Tuesday, November 14, 2017

Water from seawater

Here is a method to make clean water from the sea: Geothermal heat pumps use ground as a heat sink. The air is cooled above and the heat pumped to the ground. 
To make clean water have a huge steel cylinder above the sea. Cool the steel using a heat pump that takes heat from the steel cylinder and puts the heat into the water. The heated water will evaporate into the steel cylinder and so the process will continue with water vapour condensing on the cool steel where it is collected. Solar energy could be also be used to heat the water below the steel cylinder. See https://en.wikipedia.org/wiki/Direct_exchange_geothermal_heat_pump
If a lot of solar energy were used to heat the water below the steel cylinder the heated water could also add more moisture to the surrounding air to slightly increase chances of rain.

Heat pumps are very efficient - you can get about 4 units of cooling with 1 unit of power. Wind, wave energy and batteries could be used to power the heat pump.
Imagine a small scale system like this. If you use 1 kW of power to cool the cylinder you could get about 4 kW of cooling. So say you run it for an hour. Then you get 4kWh of cooling. It takes roughly 0.7 kWh to condense out a litre of water, so you should get about 4/0.7=5.7 litres an hour using power of 1 kW (assuming a coefficient of performance (COP) of 4). Note that as the water of the water heat sink evaporates it cools, making the system more efficient.

This whole system could be used in reverse to cool the sea and heat air in the cylinder. If the air were heated and seawater were sprayed in at the bottom, one could also create hot humid air and release it to the surroundings to increase chances of rain. One would need a huge cylinder and a lot of power to have a marked effect. With wind, wave and solar power it could work. Fortunately heat pumps do a lot of cooling or heating with a small amount of power (COP=4 or so).

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