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Final verdict on homemade GRID TIE inverters?

Discussion in 'Alternative Energy' started by arizonaguide, Dec 28, 2009.

  1. magickaldan

    magickaldan New Member

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    Well you shouldn't be cleaning with just water anyways there are certain cleaners designed just for condenser coils and will dissolve anything on the coils restoring them to almost new, and you should use a fin brush to straighten any bent fins out. If done at the beginning of every cooling season your AC won't be working as hard and thus uses less energy. I'm not gonna argue about something that's being done all over the place and works. Here's a link to those interested in it: Water Cooled Evaporative Air Conditioning
    Now this one in the article is a built one made for it but the idea is the same except they went one step farther and went with a reservoir and pump that continually re-pumps the water from the pan of the unit through the nozzles and as the level gets low it replenishes itself from the tap. Basically a standard AC fit with a sump pump and nozzles nothing other than that and the correct sensors to detect when the pressures of the fluid are too low then it shuts off the water.

    Cooling a properly working unit down to ambient when ambient is above 95*F just is not enough. Yes it will still work but the problem is it isn't as efficient as running say 70*F refrigerant through the orifice. And if your dew point is low enough that's exactly what evaporating water cooling can do for you. Say one gallon of water removes 8700 Btu, a 3.5 ton unit removes 42,000 btu/hr actually less at higher temperatures. So if you have 42,000/8700=4.8 gallons of water every hour. So if you have it running for the highest temperatures of the day for 8 hrs that equals to less than a 40 gallon tank of water. The average cost of water in the US is between $.001 and $.0025 per gallon so 40gallons*$.0025= $0.10*30days = $3.00/month.

    http://www.freepatentsonline.com/5701748.html

    The patent calls for a 3.5 ton unit 16 nozzles of 0.6gph which would bring the price of the water up to about $5.76/month * only if the AC was running continuously above 95*F for 8 hrs a day.
     
    Last edited: Jan 4, 2010
  2. Oznog

    Oznog Active Member

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    I'm having trouble with that. A foot and a half of insulation should have enough R-value that the temp in the attic is irrelevant. Second, the thermal mass in the attic isn't even high enough to heat the house all night! The mass of air and wood is not all that great. If heat were leaking though the fiberglass "all night", it would soon cool down.

    IR thermometers are great. You can scan back and forth and find out where you're losing heat/cold. In the summer, say you have the thermostat at 72F. You might scan along the drywall and find the ceiling is 73F and a wall with the sun beating down on the outside is 76F.

    I found a wall shared with the chimney frame was like 4F hotter than the room- the insulation batts had no inner wall supporting them and they simply fell off it.

    Also found that the box which has a duct going from 2nd story attic to 1st floor- with like a foot clearance between the duct and the box- has NO insulation on it! That box is just drywall and constitutes the back of a bathroom cabinet, and 2 sides are room walls. Now the third side is the outside of the house- and that DOES have FG insulation on it- but it's beside the point because the box is open to the hot attic where the duct goes down through that box area. So hot attic air gets into that box and the walls show up real hot.

    The cost of IR cameras is coming down- soon, they may be easy to pick up, which would be neat. But for now, the IR thermometer will quickly and accurately gauge where heat is coming in for real, with no guesswork and theories.
     
  3. Oznog

    Oznog Active Member

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    Water cost is not quite that simple. In Austin they assess sewer charges based on usage, which may be more than the water cost. Although arguably this deserves an exemption!

    Water IS expensive and a valuable resource, in Austin here at least they're doing everything they can to keep water usage down. In the summer, Lake Travis, our water source, can get perilously low. Same story in Az and plenty of other developed places- water is far more critical than electricity. Water is frequently a factor limiting the growth of cities, and you can't just build another dam when all the water in the area already flows to the existing reservoir.

    Anyhow, yes the idea makes sense IF you cool down to near ambient with one condenser AND THEN cool further with an evaporative condenser. However, cooling down the entire condenser with mist is very inefficient and wasteful. You don't want to load the evaporative stage down with heat that can be removed by ambient airflow.

    And misters are not actually very effective evaporative units- that's a complicated thing if you've ever looked into evaporative cooling. You've gotta first see that the evaporative power of water is not that enormous to begin with- 8700 BTU/gal IF you managed to use it all. A gallon is a huge amount of misting! Now note that you're not only using those BTU to chill the refrigerant, but the thousands and thousands of CFM of air that blow through the condenser. Chilling that mass of airflow from 95F to 70F would require far more BTU than the coolant would get!

