Meeting the list of objectives for a listed building
The energy- and carbon-reduction targets for refurbishing two listed buildings in Manchester were very demanding. Andy Bones of NG Bailey gives an insight into how they were achieved.
NG Bailey was selected by Laing O’Rourke and Manchester City Council to undertake the complex challenge of refurbishing and remodelling the interiors of two of the city’s finest Grade II Listed public buildings, with energy and sustainability at the heart of the project. The M&E package was valued at £25 million.
The Manchester Town Hall extension and Central Reference Library buildings were originally constructed in the 1930s. However many of the services had reached the end of their life-cycle.
The scheme aimed to protect the buildings’ important heritage features, whilst creating a more accessible, multi-functional public facility for the next generation.
The project partners instilled a ‘one team’ philosophy across the supply chain. It included a shared project office and the use of the NEC3 form of contract, which supports good project management between parties and the proactive resolution of issues.
The client and its design team set demanding targets to deliver energy-efficient solutions and carbon reduction, whilst increasing space utilisation, occupancy and power consumption densities.
• 30% energy cost reduction on published 2008 DEC (Display Energy Certificate) figures
• 20% of energy from low-carbon technologies
• 20% reduction in cost of water supplies
• BREEAM Very Good (Bespoke Scheme), with aspirations for Excellent
• Supporting the local supply chain
• Investment in training and apprenticeships
As the buildings are Grade II Listed, many of the areas were governed by Historic England and had to be recorded and protected during the works. Planning conditions also limited plant acoustic selections and the available space at roof level for heat rejection. The site’s city-centre location also limited the options for sustainable technology and proved a challenge for the construction team and the site logistics.
It was recognised that no one solution could deliver this challenge, so a hierarchical approach to energy efficiency and carbon reduction was adopted.
As the fabric of the structure was detrimental to architectural features and detailing, NG Bailey was unable to undertake any fabric upgrades. Secondary glazing wasn’t possible as this would restrict natural-ventilation solutions, and heritage glazing was considered too cost prohibitive.
The solution was to maximise natural ventilation and use of thermal mass. Through extensive thermal and acoustic modelling, services designer BDP utilised a natural crossflow ventilation solution, with high spaces and exposed thermal mass to offices within the Town Hall extension, as the original design intended. This provided a comfortable, low-energy environment, with negligible effect on the building fabric.
The building redevelopment included creating new spaces and environments, which required mechanical HVAC plant to be installed. These spaces had challenging design criteria, such as acoustics in the library and meeting rooms, temperature and humidity (BS5454 Archive Stores). Mechanical ventilation in the Council Chamber plant was selected to maximise efficiency and minimise energy use, such as heat recovery, high ESEERs and low SFPs.
Due to the cost of LED lighting technology, its use was limited on the project and, instead, high-efficiency lighting was selected. However, the heritage fittings were refurbished with new wiring and control gear to maximise efficiency.
Another important feature was the BEMS specification, which included over 450 meters across the project. This was essential for system commissioning and fine-tuning, and for the on-going management of the buildings’ energy use to mitigate ‘energy drift’, which is inevitable without visibility, targeting and monitoring.
To meet the 20% water-reduction target, water-efficient sanitary appliances were selected, However, it became clear that the water-reduction target could not be met without rainwater harvesting. Due to the complexity of the buildings and the existing rainwater distribution, a decentralised approach had to be taken, and six systems were installed to recover rainwater for toilet flushing. This equated to 3300 m3 of rainwater per annum and exceeded the 20% target.
To generate energy from low-carbon technology, a combined cooling heating and power (CCHP) system was installed. This consisted of two 235 kW CHP engines, a 230 kW absorption chiller and large thermal stores to maximise engine run hours and meet the peak cooling demand.
Because of the limited space at roof level and restricted noise levels, a limited amount of heat rejection could be installed. The chilled-water storage volume was increased to ensure peak summer demand could be met in parallel with the chiller plant.
Manchester City Council’s procurement strategy aimed to provide a positive impact on the local community — not only in-use, but through the procurement of materials, equipment and services for the construction — and in support of local employment.
The procurement strategy ensured local businesses had the opportunity to bid and deliver work on the redevelopment. 70 apprentices were taken on for the project — with 20 being part of the NG Bailey team — as well as four adult trainees.
Laing O’Rourke continues to be involved in the soft-landings scope, and is assisting in fine-tuning the systems to ensure the design targets are being achieved. The pilot ‘Government Soft Landings’ project has recorded a 31% reduction in cost and 22% reduction in carbon emissions against the 2008 DEC benchmark, with further savings of around £176 000 per annum identified by the MCC Key Energy Saving Group.
Andy Bones is energy operations manager with NG Bailey.