By Jonny Dymond
BBC Europe correspondent, Brussels
Rue d'Arlon, in the heart of Brussels' EU quarter, is dotted with the kind of ugly glass and concrete structures that make the area such a dismal place to work in.
The building is something of a living laboratory, with state-of-the-art technology embedded in it
Just up the road is a monument to brutalism, the European Council building. A couple of blocks along is the huge glass and steel European Parliament.
So number 63-65 Rue D'Arlon, a pleasantly proportioned townhouse, comes as something of a relief.
But there is a lot more to it than that. On the eve of the spring summit of EU leaders, as grey rain finally gave way to sunshine in Brussels, the building was crowded with Euro-players - the President of the Commission Jose Manuel Barroso, the Belgian Prime Minister Guy Verhofstadt and no less than three European Commissioners.
They were in this particular building in Rue D'Arlon because it may hold some of the answers to some of Europe's most difficult questions - questions which the leaders of the EU will grapple with over the summit.
How is Europe going to secure its energy supplies? How can Europe reduce its energy bills? And how can Europe cut back on the burning of fossil fuels that may lead to climate change?
The building, which houses a cluster of renewable energy associations, is now something of a living laboratory.
Over the past few years it has been gutted and rebuilt. As it has been reconstructed, state-of-the-art environmental technology has been embedded within.
Much of the building is heated not by oil or gas, or electricity, but by little brown cylinders of compressed sawdust. These cylinders, which are the circumference of a pencil and a couple of centimetres long, are delivered two or three times a year and poured into pipes at the front of the building.
WHAT'S IN THE HOUSE
Pellet heating system
Solar heating/ cooling
Geothermal heating/ cooling
Insulated facade and roof
Low emission glazing
Highly efficient lighting
Ventilation with heat recovery
They are then funnelled into a boiler. Energy from such pellets is both renewable and environmentally "neutral". As the pellets burn they only give out as much greenhouse gas as the trees they spring from absorbed in their lives.
The rest of the building is heated through energy transfer - the energy in question coming from four geo-thermal boreholes sunk deep into the earth in the courtyard.
Throughout the building there's innovation. In its finest room - meticulously restored - rather elegant double glazing seals out noise, cold and heat.
Two discreet vents, one up by the ceiling and another down by the fireplace, enable the room to "breathe", circulating air and drawing the heat produced during meetings out of the room and into the building's complex energy transfer system.
Up above the main desk hang two strips of fluorescent lights that unlike most strip lights give out no heat at all - the energy they consume is channelled solely into light.
This is where energy from cells is converted for use around the building
And so it goes on. Walk along the corridors and you see not clear widows but photo-voltaic cells, designed to capture energy and draw it into the building.
Five boxes sit at the end of a corridor to convert the energy from cells into power than can be used around the building. Up on the roof are panels designed to gather yet more power from the Sun.
As you walk around you find yourself wanting to catch the organisers out. Surely some of the electricity is drawn from the national grid? And won't that be produced from fossil fuels?
Yes, they admit, at present it is, but once the market is liberalised in Brussels they'll be able to choose green energy from wind turbines. Though they'll have to join the queue - demand for such energy in Belgium currently outstrips supply.
New technology does not come cheap - much of the equipment is significantly more expensive than its "old energy" equivalent. But, say the organisers, you get your money back pretty fast. The energy cost of running the building is 30% of what it would be without all the improvements.
As well allowing the EU's renewable energy organisations to practise what they preach, the house is a way of showcasing a variety of ways forward.
Once the dignitaries have got back in their cars, the building will still be open - by appointment, it is stressed - to those who want to come and see perhaps a few answers to Europe's pressing energy questions.
GEOTHERMAL HEAT EXHANGE IN THE RENEWABLE ENERGY HOUSE
In winter, water flows through the 115m deep borehole pipes and is heated by warmth from the Earth
This is then boosted in the heat pump and used to heat the house
In summer, a solar-powered cooling system cools the house
Unlike normal air conditioners which pump hot air into the atmosphere, excess heat from this system is sunk into the ground