Last night I had a dream !
I was visiting the Canada with my wife, driving on a picturesque road a few miles away from a city, the name of which I do not remember. In the distance I saw a strange building overlooking one of those breathtaking sceneries which are so many in Canada. Surprisingly, the building integrated a windmill, like the ones we see in the cattle farms of the American Westerns. A sign mentioned that the "House of the Renewable Energies" could be visited and as I am a fan, I convinced my wife to make the detour.
We parked the car down the hill and walked up to the place, together with a young couple, drawing a suitcase. They had booked a room for the week-end in the built-in guesthouse, to visit the exposition in-depth and enjoy the place. They told us that the House of the Renewable Energies had been financed by a Qatari Fund or something like that, to bring forward their "green" involvement to save the planet, as part of their communication budget. The competition had been awarded to a renowned international architecture bureau.
It was rather cold outside with a steady wind. As we approached the building we saw it was four or five-storey high and had an octagonal shape. The strange roof was covered with solar panels and the windmill was standing on a metallic tower penetrating the building right in the middle.
We entered into the hall, went to the reception desk and bought a ticket to visit the permanent exhibition, while the couple checked-in to the guest-house. There were already a lot of visitors waiting for the guided-tour.
The guide told us that the building was entirely warmed by renewable energies. The windmill was actuating a water-stirrer located down-below, and the heat thus generated was used to heat the building. Someone was surprised that just stirring the water could increase its temperature. The guide reminded the famous experiment realized by James Prescott Joule in 1847, demonstrating that there was a perfect equivalence between mechanical work and heat, and both could then be expressed with the same Unit (the Joule). Therefore the portion (40%) of kinetic energy of the wind recovered by the windmill was entirely transformed into heat by friction of the stirrer-paddles in the water.
A full scale model of the stirrer was displayed, about 2m high and 1.5m in diameter. Eight rotating paddles interlaced with eight fixed paddles and inserted into a welded metallic frame. Somebody whispered that it looked like directly escaped from a Jules Verne's novel.
The windmill was a little bit more impressive with about 5m in diameter. The 30 blades were made by mere steel-sheets slightly curved and twisted. It was presented vertically in its operating position, and mounted on something like a horizontal-to-vertical differential gear box sitting on a rotary platform. Somebody remarked that it looked like the rear axle of a 4-wheel drive car. The guide confirmed that effectively it was one, and was perfectly suited for the stress and the wear generated by the windmill.
The water stirrer was contained in the upper part of the steel column constituting the backbone of the building. The rest of the column was used as the main water tank for the storage of the produced heat, so that the building erected around the column, was naturally heated by this core. The metallic tower was sitting on top of the column.
The guide explained that the windmill starts easily with the lightest breeze since at the beginning, there is no water in the stirrer, and the rotor is free. As soon as the wind gets stronger, some water is pumped up into the stirrer and the corresponding resistive torque is applied to the shaft of the windmill. The guide warned us that the next explanations were technical and addressed mostly to specialists, and the other visitors may use this time to look at the near-by videos.
One must know that any windmill reaches its maximum efficiency when (and only when) it is forced to rotate at a very specific speed, which is related to the actual wind speed. The ratio of the two speeds must be constant and characteristics of the conception of the windmill (profile of the blades, angle of attack ...). Therefore, a tachometer is implemented on the windmill's shaft and an anemometer on top of the tower, to deliver their measurement signal to a servomechanism that automatically controls the level of water in the stirrer, so that the resulting resistive torque forces the windmill to rotate at the right speed, whatever is the wind speed.
When we joined the other visitors, they were watching a video showing the civil works and the erection of the central column of the building. In fact, the manufacturer of the steel masts of the wind-farm being deployed in the region, had signed a partnership with the project to provide and install the first section of their standard steel-mast, to constitute the main column of the building. Only a few modifications had been necessary to comply with the requirements of the project. The adaptations and specific interfaces had been welded in their workshop before being transported.
Then we went up to the terrace on the roof of the building. It was impressive! A complete portion of the roof, oriented full south, was covered with a patchwork of 160m² thermal solar panels. Their slope was calculated to optimize the heating efficiency in summer. The 20m-high metallic tower was erected in the center of the building and the junction with the roof and with the terrace was in form of a pyramidal structure supporting 3 triangular photovoltaic panels of 21m² each, tailor-made, on its south-west, south and south-east faces. The slope was steeper to boost the winter yield. The windmill was presently rotating at full speed under the steady (and fresh) wind. We were pleased to enter back into the warm building.
The guide showed us some photos of the four underground water tanks during their construction, with a total volume of 680 cubic-meters. They were thoroughly isolated (1m thick of recycled polystyrene packaging-stuff crushed locally and then compressed in place). They are used as seasonal heat storage tanks. The heat collected in summer from the solar panels and windmill being stored in the seasonal tanks up to the next winter.
A large screen displayed the present instantaneous production of the windmill and of the solar panels, as well as the temperature of the various water-tanks and other real-time pertinent technical data. The guide told us that the day-to-day data was of course carefully recorded. Then it was compiled to build various charts and tables to manage the system, and also to draw the consequences for the next projects in Scotland and around the world.
In a corner of the exhibition room, two indoor bicycles were fixed side by side. Each one was attached to a small insulated water stirrer. A screen above was displaying the water temperature in each reservoir. Two teen-agers were competing with eagerness to rise it as much as possible. A few more were watching and waiting their turn.
Somebody asked for the restrooms. "I am sure they are used to produce biogas" whispered someone. Yes they were !
When we finished the guided tour it was already night outside, although it was only 4 p.m. We decided to stay overnight. We could get the last available room, but no worries since all of them are with a nice view to enjoy the gorgeous scenery outside, in the morning.
Later, at the nice restaurant, we met again the couple from the parking. They had spent their whole day visiting around, and the lady had been for a while at the covered pool and Jacuzzi downstairs. Her husband had watched the sunset comfortably installed in an armchair in the Library, next to the fire place.
In fact, one of the four underground storage water tanks had been turned into a swimming-pool for the guest-house visitors. It still participated to the heat storage system, and was closed when too hot, at the end of summer. The surroundings of the pool were nicely decorated with wood floors, loungers and lots of green plants. Two additional jacuzzis completed the installation.
When I woke up, I rushed out of my bed to note the URL I remembered from my wonderful dream:
www.windmill-for-heating-buildings.blogspot.com
