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Thread: Solar powered air conditioning

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    Default Solar powered air conditioning

    Once in a brick veneer house I had was freezing on a sunny winters day, I then left the house to find it quite nice outside, I then thought about a system of using a solar water heater to then warm the house. Then thought, OK but most of year we are trying to keep the cool so what would you do with with the hot water? I then wondered if, in the hot weather you could use the hot water operate a refrigeration unit, like the gas fridges once popular in caravans, to use as air conditioning? I am sure it would work, but would you get enough heat out of the hot water to be effective? I was thinking of running the air though a evaporative type air con first, so the refrigerative part would be more of a condenser than a cooler. I would be interested if any people with good knowledge of heat transfer would comment on this.



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    Look at peltier units
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    I''m running about 20Kw of panels on my roof atm and have come to the conclusion that trying to heat a home with solar is useless.
    The solar radiation in winter is about 1/3rd or worse than summer depending where you are and there just isn't enough energy to go round.
    Cooling OTOH is maybe the one time you have the energy when you want it.

    From Memory, the old Ammonia/ LPG fridges worked on heating the Ammonia Fluid till it phase changed to a gas and then used the re-condensing to pull the heat out the ice box. From memory that needs over 100oC on the hot side so I don't think water would work particularly if it was only say 60oC. You could look it up and crunch the numbers.
    You Might also be able to use another working fluid that boils at low temps that you would do with solar and then use that as the cooling.
    Problem I see is these processes usually aren't that efficient and it's one thing to cool a fridge, quite another to cool a room or a house. You might need 1000L of working Fluid and bit HE's and find the temp Differenctial might only be a few degrees anyway. Again, You could look it up and see what the go is.

    I am currently working on a Solar Cold energy storage system.
    The Idea is to take excess solar generated on summer days and store it to use at Night.
    There are Ice storage systems available which take into account the huge 300%+ plus efficency of phase changing the water to ice. Ice holds 330x More cold than the same amount of water does. Don't matter if the ice iis -5 or minus 50, the efficiency is the same.

    Using ice on a DIY scale is problematic. You have to store the ice. Initial idea was use a freezer to cool and store it. Freezers have small motors that would take days to freeze their capacity and then the expansion would likley split the things. You would need elaborate Cooling tubes and you would need a LOT of tubes full of something like a glycol anti freeze to carry the cold back out. Melting a 500Kg Block of ice which would be a good size would be a problem to actualy get it to melt fast enough to get the cold out at a rate similar to a conventional AC.

    What I'm looking to do is get a 5-700L Fridge or Freezer and fill it with water and SALT. About $50 worth for 500L . This will take the freeze point of the water to a little below -20oC.
    Being that the water will remain liquid I can simply pump it through a HE at whatever rate I want. To cover the cooling. I want to use an AC compressor, condenser and evaporator from a car which has a similar thermal capacity to a mid size domestic split. Instead of 200W out of a freezer, I can pull easily 2Kw of cooling out the thing with probably an EEP multiplication factor of 3-4 easily. This means the actual cooling power would be about 6-8 KW for a 2000W input which will be from an electric motor operating of the solar PV panels.

    If I have 500L of salt water and Pull it down to -20 and take it back up to plus 20, I have over 20Kwh or thermal cold storage. At night, I can probably run a sub 100W pump and pull KW's of cooling out the system. Would be silent, cost nothing to run, be cheap and easy to build, have good capacity and easily expandable ( add another fridge and more salt) and be easily packaged to suit a normal house without turning the place into an eyesore.
    If I want more cooling power and have more power to spare ( I estimate getting 500L of brine down to -20 would require about 6 KW electrical input) and another 500L "tank" and you have a whopping 40KWH of Cold thermal storage. that's going to cool the most uninsulated house right down on even the hottest Night.

    There is a back end to this too.
    Set up your Compressor with an IC engine and an RX valve and you can use it for a very efficient heating system as well. Use the heat from the IC engine and direct it back into the condenser of the AC unit and you can get the heat from that and put it in your storage. You can probably go up to 110oC now without Boiling the water and store that heat for use at night.
    as you will be running the engine through the day when the temps are higher anyhow, No doubt you could bleed off some energy to heat the house at the same time.

    Depending on your storage containers, You could also drain the water out and Fill the storage tanks with waste Veg oil. If the tanks will take it, you could take that to 180oC with no problem giving you better capacity again. You will now have about 40KWH of heat storage. Even alone, If using a Diesel engine as the prime Mover, that would only take 4L of Oil straight up BEFORE you get in the refrigeration boost in efficiency. Even if you only get 2:1, that's a massive 80KWh of heat storage.
    You can keep the place at summer time temps with the doors of the place open!

