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Academy examinationSeptember 2007

Consulting engineer Buro Happold has been studying the performance of five new city academies to determine their true energy consumption and occupant satisfaction. How are the schools performing? Ian Pegg reports.

The threat of climate change is presenting architects and engineers with some serious challenges. Whereas a few years ago only a handful of clients and designers were keen on energy-efficient design, these days it is a common expectation. The building services engineer is regularly called upon to make big decisions about whole building concepts. With this responsibility comes a risk that things might not quite work out as expected.

There are big opportunities for those prepared to design ultra-low energy buildings, but aspiration is not enough - delivery is what matters. Feedback on the true performance of buildings - with full and accurate data on energy consumption - is equally important. Designers and clients therefore need to adopt robust methods of post-occupancy evaluation in order to identify the drivers behind energy consumption.

This article gives an overview of some of the findings from a Buro Happold-funded research project into the performance of some recently completed city academies - particularly relevant given to the massive schools building programme, and the new standards that are driving school design.

As an engineering doctorate student at Buro Happold, it was my role to investigate the application of post-occupancy evaluation in a design consultancy. This involved looking at intrinsic barriers in the industry (who pays for feedback, and how to manage the resulting knowledge), the drivers (professional interest and staff development, competitive advantage), but most of all looking at some completed buildings and finding out what could be improved.

Academies are interesting because they have more or less the same requirements, and operate with similar constraints and a similar budget. This makes it much easier to compare the findings and determine what causes differences in results. This study looks at five city academies completed between 2002 and 2005.

The key issues in the design of an academy are:

  • How can ventilation and acoustics be managed in classrooms?
  • How can mechanical cooling be avoided, while still allowing each student to have their own PC in classrooms?
  • How complex can a school get before maintenance budgets become unmanageable?
  • How can an academy have greater functionality, with better environmental conditions, while having low carbon dioxide emissions?

Engineering solutions

The five buildings in the study used a variety of approaches to tackle these issues. Some techniques were common: all the schools had high thermal mass in at least some of the classrooms. In one academy this was coupled with an automatic night-cooling strategy.

In an attempt to avoid cooling, cross-ventilation was applied in four of the academies. This worked well with clerestory vents on the first floor of one building. However, when this was coupled to a central atrium some acoustic problems arose.

Generally, mechanical ventilation was only employed when road noise was too great to enable openings in the facade. In some cases this was done by using standard constant-volume air handling units serving a number of zones with tempered air.

In an attempt to save fan power, one building used a single air handling unit and buried concrete ductwork to serve 17 classrooms. Each classroom had a damper controlled on room occupancy. The speed of the fan was determined by the number of classrooms in use.

All five buildings used full-height circulation or atrium zones. Three of the schools opted for particularly open spaces, by connecting the entire school to an atrium. This was usually done to combat bullying, allowing teachers a good view of the entire school from almost any point within the space.

Two of the schools had significant need for mechanical cooling. In one academy fan coil units have been used for internal zones.

One of the academies specialises in information and communications technology (ICT), and provides one laptop per student. It was recognised that the criteria in Building Bulletin 87 could not be achieved passively, so chilled beams were installed. Combined with natural ventilation on the north facade of the school, this approach enabled higher cold water flow-temperatures and free-cooling for most of the summer.

There was a concern that the school would use the panels for comfort cooling, rather than for peak lopping. However, data logging has showed that this didn't happen.


Energy efficiency

Figure 1 shows the energy consumption for electricity and gas for all five academies compared to DFES energy benchmarks. This revealed that gas consumption for heating was quite good, a consequence of using high-efficiency condensing boilers, compensated circuits, optimum start/stop controls, and reasonable to good U-values.

The electricity consumption is surprising, especially when compared with the DFES benchmarks. However, the results were comparable to more recent monitored data.

For example, John Cabot City Technology College(1) and Kingsmead Primary School(2) were both reported to use around 65 kWh/m2, without some of the acoustic constraints and levels of ICT provided in the academies. However, the high levels certainly warrant explanation.

