The performance gap and green buildings
A recent study of four ‘green’ buildings revealed a number of ‘performance gap’ issues. How can BREEAM help close the gap?
Report from – Dr Chris Ward
As highlighted by Dr Andrew Lewry’ article Bridging the performance gap, there is much evidence to suggest that occupied buildings usually do not perform as well as expected compared to design stage predictions, especially with regards to energy consumption; the so called ‘performance gap’.
There are a number of commonly cited reasons to explain the performance gap, which include:
- Changes to the building design and/or the design intent is not delivered on site
- Poor build quality (such as gaps in insulation and accidental thermal bridging)
- Substitution of building elements and/or services equipment from those originally specified
- Inadequate or incomplete commissioning
- Changes in the way that the building is occupied and operated from that assumed during the design
- Building controls that operators and users find difficult to understand and operate effectively
- Lack of facilities management, energy monitoring and/or maintenance of building services
- Behaviour of occupants (e.g. opening windows, blocking air inlets/outlets)
Assessing how well ‘green’ buildings perform
A recent BRE Trust funded research project has studied four buildings with ‘green’ credentials that were constructed within the last seven years, in order to assess how the buildings were operating in use compared to design predictions. The project involved a combination of physical monitoring and occupant surveys over the period of a year, which looked at a variety of issues, including energy and water consumption; thermal comfort; ventilation; visual comfort; and acoustic comfort. The four case study buildings comprised:
- A 3,750m2 three storey naturally ventilated commercial office building containing 15 office units and occupied by a variety of tenants and owner occupiers.
- A 10,500m2 two storey mixed mode ventilated secondary school accommodating over 1,100 pupils.
- A 2,100m2 two storey naturally ventilated primary school accommodating 300 pupils.
- A 1,100m2 three storey naturally ventilated higher education office building containing a mixture of open plan and cellular office space accommodating staff and research students.
Identifying the performance gaps
While all the buildings were performing as designed for most performance aspects, there were instances in all cases where performance gap issues were found, both in terms of energy consumption and occupant comfort. Unsurprisingly, these instances all align with the commonly cited reasons to explain the performance gap, notably:
- Inadequate commissioning Building Management Systems (BMS) and energy sub-meters in three of the buildings were not operating correctly due to poor installation and commissioning. This imposed limitations on the extent of energy monitoring possible for each building. On-going technical issues with the secondary school’s biomass boiler meant this was offline for the majority of the monitoring period, leading to increased gas consumption compared to design predictions.
- The building not being occupied as intended Space designed as a corridor/intermittent break out area in the primary school was being used as permanent teaching space causing ventilation and noise problems in adjoining classrooms. The design assumptions on use patterns in this space were critical to maintaining comfort in classroom areas, so this change of use means it is difficult for the school to mitigate these unintended impacts.
- Poor understanding of building controls In all four buildings the occupants lacked knowledge of heating and cooling controls and how these could be used to alleviate comfort issues with the internal environment. This was highlighted by one of the commercial office units, where the heating set point was too high, leading to thermal comfort issues and unnecessary gas consumption.
- Behaviour of occupants In one of the commercial office units, there was reluctance by occupants to open windows due to a noisy external environment. As the servicing strategy relied on openable windows in certain conditions, this contributed to ventilation and thermal comfort issues and led to the widespread use of electric fans for cooling. In the secondary school building, the automated opening windows was restricted by management during working hours to minimise disturbance to teaching activities, leading to ventilation and thermal comfort issues.
- Lack of energy management policies and procedures Both office buildings had no policy/initiative to encourage staff to turn off IT equipment at the end of the working day, so computers tended to remain switched on, which was contributing to higher than ‘typical’ practice electricity consumption.
The project also highlighted the on-going issue of comparability between actual energy performance data via meter readings and predicted energy performance via data generated from models used for compliance such as Energy Performance Certificates and Part L of the Building Regulations.
The project findings have added to the increasing evidence base on issues that contribute to the performance gap and the potential causes of these in commonly used solutions. It clearly shows that buildings designed to be ‘green’ are not immune to these issues.
The performance gap and BREEAM
The project findings are of particular interest to BREEAM since closing the performance gap is seen by BRE as a fundamental consideration in ensuring that BREEAM continues to set the standard for best practice in sustainable building design, construction and operation.
The current BREEAM UK New Construction 2014 and BREEAM UK Refurbishment and Fit-out 2014 schemes include a number of requirements that aim to minimise performance gap related issues at the design and construction stage, for example in terms of commissioning, handover, aftercare and unregulated energy consumption. With respect to a building’s actual operational performance, the BREEAM In-Use International 2015 scheme can be used to identify potential performance gap issues in terms of the asset’s physical performance, building management and occupier management.
In terms of the performance gap for future development of scheme requirements, BREEAM’s research and development programme continues to draw on the latest knowledge and best practice on this topic, including the findings from the above project and from other initiatives such as Innovate UK’s Building Performance Evaluation programme and CarbonBuzz. This information is used to inform the rolling programme of technical updates to BREEAM schemes. Using the most up-to-date and robust science and evidence ensures that BREEAM continues to promote the design, construction and operation of buildings that minimise the performance gap.
Dr Chris Ward is a Senior Consultant within the BREEAM technical team. Chris currently manages BREEAM’s research programme and oversees the maintenance of BREEAM’s science and evidence base.