CASE STUDY | 80 CHARLOTTE STREET The faades incorporate openable windows. When the windows open, the heating and cooling switches off ducts behind louvred panels at the core. If you take the fresh-air ducts out of the main floor plate, you can squeeze the floor height down, explains Patel, who adds that the fresh air supply rate of 1.6L.s-1.m-2 is at the higher end of the British Council for Offices scale, based on an occupancy of one person per 8m2. In addition to mechanical ventilation, the faades incorporate openable windows, allowing the building to operate a perimeter mixed-mode ventilation strategy. When the windows open, the heating and cooling switches off. The roof as well as housing the ASHPs is home to 80m2 of roof-mounted solar thermal panels. These preheat the domestic hot water (DHW), which is then topped up by heat from a dedicated set of ASHPs, to raise its temperature to around 65C. We looked at various renewable technologies for the domestic hot water, but, at that point in time, there were limited options from an all-electric perspective, Patel explains. Using dedicated heat pumps also enables the system to be run out of hours. The solar system is self-regulating and sized at peak summer demand. At the limited times when the system generates more heat than required, radiators within the solar system ensure the water and components dont overheat. The DHW tanks also include an electrical element as backup, but Patel says these are not intended to be used under normal operation. At the outset of the project, Arup conducted a CIBSE TM54 study to get an idea of the expected performance of the building. Once the building is fully occupied, in-use electricity data will be analysed and compared against the TM54 modelling calculations completed at the design stage. We have a smart system that links everything together, so were able to understand, from an energy perspective, how much we are consuming and where, on both the landlords side and the tenants side, says Patel. As Arup is one of the buildings main occupiers, Derwent London will have a unique opportunity to work with the engineer to optimise its operational energy performance. Our commitment to Derwent is that well do all the commonly employed checks across Derwent projects, such as seasonal commissioning, energy monitoring and targeting, says Patel. In addition, as a tenant, well do this at a granular level; for example, we can measure the contribution were getting from the lighting switching off when daylight levels are good enough, and from opening the windows in the summer. We have real-time occupancy data alongside power consumption. According to Derwent, the building achieved Breeam excellent at design stage and is targeting Leed Gold and an Energy Performance Certificate B rating. Derwent London is now targeting all-electric heating and cooling systems for all its new developments, to help it achieve its goal of a net zero carbon portfolio by 2030. 80 Charlotte Street will be the reference point against which all of its subsequent developments will be measured. CJ THE IMPACT OF COVID-19 The building was completed at the start of the coronavirus pandemic. Since then, Patel says Arup has carried out a retrospective review of the systems with Derwent, to try to understand all the systems and how we might then address Covid with these. For example, the review found that opening windows in addition to the mechanical ventilation was beneficial. The building has a really good ventilation rate, but we have the opportunity to open windows and give it a boost if we need it although you wouldnt choose to do that all of the time from an energy perspective, says Patel. Completion of the building during the pandemic also required changes in the way commissioning was undertaken. Many of the inspections, for example, were carried out remotely, using video links along with factory tests, where data and monitors were witnessed remotely. You can have FaceTime calls and WhatsApp videos where you can say this is the gauge I want to see. We embraced technology to shift the way we do things, says Patel. Some commissioning had to be done in person, however, including the black building tests, where multiple things were happening at once. At such times, Patel adds, design and build contractor Multiplex ensured that attendees could safely maintain social distancing on site. The scheme includes a roof terrace and a new public pocket park (left), based on New Yorks Paley Park 40 February 2022 www.cibsejournal.com CIBSE Feb22 pp36-38, 40 80 Charlotte street.indd 40 28/01/2022 16:23