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Home Desalinator/HVAC

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Much of the drama concerned with people watering their lawns, in the middle of the yearly drought on the West Coast, seems to be from people who live a couple of hundred yards from the Pacific Ocean. Oh, come on.

Start delivering salt water to houses.

In the winter, (electrically or other) heat the tank and let the steam return give fresh water.

In the summer boil the water in a vacuum at room temperature, using the tank as a cold source for house cooling, letting the water condense and cool outside.

A freshwater storage tank would be an idea, for times when you don't need the heater or a/c on.

Occasionally put a bucket of salt out at the curb for pick-up and return to the ocean.

FlyingToaster, Jul 09 2015

Vacuum desalting Vacuum_20Desalting
An old Idea. Desalting doesn't have to be quite so energy-intensive. [Vernon, Jul 10 2015]

Article about California's drought http://www.theregis...pe_out_the_drought/
"How much of ONE YEAR's Californian energy use would WIPE OUT the DROUGHT?" [Loris, Jul 31 2015]

Rarefaction_20A_2fC [FlyingToaster, Aug 01 2015]

[link]






       No, it won't. It will use more energy. Making brine is an endothermic process.
WcW, Jul 09 2015
  

       Err, I changed the entire post : you were responding to the original last line which said it uses the same amount of energy as an air conditioner. Are you saying it takes more energy to distil water from salt water than from fresh ?
FlyingToaster, Jul 09 2015
  

       But it's still a poor use of energy on both ends.   

       I'd rather see people using combined heating/cooling technology, better insulated (maybe largely underground) houses, and rainwater (including yard runoff) capture.
Custardguts, Jul 09 2015
  

       //still a poor use of energy// True, unless you count the energy required for large-scale desalination. This way the energy is being used more efficiently, to mitigate poor design as well as provide fresh water where none exists.
FlyingToaster, Jul 09 2015
  

       ...But Desal plants don't use distillation - they use reverse osmosis and have all sorts of energy recovery mechanisms built into their mechanics (pressure recovery being one of them I believe). I'm pretty confident (partly based on the fact that large scale desal is done by RO rather than distillation) that RO is significantly more efficient than distillation.   

       But more than that I just think desal in any form should be limited to ships, liferafts and remote islands - because it's so energy intense. Let the sun do the work, and then just collect the rainwater.
Custardguts, Jul 10 2015
  

       Why do people water their lawns?
pocmloc, Jul 10 2015
  

       The energy cost of desalinating water is, I think, insignificant to the general energy demands of each human in the near future.   

       We don't need better efficiency, we need more energy.
Voice, Jul 10 2015
  

       The idea that using more energy is evil is misanthropic. There are a dozen carbon neutral and/or environmentally friendly ways to create more energy.
Voice, Jul 10 2015
  

       // The idea that using more energy is evil is misanthropic //   

       It is actually a positive thing that pretty much all humans consider waste to be evil (or at least undesirable). The issue is in priorities. Some people consider wasting energy to be more evil than wasting opportunities by not using energy. Some prioritize time wasted cleaning up after themselves, leaving a mess in their wake or just throwing everything away rather than figuring out what could be reused. Other people waste a lot of time salvaging material that others might throw away, but since they get significant personal satisfaction from the task, that waste can't be calculated monetarily.   

       Transportation cost are an area for possibly large efficiency improvements, but be careful you don't waste more resources building multiple mini- factories when it would use less resources to make a smaller number of large efficient factories and ship things around the world. (Ignoring artificial advantages currently in place for manufacturing in countries with lax environmental and labor laws.)
scad mientist, Jul 10 2015
  

       Salt water swimming pools and salt water fish ponds may figure in somewhere. Perhaps, A hydrotherapy tank filled with salt water.   

       An evaporation cooler (swamp cooler) ought to work with salt water as well as fresh. Redesigned to deal with salts and the sea smell.   

       replies- / do people water their lawns? — pocmloc/ People water their lawns because they die if they do not.   

       bucket of salt out at the curb = NaCl, plus a bunch of other stuff.
popbottle, Jul 10 2015
  

       //Are you saying it takes more energy to distil water from salt water than from fresh ?// Yes, it does.
MaxwellBuchanan, Jul 10 2015
  

       //People water their lawns because they die if they do not.// wow, I didn't realise neighbourhood vigilante action against neglectful householders was getting that serious.
pocmloc, Jul 11 2015
  

       Those housing organizations take things pretty seriously.
Voice, Jul 11 2015
  

       I am picturing a clear plastic dome on a pillar. Above it twirls one of those helical windmills. Water is pumped into the dome via windmill and then it sits, baking in the sun. Evaporate on the dome trickles down the edge, down the inside of the pillar and into a fountain, which is used as a reservoir to water the garden. Distillation efficiency falls as the reservoir gets saltier and so periodically the dome discharges brine back onto the beach, then refills.   

       When the windmill is not pumping water it is charging a battery that is used to power the garden lights at night.
bungston, Jul 14 2015
  

       [+] also use the salt water for the toilets and sewage.
pashute, Jul 15 2015
  

       I once saw a Greek application of using salt water to cool a hotel. I cannot find the link now.   

