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Home Forums General Discussion Solar A/C

This topic contains 12 replies, has 7 voices, and was last updated by  Anonymous 7 years, 3 months ago.

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  • #36626

    salvor
    Member

    Is it possible to run my central A/C unit via solar power? I have not seen an inverter that can run 220v.

    #40669

    hardworkinghippy
    Participant
    #40670

    revinger
    Participant

    Salvor,

    While it is technically possible to do so and there are 220 volt inverters available. The required power is going to make it a very expensive proposition. Multiple times more costly compared to providing power for the rest of your house.

    I have 9.5kw surge rated generator and it ‘barely’ will provide enough to start the central air in my house. I went without a/c last summer, it just wasnt worth it. I was able to get by opening the house up at night and use fans to get the house cooled down to outside temps.

    By late afternoon the house would get a bit warm but the A/C that wasinstalled in this house could not do much better anyway.

    If you have the dollars the A/C could be run off of solar and inverters but it was out of my price range. I had to be satisfied with running everything else and forget the central air conditioner.

    Bob

    Somewhere in Illinois

    #40671

    revinger
    Participant

    Guess I should add that the way the inverters I am familiar with provide 220 are two ways.

    1. stacking where two like sized 120v inverters have an option that allows them to synchronize and work together to each provide half of the 220.

    2. feeding a 120 volt invert through a step-up transformer that converts the 110 to 220.

    bob

    somewhere in Illinois

    #40676

    salvor
    Member

    Hardworkinghipp I looked at those inverters. They are pretty expensive. I guess the only way I can power my A/C is with a windmill.

    #40698

    elnav
    Member

    Salvor, it is technically possible to run air conditioning with an inverter but you probably do not want to incur the expense for the batteries needed. Most of my clients require some A/C because they are in southern climates. but they also spend several thousand dollars on a big battery bank.

    There are two ways to get 220V for an air conditioner. European market inverters normally come as 230V and at least one brand ( Victron also sold in the US ) can be switch selected for either 50Hz or 60 Hz operation. The second way is to use a step up transformer to boost 120V up to 220V. for one recent job we found a 4 kVA rated transformer that only cost USD $109 plus shipping.

    Most of the existing home air conditioners tend to be hard starting. For off grid use I recommend adding a soft start module that eliminates the huge start surge. Submerged well pump owners have been using this technique for several years already.

    For power conservation I suggest you consider using a small RV unit just to cool off the room you intend to use the most be it living room or bedroom.

    Central air conditioning units are often five or ten ton capacity and would require far too much power. Note! one ton = 12,000 BTU

    #40699

    hardworkinghippy
    Participant

    Why not insulate your home better and introduce some shade on the south side of the house so that it become solar passive and you get the sun in the house in winter but not in summer ?

    Have a look at these photos to see what I mean :

    Sunshine in a winter solstice kitchen (passive solar : bioclimatique)

    You could run some DC fans from a small solar array and you won’t need an inverter. The problem with wind generated power is that you probably don’t need a/c when the wind is blowing.

    #40702

    elnav
    Member

    Insulation only goes so far and does nothing to alleviate high humidity. In some coastal climates the air conditioning is as much to dehumidify as it is to cool. I have now lived in both coastal and mountain climates. House air conditioning also called HVAC uses a heat pump that is reversible. Something not often given consideration is the age of the house resident. Especially by younger people looking at energy conserving houses. My clientele tend to be the empty nesters who are approaching(early) retirement age. Guess what? It is almost always the wife who demands air conditioning. Strange I thought. After some thinking about it I realized there was a rational explanation. All of these wives were approaching that age when they suffered from ‘hot flashes’

    The flash of enlightenment happened when my wife complained about not being able to open a window when it was a snow storm outside with -5 C temps. She complained about being hot and I was freezing in the +10C temperatures indoors. I checked it out with a few friends in the same age group. Sure enough the pattern held true.

    To someone in the twenty something to forty something age group it may seem asking for air conditioning but to someone experiencing hot flashes it is a matter of crucial importance.

