with Morgan Sindall and Buro Happold, by proposing to make the building zero carbon. Ed presented the design approach, the operations strategy, and the results of their integration into the project.

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The design relied on several key aspects:

  • the use of passive design to minimise the energy loads
  • maximising the efficiency of the energy used
  • Use of a BIM model from concept stage and then on into detail design to visualise the building
  • reducing of on site waste by careful scheduling of all materials used

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The passive design features include:

  • a long south-facing façade (with woodlands to the north), made possible by the east-west orientation of the site
  • intake of cool air from the woodland to the north of the building to naturally ventilationl the damp, hot air inside the stables from the horses, using forced air movement induced by solar chimneys along each stable line
  • clerestory windows for natural light
  • rainwater harvesting

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The main drivers for specification of materials were performance and longevity: FSC timber, zinc, steel, glulam, and brick. Some of the materials salvaged from a run-down building which existed on the site previously were reclaimed.

The operational strategy was based on treating the organic waste from manure and bedding as a resource, rather than a problem. Ed described how various biomass options were explored at design stage in this ‘pooh power project’, from anaerobic digestion to making fuel pellets. However, a more straightforward solution was adopted: passing the waste through a shredding unit into a store which directly feeds the biomass boiler.

The resulting heat is either used in the building (the bedding, stack rooms and offices have underfloor heating), stored in a heat store, or used in a heat rejection unit to power Sterling engines which create electricity. Half of this is used on site, and half is exported back to the grid. The project also includes also gas-fired back-up boilers.

Ed Hayden, Scott Brownrigg

Ed Hayden, Scott Brownrigg

The results? A quick cost analysis showed approx £980,000 combined capital cost for all the systems andapproximately £135,300 cost savings/annum, resulting in a 7-year payback period. That doesn’t sound too bad at all. It remains to be seen how the entire strategy works over a longer period of time, in terms of both maintenance and in use energy costs.

The Q&A section was very animated, with questions varying from: lessons learnt from the project  (‘ideas need to be simple, and passive strategies must be applied first’), onto biomass options (anaerobic digestion or landfill carbon sequestration options), to the sizing of the stack sections using the BIM model for fluid dynamic modelling. The team intends to monitor the buildings over the next few years and see how they perform in use, and to compare the results with the design data. The need for direct feedback from building users was also highlighted.

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The discussions carried on informally long into the evening, after an informative and enjoyable talk which highlighted how sustainable ideas can be creatively tailored to suit the site and specifics of a particular project.  

Overall, this felt like the beginning of a very promising week. I look forward to the next events in the Green Sky Thinking series.

Sarah Yates of Open-City, organiser of Green Sky Thinking

Sarah Yates of Open-City, organiser of Green Sky Thinking

All photographs: Minna Kantonen

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