       It was shown to me by a business consultant trying to convince me to use an invention of mine in Greece. It was during that day that the banks were burned down and people killed in the riots. Both of us had not seen the news yet.
pashute, Jul 15 2015
  

       It is a terrible habit to fail to think things through. Introducing a lot of salt into the septic sewer system would pretty much make waste treatment and surface return an impossibility anywhere that wasn't actually discharging treated water into the sea. It would sorta be like assuming that the fact that the water had salt in it wouldn't cause an energy penalty when you distilled it.
WcW, Jul 16 2015
  

       ^ Also like assuming the comment referred to communities too far inland for a salt-water return to be feasible.   

       Salt-water requiring more energy to distil than fresh, while interesting, isn't particularly relevant to the post, which is about using thermal products of vacuum distillation to heat or cool a house.
FlyingToaster, Jul 16 2015
  

       Actually it is quite dujour. When you boil and distill water from sea water the product brine actually contains quite a substantial fraction of your energy, a fraction you can only get out by returning the product water to the solution. In this way when you "take the brine back to the sea" you are also taking a fraction of your heat energy back to the sea and pissing it away. And when you take the distilled water and pour it out on your lawn (a technique I don't recommend because it will kill you grass) you are also pouring out a substantial fraction of the energy there as well. You seem to believe that the energy is somehow efficiently conserved but even if you live right on the shore and can brine the water only slightly there is a tremendous amount of energy in separating the water from the salt, which is not returned to you unless you complete the cycle and return the distillate to the brine.
WcW, Jul 16 2015
  

       No, I'm saying that if you want to make fresh water from salt water, you might as well heat or cool the house at the same time. Or vice versa.   

       What's the energy difference between boiling out a litre of fresh, compared to ocean-level salted, water ?   

       RO is interesting, despite apparently wasting 80% of the intake water (a stat I saw on a commercial site), but I haven't found a hit for "renewable RO filters" yet.   

       A salt water/brine sewage treatment plant would be a neat exercise, though I suppose the only difference would be the digesters' bacteria, or lagoon flora for smaller sites.   

       Why would distilled water kill grass ? Random ions ?
FlyingToaster, Jul 16 2015
  

       Based on my calculations the enthalpy of the salt represents a 900 joule penalty per gallon or around a 10% increase in energy over cycling fresh water. The boiling point is higher, and the specific energy is higher. Irrigation with distilled water shouldn't have a dramatic effect on plants but I suspect that the complete lack of minerals and ions as well as the fact that it is degassed could have a deleterious effect on your lawn.
WcW, Jul 16 2015
  

       I was thinking about this because of (link). I'm putting this as an anno rather than its own idea because I'm not entirely convinced as to the efficiency.   

       Getting pure water from seawater via distillation is apparently inefficient compared to filtering it.
OK, but what if the heat energy was free?
Suppose we use the waste heat from the air-con system to heat (and increase the evaporation rate of) seawater. Then we get more water exactly when we need it, when it's hot. There's no need for the infrastructure of the enormous tank.
It's true that we need to dump the heat, and that may involve a large radiator, but hey.
Loris, Jul 31 2015
  

       //Suppose we use the waste heat from the air-con system to boil the seawater.// That works to heat the water and even makes the air conditioner more efficient. But at a certain point, whose math I don't know, the air conditioner will have to work harder to both heat the water on one side and cool the air on the other.
Voice, Jul 31 2015
  

       ////Suppose we use the waste heat from the air-con system to boil the seawater.////   

       Hmm, hang on. That's a mistake. We don't need to boil the water. I meant that we should raise the temperature so that more evaporation occurs. I'll fix that in my comment.   

       //But at a certain point [...] the air conditioner will have to work harder to both heat the water on one side and cool the air on the other.//   

       The air-con may have to work harder, but how much harder depends on how big and efficient the radiator is.
If we had a big enough salt-water reservoir, and a large enough radiator (in which condensation occurs), then the increase in the temperature differential (over that used in standard operation) would be negligible.
The question then is how much of an increase in AC effort would there be for reasonably sized equipment. I haven't done any maths on that either.
Loris, Aug 01 2015
  

       You could of course, simply immerse a regular A/C's coils(radiator) inside a partial-vacuum salt-water boiler. Then you'd have two heat-transfer systems, in series, using this idea for the second half.   

       Or you could cut out the middleman and just use this idea: room temperature boils the water and the steam is removed to the outside, leaving a cold tank full of brine.   

       (the idea is Rarefaction A/C <link> with an open cycle - the heat-laden distilled water isn't returned: it just cools to outside ambient and is then used as fresh water)
FlyingToaster, Aug 01 2015
  

       Capturing the condensate from your AC is worthwhile. Boiling water to create more condensate however is crazy :- ) By all means build a home desalination plant but don't use your AC to do it... not cost-effective in energy.
gtoal, Aug 03 2015
  

       For heating, it's almost a regular steam heating system, except it boils saltwater, and the steam isn't recirculated back into the boiler after it condenses.   

       For cooling, it's the same principle as a compressor-based air-conditioner except, instead of compressing on one side, it creates a vacuum on the other. And, of course, the medium (steam/water) isn't recirculated.   

       In both cases the energy required is slightly more than that required to do so regularly, but you end up with freshwater as a byproduct..
FlyingToaster, Aug 04 2015
  
      
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