    And for this to work, the mist must be dissociated (evaporated) into clear vapor BEFORE leaving the condenser. Because mist is not actually much cooler than the incoming water. This is a significant technical problem! Now when the air's 95F and 25% RH in the desert, at first the mist evaporated quite quickly, but as temp drops and RH increases, the affinity for evaporation goes down dramatically and mist does NOT dissolve quickly. In a traditional AC system condenser, there'd only be a fraction of a second between misting, going through the intake fan, and existing the condenser- meaning only a fraction of the water could be evaporated and it'll be a bit cooler but can't get anywhere near the dewpoint, and more water won't help- it'll only leave mist in the exhaust air which won't cool the condenser.
     
  4. dave

    Dave New Member

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  5. magickaldan

    magickaldan New Member

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    It really depends on the user but depending on the circumstances, can be cost effective. But as you've stated in your area probably wouldn't be too good of an idea because of water problems but around here a lot of people do it, especially on larger commercial buildings. I have even seen service technicians use a soaker water hose on larger commercial buildings Roof top units in the summer. It's a tried and true method that works, it's hard to imagine how it works but it just does.
     
    Last edited: Jan 4, 2010
  6. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    There is a very old fashioned type of evaporative radiator or heat exchanger that still has outstanding heat exchange rates when used in high ambient temperatures and low humidity applications but does require a little more complex heat pump exchanger system for it to be to be used with a modern Air conditioning system.

    Its basically the old screen type evaporative radiators they used for the stationary engines back in late 1800's to early 1900's. All it is is a set of fine mesh screens set at a specific angle with a tub of water under them that has a low velocity air flow blowing through them and a basic circulating pump that keeps circulating a small amount of water up to the top of the screens where it trickles down the screens and back to the tub.

    To work with a modern AC heat pump system you would need to replace the condenser coils with a heat exchanger that transfers the heat from the AC compressor to the water where it is then run down the screens to cool it off entirely by evaporation.

    The water loss is entirely evaporative so there is no sewer or other system connections. Its just a tub with a pump and float valve that keeps it at the right level. As far as cleaning goes the old systems often used stainless steel mesh screens that could easily be cleaned by just have the mineral and scale that builds up shaken off of them when it got thick enough.

    Hanging out at the antique shows and asking questions about the odd machine out of the bunch pays off some times! :D
     
  7. Oznog

    Oznog Active Member

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    It's important to note that the performance of any evaporative cooler is strongly dependent upon ambient temperature, pressure, and RH.
    At best, unless you can pre-cool the air, the evaporation effect can ultimately cool down to the dew point, but no further. At higher altitudes, the dew point is substantially lower and evaporative cooling is more effective. Likewise, low humidity locations have much more capacity than high humidity locations.
     
  8. arizonaguide

    arizonaguide New Member

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    Wow! This has turned into a GREAT thread! Lotsa thinking and brainstorming, and learning here.

    Yup! Same here. We have at leat 18" of blown insulation, and with the attic temps varying between 120-170deg F during the summer the insulation gets HEAT SATURATED. This is the result of tremendous solar gain, and the resulting heating of the dark asphault shingles to "egg frying" temps. This heat from the shingles conducts and radiates down through the roof sheathing, and THAT heats the attic air itself to up around 170deg...in effect the insulation itself becomes a big 170deg "thermal mass".

    If I was made of money, I would replace the asphault shingles with an insulated/standing-seam steel roof of an off-white color...and that would result in a cooler attic and insulation, and in fact if the roof itself was insulated I could actually cool/convert the attic.

    I have thought of putting BATT insulation into the roof-rafters themselves, in effect insulating the roof...but the cost is spendy, and I also don't want to climb around on the BLOWN insulation while I try to insulate the roof from inside the attic space. That would result in the insulation being "packed down" and losing the R-value. That's the same reason I don't want to clear the eve-vents from inside. I don't want to have to climb out to the edges of the attic and clear the little existing vents by hand...and pack down the insulation in the process.

