US energy researchers have devised a new way to save billions: tailor the air-conditioning to the needs of the people in the room.
Scientists at Pacific Northwest National Laboratory in the state of Washington have calculated that they could boost energy efficiency by 18% simply by customising air movement according to whether the room is empty or full.
A sensitive detector that could “count” the people in a room could turn down – or turn up – fan speed to the right levels automatically. Occupancy sensors already turn off needless lighting in offices: the next step would be ventilation, says the new report.
“This is the reason you often feel cold when you’re in a big space like a conference room or cafeteria without a lot of people. Technology today doesn’t detect how many people are in a room, and so air flow is at maximum capacity nearly constantly”, said Guopeng Liu, lead author.
He and colleagues focused on a typical office block 12 stories high and with a basement, covering an area almost as big as a football field. Such buildings in the US cover 4.4 billion square feet, at least 40,000 hectares, of urban space.
They calculated that advanced ventilation controls could save $40,000 a year in costs in such a building in 13 of the nation’s 15 climate regions.
In two cities in very different climates, Baltimore, Maryland and Fairbanks, Alaska, savings could be more than $100,000 a year per building. The only catch so far is that the technology has yet to be perfected – and of course must then be installed.
In the region, the wind often drives turbines at times when demand is low. But it should be possible when demand is low to use the surplus power to compress air and tuck it away in an underground geological storage structure: as the wind dies away and the power demand rises, the stored air could be released to the surface, where it would warm up, expand and drive the turbines.
Compressed air storage plants – one already exists in an old salt mine in Alabama, another in Germany – could return as much as 80% of the energy they take in: energy that would otherwise be wasted.
Aiming for the heights
But, of course, subterranean technology offers yet another solution to the energy challenge, according to a recent paper in Science. Two scientists from the University of Utah point out that geysers in California already deliver 850 megawatts to the grid; steam from an Italian volcano at Lardarello turns out nearly 600 megawatts and 90% of homes in Reykjavik in Iceland are heated by geothermal water piped from the rocks.
The hard bit is getting at the subterranean heat. Just two per cent of the thermal energy trapped at depths of 3.5 to 10 kilometres would, the researchers calculate, yield 2,000 times the current annual energy use of the United States.
Meanwhile, in Switzerland, energy research is looking up: at an experimental power plant flown like a kite, at heights of 300 metres. Wind turbines right now reach no more than 100 metres.
Researchers from Empa, the Swiss Federal laboratories for materials science, and other institutes, reason that the most reliable and powerful wind currents are at higher altitudes. So they have begun to develop Twingtec – a high technology kite fastened to a reel at a ground station.
As the kite soars, the line tenses and the reel unwinds: the movement gets converted to current by electromagnetic induction. Once the kite gets to its maximum height, the reel tugs it in so it can rise again. The prototype has already been tested in the Jura mountains, not far from Bern.