Original Message: ----------------- From: Charlie Bell char...@culturelist.org Date: Mon, 13 Jul 2009 19:25:51 +1000 To: brin-l@mccmedia.com Subject: Re: Drinking Water From Air Humidity
Charlie wrote: >Read it again properly, and don't treat me like a first grader. I asked how much energy is required and you said none. I read the reply three times, an d at best the answer seemed to sidestep the question.....as did every promotional piece on it. Having lived in a hot humid climate, and having gone through a month of humid weather with no rain, I have some feel for how energy intensive this process is in the middle of the day in Houston, where it is extremely humid. Far more humid than more deserts. >It's a WIND TURBINE. I said it was a wind turbine in my original post. Right, and there are wind turbines that passed me on the road capable of generating multiple MW per hour. I was trying to find out if anyone had numbers on the name plate capacity of the turbine vs. the liters per day. Because it clearly won't work well at any time but the pre dawn hours in the desert. The collectors have to be cooled below the dew point. Let me give a US example. In Las Vegas yesterday, in the heat of the day, the temperature was 42C, while the dew point was -1C. Even shaded, it takes tremendous power to keep collectors that cold while deliberately being exposed to a very hot wind. At the coolist hour, the temp was 28C, and the dew point rose to 4 C. At that temperature difference, with a perfect lossless system, roughly 10% of the total cooling has to be added as power. Between the cooling necessary to keep a panel cooling the atmosphere as it blows past it, and the energy emitted by the latent heat of vaporization, there's quite a bit of energy per liter involved. How much involves a lot of specifics. Inherently its the type of problem one usually solves by reading the specifications....because I'd have to guess a lot on the efficiency of the unit in only cooling the air it takes water out of and maximizing how much it cools it. For example, if the dew point is 2C and the condensor is 1C, one only takes the water that represents the water capacity of air at 2C vs. 1C out of the atmosphere. So, one would need to pick a lower temp....but how low depends on specifics, and is a days long enegeering problem. But, none of the promos offer specifications. >No external source of energy. Self contained. OK if you want to be >super pedantic you can say wind or light is the external source of >energy, but to me that means energy that has to be transported to site >like fuel or power lines. But, self contained electricity units are very ineffecient and thus expensive. In a sense, self-contained energy production is usually seen by the public as "not counting." But, if we were to compare its efficiency vs. desalinisation in energy/liter, we'd need to know the energy per liter numbers....something that's just not available. In essense, for this to work in the desert, it would have to cool condensors to below freezing to then cool the air below the dew point. And, this system would only work at all decently in the few hours before dawn if the wind was blowing hard. In other words, I'd bet a case vs. a bottle of beer that it's a lot prettier on paper than in practice as a means of providing, say, Las Vegas, with drinking water. Because turbines supply the energy doesn't mean that its energy efficient. Dan M. _______________________________________________ http://mccmedia.com/mailman/listinfo/brin-l_mccmedia.com -------------------------------------------------------------------- mail2web.com - Microsoft® Exchange solutions from a leading provider - http://link.mail2web.com/Business/Exchange _______________________________________________ http://mccmedia.com/mailman/listinfo/brin-l_mccmedia.com
