Last night
I had a dream !
I was
visiting the North of Scotland, 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 Scotland. 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 for heating the building. Someone was surprised that
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 could
then be expressed with the same Unit (the Joule). Therefore the portion (40%) of the 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
