Renewable Energy for Heating and Cooling at the New Oslo International Airport

by the CADDET Norwegian National Team

Boiler construction in the biomass furnace at Oslo's new airport.

Introduction

The Norwegian Parliament decided in 1992 to build the new main airport for the Oslo area at Gardermoen, about 40 km north of Oslo. The airport will have two parallel runways serving 11­12 million passengers yearly when it opens in October 1998.

 Parliament stipulated that the thermal installations serving the airport area should be based on water-borne systems. Thermal energy in this context stands for the production and distribution of heating and cooling energy. Water-borne systems were chosen to make use of several energy carriers, rather than only electricity (the most common in Norway), and to utilise energy from areas with excess heat in areas that have heat requirement. The priorities are to achieve effective energy use, concentrating on renewable and low-pollution sources.

Maximum capacity needed:

Annual energy sales:

Basis of production:

District heating purchase:

Other energy production:

District heating network

(including trenches):

District heating temperature:

Estimated number of customers:

Oslo Airport (OSL)

22 MW

30 GWh

Heat pump ~4 MW

16 MW from GFAS

Oil-fired boiler 2+3x8 MW

Electric boiler 10 MW

4.6 km

70/40C

10

Gardermoen District Heating (GFAS)

24 MW (without sale to OSL)

50 GWh

Bioenergy 8 MW

­

Oil-fired boiler 3x8 MW

~8 km

120/50C

15

The Airport Area

The construction of the airport runways and buildings is being carried out by a shareholding company, Oslo Airport AS (OSL), owned by the Norwegian Ministry of Transportation. The airport covers an area of around 13 km2 and will include a variety of buildings including the public areas and facilities belonging to catering companies and aviation companies, with hangars and buildings for air cargo, etc. Some of the buildings will be very large; for example, the departure hall has an area of 130,000 m2 and Scandinavian Airlines System are building a hangar with an area of more than 50,000 m2.

The Systems

Within the area of the airport there will be two parallel district heating systems. They are summarised in the table above.

After the airport opens in October 1998, an increased demand within the area is expected, and the energy centres may be expanded.

The thermal energy requirement for the area is fulfilled using several energy carriers. An energy centre based on groundwater heat pumps, oil and electricity with an accompanying district heating network will provide for the airport buildings and service buildings such as the fire station, control tower, etc. Additional buildings within the regulated area of the airport may receive district heating from a private shareholding company Gardermoen District Heating (GFAS) owned by the local electricity distributor, Gjerm Energi and Viken Energinett from Oslo. GFAS's main fuel will be wood chips, bark and forestry residue, with a humidity of 50­60%, while oil is used for peak loads and stand-by.

Groundwater Preservation

The airport is constructed on top of Norway's largest groundwater reservoir. The reservoir is larger than 100 km2 and is filled with rain water filtered down through the ground. The airport will increase the area covered by bitumen from 0.5 km2 to 5 km2. This would cause a decrease in the natural drainage of water of 1,000,000 m3/year, therefore a complicated drainage system will be built to prevent this loss.

The groundwater reservoir will be used as intermediate storage for excess heat from OSL's heat pumps and district heating system in summer. In winter, the heat will be recovered from the ground and used. Locally, the level and temperature of the water will be affected: in the summer the temperature in the well area will increase from 4.5C to 20C, and during the winter it will decrease again down to 4.5C. However, the effect on the groundwater balance will be small compared to natural variations.

Norwegian Energy Tradition

Until now, large hydro-power resources have provided Norwegians with considerable amounts of relatively cheap electricity. This situation has led to extensive use of electric resistance heating in homes and commercial buildings, compared to other European countries. Due to increasing development costs and growing environmental concern, the hydro-power capacity seems to have reached a ceiling and further large-scale exploitation is not expected.

A liberated electricity market has contributed to fairly low prices for electricity, boosting consumption with an annual growth of about 2%. Combined with low oil prices, incentives for introducing new and more costly measures are not very large. However, there is a growing expectation that energy prices will rise because of the future restrictions on greenhouse gas emissions that are necessary to fulfil Norway's Kyoto commitments. This price uncertainty, combined with increased governmental stimulation of sustainable energy production (wind, biomass, heat pumps) seem to be slowly increasing the installation rate of water-borne heat, the first criteria for establishing bioenergy and other re newable energy sources on the market.

Heat Pumps at OSL

The heat pump installation at OSL has seven large Sabroe piston compressors with ammonia (NH3) as cooling agent. In summer the installation will provide a district cooling network with temperatures of 7/17C. The unusually large temperature difference of 10C reduces the amount of circulating water. Less flow means less wear on the pumps and better efficiency of the compressors. The total cooling capacity is 8.8 MW using 630 m3/hour of circulated water.

The large groundwater reservoir under Gardermoen will be used as both heat storage and heat medium for the heat pumps. Three kilometres of plastic piping connect the the energy centre with the 18 wells, nine warm and nine 'cold'. Each well is drilled 45 m down with a diameter of 250 mm. Water will be pumped from the warm to the cold wells at a rate of 270 m3/hour when the installation works as a heat pump. A temperature difference of 26C (30/4C) gives a heat withdrawal of about 8 MW.

Bioenergy at GFAS

The main part of the district heating in the GFAS system will be produced in a bioenergy unit from Ekotrans Termik. The furnace is of a traditional design with moving grates, where a number of grates move back and forth feeding the fuel. The warm flue gases are led to the boiler, to preheat the district heating water.

After the boiler, the hot gases (at about 130C) are led to a small cyclone; the first step in purifying the smoke. The cyclone removes around 90% of the dust, leaving only the smallest particles. An electric wet-filter then decreases the temperature to around the condensing point of 66C. The hot gas then enters a condensing tower filled with 8 cm diameter 'plates' of plastic to provide a large surface area. Water is injected from the top absorbing the heat. This water passes through heat exchangers with the returning water from the district heating system. The condensation process reduces the emission of particles and gives a better utilisation of the energy. The amount of heat recovered depends on the humidity of the fuel and the temperature of the district heating water. With 50% humidity and 40C on the returning water, the flue gas condensation is calculated to give additional capacity of 1.8 MW at 6 MW installed capacity in the bio-boiler. After condensation, the clean fumes are vented from chimneys at a temperature of about 50­60C.

Customer Centres

The heating systems of the district heating customers are physically separated from the district heating system by heat exchangers. OSL and GFAS are responsible for installing heat exchangers, gauges and control systems. To make the most of the energy it is important that the returning water has a low temperature. There are strict requirements for the buildings: the heating systems are to be based on mass regulation, and the heat load is preferably placed in series where the high temperature is first utilised for ventilation and radiators, and thereafter the lower temperature water heats floors and melts snow. Thus it is planned that the return water temperature will be very low indeed.

Conclusion

The energy centres are already in use, delivering environmentally-friendly heat during the construction period, avoiding the use of heating fans fuelled by propane or mobile oil boilers. The experience from the first few months' test use of the heating systems is very good. Initial problems have been of the kind and extent to be expected with such a complicated and large construction site. Oslo airport opens for traffic on 8 October 1998.

For more information contact the CADDET Norwegian National Team in Rud.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.