Excellent system which should, on average, be environmentally beneficial. Similar ideas exist for mining the temperature difference of the oceans, for example. In most of them, the USEFUL energy gained is represented as being 'renewable,' or being drawn from a source too large to affect. This may be true, but do we really know how our "energy-mining" will affect natural systems?

Your points are all well taken. Really they are.

But.

There is no such thing as "coldness." Only heat.

I heart physics.

You are quite right, sir -- in fact when I wrote "coldness" I was consciously aping the language of the company's FAQ, which refers to it thusly.

Actually, Enwave has a great idea. Geothermal heating is used now in many applications, usually by running air ducts or coolant pipes underground to exchange the heat or chill of a building with the near-constant, cavelike temperatures just a few feet beneath the surface (about 53 deg F).

In Enwave's case, the cold water mass IS indeed renewable. Water has its greatest density at 4 deg C. Water near the surface of the lake would be cooled to that temperature or lower each winter. The newly chilled 4 deg C water mass would sink to the bottom where Enwave could use it the following summer.

Worrying about the negative effect of such a system is a little like worrying that we will cause unusual calmness if we build wind-turbines for electrical power generation.

I think Enwave's biggest problem would be zebra mussels clogging the intakes.

The cold water is in fact renewable.

The bottom of the lake is cold because of all the water on top of it. Water is heavy. Water, under pressure, gets cold.

Guess how your refrigirator or air conditioner works? A compressor puts a coolant (usually freon, it freezes at a really low temperature) under pressure, and it gets cold. a fan circulates air over the cold coils of coolant and voila: cold air!

I'm sorry but in general compressed things don't "get cold" - when was the last time you pumped up a tyre? Didn't you notice the pump getting extra hot?

The phase change from gas to liquid releases heat - its an exothermic phase change. Refrigerators work on the reverse process - the endothermic phase change of liquid to gas which absorbs energy and hence cools the surrounding system. The compression of the refrigerant actually heats it and must be dissipated by cooling fins. The endothermic properties of liquid to gas phase changes (boiling) is why you have to heat water to boil it.

In general compressing anything raises the temperature at which phase changes occur. So nitrogen that is usually liquid at 77K can be liquified at room temperature if you compress it enough.

Actually, Enwave's system does not return the water to the lake after it's been used at their energy transfer site. Once they pump it up to the Island and loop it through their facility, they pass it back to the filtration plant for processing and introduction into the city's potable water supply. It then returns to the lake via the sewage treatment plants and the storm sewer outlets.

Interesting discussion all around! It's certainly true that one single Enwave system wouldn't have much of an effect at all on lake as huge as Lake Ontario. But then again, the first automobile didn't produce enough greenhouse gases to be even slightly noticeable, either. It's all about scale. Once we had hundreds of millions of cars on the road, the tiny amount of pollution each one produced (tiny on a global scale, I mean) added up to quite an effect. The same deal applies with Enwave's system. It's presented as being an "energy for free" system -- coming from a totally renewable resource. But that resource is not infinitely renewable. Put a couple thousand Enwave plants -- or even a couple hundred -- on the shores of Lake Ontario, and you would, over a period of a few decades, begin to heat the lake up. Sure, it's unnoticeable in the short term, but the entire history of environmental damage is one of people telling themselves that tiny incremental changes in the ecosystem don't matter -- until, whoops, thirty years later, they do. But the whole thrust of the advertising of Enwave's system perpetuates this slightly daft idea, very common in the energy industry, that the laws of conservation of energy do not really exist: That energy can be created from a mythical "limitless", infinite source, and that, once used to power our cars or cool our houses, it just sort of vanishes, without a trace.

The only source of energy that's even slightly limitless -- and in the long run, it isn't either -- is the sun.

I would be unhappy if the warmed water were returned to the bottom of the lake, but it should generate a small impact at the surface, since the lake is subject to water/air heat exchange. The water at the bottom should renew each year, as cold water sinks from the surface.

Note 1: this is why life on Earth is possible, water freezes from the top.

Note 2: this can't hurt more than running conventional A/C, the waste energy is released as heat in either case.

The BTU pumped divided by the BTU of waste heat (both as BTU/hr) is the effeciency, on a good A/C as high as 12. Wonder what the overall effeciency of this system is, and what it is subtracting the energy which would be used to draw lake water anyway?

Clive,

I'm writing from Toronto, as you know, and your worries were my first thoughts as well when I heard about Enwave a couple years back. I've been travelling out to the island and watching the tugboats build the huge pipe. It's, literally, cool, but will it eventually cause heat?

My conclusion is, maybe, but the important thing is that we learn from our crappy environmental ignorance in the past and monitor the effects of our efforts. This heat exchange system is better than what we were doing, so the net effect is positive. If we notice an upward trend in the lake temperature, well then we'll have to get our brilliant people to work on the next idea, won't we? As with all things environmental, the real problem is not a lack of ideas, it's a stubborn lack of will.

One thing I do know, if there's a limitless source of anything, it is winter in Toronto. No shortage of friggin' cold here.

My father hooked up a system similar to this about 25 years ago to heat our backyard swimming pool in suburban Toronto. He pulled cool water from the pool, ran it through the house A/C system where heat was transfered from the warm air the A/C pulled in to the cool pool water. The warmed water went back into the pool and the cooled air circulated through the house. I was only 12, but I remember being impressed.

Good lord, your dad actually did that? Mad, mad propz.

Bill, John, yeah, I'm quite sure you're right that the environmental impact of the Enwave system is incredibly smaller than the energy usage of normal air conditioning! I was just being all snotty about how Enwave promotes itself as a free-energy solution ... grumble grumble ... but of course it's infinitely preferable to having regular a/c's blasting away and sucking up huge amounts of electricity all summer.

Guys...the exchanged water does not get returned to the lake...it gets introduced into the municipal water system. There is no return pipe!!

Ergo, no noticeable increase in lake temperature. The only difference here is that Enwave is using the water first foir cooling before it gets introduced into the water system. The water plant inlets are doing the very same thing. Either way, the municipal system get the same water.

I thought the online FAQ said the water was returned to the lake, albeit without having been physically mixed in with other water?

Either way, the issue is still the same. If you remove cold water from the lake, doesn't that by definition heat the lake up, by some tiny increment?

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