    While using Brine for cooling does not have the dame thermal capacity for the same volume of water going through phase change, a 500L chest Freezer or fridge on it's back is a very practical size and storage type unit that is far from overly bulky and Holds a really worthwhile about of thermal storage. The Input of about 6KWh of energy from surplus solar is practical for most decent setups ( walk in the park for me at double that) and works out multitudes better than selling the power back to the grid for .10C Kwh and buying it back some hours later for .30.
    With an IC engine it would still work out cost effective if one had to buy fuel and also ideal for off grid where even in summer a decent AC may tax a battery system or the inverters.
    If one can use waste oil, Veg or WMO, then it would provide an investment that would be impossible to beat especially if the engine was sized large enough to drive an alternator for battery charging at the same time.

    Hoping to get the AC unit and a suitable fridge/ freezer in the next few weeks and put it all together.

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    Quote Originally Posted by hinekadon View Post
    Look at peltier units
    Yeah, and then look for something practical. (facepalm!)

    Peltiers in sufficient qty to cool a room would cost a bomb, take up a lot of space, be complex to move the thermal energy to where it was needed but most of all, would use a shit load of power to do anything practical and worth while.

    Work Great on my powered esky, whole different ball game to cool a room or duplicate even a small split systems cooling performance.

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    Thanks.for the replies. I am doing some researching on the net. It is not a subject I know much about at present but apparently there are some systems that will do what I want. We are going to build a new house and it will be off grid, that is why we are looking at a system that needs only a small amount of electricity.
    Regards
    Mike.

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    I have been looking at setting up a system that uses and stores excess solar energy.
    I plan to do it DIY and use an AC system out of a car and Drive it with a Diesel engine. This would use no power virtually other than for a couple of fans and could in fact be coupled with an alternator to proved power or charge batteries at the same time. Not that I think you'd need to if it were hot enough to run AC but if you needed more power at night.....

    There is no magic bullet with this. Efficent AC has an eer of 5X input which is You can get 5KW of cooling out of 1Kw on input, but that's it.
    Your best bet far and away is to build the house with very good insulation including double glazed windows ( and doors if appropriate) and reduce your heating and cooling like that. You should also pay attention to the direction the house faces and look at things like Verandahs to keep the sun direct off the building and insulate under the floors or particularly the slab if thats the type of construction to be used.

    There are a great many things one can do to make an off grid place very efficent and they don't have to be expensive at all, just use good and well thought out planning instead of the overwhealming trend these days of throw it up as fast and cheap as possible before moving onto the next dog Box.

    Probably past it now but I'd Love to build a home and incorporate some of these energy saving ideas. Not a greeny by any stretch but I love DIY and independence as well as going against the grain for a better result than what everyone else is doing.

    If you want to use less power, the start of the goal is not at finding effecient AC, it's building the house so it needs as little AC and heating as possible.

    What are you going to use for your battery pack, what voltage you going to run, how much solar you going to be throwing at the place and what are you going to set up for backup power?
    Be keen to hear more about your setup.

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    Quote Originally Posted by george65 View Post
    If you want to use less power, the start of the goal is not at finding effecient AC, it's building the house so it needs as little AC and heating as possible.
    Plus what has already been said ensure that air infiltration is reduced to a minimum. I am not sure about airtight houses though - supposedly the air changer costs peanuts to run but if the power goes out ... I have seen one installation where there was an elaborate airlock system at the front and then from the dining room a sliding door to the back yard. Sheesh!

    Note that next Sunday, 15 September, is Sustainable house day. Should be something in your area or nearby to have a look at.
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    how about looking at subterainian temperatures they hang around 18-20 degrees so pumping a liquid thru the ground should change its temp up or down in a radiator in the house the under ground abodes in coober pedy. that sounds sensible to me ????
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    I have a solar heating system that works quite well in winter.
    They are pieces of glass mounted in the walls, AKA windows with northerly aspect that are kept closed in winter. The sun is low and shines right into them, the green house effect does the rest.
    Outside might be 15˚ air temp and inside a comfortable 22˚.

    I also have a lot of rubber on the roof initially designed to heat the pool, that I have diverted to heat water in about 500l of tanks for washing and showers. Even in winter 1-2 hours of sun is enough for hot water.
    In summer I don't know where to put all this hot water other than back in the pool, where it would get too hot to be refreshing.

    What I can't do is use this hot water to COOL the house. It would have to be way hotter.
    This has to do with the carnot cycle, is complicated and has been discussed between me and Trash in the past to death.
    This is as far as I got:


    Far simpler and more efficient is to just install PV panels that are cheap as chips and power a standard aircon.

    For the record I don't have an air conditioner. In summer ocean breezes cool the house at night and vegetation that is leaf free in winter provides shade in summer.
    House is well insulated so as long as the windows are closed in the day it is usually temperate inside up to around 4:00, when the ocean breezes kick in.
    Being double story helps a lot too to manage the climate control.

    .... unless we get the nasty westerly winds, then the evenings are spent in the non heated pool.


    Just saying all this as an inspiration if you are planing to build your own house.
    Last edited by Uncle Fester; 16-09-19 at 10:44 PM.
    This era of thoughtless consumption must end so we can encourage a world of creative geniuses rather than consumer idiots.


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