Our feasibility study enabled City University London to review and consider options for thermal improvement to their Northampton Square campus in order to achieve their HEFCE commitments for carbon reduction.

The University, Drysdale and Tait buildings are a suite of buildings to the north of the campus designed by Sheppard Robson Architects using similar construction, materials and forms. They were built for City University over a thirteen year period from 1961 to 1974.

The Tait building, completed last, was taken as representative of these and after carrying out a visual analysis of the external fabric, we grouped options for improvement into low, medium and high levels of intervention with lessons that could also be applied to the Drysdale and University Buildings.

A thermal model was then built and tested, which established the reduction in energy consumption and carbon emissions for each option compared with the baseline, (existing condition). From this, the costs to implement each option against its life-cycle costs and associated payback periods were set out. Maintenance, phasing, interfaces with other planned projects within the University and any Planning implications were also considered.

The conclusion of the report therefore, set out a clear comparison for each option to assist the University with their decision making.

In appraising each option, we also considered how decisions made now could keep other options open for a later date. This is important when the benefits relate to an uncertain variable, such as the future cost of fuel.

Although the study focused on the technical aspects of how to improve the thermal performance of the building envelope, we endeavoured to present the work in a way that would be useful for the University in making wider decisions to meet their carbon reduction targets.

In order to do this, we categorised envelope types, (walls, roofs, windows) and identified key interface and junction issues. The performance of the linear cold bridges at the heads and sills of windows were also analysed as part of the thermal modelling. The study did not review any cooling requirements or detailed facade design for the level options.

We appointed Ramboll as sub-consultants to carry out the thermal modelling, using IES and Therm software.

Integrated Environmental Solutions (IES) Virtual Environment software is accredited for assessing the compliance of buildings against Part L of the Buildings Regulations. A 3D model of the building was created and, using hourly weather data and information on the building fabric and services systems, a detailed thermal analysis was produced.

‘Therm’, (version Therm6.3.45 was used), is a thermal bridge and condensation risk analysis software. It was used to identify thermally weak points in the façade system options. The software produces a two-dimensional thermal analysis of the component and/or façade, and was used to calculate frame U-values.

The materials of the building fabric were included on a layer by layer arrangement, according to the build-up, with the thermal properties of each layer such as thickness, thermal conductivity, density, and specific heat capacity included. The properties of the windows/glazing were also assessed to include the thermal performance of the window frame, the reflectance of outer/inner face of the glass, light transmittance, and the G-value/shading coefficient.

To inform the model, information was provided by City University on room types, sizes, occupancy, IT and service loads, lighting and daylighting and an air pressure test was carried out to determine the building’s air infiltration rate.

We also carried out a window survey which was included in the model and tested options for solar shading to south facing offices as a separate solar gain study.

The parameters modelled were:

• Annual heating energy consumption (Kwhr)
• Annual Carbon emissions (Kg CO2)
• Peak heating load in the winter (KW)

Optimising the performance of the fabric is just one aspect of successful carbon management, together with how the space is used – including cultural and behavioural issues – and what energy consuming services supply the space.

The study focused on the fabric of the building. Nevertheless, we are very conscious that, when it comes to making investment decisions about managing existing assets, the problem must be looked at in the round.