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HOW PRACTICAL IS HARVESTING WATER FROM THE AIR?


HOW PRACTICAL IS HARVESTING WATER FROM THE AIR?30-10-2021 22:01
HarveyH55Profile picture★★★★★
(3804)
https://hackaday.com/2021/10/29/how-practical-is-harvesting-water-from-the-air/

Systems such as those built by companies like Tsunami Products are referred to as atmospheric water generators of the cooling condensation type. They work on much the same principle as a modern air conditioner, relying on a refrigeration circuit. The refrigeration circuit is used to create a cold surface upon which water from the air condenses and is collected. From there, the water is filtered and purified to remove any viruses, bacteria, or other contaminants that may have been captured from the air.


A Tsunami 500 unit pictured next to a human being for size.
It seems straightforward enough; the basic principle at play is quite simple. Collect water that condenses on a cool surface, filter it, and drink it! However, there's a reason that we don't typically look to the air itself as a source of water. That's because of the energy cost, which is, in a word, significant. Essentially, running such a machine is functionally equivalent to running a large air conditioner.

For example, the smallest unit offered by Tsunami Products is the Tsunami 500, which costs on the order of $30,000 and is reportedly capable of delivering up to 204 gallons (773 liters) of water per day. That's a lot of water, approximately enough to cover the daily needs of two Americans – 82 gallons of water each. To capture that water, the Tsunami 500 uses an astonishing 5.8-7.5 kilowatts, depending on ambient conditions of temperature and relative humidity. Multiply that out over 24 hours, and that water came at the cost of 139.2-180 kilowatt-hours. Looking at the best case, that's around 0.68 kilowatt-hours per gallon. In comparison, desalinating seawater, which is already considered energy-intensive, can be done for just 0.0113 kilowatt-hours per gallon.


Another wacky solution to a non-issue...

Humid areas, also tend to have ample rainfall. Which, of course, is freshwater... Burning energy, to lower the temperature enough to condensate, isn't going to work well, in areas that have humidity, but just too damn hot.

When it does rain, most places focus on getting rid of the excess freshwater falling from the sky. Diverting much of it as they can, into rivers and streams, to be disposed of in the oceans. Mostly, to avoid flooding... Probably why the ocean levels are rising, at an alarming rate. There is no real shortage of freshwater, just the lack of making use of what's freely available.

Sort of been amusing, how millions of gallons are bottled, shipped, and sold, worldwide. Yet, nobody is willing to ship tanks full in bulk. Or construct a pipeline system. Freshwater falls freely, in excess, and mostly goes to waste (oceans). Areas with a constant surplus, could be selling it, rather than disposing of it. In drought prone areas, there is a good market for freshwater. A free product, with many willing customers. Any excess, could go to fill lakes and reservoirs, used for hydroelectric production. Electric companies would be willing to pay for it too, since it ensure they can maintain peak production, even extend their customer base.
01-11-2021 00:34
Into the NightProfile picture★★★★★
(16460)
Here's a few problems that come with shipping water long distances:

You have a few options: truck, train, pipeline, or canal (viaduct).

Water is heavy. Only a limited amount could be shipped by truck or train. That costs fuel. Not really practical.
This leaves pipelines or canals.

Canals must be built with a proper slope pretty much anywhere you don't have a pump. Water loss due to evaporation is a problem all the way. Water will only flow as fast as the slope is set (assuming the pumps aren't overloaded).

Pipelines don't have the evaporation problem, but there is friction all the way. The longer the pipe, the greater the friction. This actually follows Ohm's law. Substitute friction for resistance. Pretty soon you get the idea what happens to the current (flow) in the pipe, the longer the pipe.

You can increase pressure (like voltage in Ohm's law) using a pump. That's what pumps do. A given pump will only develop so much pressure. Over long distances (high resistance), the pump has to be enormous just to get a bit of flow.

One way you can lower the resistance is to use multiple pipes. This is the same as using a larger pipe. This is why water pipelines typically use more than one pipe if high flow is the issue.

Gravity also affects water (unlike electrons). This produces a dynamic resistance that has to added to the pipe friction. Pumping uphill is harder. Using the weight of water vs the height, you can calculate the dynamics resistance. It's actually like adding a negative voltage countering your voltage source.

Suction pumps use the weight of air above the water to help the water up the tube with the assistance of a pump. At 32 ft, you reach the limit of a suction pump. You can pump in stages, of course, but each stage must be open to air. Mines, which have to get water out of them oftentimes, used to use staged suction pumps of exactly this sort.

Nowadays, deep wells (over 32ft) and other situations requiring more head on the pump use centrifugal or piston pumps. You can develop over 3000psi with one of these babies! Enough to get over that 250 ft ridge.
Better have a pipe built to take it though!

Just such a pipe and pump exist at Grand Coulee dam in Washington. Irrigation water is pumped into the head of a canal system (Banks Lake) from Lake Roosevelt. This pumping station uses about 1/3 of the power the dam produces to run. It takes that kind of power to pump that kind of water up that kind of hill. This irrigation system has about 300 miles of main canals (not one 300 mile long canal!), with various feeders going to each user.
Edited on 01-11-2021 00:36
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