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Tecumseh's line of compressors for solar power air conditioning?

Discussion in 'Home Power and Microgeneration' started by N9WOS, Jun 10, 2010.

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  1. N9WOS

    N9WOS Guest

    This is something that caught my attention. For people looking for a viable
    solar/dc based air conditioning system for their home. Tecumseh is making a
    masterflux branded line of compressors called sierra, for 12/24/48 and
    higher volt operation.

    http://www.masterflux.com/products/sierra/

    They also have complete condensing units built around them.

    http://www.masterflux.com/products/condensingunits/

    High temp is basically the same operating range as AC service. Basically an
    evaporator temp above freezing.

    They have a rated capacity range from 3000 to 6000BTU with a condensing temp
    of 130F. In the real world, with an adequate condenser, condensing temps
    will not be close to 130F. So that is the worst case scenario. Actual real
    world capacities will be closer to 5000 to 10000 BTU with more normal 100F
    condensing temps.

    The only reason you see higher condensing temps on their complete condenser
    line is because they are not really optimized for AC service. The condenser
    coil isn't really large enough to support the higher evap temps and higher
    capacity.

    At a power draw of 374 watts for 3753BTU at 55F evap, and 130F condensing,
    you still push over 10EER which pretty respectable for 130F condensing temp.

    If you got a reasonable sized 1 to 1.5 ton condensing unit and put that
    compressor in it, you would not see over 10F above ambient condensing temps.
    That will help capacity and EER for AC service greatly. You would have to
    change the condenser fan over to a 12 DC type. Inside evaporator could be
    anything from a small fan coil, or a wall mount unit.

    Basically the above system with two 200W panels and an AC with a couple of
    golf cart batteries for a buffer and you will have climate control during
    the day time. With big enough GC batts and you could carry cooling into the
    night hours.

    A lot more efficient than running a window shaker on your existing
    inverter/solar installation.

    Granted, 3 to 5kBtu isn't a lot. But in a well insulated house, or part of a
    house, it will make things a lot more comfortable.

    Yes, you would be talking about approximately $4000 for a 5000BTU ac, but
    considering How much a normal central air system cost. Even a mini split of
    that size will cost over $1000. And it doesn't use AC power, so no electric
    bill. 4K bucks for a solar ac doesn't sound that bad.
     
  2. vaughn

    vaughn Guest

    But our high-efficiency window shaker claims 6000 BTU for only 500 watts. I
    could run it from a modest PV system and still afford the inverter loss.
    Perhaps not always. Some inverter mini-splits in that size range do far better
    than our humble 12 EER window shaker.
    Our bedroom mini-split already has a DC fan on the inside unit. They did that
    so it could operate from low voltage wiring. Is that common these days?.
    Even here in hot-humid south Florida, it might cool one room very well.
    Since the wife and I are empty-nesters, we save on our power bill by using a
    "cool room" concept most of the day. The central unit stays off until just
    before supper while we cool the study with a 12 EER 6000 BTU window shaker. At
    night, the central unit goes off again while we cool our bedroom with a little
    mini-split. That solar AC would sure be nice in our study to replace that loud
    window shaker, and our need for cooling would exactly track the period when the
    panels were producing full capacity. But not for $4,000! At that price, no
    unit would last long enough to pay for itself.

    Anyhow, thanks for the links. Now I can dream!

    Vaughn
     
  3. N9WOS

    N9WOS Guest

    Yes, you would be talking about approximately $4000 for a 5000BTU ac, but
    The system I am referring to is not for people on the grid. It is for off
    grid houses. Most of the 4K price tag I listed was solar related stuff to
    power it. In an off grid situation, the price of the panels and equipment to
    power it always comes into the price factor. The total actual cost for just
    the DC powered air conditioner components is only about $1200. The solar
    equipment related stuff is about $1800. And throw in about $1000 for labor.

