City Hall is the latest green office to miss its energy targets. But when it comes to low-energy buildings, the fault may lie with facilities managers, not designers.

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.
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 …

What can go wrong …

The performance of naturally ventilated buildings can be affected by design and operation issues. These are the most common problems, as identified by construction researcher BRE:

  • Thermal plumes can build up outside the building and compromise the performance of the passive ventilation system by entering through vents and windows. This could be caused by dark surfaces absorbing heat. The remedy could be costly, as it may involve recladding.
  • Flat roofs next to windows can absorb solar radiation, giving rise to solar plumes.
  • Windows may be installed that do not allow for adequate ventilation. See Natural Ventilation for Non-Domestic Buildings for a guide to correct specification.

  • In hospitals, natural ventilation can be compromised if windows are not openable for safety and security reasons.
  • People don’t understand that opening windows too far on warm days will let in hot air and compromise natural ventilation.
  • Night-time cooling can be curtailed if windows are shut for reasons of noise or security.
  • Large amounts of IT equipment may prevent cooling.David Butler, the head of BRE’s heating, ventilation and air-conditioning department, says he sees as many problems with mechanically ventilated buildings, but adds that naturally ventilated systems are potentially more difficult to design and operate. Remedies can also be more costly, as it’s not just a case of turning up the air-conditioning. Systems may have to be redesigned.

  • The building manager’s view

    Property group Jones Lang LaSalle manages more than 50 properties in the City of London, and Peter Carr, the national operations manager, admits that a good connection between the design and management of buildings is often lacking.

    Carr says clients don’t appoint property agents early enough for them to have an input in the design brief. Consequently, when the project is handed over, the client finds its building doesn’t fit its requirements.

    Jones Lang LaSalle’s management by design initiative encourages clients to communicate with design teams. Carr says some clients are moving down the right path, including Standard Life, which used the management by design process to inform the design of building services over a three-year period.

    Management by design covers maintenance regimes as well as the control of services. Carr says an intimate knowledge of the building services enables clients to optimise the amount of “free” cooling available.

    Second-hand buildings pose a particular problem. Carr says the information about the building often gets lost in the ether. “We have to root round for the information by talking to architects and services engineers and then compile the logbooks,” he says.

    The constant advances in technology also hamper the management of services, says director Tony Bones. “Trends change every five minutes, which means we often have to change the building management system of buildings before they work,” he says. Bones says a good relationship with the BMS supplier is essential for a building to work properly, especially for naturally ventilated buildings.

    How it’s supposed to work

    Natural ventilation is increasingly being used to provide thermal comfort as well as healthy indoor environments. Ventilation is created by pressure differences between the outside and inside of buildings and is driven by wind and temperature. Wind drives cross-ventilation, while the temperature effect, also known as the stack effect, is created by warm buoyant air as it rises in a tall confined space. Vents or windows allow cool air to enter at the bottom of the stack, forcing the warm air up out through high level vents. Ventilation can be used through the night to cool the building structure and this curbs the temperature rise during the following day. Buildings with high thermal mass are more effectively cooled than lighter structures. Designers often specify mixed mode systems, where natural ventilation is backed up by mechanical ventilation and cooling. For example a small chiller could be used to cool air entering a building. In the case of the Greater London Authority’s City Hall, air is partly cooled by water from boreholes below the building.