Green engineering on a brown-field site
Alexandra Krstanovic explains how Faber Maunsell delivered the University of Nottingham’s requirements for sustainable design and integration of renewable energy sources for the Gateway Building on the extension to its Jubilee Campus.
The extension to the University of Nottingham’s Jubilee Campus by Make Architects is an exemplar project comprising three landmark buildings, a public boulevard, and a 60 m high sculptural tower — the tallest in the UK.
Located on a 7.5 ha brown-field site close to the city centre, the £21.5 million development is not only intended to consolidate the university’s academic reputation, but also foster stronger links with the world of business and commerce. At the heart of this strategy is the Gateway Building. A zinc-clad business incubation unit that physically connects the university to a science-based innovation park planned for the eastern side of the site.
The university’s brief for the development of the extension to the Jubilee Campus Extension placed a considerable emphasis on sustainable design and integration of renewable energy sources.
Faber Maunsell carried out renewable-energy feasibility studies during the pre-planning and outline stages of the design to determine the most appropriate approach for the development. A range of options was considered, including wind, solar, biomass and ground-coupled heat pumps.
Central to the environmental success of the project are the use of high-performance facades combined with geothermal heating and cooling.
A heat-pump system was found to offer the greatest savings in terms of energy consumption and associated CO2 emissions. Taking into account items such as the site potential, energy-demand profiles and site restrictions, the use of a geothermal system was considered appropriate to help maximise the development’s potential for the sustainable design and energy conservation, along with mixed-mode ventilation strategy, high thermal mass and the use of night-time cooling.
Analysis of the peak heating and cooling loads and, more critically, the seasonal demand profiles, led to investigating the suitability of a nearby man-made lake to support the required extraction and rejection of heat from the development.
Reverse-cycle heat pumps replace conventional boilers and chillers by using the embodied energy of the lake. Highly efficient stainless-steel heat exchangers submerged in the lake reject or absorb the embodied heat within the lake. Heat pumps compress and transfer the heat energy to the building to pre-heat domestic hot water and provide all space heating and cooling. Although the lake temperature fluctuates with seasonal ambient variations, the inherent efficiency of the heat pumps and heat exchangers within the lake enable high coefficients of performance to be realised.
Fresh air is delivered internally via a low-velocity, low-pressure underfloor system. The warm stale air is extracted through high-level return air grilles within each treated space and delivered back to the air-handling units for heat recovery by thermal wheels.
Thermal mass, provided by exposed concrete columns and slab soffits, maintains temperature stability while facilitating night-time cooling.
Externally, the highly insulated and airtight facades employ optimum glazing levels (around 40%) and orientation to ensure good levels of natural daylight, while avoiding solar gain and glare.
All rainwater run-off from the buildings is collected and returned to the lakes on the site.
An area of the scheme that presented a particular environmental challenge was the Gateway Building’s full-height entrance/ reception atrium. The original intention was to a use a system of opening rooflights to provide daylight and additional natural ventilation. However, this proved problematic as it was felt that the glazing would be difficult to clean, require costly fritting and/or solar shading to limit heat gain and would provide only limited cross ventilation due to the lack of opening windows at low level.
The solution was to specify Monodraught SunCatchers comprising square ‘topdown’ WindCatcher ventilators with centrally mounted 1.5 m-diameter SunPipes — the largest ever-produced by the manufacturer. Incorporated within the Monodraught modules are motorised dampers that enable return air from the occupied spaces and atrium to be returned to the thermal wheels within the central air-handling units to recover heat during the heating season when desirable, or allow the air to vent straight to atmosphere during periods of peak cooling.
These modules can also provide night-time cooling without the attendant risks of leaving windows open, minimising the energy consumption of the air-handling units. They also have few moving parts (none externally), resulting in low maintenance.
Among the benefits claimed for the system are that it is effective in both sunny and overcast/rainy conditions, does not contribute to solar gain or heat loss and that it can provide significant daytime electricity cost savings when used instead of artificial lighting.
In contrast to traditional installations, where SunCatchers are employed to provide independent natural ventilation for entire rooms or spaces, here they work in conjunction with the building’s primary ventilation system.
Alexandra Krstanovic is a regional director with Faber Maunsell.
Architect: Make. Structure: Adams Kara Taylor. Services: Faber Maunsell. Quantity surveyor and project manager: Gardiner Theobald. Contractor: Rok Sol. Client: University of Nottingham.