    I would say that if you compare that $4K price to the rest of the system
    needed to power a window shaker from solar power, in an off grid situation,
    it wouldn't be so clean cut.

    500W + inverter losses.
    Assuming 90% inverter.
    That makes it 550W
    Plus other losses.

    So, 600W of PV for continuous run during the day time. (Same as the layout
    for the other system.)

    That is $1800 in panels.
    $400 to $600 for the charge controller.
    $200 for batteries.
    $600 to $900 for pure sine wave inverter.
    Paragon Eco Air Conditioner $260

    Total real world price. $3260 to $3750
    And that is not including labor.

    And just so you know.

    That 12 EER rating for the window ac you referenced is based on relatively
    mild conditions, with a warm house. 95F outside condenser intake air, and
    80F inside air. A 15F split. EER varies depending on the temperature split
    you are moving the heat across. When outside temp goes up, and the inside
    goes down, then the energy required for moving heat goes up, and EER goes
    way down. When it gets over a 15 degree split , then 12 EER is out the
    window. If you want the inside set to a more reasonable 75F and the AC is on
    the sunny side of the house with 100+ ambient intake air. Your 6000 BTU unit
    will be pulling more like 600W to 700W. With a real EER of around 9 or less.

    The one compressor I listed was rated at 130F condensing which is around
    110F to 120F ambient. Or around 15F to 25F higher outside ambient than your
    12 EER unit was rated at.

    So, to match the specs of the one I listed, you will probably need 800 watts
    worth of panels. That will push the total price of over 4K before labor.

    Yes, you may already have the inverter and batteries. But the additional
    panels, charge controllers, will still have to be dedicated to supplying it's
    consumption. So, you are still talking about $3k+ for the equipment
    dedicated for the AC.
     
  4. vaughn

    vaughn Guest

    Oh yes, I realize that EER ratings are rarely achieved in the real world, much
    like auto MPG ratings. Still, they are somewhat useful for comparing one
    product to another. In my case, I have verified the power draw of that window
    shaker, but that really means nothing because I have no way of measuring how
    many BTUs it is actually moving.
    Yep, you just can't win. Someday I do hope to splurge and replace that window
    unit with a little mini-split unit. The one I have in my bedroom makes every
    window unit I have ever qwned seem crude. It is so quiet you have to look at
    the display to see if it is running.

    Vaughn WB4UHB
     
  5. Neon John

    Neon John Guest

    Vaughn,

    For quite some time I've been working on a scheme to air condition my
    RV using battery power at night, recharged in the day by generator.
    I'm a little stalled right now due to health problems but hopefully I
    can get back to work on it soon.

    Anyway this is what I've come up with. The AC unit is the 16SEER DC
    mini-split from here:

    http://www.heatandcool.com/

    Center of the page. This is an inverter unit that has a variable
    speed compressor and fan. Of particular interest to me is that it is
    transformer-less. That is, the AC coming into the unit is immediately
    rectified and filtered to about 165 volts DC. Also of particular
    interest is that the compressor soft-starts so that there is no inrush
    spike.

    A 12/120 volt inverter operates by first stepping the 12 volts up to
    about 165 volts using a high frequency DC/DC inverter and then chops
    it into a 60 hz pseudo-sine wave.

    The connection should be obvious. Tap into the inverter and bring out
    the 165 volts DC and feed that into the AC. At that point the AC can
    run from 12 or 24 or whatever input voltage your inverter uses.

    The AC requires no modification - the DC can be piped in directly
    through the power cord.

    What I've done so far.

    -installed a sufficiently large battery bank in my RV
    - Modified a 2kW inverter to bring the 165 volts out to a terminal
    strip.
    - gotten the service manual for that unit and verified from the
    schematic that I can feed the DC voltage directly in.

    Yet to do.

    Buy a unit and hook 'em up.

    I'm in the process of building a custom motorhome using a medium duty
    cube van. It is super-insulated so that this small unit will heat and
    cool the unit even in extreme weather. Hopefully I can get back to
    work on this shortly as my medical problems abate.

