Energy audit for Wiltshire Council's Bourne Hill Offices

An evaluation of a unique development in historic Salisbury

CSE was engaged by Wiltshire Council to undertake an evaluation of their Bourne Hill Offices in Salisbury. This is a striking combination of the 18th-century Grade II* listed four storey council offices and a boldly modern three storey linear extension that was added in 2010.

Funding for this study has come from the Technology Strategy Board’s Building Performance Evaluation scheme, and Bourne Hill is one of a group of buildings that are 'pilots' for Wiltshire Council's certification to BS (EN)16001, the Energy Management System standard.

Martin Holley is CSE's Senior Technical Project Manger. "Bourne Hill offers a rare opportunity to study a building that combines the new and innovative - including green roofs and steel fin solar shields - with an existing highly protected heritage building. Similar studies have generally focused either on the brand new or on the old; it is not often that one building can provide both.

"Wiltshire Council sees new ways of running an office - 'hot desking'* and flexible working - as the way forward. They've made much of the financial savings, technological improvements and benefits to personnel that this provides, but the impact on building performance has not yet been considered."

Below: three views showing the formerly exterior brickwork of the 18th-century building now adjoining the unashamedly modern 21st-century extension

Click on the thumbnails above for more photos of the Bourne Hill Offices

Looking into the performance gap

The overall aim of the TSB scheme is to address the ‘performance gap’. That's the difference between the intended performance of a building when it was originally designed (in terms of energy and other factors such as occupant comfort), compared to its actual performance now it's in use. A building's energy performance has to meet Building Regulations when it is being designed. But if buildings are actually using more energy in use than they were predicted to, we are not really achieving the CO2 reductions that we say we are.

At the design stage, the performance of the building is estimated through, for example, modelling of the systems, and by the production of an EPC. The most common method of assessing the performance of a non-domestic building when it's in use is the production of a Display Energy Certificate (DEC), but this is only mandatory for public buildings, so the performance of most buildings in use is rarely measured at all, except in terms of the cost of energy bills.

We worked with members of Wiltshire Council’s Facilities Management team to carry out a Building Performance Evaluation of the Bourne Hill Offices in Salisbury as they were being used. Our 52 research tasks included:

  • Carrying out a Building User Survey 
  • Carrying out a thermographic survey
  • Analysis of the designed vs. actual electricity and gas consumption data and reconciliation of sub-meters using CIBSE’s TM22 tool
  • A review of the impact of planning constraints on the listed part of the building
  • A review of the handover/commissioning process
  • A review of Facilities Management processes
  • Analysis of data such as internal and external temperatures, CO2 levels, insolation etc.

Findings from Bourne Hill

Summary data will be published via the Carbon Buzz online platform and the final report will be available on request from the Technology Strategy Board.

Overall, the building was shown to perform better than standard benchmarks in terms of electricity consumption, and marginally lower for gas.

By sharing energy consumption data with the on-site Facilities Management team, Wiltshire Council identified that the hot water system was causing unnecessary out of hours gas consumption. By altering the timings on the system they have reduced their consumption by approximately 20%.

Taking part in this project has prompted the council to revise the way they procure new buildings. They will now require greater focus on the commissioning of systems and the involvement of the building designers for a few months post-construction so that they can help users understand how the building was designed to function, how to best use the systems to ensure they are working as efficiently as possible, and so that they can learn about how their designs work in use and influence their future projects.

Other main findings include:

  1. The importance of designing interfaces for Building Management Systems (BMS) that are easy to use and do not require specialist controls knowledge to operate effectively. In the case of Bourne Hill, despite having a very comprehensive network of sub-meters, the data from them will never be routinely used as it takes too long to download and is presented in a very confusing format.
  2. More focus needs to be placed on the commissioning and handover processes to make sure that the building services are working properly and set up in line with the needs of the user before people move into the building.
  3. Comfort is multi-faceted in nature and you can never please everyone in a large open plan office space – we recommended a number of possible behavioural interventions to help address this.
  4. The need for flexibility in design – buildings aren’t always used in the way they were designed to. Bourne Hill has only been occupied since autumn 2010, and the way that it is used has changed more than once. For example, the number of occupants has changed from the assumptions on which the ventilation and heating systems were based at the design stage – most recently the local police force have moved in.
  5. More research is needed into the thermal performance of traditionally constructed buildings (something we are addressing in our current project with English Heritage)

Below: drawing by architects, Stanton Williams, of the Bourne Hill Offices next to Salisbury Arts Centre formerly St Edmund’s Church.


Excuse me? 'Hot desking'?
In most offices, desk space is allocated on an individual basis - you sit here, and he sits there. Increasingly, larger organisations are exploring 'hot desking' options in which staff are issued with laptops that can be docked at any desk within the office (or, indeed, other offices on different sites) so that staff can choose where to sit, or they can work from home. At Bourne Hill Offices, Wiltshire County Council is providing two desk spaces for every three staff – and anticipiating savings from by cutting down on space requirements and the associated costs.


Photos © Hufton & Crow Photography 

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