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Low-energy technology for buildings is one of those ideas that looks good in theory, but doesn鈥檛 work in practice. At least, that is the conclusion many developers will be tempted to draw from the news that the Greater London Authority鈥檚 City Hall is using 50% more energy than intended, consuming 376 kWh/m2 of energy a year rather than its target of 250 kWh/m2.

In fact, the problem with buildings such as Foster and Partners鈥� City Hall, which uses a ground source cooling system, is often the way that they are used, rather than the technology that they incorporate. Chris Twinn, a director of Arup, was the project engineer for City Hall. He points out that the building had higher occupancy levels than were envisaged in the design brief, which meant that the pumps had to work harder.

Twinn suggested that an additional heat exchanger could have been more energy efficient; however, a spokesperson for the Greater London Authority said borehole abstraction accounted for only a small amount of the energy used in City Hall. He said: 鈥淎ny additional plant installation would require capital expenditure and would not provide a significant energy saving.鈥�

Even if the design brief is accurate, building managers often do not understand how low-energy buildings should be controlled. This could be because the designer has not passed on the information, or because the fit-out is not carried out by the building鈥檚 designers. 鈥淎t the moment, it鈥檚 fit and forget,鈥� says Twinn.

The consequences of poor building management can be greater for naturally ventilated buildings than mechanically controlled ones. At the Michael Hopkins-designed Inland Revenue headquarters in Nottingham, natural ventilation did not cool the office because the building managers left IT systems on 24 hours a day. This meant the thermal mass of the building鈥檚 concrete elements, which the design relied on to absorb heat during the day, was not being sufficiently cooled at night.

Comfort in BRE鈥檚 Environmental building is good even on hot days, but higher than expected air leakage rates means it鈥檚 not quite as energy efficient as was hoped.

David Strong, managing director of BRE Environment, says facilities managers tend to control naturally ventilated, passively cooled buildings as if they were mechanically operated. He says that most do not have the tools or expertise to manage complex buildings correctly. He says: 鈥淎lthough we have all the design tools, there is a dearth of knowledge about managing climate-adaptive buildings.鈥�

The closest thing building managers have is CIBSE鈥檚 recently revised manual Natural Ventilation in Non-Domestic 黑洞社区s, which includes guidance relevant to building managers.

There鈥檚 a high level of sophistication that facilities managers don鈥檛 yet understand. They鈥檝e got used to fan coils but now they have to learn about thermal mass

Twinn says part of the problem is that building managers believe naturally ventilated buildings are simple to operate because they contain fewer services. 鈥淭here鈥檚 a high level of sophistication that facilities managers don鈥檛 yet understand. They鈥檝e got used to the fan coils but now they have to learn about thermal mass and it鈥檚 a steep learning curve.鈥� For natural ventilation systems to work, windows or vents must be left open all night to let air cool the thermal mass. The cooling will be compromised if somebody closes the windows because they鈥檙e working late and feel cold.

Another problem that can arise through a lack of understanding on the facility manager鈥檚 part is the installation of enclosed offices in open plan spaces, which can block cross-ventilation flows.

One way to improve facilities managers鈥� knowledge about natural ventilation would be a provision in the contract between the design team and procurer to provide training, according to Strong. He says the UK should examine a US pilot scheme, operated by the Architectural Energy Corporation and sponsored by the US government, where occupiers and designers are rewarded if the energy performance of a building beats a benchmark standard. 鈥淚t鈥檚 an incentive for the designers to stick with the building.鈥�

The role of design teams is vital. Twinn bemoans the fact that on City Hall the design team was brought in so late in the process, which made it harder to incorporate a low-energy ventilation scheme. He has the sympathy of John Palmer, regional director at building engineer Faber Maunsell. 鈥淧eople come along with the finished design and they want it to be sustainable, but it can鈥檛 be done. Air moves in mysterious ways.鈥�

The underperformance of low-energy technologies could have repercussion for the government鈥檚 drive to cut carbon emissions. 鈥淭here is a real danger that if buildings designed to deliver low energy fail, the developers will walk away from them,鈥� says Strong. They need more care, both in design and operation, than air-conditioned buildings. The government could be about to miss a prime opportunity to improve the energy performance of completed buildings. It is currently deciding whether to force landlords to display the 鈥渙perational energy鈥� performance of their buildings under the certification requirement of the Energy Performance of 黑洞社区 Directive.

Strong says this will not happen if the government opts for an 鈥渁sset鈥� rating instead, which measures the theoretical performance of the building based on design. 鈥淥perational ratings have great potential as they allow meaningful data to be compared,鈥� he says.

More effort may be needed to make this technology perform well, but the rewards are undeniable. Even City Hall uses one-third of the energy that is consumed by a typical high-spec office 鈥