Closing the performance gap

As we drive the performance of our building stock, it is becoming clear that one of the key challenges we must address is narrowing the gap between design and actual performance. The industry needs support to ensure we use more accurate modelling and data in order to understand how the building will perform in operation. If we don't, the gap in performance can be as big as 200-450% greater than predicted.

With project costs squeezed and ‘value engineered', all too often performance suffers. By allowing design teams more time to spend on modelling and considering how the building will be used by its occupants, rather than being forced into ‘default values' and specification, we will go some of the way to eliminating this performance gap.

Understanding the gap

The performance gap has two components: the compliance gap and the actual performance gap. The modellers estimate 50-70% is the compliance gap and can be solved by more realistic modelling mirroring the conditions more closely. The reasons for the second and larger actual performance gap are generally unknown. There's speculation about this and assumptions, but little in the way of hard evidence.

When a building is managed effectively, property value is maximised. A high performing building will ultimately generate maximum profit via high and continuous rental income, low operating and maintenance costs and low depreciation.

Modelling tools are used for compliance, which means they use standard default values for the building design. All the operational plant which controls the building is then set at these ‘standardised driving' conditions and the occupancy density (i.e people versus square metres) is based on industry averages.

As a result these standard default values underestimate the usage by up to 100%. Software is used to meet building regulations and energy performance certificates, as well as being used for ranking rather than the operation of the building. When you pass the design stage, it's essential that real numbers are inputted and this can be done via modelling techniques such as the Green Deal software developed by BRE. This allows users to tailor the usage of the building to match real operating conditions in. It allows you to work out what it should and shouldn't be. 

But from that point onwards much depends on how well the building is commissioned; what maintenance strategies and schedules are put into place; and how the building is managed. If this doesn't happen you begin to see divergence. Buildings need to be commissioned properly with particular attention made to control systems and the needs of the occupants. 

The power of management

Building management systems (BMSs) and building energy management systems (BEMSs) are powerful tools in ensuring that buildings are run efficiently and provide the desired environment for the occupants. As technology becomes cheaper and advances more rapidly, control systems need to be flexible, upgradable and have the facility to easily communicate and integrate with other systems.

However, care needs to be taken in their operation, and staff using these systems need to be fully trained. Ongoing commissioning and preventative maintenance needs to be carried out to ensure the potentially large energy savings are realised, operational costs are controlled and expensive failures do not occur. End-user needs should be taken into account, while staff training and awareness-raising should be carried out to get the building's occupants involved.

Ongoing commissioning is essentially a higher form of maintenance. Maintenance simply deals with faults. It's also important to consider management issues. Is the right environment being provided? Is it being provided in the proper place? Is the building being turned off at the right times?

If it is not managed properly, the performance gap will only get worse. Modelling doesn't help with the building in-use but baselines the building predicted performance. It starts by putting decent controls in so things are turned off when they are not occupied. Once you have control of the building, you can put the management systems in place so that building is optimised for energy usage. 

Focus on people

One of the most important things to remember is that a building is built for the occupant. In terms of costs, staffing is around 95% and workplaces are key to productivity. Any reduction in productivity has a large effect on a business's bottom line; after all 95% of operational costs are the staff. Buildings therefore need to be efficient, responsive and innovative, which is why it is so important to optimise the environment in first place.  

It's imperative that the industry treats the underlying causes not the symptoms. It's like the heart problem analogy. A surgeon might repair a damaged heart with a stem cell but not treat the inherent diet and lifestyle issues.

One of the main problems is that architects are not bringing the design teams early enough in the design process. The later you do this, the more expensive it gets and reduces the benefits in the long term. By engaging with the performance gap, it's possible to deliver the triple bottom line of people, planet and profit.

By Dr Andy Lewry, Principal Technical Consultant, BRE Global

Visit: www.breeam.com