This month the cost and research departments of Mott Green & Wall and Davis Langdon & Everest, examine the cost and specifications of services for low energy university buildings.
The higher education estate comprises a total floor area of 9·3 million m² and has an estimated replacement cost of £ 18 billion. However, many post war buildings have reached the end of their design life and this together with a history of under investment in the sector, means that over two thirds are in need of repair or refurbishment and are currently incapable of meeting the changing needs of the sector.

In order to meet the government targets of providing wider access to higher education, it has been estimated that a figure of £ 5.1 billion is required to repair, replace and modernise the buildings, services, IT networks and libraries of higher education institutions over the next three years. There is also a significant recurrent investment required to enable the institutions' to manage their infrastructure on a sustainable basis.

The total annual income of English universities and colleges for 1999–2000 amounted to just under £ 10.5 billion, with about 60% coming from public funds. The main sources are the HEFCE grant, which distributes public funds allocated to it by the DfEE (the largest single source, at 39%) publicly funded tuition fees, and income from research grants and contracts awarded by the research councils and government departments.

The remaining 40% comes from private finance comprising research income, overseas student fees, charities, residences and catering and other income.

Many higher education institutions have already enjoyed considerable success in attracting private investment, through loans and other forms of borrowing. The government has made it clear that it looks to universities and colleges to make greater use of private finance, to help fund these upgrade works.

The PFI market in the sector currently appears small, however the HEFCE is actively encouraging institutions to consider this alternative means of finance. PFI is most obviously applicable to non-core activities which generate a direct income flow, such as catering and sports facilities, student residences and conference facilities. However, it can also work for projects involving academic buildings, in the same way it does for hospitals and prisons. Research collaboration, with higher education providing the academic environment and industry the buildings or equipment, exploits the strengths of both sectors working together, and is another area where there is potential for attracting private finance.

Design issues
The higher education sector in the UK includes some 200 universities, covering a wide range of building types, user occupancy patterns and research activities.

The article concentrates on buildings of a non-scientific use, where the developments in low energy design over the last decade have led to this being the preferred solution for this application.

Such buildings typically comprise office space for academic staff, classrooms, tutorial areas, seminar rooms and large lecture theatres. Library space may also be included, but such spaces tend increasingly to be separate stand-alone buildings.

The occupancy patterns vary between the different areas, and this affects how each is serviced. The teaching areas have a variable occupancy pattern with some transient periods, but generally medium to long-term use. Academic staff offices are mainly cellular space with single occupancy, while lecture theatres have dense occupancy for short periods. Libraries on the other hand have long-term occupancy, some at high density, and a high usage of computer terminals.

Being effectively owner occupiers, universities are also interested in the long-term costs of owning and operating the building and so are committed to minimising both energy and maintenance costs throughout the buildings life. This also affects the servicing solutions that are adopted.

There are various different strategies for designing a low energy building with the choice of approach being influenced by a variety of factors. Whichever solution is adopted the aim is to minimise running costs and maximise occupant satisfaction. This means achieving stable space conditions that fall within acceptable comfort parameters for the majority of the time, and providing a system that allows conditions to change quickly in response to other fluctuations, such as the weather. The key features common to most low energy schemes can be summarised as follows:

  • Highly insulated, well sealed building. Air tightness has always been a problem in low energy buildings and more attention to detailing is required in design, specification and workmanship.

  • Making use of the thermal mass in buildings to control temperatures, by exposing the slabs so they can absorb the heat from the space during the day.

  • Generous floor to ceiling heights to facilitate the use of natural ventilation and daylighting.

  • A flexible window opening system, usually comprising a mix of low level manual and a high level automatic control (which can be over ridden by the occupants). A night cooling strategy controls the high level ventilation, with background ventilation being provided in winter from trickle vents.

  • The provision of some form of shading to south facing windows to deal with direct solar gain, using motorised external louvres, deep reveals, overhangs etc, although multiple small windows may be used rather than large glazed areas to reduce the effects. Secondary internal manually operated shading may also be provided. However, it is also important not to reduce the levels of daylight entering the space.

  • A shallow plan form to aid good natural ventilation. Ventilation strategies depend on the size and form of the building, with single side, cross flow and side to centre ventilation using exhaust ventilators at roof level all being used. Given the right circumstances, single sided ventilation works well, with the more advanced forms of ventilation such as stack effect or wind driven, being less robust.

  • Use of a lighting control system to maximise the benefit of natural daylight. However, this is only cost-effective if it displaces the need for artificial lighting. Most systems rely on presence detection for activating the lights, however a demand responsive system of absence detection, where the lights are switched on manually and go off automatically, is more energy efficient.

  • Use of a separate compensated lthw heating system, with condensing boilers and variable speed pumps.

