CAE Reading and Use of English Part 7
You are going to read a magazine article about ways of reusing escaped heat. Six paragraphs have been removed from the article. Choose from the paragraphs A – G the one which fits each gap (41-46). There is one extra paragraph which you do not need to use.
City of Heat
Escaped heat costs us money and affects our climate. Chelsea Wald reports on a grand plan to capture it and put it to good use.
Deep in the tunnels of London’s underground railway, as in many around the world, it’s so hot it can feel very uncomfortable. And yet in the basement of a building only a few metres away from the station a boiler is firing to heat water for someone’s shower.
Recapturing it wouldn’t just benefit our wallets. It would reverse some of the damaging effects on the climate. The good news is that several cities have found a way to hunt down their surplus heat in some unexpected places. These cities are building systems that deliver heat in much the same way that suppliers handle electricity and water. Could they point the way to the next energy revolution?
It was also estimated that given the right technologies, we could reclaim nearly half of that energy, although that’s easier said than done. ‘We often talk about the quantity of waste heat’, says David MacKay, chief scientific adviser to the UK Department of Energy and Climate Change, ‘but not the quality’. Most of what we think of as ‘waste heat’ isn’t actually all that hot; about sixty percent is below 230°C. While that may sound pretty hot, it is too cold to turn a turbine to generate electricity.
There, buildings tap into the system to warm their water supplies or air for central heating. Many countries are encouraging such cogeneration, as it is called. A US initiative, for example, might save the country $10 billion per year. And cogeneration allows power plants to bump up their efficiencies from thirty percent to almost ninety percent.
As it happens, there is an existing technology that can siphon energy from such temperatures, although applying it on a large scale to capture waste heat is as yet unachievable. Ground source heat pumps have been helping homeowners save on heating bills since the 1940s, when US inventor Robert Webber realised he could invert the refrigeration process to extract heat from the ground.
The mechanism for this is simple. A network of pipes makes a circuit between the inside of the
dwelling and a coil buried underground. These pipes contain a mix of water and fluid refrigerant. As the fluid mixture travels through the pipes buried underground, it absorbs the heat from the 10°C soil.
This system is powerful enough to efficiently provide heat even in places as cold as Norway and Alaska. It is also cheap. Scientists around the world are now working on the idea that the way ahead is to develop city-wide grids using source-heat pumps to recycle waste on a grander scale, from sources such as subways and sewers.
A But that’s not all it can do. Reverse the process and it can cool a home in summer. If the ground is cold enough, it simply absorbs the heat from inside the building instead of from the ground.
B It’s an attractive proposition. A report in 2008 found that the energy lost as heat each year by US industry equalled the annual energy use of five million citizens. Power generation is a major culprit; the heat lost from that sector alone dwarfs the total energy use of Japan. The situation in other industrialised countries is similar.
C Yet even this is just a drop in the ocean compared with the heat lost from our homes, offices, road vehicles and trains. However, waste heat from these myriad sources is much harder to harness than the waste heat from single, concentrated sources like power plants. What’s more, it’s barely warm enough to merit its name. Reclaiming that would be an altogether more difficult proposition.
D A more successful way of using the heat is to move the heat directly to where it is needed. A number of power plants now do exactly that. They capture some or all of their waste heat and send it – as steam or hot water – through a network of pipes to nearby cities.
E The system takes advantage of the fact that in temperate regions – regardless of surface temperature – a few metres underground, the soil always remains lukewarm and stable. These pumps can tap into that consistent temperature to heat a house in the winter.
F While this is not what you might consider hot, it nonetheless causes the liquid to evaporate into a gas. When this gas circulates back into the building, it is fed through a compressor, which vastly intensifies the heat. That heat can then be used by a heat exchanger to warm up hot water or air ducts.
G Rather than stewing in that excess heat, what if we could make it work for us? Throughout our energy system – from electricity generation in power plants to powering a car – more than fifty percent of the energy we use leaks into the surroundings.