Manchester Civil Justice Centre

A unique combination of natural ventilation and daylighting coupled with the use of aquifer water cooling helps cut energy costs by more than 20% for this landmark public building.

Described as a 'fourteen-storey filing cabinet', the £110 million, 35,212m2 (gross) Manchester Civil Justice Centre is the largest court building to be developed in the UK

Civil Court Building Manchester
Cantilevered courtrooms are a distinctive feature of the Manchester Civil Justice Centre (Reproduced with permission from Mott MacDonald)

since 1892. Its designers were set very strict briefs on the internal environments of its 47 courtrooms, requirements that sometimes took precedence over the sustainability of the project. Internal temperatures had to be maintained between 21°C and 24°C at all times, with the maximum possible use of natural daylight. However, the unique layout of the building, with its vertical stacking of courts, corridors and meeting rooms, created unique opportunities for environmental and engineering designers Mott MacDonald.

Originally the target was to achieve a 'very good' BREEAM* rating, but this was later uprated to ' excellent' at the instigation of the end tenant, Her Majesty's Courts Service and the developer Allied London Properties. A final rating of 'excellent' was achieved.

Several possible microgeneration options were considered. For instance, a wind turbine mounted on the roof of or integrated with a 100 m high building standing well above its neighbours can be very effective. However, Mott MacDonald could find no suitable units available. Cogeneration was ruled out on the grounds that the heating load in the building was relatively small. Site investigations, however, revealed that below the building, at a depth of 100 m, there was an aquifer holding water at a temperature of 12°C with obvious space cooling potential.

Tests confirmed that water quality was excellent. This came as no surprise, as a world famous brewery nearby draws its supplies from the same aquifer. Mott MacDonald's preferred solution would have been to abstract cooling water directly from the aquifer and reinject the used water some distance away after use. Unfortunately, a fault in the underlying sandstone would have allowed the water to circulate too freely, warming up the area around the extraction point. A closed loop indirect system would have needed a lot more boreholes, and would have achieved temperatures no lower than 14°C.

The third option was to take advantage of the proximity of the navigable River Irwell and discharge the used water into that. After two years of negotiations with the Environment Agency, a licence to abstract 40 l/sec from two 300 mm diameter boreholes was granted along with approval for discharge into the River Irwell. The Environment Agency insisted on a third borehole to monitor water levels and temperatures. Abstracted water performs two distinct functions:

1. Cooling of the dramatic ten-storey atrium is down to an underfloor network of 20 mm diameter medium density polyethylene (MDPE) pipework, cast into the floor screed, containing water, which passes through a plate type heat exchanger where it is cooled by the aquifer water.

2. At peak load conditions localised areas on concourses used for waiting areas have underfloor displacement cooling provided.

Late afternoon solar gain through the west-facing glazed atrium could have been a major cooling load: Mott MacDonald's solution was to provide active ventilation to the double skinned glazed façade with a 900 mm central cavity. In winter the cavity is closed off and the façade acts as a thermal buffer; in summer, dampers at top and bottom of the

* BREEAM is the UK Building Environmental Assessment scheme developed by the Building Research Establishment and launched in 1990. There are four possible ratings, apart from failure: 'pass', 'good', 'very good' or 'excellent'.

cavity open at 18°C, creating a solar chimney which draws air in from the outside and discharges it into atmosphere. At the same time, the aquifer water is used to reduce the size, cost and energy consumption of a conventional vapour compression chiller installation.

This feeds an underfloor variable air volume (VAV) system, which comes into operation when the natural ventilation provided fails to maintain the internal temperatures of the various sized courtrooms (between 60 m2 and 180 m2) below 24°C. Floor to floor heights vary, being 4.4 m on levels 2 to 4 and 5.6 m on levels 5 to 10. Ceiling height in the courtrooms on levels 2 to 4 are 3.0 m high and on levels 5 to 10 they are a stately 4.5 m, compared to a more conventional 3.0 m in adjacent consultation rooms. Such a large height difference creates substantial voids above the lower height rooms, voids that have been utilised to provide both ventilation and natural daylighting.

Manchester Civil Justice Center
How fresh air circulates through the courtrooms (Reproduced with permission from Mott MacDonald)

Orientation of the tall narrow building is crucial here. Its long sides face east and west, with the west façade lying athwart the prevailing winds. Ten 7 m X 1.2m and eight 7m X 0.8 m wind scoops trap the wind and direct it into horizontal ducts running along the building's centreline above the consultation rooms. Acoustically lined spurs connect the ducts to vents mid-way up on the inner walls of the courtrooms, which are all located on the east side of the building. High-level vents on the outer eastern court walls above the judges' corridors allow stale air to escape, via an energy recovery ventilation system based on air-to-air enthalpy wheels in winter or by discharging to atmosphere through dampers in the eastern façade in summer, negating the need to run the extract air fans.

Sequential motorised dampers at inlets and exhausts control airflow through the ducts. Inlet dampers close at less than 14°C and more than 21°C; if the temperature within the courtroom falls below 21°C, air warmed by high-efficiency gas-fired boilers with heat recovery in the flues is supplied by the air handling units. Above 24°C the chilled water air handling units supply air to the spaces. Mott MacDonald calculates that the supply of pre-cooled

Cooling air intakes are blended into the façade (Reproduced with permission from Mott MacDonald)

water from the aquifer increases the COP of the chillers from 5.2 to 6.0, effectively a 15% boost. No chances are being taken: if there are long-term problems with the aquifer supply, then an extra chiller could be installed on a spare chiller platform in the plant room, and there is space on the roof for conventional cooling towers; condensing water pipework will have been installed within the building core for future connection if it was required.

The main horizontal ventilation ducts also act as giant lightpipes. Inner top and bottom surfaces are painted white, sides are glazed. Light from the atrium bounces through the ducts into the courtrooms, which also benefit from clerestory windows above the outer judges' corridors. At dusk, low energy dimmable lighting takes over.

According to Mott MacDonald's calculations, the total package of energy saving measures, both active and passive, will cut energy demand by 20% over a conventional equivalent. This represents a potential short-term saving of £73,000 a year. More importantly, the planet will benefit from an annual reduction in CO2 emissions of no less than 540,000 kg.

Client and end user: Her Majesty's Courts Service Developer: Allied London Properties Architect: Denton Corker Marshall Structural engineer: Mott MacDonald

Environmental and building services engineer: Mott MacDonald Design and build contractor: Bovis Lend Lease

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