RENOVATION
‘No project of this nature could be attempted without the assistance and cooperation of the building users and the client’s asset management and operations staff.’
The business case The value drivers that incentivise organisations like the Trust to consider this type of project fall broadly into two categories, what we might call ‘pushes’ – those factors compelling the organisation to act because failure to do so would result in unacceptable levels of risk to their business – and ‘pulls’ – the opportunities that exist to improve performance. In the case of Guy’s Tower, the main push
was the condition of the concrete facade and windows, but different approaches were adopted for the User and Communications tower facades. The User tower has a horizontal profile with balconies wrapped around all but the lowest levels faced with pre-cast concrete panels. These were in relatively good condition for their age, but had become badly stained through the deposit of carbon and other particles in water trickling down the external surfaces. The Communications tower is encased in an in- situ concrete profiled cladding forming a dramatic vertical effect. However, the concrete here was suffering badly from spalling. The Trust had taken appropriate measures to manage this by undertaking regular, roped access inspections to check the spalls, break off loose material safely and seal. However, it was clear that this would only be a short-term solution and that something more radical was needed. The chemical changes in the concrete that cause spalling cannot be detected, so that it is
impossible to predict where they will occur next. The deterioration is progressive, however, and if left unaddressed the risks to safety and to operational and business continuity would have become unacceptable. In addition the windows, although double-glazed units, were at the end of their working life, with the frames in particular being badly corroded. Even though the original thermal performance of the facade would have fallen short of today’s standards, the condition of the windows and frames only served to exacerbate the poor energy efficiency of the building, particularly under winter heating loads. On the pull side, in dealing with the
deterioration of the concrete and failing windows, the Trust recognised that there was a big opportunity to reduce cold bridging in the User tower balconies and to make significant improvements in the performance of the facade. Improving energy efficiency, reducing consumption and reducing carbon are on the agenda for all organisations and for the Trust in particular, which has a strong commitment to sustainability and was already seen as a leader in the field of carbon management in the NHS. The Trust therefore wanted to use the Guy’s Tower project to make further advances in this area. Although the Trust was committed to
investing a significant sum of money in the project, this was conditional on achieving value for money. If sufficient paybacks on
This image shows the concrete balcony panels being cleaned. The impact this will have can be clearly seen.
energy and carbon could not be demonstrated in a business case, the Trust Board of Directors would not allow the project to continue. The Arup team were able to achieve this through a process of thermal modelling and analysis.
Energy consumption The project was confined solely to the external facade and did not encompass the tower’s building services and on this basis, the Arup building services team estimated that the project could only influence 18.5% of total energy consumption. 3D thermal models of the tower were built to assess the likely impact of the façade design options. Individual room models were also built for each facade to show the effects of the façade refurbishment from a cooling plant perspective. Two separate models were built, a base model to provide a common comparison point, and a refurbishment façade option, proposed by Penoyre & Prasad, which would meet the latest thermal standards. The thermal analysis indicated that re-cladding the tower to provide this compliance would result in a 7.6% reduction in annual energy consumption, compared with current levels.
An exploded view of Guy’s Tower showing the different sections of the buildings. IFHE DIGEST 2013
‘Guy’s Tower is a good example of what can be achieved with the refurbishment of an old building that would once have been considered beyond salvaging, or at the least not worthy of the investment..’
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