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Eawag Forum Chriesbach: reaping the rewards of sustainable construction

A five-storey office and research building for 220 people that requires scarcely more energy from external sources for heating and cooling than one or two single-family houses? Eawag’s Forum Chriesbach fits this description.

At a meeting held today, two years after the building was opened, the architects, planners and clients concluded that the results, in terms of energy use and costs, have been positive. The internationally renowned Forum Chriesbach is already regarded as a model for a new generation of buildings, even though there is still room for optimization.

In its first two years of operation, Eawag’s new building at the Dübendorf site has been shown to function as intended. The values envisaged by the planners accord well with the measurement data. Any deviations that have occurred are attributable to changes in general operating conditions. An approach that has proved particularly valuable is reliance on simple principles, such as optimal thermal insulation of the building envelope and effective interaction between design and technology.

Minimal energy required for cooling

The building’s performance has been particularly good with regard to the energy required for cooling during the summer. Worldwide, cooling energy requirements are increasing, especially for glass fronted office buildings. Rather than using a high-tech system, Forum Chriesbach exploits the chimney effect in the atrium to cool the building overnight in the summer. This ventilation, combined with air supplied from an earth-to-air heat exchanger, means that air-conditioning is not required for the office rooms. Even during the hottest summer weeks, the indoor temperatures barely exceeded 26°C, which was greatly appreciated by staff. The pleasant working climate was also confirmed by measurements of CO2 concentrations in indoor air: with a mean value of 0.6 litres of CO2 per m3 air, these were very low.

Heating requirements were somewhat higher than predicted. Instead of 29 MWh, 67 MWh per year was supplied by the on-site district heating network. This is still equivalent to only 6 kWh per m2 treated floor area; expressed in different terms, for an area of 11,000 m2, the energy consumption is the same as for two conventional single-family homes – a value clearly below the stringent swiss “Minergie P” requirement. The higher heating requirements are partly due to room occupancy levels, which are lower than projected. As a result, fewer internal heat sources – from employees to computers – are available. In addition, following staff feedback, the temperature of the air supplied had to be increased slightly to 21°C.

In the case of electricity, 195 MWh was supplied from the grid per year rather than the planned 121 MWh (i.e. 17 kWh per m2 treated floor area). This was mainly due to the staff canteen aQa – producing more than 260 rather than 150 meals per day – and the more frequent and extended use of corridor lighting. On the other hand, the photovoltaic system on the flat roof generated not 60 but 71 MWh and the thermal solar collectors supplied not 24 but 26 MWh per year.

Fine-tuning essential

A building on the scale of Forum Chriesbach is not simply “finished” once the keys have been handed over. Herbert Güttinger, who as head of the Eawag Eco-Team was already involved in the planning stage, explains: “We had to learn that a lot of things aren’t immediately correctly adjusted so that they work properly. So operational optimization is far more than just remedying defects within the warranty period – it needs expert management.” As an example, he mentions the automatic system used to open the tilt windows for overnight cooling, comprising more than 200 electric motors. The power consumption of these motors was much too high, as they were – needlessly – permanently switched on. Adjustment of the control system has “saved” 20 MWh per year, which is almost a third of the total power generated by the rooftop photovoltaic system. Fine-tuning was also needed for the system controlling the blue glass fins that shade the facade. The spring and autumn settings were depriving the interior of precious daylight.

Worthwhile additional investments

At CHF 30 million, the construction costs for Eawag’s new headquarters were within the credit limit approved by the Federal Parliament. These costs were analysed by an independent building systems engineer, Andreas Pfeiffer of Reuss Engineering AG. He calculated that the additional investments – compared with a similar, conventionally constructed building – amounted to just under 5%. The somewhat higher life-cycle capital costs are however offset by the lower operating costs. The annual costs (capital and operating costs) for Forum Chriesbach are already CHF 10,000 lower than for a conventional building. If energy prices rise as expected, this advantage will become even more marked over the years. Pfeiffer concludes: “Higher returns can be achieved with energy- and resource-efficient buildings.” In addition, he believes that a building constructed on sustainable principles offers further benefits which are difficult to quantify in economic terms, such as high value preservation, or satisfaction and prestige for users and investors.

Need for team spirit

In a pioneering project of this kind, planning plays a particularly significant role. It is essential that the client should not only provide clear specifications when inviting architects and planners to tender, but should remain part of the team throughout the project. Room for improvement was identified both in the construction processes and in the assignment of responsibilities. Bob Gysin of the architectural firm Bob Gysin + Partner (BGP) makes no secret of the fact that the subordinate position of the architects vis-à-vis the general contractors gave rise to some friction. But, as Gysin says, “If all the specialists are not only experts in their own field, but also prepared to engage intellectually with other disciplines, convinced that significant innovations can be achieved by working together, then that’s a recipe for success.”

Taking stock

The detailed energy statistics and the construction and operating costs for Forum Chriesbach were the focus of today’s meeting at Dübendorf, attended by around 140 people. The accompanying project carried out by the two research institutes Eawag and Empa and the engineering consultancy 3-Plan Haustechnik AG was supported by the Federal Office of Energy and the ETH Board. Eawag’s new headquarters, designed by the architectural firm Bob Gysin + Partner (BGP), has been in operation since June 2006. From the initial planning stage, the clients aimed to make the building a model of sustainability in practice, not only environmentally, but also in social and economic terms. The need for action in the building sector is clear: households and workplaces account for more than half of our total energy consumption.

Andri Bryner | alfa
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