COOLING CHILLED BEAMS
above ground level in the former courtyard. Completed last year, the building was designed by Devereux Architects working with Downie consulting engineers. The challenge for the design team was to maintain the building’s environment in a sustainable manner within the confines of an extremely restricted location. A detailed thermal building model was produced to assess the effects of the surrounding building on the new development, and vice versa. This established that significant cooling would be required to maintain comfortable conditions. A number of primary cooling systems
were considered, including traditional vapour compression refrigeration plant, but these either did not achieve the school’s aspirations for sustainability or were not technically viable. ‘Ground linked closed loop’ systems were considered too restrictive to provide even a small percentage of the project’s needs; and the limited roof space restricted the available scope for the inclusion of air source heat pumps. With no way up and no way out, the
design needed to consider an option that explored a deeper solution in the form of ‘open loop heat transfer’. With a potentially abundant source of ground water at around 12C, it would be possible to cool the building efficiently using chilled beams. Chilled beams have been in use in
Cooling for the building is provided by chilled beams supplied by SAS International, which was part of the project team
With no way up and no way out, the design needed to consider an option that explored a deeper solution in the form of ‘open loop heat transfer’
Keppel Street building, completed in 1929. It provides teaching and research accommodation for around 1,000 students. The development of its South Courtyard development was key to the improvement programme. However, due to the constraints of
the site and planning restrictions, there was no possibility of extending outwards or upwards. The original building can effectively be thought of as an upside-down capital A. The South Courtyard was an under-utilised open area that also housed two lecture theatres dating from 1957. The new development rises five storeys
48 CIBSE Journal November 2011
buildings for more than 20 years, and much is known about their reliability, very low maintenance needs, and design performance. For the refurbishment of the School, the key challenge was commissioning them in a way that would meet the client and architect’s aspirations for a clean, efficient, modern, minimal aesthetic. To achieve the required design capacity,
active chilled beams (forced air movement) were employed with a catalogue design output of 140-160 W/sq m cooling output, depending on which technical data is used: most technical data relates to ideal installation scenarios and is usually produced in near-laboratory conditions. Passive units (using natural convection) will achieve up to 100 W/sq m and, if fully exposed to the space, approximately 80% convective cooling and 20% radiant cooling, as opposed to an active unit which is mainly convective. Active chilled beams will operate at an air pressure of up to 200 Pa; operating more than two units in series is not a good option due to high cumulative
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SAS International
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