The need to bridge the energy performance gap between predictions of building energy use at the design stage and the measured results once the buildings are operational is a hot topic right now in the building services industry, says Mark Northcott

For environmental, legislative and financial reasons, high energy consumption is a real problem for commercial and industrial buildings which typically consume 1.5 to 2.5 times the energy they were predicted to use at design stage.

One tool that has been introduced to promote smarter building design is BIM (Building Information Modelling), a model-based, collaborative, shared knowledge resource for all sectors of the building services industry. BIM offers detailed data to support the way buildings are designed, constructed and operated, increasing productivity throughout the lifetime of a building.

CarbonBuzz is another platform that aims to close the gap between designed energy use and actual energy use by providing the means to benchmark and track project energy use from design to operation.

We in the heating industry can play a key role in helping close the performance gap. After all, heating and hot water production account for around 40 per cent of our carbon emissions and can account for 60 per cent of our total energy use, according to the Carbon Trust, with boilers still the most prevalent form of heat generation in commercial buildings. Providing 3D digital BIM files of our boilers is a good starting point. But there is a more contentious area that we could also address: boiler efficiency figures.

Very different results
Condensing boilers - especially those in their fourth or fifth revision - can achieve outstanding efficiencies of up to 107 per cent NCV or 98 per cent GCV. But do these figures reflect how they are used in reality?

The fact is, testing a boiler's efficiency in controlled test conditions will produce very different results to real life operation where these maximum combustion efficiencies simply cannot be replicated. Condensing boilers work most efficiently when operated at low temperatures (30-50°C) and half load. When operated at higher flow and return temperatures, as is the case in many installations, the efficiency figure can come down to the standard 80 per cent GCV. That difference of around 10 to 15 per cent in efficiency levels is a significant figure which could account for some of the discrepancy between predicted and actual energy use.

I like to draw an analogy between boilers and cars. Cars are designed to be at their most fuel efficient when driven at 55 mph. At this speed, drivers achieve more miles per gallon and lower carbon emissions. But obviously we can't all drive at 55mph all the time. A more realistic scenario would be a mix of town driving and motorway driving - known as the 'urban cycle' and 'extra-urban cycle' - which would give us fewer miles to the gallon.

Similarly with boilers. There are warm days, cold days and then absolutely freezing days and the boiler has to adjust or modulate accordingly with differing results. Where the analogy ends is that car manufacturers provide not only their maximum fuel efficiency figures but also those for the urban and extraurban cycle. A combined fuel consumption figure presents the average of the two figures to provide drivers with a more realistic calculation of the fuel efficiency of their car on the road.

Of course, this system is not without its flaws, with a recent report by Transport & Environment finding that fuel efficiency tests are being manipulated through loopholes such as supercredits to meet their CO2 limits. However the principle remains valid.

Calculating the 'seasonal efficiency' of a boiler will provide us with a more accurate evaluation of its actual, real life efficiency. Given the question mark that hangs over our national energy security, the steep carbon reduction target we must meet by 2050 and our financial and environmental need to cut energy consumption, isn't it time for boiler manufacturers to adopt this more realistic approach to presenting efficiency figures?

Smarter system design
By providing a range of figures on our boilers from the maximum combustion efficiency to the seasonal efficiency, we can not only help close the gap between predicted and actual energy use, but assist in smarter system design for the greatest energy savings. The real challenge for boiler manufacturers lies in the UK's high proportion of existing, inefficient building stock. These buildings often have old heating systems in place which, by their nature, require more nergy to heat. Even high condensing boilers would struggle to achieve their maximum efficiency levels on such a system - with or without the addition of a smart control.

So rather than sitting on our laurels, we boiler manufacturers should get real. By presenting more accurate figures on the varying efficiencies of our boilers, we are free to challenge the conventionally accepted condensing efficiencies and innovate for optimal operation under all conditions. At Remeha Commercial we are looking just that, looking beyond condensing technology to 'super condensing' heat recovery systems that deliver full time maximum combustion efficiencies regardless of primary circuit temperatures. It's revolutionary thinking like this that will help move the nation forward to a low carbon future.

// The author is managing director of Remeha Commercial //