  • Where mechanical ventilation is necessary in central core areas, systems are time switch controlled. Similarly where mechanical ventilation is provided to rooms with highly variable occupancy (such as lecture theatres), measurement of CO2 levels and variable speed drives on the fans ensures energy is not wasted on unnecessary ventilation.

  • Predictable occupancy patterns. In naturally ventilated buildings, extended hours of operation can seriously compromise night time cooling strategies.

  • A high degree of cellurisation. This scores highly in terms of occupant satisfaction and also offers more opportunities and potentially fewer downsides for natural light, natural ventilation and individual control.

  • The provision of training for the higher degree of user control that naturally ventilated buildings provide. Occupants generally prefer resolving their own problems rather than having solutions imposed on them by automatic controls etc, and one of the main reasons why buildings don't perform is that the occupants do not understand how they are supposed to work. Also, low energy solutions need more fine tuning and engineering support than many occupiers are prepared to provide, which in turn leads to a less than satisfactory performance.

  • It is important that all devices subject to occupant controls are robustly designed, as the failure of these has been a recurrent problem in such buildings in the past.

  • Advanced naturally ventilated buildings need sophisticated controls to optimise building performance. However, this has to be balanced with the provision of a good range of physical controls with clear intervention strategy for occupant operation. One of the problems with low energy buildings is the difficulty in getting the controls to work as intended.

  • It is essential that thermal simulation is carried out on the design to establish that the ventilation strategy works satisfactorily.

Mixed mode systems
In well designed naturally ventilated buildings, mechanical ventilation is only usually necessary to serve internal core areas, and specialist areas with particular cooling or ventilation requirements, eg computer rooms and lecture theatres.

However, the specific limitations of natural ventilation mean it cannot reliably be used in certain situations. In these cases, designers tend to opt for mixed mode solutions. These usually either mean providing mechanical ventilation or comfort cooling to deep plan rooms or internal spaces, where it would be difficult for fresh air to penetrate (and using natural ventilation in all other areas), or cycling between mechanical ventilation and openable windows (in the same space) depending on the season and the load, with the possible provision of cooling in peak summer only.

On this last point, use of cooling as a means of reducing peak summertime temperatures in this way needs careful analysis at the design stage, of overheating criteria and occupants likely response to higher temperatures, to ensure it is absolutely necessary.

Some low energy designs have successfully used the Termodeck hollowcore slab system as a form of low pressure drop mechanical ventilation with heat recovery and openable windows (and with no allowance for mechanical cooling). The ventilation supply air is passed through precast hollowcore concrete flooring to adjust its temperature actively. This makes better use of the available storage mass than natural ventilation, allowing acceptable conditions to be achieved with heavier loads.

Energy consumption
Analyses have shown that naturally ventilated buildings can reduce energy consumption by over 50% compared to typical university academic buildings. The avoidance of mechanical ventilation and the increased use of natural light results in significant reductions in electricity use, and there are also potential savings in heating energy consumption, perhaps considered unusual for a passive building, due to the buildings form, fabric insulation levels and use of condensing boilers etc.

Mixed mode designs generally use more energy than naturally ventilated solutions due to the increased usage of mechanical ventilation, but are still substantially less than the fully air conditioned alternative.

Cost model
The cost model is based on the analysis of a new academic building forming part of a wider campus development in the south east.

The building comprises two four-storey blocks and an internal three-storey block, with a total gross internal floor area of 12 800 m².

The four-storey blocks are predominantly naturally ventilated with exposed concrete slabs, using a single sided system with high and low level vents. The vents are not provided with automatic control and are manually operated. The internal classrooms and seminar rooms are provided with either chilled beams or displacement ventilation (depending on the depth of floor available).

The three-storey block houses lecture and seminar rooms and is served by a displacement ventilation system throughout, with high level extract. The building is not heavily glazed and so external shading was not required.

Project Parameters

Procurement
Two stage design and build
Main contract
JCT 98 with contractors design
Subcontract
Domestic form of sub contract
Basis of tender
Specification and drawings
Overall contract period
82 Weeks (for whole campus scheme)
Value of services (including lifts)
£ 4 295 300

Main design parameters

Thermal conditions
External
Winter: -4°C, 100% rh
Summer: 27°C db, 21°C wb
Internal
Heating/cooling
Naturally ventilated areas: 20°C minimum, 27°C maximum not to be exceeded for more than 2·5% of the year.
Mechanically ventilated/comfort cooled areas: 20°C to 26°C.
Circulation and toilets areas: 18°C minimum
Ventilation
Mechanically ventilated areas: 8 litres/s/person
Heating systems
Low temperature hot water: 80°C flow, 60°C return
Electrical supply
400 V, three-phase with separate cpc
Lighting
Classrooms, seminar rooms, lecture theatres and offices: 300 lux
Reception area: 200 lux
Circulation and toilet areas: 150 lux

Related files/tables