Figure 2 shows the electrical breakdown by end-use. Data was gathered using electrical profiling equipment in the LV panels and distribution boards.

Lighting consumption in academies A, B and E was up to four times higher than academies C and D. While installed loads were equivalent, the major difference was control. Figure 3 shows the control of manual lighting in school B and automatic lighting in school C over one month. The simple use of PIRs saved 30-40 percent compared with manual switching.

Subsequent investigation showed that manual control of circulation lighting in school B was particularly bad, a characteristic that was repeated to varying degrees in schools A and E. The schools with large connected atriums had the highest lighting energy consumption, for the following reasons:

  • No-one owned the central atrium spaces, and therefore no-one took responsibility for switching the lights
  • The spaces were well daylit, but in school B the finishes were dark. Without lighting on during the day, teachers complained of a gloomy feel to the spaces, though overall they loved the openness of the school
  • The occupancy of the schools was complex and varied on a daily basis and between school terms. This meant that lights were not switched off outside core hours

The 24h security required lights to be on for security cameras and for walk-rounds.

The base load drove the energy consumption in all schools. After lighting, the fans, pumps and controls caused the highest consumption. This was in part due to poor time control of systems.

Interestingly, school C has ventilation equipment that defaults to off when the spaces are not occupied. Even though the academy had the highest proportion of mechanically-ventilated spaces, it had one of the lowest electrical consumption for fans, pumps and controls.

Clearly, some schools with low energy features may produce more carbon dioxide, not less. Care is needed, and the following guidelines for designers may be useful for designers attempting a low-energy design.


Design lessons

ICT can represent as much as 20 percent of a school's electricity consumption, a proportion that will become more significant as other equipment becomes more energy efficient.

The likelihood is that the student/computer ratios will creep up. We need to be aware of this and influence the ICT consultants on our projects to procure the most efficient equipment.

Schools of the past were expected to be entirely free running from April to October, with many rooms either noisy or hot. New schools come with a higher set of expectations. However, designers must review the standards and determine their effect on energy. The key lesson is to only provide high standards when they are required, not as a default state.

School buildings are now used for a variety of purposes, particularly during out of school hours, such as adult classes, community events, and after school lessons. This is raising the run-times of central plant and lighting systems.

Buro Happold's research showed that the default is usually full power at all possible times that the school could be occupied. This is one of the key reasons that school C performed so well: all default states were either off or low power.

Decentralising HVAC and zoning the building can make default-to-off easier to achieve. However, this may have knock-on effect on capital cost and space needs. Designers need to argue that the energy benefits may justify higher capital costs and a different approach to design.

It is often said that high energy consumption is caused by the behaviour of building occupants. However, others have shown that decisions regarding energy consumption are highly influenced by assumptions of occupant behaviour. This is why designers should close the loop between design expectation and reality if schools are to become truly low-energy.

In order to improve the internal environment to ensure passive design features work properly, schools are incorporating automatic windows and solar shades that respond to internal and external conditions. A certain level of expertise and experience is required to operate and maintain such systems.

This study showed that, in all five academies surveyed, the facilities management staff had little relevant experience with building services. Only three of five facilities managers interviewed were able to operate their building management system. In the other two schools, the systems were not optimised to respond to changing requirements. This led to plant overruns and less than optimum internal conditions.

Designers need to advise their clients on the likely operational and maintenance implications of the schools they are designing. If complex controls are unavoidable, they should at least ensure that the client is well-prepared.

The facilities managers often felt they were not well prepared to operate the building management system. If these buildings are to perform as intended, provision of training and suitable documentation must be improved.

References
(1)Standeven M, Cohen R, Bordass W, and Leaman A, 'PROBE II: John Cabot City Technology College', BSJ October 1997.
(2)Design of Sustainable Schools, Case Studies, Department for Education and Skills, 2006.

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