    Anyway, you could put together something like this for not all that
    much money. The solar panels would be the big expense but perhaps you
    could find some surplus/used. Even if the solar panels could not
    supply all the operating power, they could help out. Just wire up a
    suitably sized RV converter (Progressive Dynamics Intellipower/Charge
    Wizard is my favorite) to supply power from the line to the inverter.

    John
     
  6. vaughn

    vaughn Guest

    If you look at the 13 SEER unit on that page, you are looking s something so
    close to my bedroom unit that I am willing to bet they shared the same Asian
    factory. Mine came from here:
    http://www.comfort-aire.com/residential/17-ductless-mini-split-systems/45-s-series-single-zone
    They seen to have about the same product mix. I ended up with the 13 SEER unit
    because mine was a "bother-in-law" deal and that was what I was offered! I
    managed to install it myself in only about 10X the time a professional would
    have taken, but am happy with the results. It did not have pre-charged lines,
    so you need a vacuum pump to install. That turned out to be good for me because
    it helped me detect a leak in one of my flare connections before I lost any
    refrigerant. (I would love to replace the window shaker in our study with
    another of those units, but it really is hard to justify.)

    I have long suspected that "inverter" ACs actually ran on DC, but there really
    is very little information on them. Actually, almost anything with a
    transformerless switching power supply should be convertible to DC. The main
    question is what range of DC inputs can be tolerated. Finding the answer via
    the experimental method could be expensive!

    John, please keep us informed on that project.

    Vaughn
     
  7. If the AC line specs are 120v +/- 10% then 152 volts DC is the low end
    of the required input. Which should fall into the range of of the +buss
    of of a MSW inverter. Don't forget depending upon the inverter, you'll
    only need the + buss voltage as most MSW inverters have + and - 165vdc
    (it's probably closer to 150vdc for a MSW).

    Cheers
     
  8. vaughn

    vaughn Guest

    Oops! Would that limit you to half power from the inverter?

    Vaughn
     
  9. If the inverter has a split bus I don't think it would limit the power.
    in normal operation each bus is subjected to alternating 8ms of loading,
    I don’t see why one can't constantly load one of the buses, but you
    never know.
    The AC DELCO inverter I have looks robust enough (multiple parallel
    transformers for each bus) to pull this off.

    You do need to check regulation, since MSW inverters adjust their AC
    output pulse width to maintain 115v.
    The bus is the output of just a raw DC-DC converter with no regulation.
    But a good thing is there is most likely some form of circuit protection
    (Over current) built in, at least one would hope.

    Cheers
     
  10. EXT

    EXT Guest

    Since Tecumseh went bankrupt last year, who bought the name and is
    manufacturing the equipment under that name, so that they can sound more
    legitimate. It certainly isn't the Tecumseh we remember.
     
  11. Guest

    Hey, I have gone down this rabbit hole. Kingtec Solar air conditioners have been developed to do what your talking about.

    It's more than just a compressor. Here is a description of one of our products.

    Solar window unit description: 16000 btu -- E.E.R. 18.6

    Kingtec Solar air conditioners come completely ready with built-in connectors for solar panels, power converter and batteries. All the necessary cables are provided. The A/C has a 45 amp mppt solar charge controller inside the unit. There is an external enclosure for the AC to DC power converter option. All of the necessary DC overcurrent protection fuses and breakers are installed in the air conditioner. Quick fuses for solar surge protection and grounding are also installed in the unit. The air conditioners come with two year warranty on parts and one year on the compressor


    So - How much did you say you were willing to pay?
     
  12. Vaughn

    Vaughn Guest

    Not that much! At least, not yet. That thing (not even counting the PV
    panels) would cost us what we pay for two years of power bills for our
    whole house, yet the compressor is only warrantied for one year!

    A conventional unit powered by an inverter might make a lot more sense.
     
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