The cost model considers the retrofit of a 16-storey office in a city such as Birmingham
Decarbonising an office or commercial portfolio presents numerous obstacles, ranging from planning, financial and legislative challenges to competition within the marketplace for green office space.
Continuous improvement of building performance in terms of Part L and reducing carbon emissions has resulted in building owners looking to replace non-renewable technology with electric plant and equipment. Tenants, too, are seeking green buildings that support environmental sustainability while offering a comfortable workspace that enhances employee wellbeing.
Large-scale capital investment in decarbonisation poses significant financial challenges for landlords, including lost income when tenants vacate buildings during refurbishment.
The market
The growing number of air source heat pump (ASHP) manufacturers in the marketplace is reducing the cost per kilowatt of large-scale heat pumps, making them a more attractive solution.
The latest models are available in smaller units that can be installed in modules. These operate more efficiently, matching actual building demand in real time. This approach does come with a cost premium, however.
Technical innovation and regulatory pressure to phase out refrigerants with high global warming potential (GWP) are driving the uptake of natural, low-GWP refrigerants such as propane and CO2. The availability of these in ASHPs is limited at present, and attract a cost premium. There are also risks around flammability and system complexity.
Considerations
Effective office decarbonisation planning requires careful consideration of key factors to produce a robust variability study that supports investment decisions that enhance asset value. For ASHPs, these include:
- Structure. Implications of increasing potential roof loads, as a result of placing additional plant on the roof, that requires additional steel work; interfaces with existing building elements, such as insulation; potential noise and vibration transfer.
- Architecture. Requirement for additional plant screens or noise-mitigation measures around plant. Formation of new plantrooms at roof level, with structural and service implications. Major architectural interventions, such as recladding the building, as well as associated planning approval implications.
- MEP. Requirements for wholesale replacement of existing equipment to accommodate ASHP installations, and replacement of obsolete/end-of-life systems. Upgrading of incoming power to support all-electric system.
- Programme of works. Retrofitting ASHPs can involve a lengthy programme, meaning lost rental income. Consider: design period; planning applications; notice and decant of existing tenants; tender and construction period; testing and commissioning; marketing and reletting of the building.
Cost model
The cost model looks at replacing existing gas-fired boilers and roof-mounted air cooled chillers with roof-mounted ASHPs using natural refrigerants. The building is a 16-storey office block (one basement level, 15 storeys above ground) with circa 400,000ft² GIA and 270,000ft² NIA. Located in a city centre outside of London, the office reaches practical completion in 2025. The model assumes the building is vacant during works and that the incoming electrical supply does not need upgrading.
About the author
Gaby Boyles is a quantity surveyor within Aecom’s engineering cost management team and decarbonisation lead