Pass masters

As befitting a nation whose land could be swamped at high tide, the Dutch take more than a keen interest in global warming. Having spent the last 50 years reclaiming polders from the Ijsselmeer the country is not too keen to lose them. A sustainable lifestyle is not only necessary, it's non-negotiable.

Working with the environment has therefore become second nature to the Dutch, who play the low energy card at every opportunity. Even at a new football stadium in Arnhem the buildings bristle with renewable energy techniques, from borehole-driven heat pumps, to solar panels and photovoltaics.

Built as part of the Netherlands preparations to co-host Euro2000, the new home of first division club Vitesse in Arnhem looks nothing more than a giant aircraft hanger. Gleaming in morning sunlight, it is certainly a workhorse of a building. A giant gridframe of steel girders acts as runners for 540 000 tonnes of a twin half-cylindrical sliding, weather-friendly roof. The otherwise bland facades of E-glass and battleship grey acoustic-layered steel covered walls encompass one million cubic metres of enclosed space.

On the south-side one finds a sliding pitch where Yorkshire grass grows on well-drained soil and gravel set in an heated concrete dish. Weighing 11 000 tonnes the whole pitch, using German shipyard techniques, is pushed and pulled into the central arena by four hydraulic rams on 392 Teflon soles. Here, 28 000 people can watch football on recycled plastics seats, protected beneath the retractable roof.

Surrounding the central arena, with its multi-functional use for concerts, exhibitions, and other public events, is a complex of restaurants, banqueting rooms, sports facilities, kitchens and administration offices.

Bald Bierens, chief designer of building services consultants Tebodin, believes that simple technical solutions are the starting point for any multi-functional building where the need for flexibility demands a balance between the different energy systems.

NUON, the provincial gas and electricity provider, determined the conceptual design, attracting a £1.8 million EC grant to demonstrate the energy-saving systems for application in similar large-scale building projects. The grant paid for heat pumps from day one, with groundwater energy storage as a later addition.

Renewed interest in heat pumps derives from technological developments in heat pump efficiencies of up to 60%. Furthermore, electric power utilities such as NUON have found that heat pump technology strengthens their control of the heating market. In addition the Dutch government, seeking to support the industry, gives a 20% subsidy to all heat pump projects.

Another NUON concept has been to utilise 15 years of hands-on knowledge and availability throughout The Netherlands of groundwater aquifiers. In the case of Arnhem's Gelredome Stadium, the system is used in combination with heat pumps for winter heating of the sliding pitch and arena. In summer, cooling is reserved for the air handling systems serving various function rooms around the arena perimeter.

In winter, the heat pump capacity of 410 kW supplies 70% of the required heat, the remainder coming from gas-fired solar-assisted boilers. Groundwater is extracted from 80 metre deep wells and used as the primary heat source for the heat pumps (figure 1). After heat transfer the colder water is pumped back to a second well through a sealed system. In summer it was considered that the cold storage system could provide a cooling capacity of approximately 2800 kW. However, a problem has resulted due to a change in weather patterns and infrequent use of the building.

While the old continental high summers would require an extra 10% of cold energy with the heat pump acting as a chiller, global warming has created a long period of low temperature summers and mild winters.

Along with the infrequent usage, the stadium is returning too much cooling water to the aquifiers, which could affect drinking water elsewhere (table 1).

For an estimated period of 20 years this cross-looping will be solved by having the wells set far apart. This is leading energy suppliers to educate bottom line company accountants and boardroom chairmen to appreciate that balancing the natural source of energy supply and balancing the books are elements of the same equation.

Compared with a conventional installation for chillers and cooling, and gas-fired boilers for heating, ground energy storage coupled to heat pumps results in a 45% energy saving (table 2).

In addition to the lower energy consumption and subsequent reduction in emission of combustion gases, other advantages include: