Practical sustainability
Using an absorption chiller to provide air conditioning provides summer load for the university’s central combined-heat-and-power plant.
Natural ventilation, exposed mass and air-conditioning using an absorption chiller served by hot water from CHP plant have been brought together to service a new building at Warwick University.Designing an energy-efficient and sustainable building is quite easy — provided the client is open to these concepts and the building-services consultant is involved at an early stage. A balance can be achieved between the additional costs of passive-design measures to minimise the need for mechanical and electrical services and the cost of plant to provide those services so that the building-services consultant receives a fair reward for his design work. Such was the case for the design of a new building to house the Mathematics Institute and Statistics Department at the University of Warwick.
Concept stage Andy Morris, lead project engineer with consultant Hoare Lea & Partners, tells us that the practice became involved in the design of this 3-storey 8000 m2 building through a process of competitive fee bid and interview. It was thus at the concept stage that Hoare Lea was involved with developing the brief with the academic staff who would occupy the building and the university estates office. Andy Morris says, ‘This inclusive approach allowed the end users to identify their departments’ objectives for the project. These could therefore be engineered in from the project’s conception.’ The service brief was to provide a functional, flexible and comfortable internal environment capable of meeting the current needs and future expectations of the two departments, whilst minimising energy consumption and carbon emissions. The building includes an undergraduate teaching centre with five lecture theatres, all with extensive audio-visual facilities; these facilities are not an integral part of the Mathematics Institute or Statistics Department and are to be booked centrally. Accommodation for both academic departments includes a departmental library, common rooms, seminar rooms and work areas — all located around a common ‘street’.
CHP The building is arranged in a collegiate style, with a number of courtyards next to academic offices providing break-out space. Electricity and hot water from a central combined-heat-and power plant installed about three years ago was available for utilisation. Electricity from this plant is used entirely on the serves the entire campus so, unusually, its capacity was power led — not heat led. There is a heat dump available for use when it is beneficial to generate electricity because the grid supply is expensive but there is insufficient demand to use all for the waste heat. The use of waste heat from the CHP plant is growing all the time as more buildings are connected to the hot-water distribution system and boiler plant removed. The comfort criterion for the new building was defined as internal temperatures not exceeding 28°C at any time during the year. As far as possible, air conditioning was to be avoided and maximum use made of other methods of environmental control such as exposing the concrete mass of the building, night-time ventilation, natural ventilation by day and solar shading. Andy Morris explains that the results of the first calculations indicated maximum internal temperatures reaching 29 to 30 °C. That initial assessment was followed by a full-year performance analysis using computational fluid dynamics to assess the effects of changing the angle of the large area of Brise Soleil on the south aspect of the building, different types of glazing, window setbacks and size of night-time ventilators.
Acceptable performance The result was internal temperatures peaking at 28°C for all but a few academic hours in the year, a building performance that was considered acceptable. Energy consumption was also an important issue, with a target of being better than the Part L of the Building Regulations of the time by 10% so as to comply with the forthcoming, and now current, Part L. The energy performance was assessed using the whole-building method. ‘It passed by a mile,’ says Andy Morris — largely helped by the use of waste heat from the central combined-heat-and-power plant to heat the building, provide domestic hot water and drive an absorption chiller to provide air conditioning for lecture theatres and IT rooms. Indeed, the assessment was re-calculated as if the building had its own boilers, and it still passed. Even with an electrically powered chiller, the energy performance of the building would still have exceeded the requirements of the current Part L. The CHP plant makes an important contribution to achieving low carbon emissions.
Absorption chiller This project represents the largest first use of an absorption chiller on the university campus and provides a demand for waste heat all year round, but particularly in the summer months — increasing the effective use of primary energy to the CHP plant. There are plans to install more absorption chillers in the future. The development of the sustainable brief was realised by selecting a structure with exposed concrete mass and a night-time ventilation system implemented through hopper windows. Waste heat from the campus CHP plant is used for basic heating, via radiators, and domestic hot water and to power the absorption chiller. Mechanical cooling is avoided in academic offices, corridors and the full-height entrance area.
Lighting Having exposed the building structure to gain energy benefits, it was essential that the lighting design avoided creating an austere environment. Exposing the mass of the building raises the ceiling height so it is better to suspend the lighting. There are two benefits. First, the exposure of the soffit is maximised. Secondly, the use of luminaires with a balance of uplighting and downlighting maximises the feeling of space where the soffits are seen. Users in academic offices are provided with simple dimming control, and the lectern in lecture theatres has similar lighting control built into it. In the full-height entrance area, maintenance issues have been considered in selecting the lighting. Spotlights around the outside of the balcony walls point at multi-facetted mirrors suspended from the underside of the roof to provide downlighting. Lamps in these fittings can be changed from the balcony. Effects lighting in the entrance area is provided by fittings using light-emitting diodes of various colours. LEDs have a very long life — 30 000 to 40 000 h — and the intention is that they will only be changed when the ceiling is painted. Lighting in lecture theatres and seminar rooms is by compact fluorescent lamps, which will be changed in bulk. In areas where mechanical cooling is necessary, it is provided by a range of techniques using chilled water from the absorption chiller .
Displacement ventilation There are two lecture theatres at ground level, one with 350 seats and the other with 250. Air conditioning is provided by displacement ventilation, with air delivered through continuous grilles in the vertical step behind each row of seat. Because cool air is delivered around people’s ankles (as is usual with this type of system), its velocity has to be very low. The plant rooms providing the conditioned air are immediately below these lecture theatres, so noise from the plant must be minimised. From inside the plant rooms themselves, which are effectively two air-supply plena, the effect is of the lecture theatres being an integral part of them, with direct lines of sight through the grilles into the lecture theatres. Return air is taken out through the ceilings and the backs of the rooms.
CFD Because of the very precise air conditions required, computational fluid dynamics played a key role in the design of this system. There are three lecture theatres at first-floor level. Two have 75 seats, and the third has 85 seats. Air conditioning is again provided by displacement ventilation, with air passing up through ductwork in the front corners of the two lecture theatres below and introduced through low-level grilles in the front walls. Exhaust air is drawn out through the ceiling. Where heat loads are greater, notably in the two IT rooms, it has been necessary to use fan-coil units installed above suspended ceilings. Fan-coil units also serve seminar rooms that are remote from the plant rooms so that it is not practicable to use displacement ventilation. And the success of the project? The estates office feels that the building-services design successfully combines the user requirements with the sustainability and energy-conservation measures to provide an efficient and attractive environment for academic teaching and research.
Team members Project manager: University of Warwick Architect: R H Partnership Architects Services engineers: Hoare Lea Consulting Engineers Quantity surveyor: Northcroft Main subcontractor: Balfour Kilpatrick
Related articles:
