Header image

CASE STUDY | 80 CHARLOTTE STREET roof has to have sufficient area to cope with the larger footprint of the ASHPs compared with that of a conventional gas-fired boiler with the same output. Chilled water, whether generated by the ASHPs or chillers, is supplied to soffit-mounted fan coil units (FCUs) distributed around the floor plates. The FCUs are controlled in two zones: a perimeter zone and an internal zone. To help minimise perimeter cooling loads Arup worked with Make to optimise the location of the glazed and opaque areas of the faade. Glass is generally at high level to contribute to daylight levels on the floor plates, Patel explains. An LED lighting system further minimises energy use in the main office areas. This is coupled to a DALI controller and daylight sensors, to allow light fittings to be dimmed automatically in response to ambient light levels. While the buildings faade is almost entirely new aside from the retained section in the conservation area on Whitfield Street it has been designed with the local vernacular in mind, referencing Fitzrovias variety of buildings, but with a very rational glazing proportion. What is important is that the ghost of the existing building still exists, says Patel. The new building incorporates the existing buildings low floor-to-floor height of around 3.3m, which Patel describes as super lean. With such a low floor height, the supply of fresh air to the office floor plates could have been an issue. However, the design teams decision to Three full-height atria provide routes for ventilation ductwork relocate and consolidate the cores of the existing buildings into the centre of the plan has enabled the creation of three full-height atria. These allow natural light into the heart of the building and, through integration of engineering and architecture plus an innovative design approach provide a route for the ventilation ductwork. Working with Make ensured we had atria in all of the right places, which gave us the opportunity to distribute the fresh air, says Patel. Three fresh-air ducts drop down these atria from roof-mounted air handling units, to supply air to the floor voids on each of the office levels. Fans in the perimeter trench heaters help draw the air across the floor plates, and the air returns to the AHUs through a series of EMBODIED ENERGY The building is being promoted as having lower embodied energy. According to Derwent London, it has been designed to achieve 28% lower embodied carbon intensity than the RICS benchmark, with estimated embodied carbon of 850kgCO2e.m-2, versus the RICS Building Carbon Database (offices) average benchmark of 1,177kgCO2e.m-2. When we designed this building, its fair to say that embodied energy was not as high up the agenda as it is currently; that said, the systems we have chosen are robust from an embodied carbon perspective, says Patel. 38 February 2022 www.cibsejournal.com CIBSE Feb22 pp36-38, 40 80 Charlotte street.indd 38 28/01/2022 16:23