    #40705

    elnav
    Member

    Because the original post talked about running central air from an electric power source I totally forgot a discussion I had with a colleague a couple of years ago.

    I had come across a reference to central air conditioning in the pre-electrified Arabian peninsular. during the discussion my friend said he had visited such a home while working in the United Emirates. well that got my attention. Seems the Arabs of the nor tenth century had developed a form of central air in the same way Romans had developed central heating before the time of Christ.

    As hard working hippie has already mentioned insulation is the key.The Arabs used crushed coral or blocks cut from coral to build walls a couple of feet thick. The design of the building is also key. A central atrium is surrounded on four sides by rooms having few windows and none facing out on the exterior side.

    A corridor goes around the building returning to a corner on the soutnern wall. At one or both corners a square tower at least 30 feet high is erected and the interior is divided by diagonal walls forming triangular vertical air shafts. The tower walls are thin so sunlight heats the south facing wall. The northern wall being in shade is somewhat cooler than the opposite side. The air shaft on the southern side is connected to one end of the corridor circling the building interior and the northern air shaft connects to the opposite end. A wall prevents direct connection of the two ends of the corridor. Solar heating forms a thermal chimney effect in the south side air shaft and hot air rises. Meanwhile the cooler north air shaft permits cooler (relatively speaking) air to drop and enter the corridor as make up air replacing the hot air being exhautsed. As a further cooling effect long strips of fine mesh muslin cloth hangs in the north air shaft and is constantly wetted by water being dripped on the cloths. As the water wicks down along the cloths evaporation causes additional cooling and the air entering the corridor is about 15 degrees celcius cooler than the ambient air.

    considering the owner of the building was an engineers and my fried also ghad considerable technical training I am inclined to believe the description and how it worked. The building in question had been in the engineer’s family for generations and he found no reason to change a non electrical solar powered system when it obviously was working. About the only modernization was replacement of the slaves that used to carry jugs of water to the top of the tower. Now a water pump piped water to the top an

    d sprinkled water on the cloths used as evaporation screens.

    While visiting the south I have experienced evaporation type air conditioning and can attest to how refreshing and cooling it can be. Especially in the desert. in parts of the southern US they are coloqually refered to as swamp coolers. This may give you an ide of how to cool a house with little or no electrical input.

    #40714

    Anonymous

    Here’s a little food for thought..

    http://mb-soft.com/solar/saving.html

    #40717

    elnav
    Member

    Excellent link 12Vman. Many of the current generation who are looking to go off-grid are too young to remember the first oil crisis we had in the seventies. Back then a number of architectual proposals emerged to take advantage of this earth tempering effect. It ranged from burying houses under several feet of earth to actually digging down underground. The absence of windows was one of the biggest obstacles to widespread acceptance of the concept.

    Today’s ‘geothermal’ systems are an outgrowth of this early thinking. Instead of using air to transfer the heat, liquids such as water or ethylene glycol is used to effect the transfer.

    The downside being the need for a sizable plot of land from which to extract the heat in winter or collect the cold (technical purists please forgive the inaccuracies in that last statement)

    Some geothermal systems use vertical pipes to get around the land area restrictions. Somehow I doubt it would be as successful with an air pipe system.

    Some places have land that does not lend itself as well to this cooling method. Cost of digging or trenching in near solid rock makes it cost prohibitive.

    #40721

    DavidWells
    Participant

    Been looking for something like this. Thanks 12vman. Your check is in the mail =)

    #40724

    Anonymous

    This can be done through passive solar, solar thermal energy conversion and photovoltaic conversion (sun to electricity). The U.S. Energy Independence and Security Act of 2007[1] created 2008 through 2012 funding for a new solar air conditioning research and development program, which should develop and demonstrate multiple new technology innovations and mass production economies of scale. Solar air conditioning will play an increasing role in zero energy and energy-plus buildings design. Air can be passed over common, solid desiccants (like silica gel or zeolite) to draw moisture from the air to allow an efficient evaporative cooling cycle

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