Ventilated spleen

Low-energy technology for buildings is one of those ideas that looks good in theory, but doesn’t work in practice. At least, that is the conclusion many developers will be tempted to draw from the news that the Greater London Authority’s 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’ 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: “Any additional plant installation would require capital expenditure and would not provide a significant energy saving.”

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’s designers. “At the moment, it’s fit and forget,” 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’s concrete elements, which the design relied on to absorb heat during the day, was not being sufficiently cooled at night.

Comfort in BRE’s Environmental building is good even on hot days, but higher than expected air leakage rates means it’s 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: “Although we have all the design tools, there is a dearth of knowledge about managing climate-adaptive buildings.”

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

There’s a high level of sophistication that facilities managers don’t yet understand. They’ve 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. “There’s a high level of sophistication that facilities managers don’t yet understand. They’ve got used to the fan coils but now they have to learn about thermal mass and it’s a steep learning curve.” 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’re working late and feel cold.

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

One way to improve facilities managers’ 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. “It’s an incentive for the designers to stick with the building.”

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. “People come along with the finished design and they want it to be sustainable, but it can’t be done. Air moves in mysterious ways.”

The underperformance of low-energy technologies could have repercussion for the government’s drive to cut carbon emissions. “There is a real danger that if buildings designed to deliver low energy fail, the developers will walk away from them,” 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 “operational energy” performance of their buildings under the certification requirement of the Energy Performance of Building Directive.

Strong says this will not happen if the government opts for an “asset” rating instead, which measures the theoretical performance of the building based on design. “Operational ratings have great potential as they allow meaningful data to be compared,” 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 …