    So that's why I'm trying to design eve-ventilation that can be installed from the outside. Perhaps some 3"pipes installed up into the eves and into the attic from the outside. Far enough to stick just above the 18" of insulation.

    Push them up into the attic with a screen installed on the end..which would keep the varmits out, as well as not let them fill with blown insulation when I push them up. So, if I get a few (10 or 15) good 3" eve-ducts (cheap 20" lengthes of PVC pipe) installed, combined with the existing PEAK vents AND a good powered PEAK FAN-VENT that should help!. I should be able to do all that work myself for around $100.

    THEN, if I could figure out a inexpensive way to "reflective" coat the shingles, and keep them from heating to 250deg like they do...I should be able to cool the attic and stop the HEAT-SATURATION of my attic insulation.

    Then, I have to figure out some "cost effective" way to actually produce "SOLAR COOLING"! :)
    I still want to research further into the Absorption Chiller technology...or some other ways to capture that tremendous amount of HEAT ENERGY and use it to produce cooling.
     
    Last edited: Jan 6, 2010
  9. magickaldan

    magickaldan New Member

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    Maybe if you had something like a leaf blower you could blow the insulation from the outside off of the eaves vents up back into the attic?
     
  10. arizonaguide

    arizonaguide New Member

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    Hey! That's actually a great idea! I may try that!!! :)

    Here is my general idea about the vent "pipes"
    [​IMG]
     
  11. smanches

    smanches New Member

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    Strange they didn't put in the dividers that are meant to prevent the insulation from clogging the vents. They are specially made for just that purpose.

    I suppose I keep saying that about my house too. I guess I just can't believe how cheaply they build them.
     
    Last edited: Jan 6, 2010
  12. arizonaguide

    arizonaguide New Member

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    Yeah, I wonder how many insulation contractors actually do install the stops at the eves before getting in the attic and blowing away!
    Most of the time it's in a colder climate (insulating from "heat loss" from within rather than heat infiltration), and the lack of airflow may never get noticed...that is, until the moisture in the attic air doesn't get properly vented...and that person ends up with condensation and then ICE in their attic. SOME ventilation is important, even in cold weather.

    Cheezy sketch above, I know..but you get the idea. I still like the additional idea of putting a leaf blower against the outside of the existing vents and trying to "blow-back" the insulation away from the existing vents. I will try that in addition to putting my 10-15 "pipe" vents, and a new powered fan-vent.

    I sure appreciate the help, and I appreciate the moderators letting this thread get into a bit of "non-electronic" theory and brainstorming...as it sure has given me pause, and forced me to realize and prioritize the steps/cost-effectiveness of different modifications and upgrades. Lotsa GREAT info in this thread!!!
    :)
     
  13. Oznog

    Oznog Active Member

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    There should already be soffit (eave) vents there, and dividers to keep the insulation from falling onto the vent grating. Even a 3" pipe is not really big enough cross section for a lot of airflow, if you could find the room. And also note that you must have a metal grill on that pipe to keep rats and squirrels out.

    Yup! Same here. We have at leat 18" of blown insulation, and with the attic temps varying between 120-170deg F during the summer the insulation gets HEAT SATURATED. This is the result of tremendous solar gain, and the resulting heating of the dark asphault shingles to "egg frying" temps. This heat from the shingles conducts and radiates down through the roof sheathing, and THAT heats the attic air itself to up around 170deg...in effect the insulation itself becomes a big 170deg "thermal mass".

    I'm sorry but this is gobbledygook. There's NO such thing as "heat saturation" in insulation at all. Functioning (not wet, not packed down) R20 insulation means the hot side stays hot and the cold side stays cold, indefinitely. There will be a small leakage from a hot attic into the room, but the room will cool the bottom side of the foam (or vice versa for winter use). The foam never "saturates" and does something different. And note that in the winter, heat lost through poor insulation heats up the attic, which slows down loss through the insulation. Venting the warmed attic in the winter will only accelerate heat loss. But if your insulation is good, there is not a huge loss through the attic.

    Again I gotta point out you're going off the deep end. There is only a marginal gain from cooling the attic further, assuming your insulation is good. If the insulation is not good, get better insulation! And second the ridge and soffit vents are popular BECAUSE they're exceptionally effective- much more so than any powered fan, BTW. The volume of convection air is very high, even though the air speed is unnoticeable. A solar fan is a fairly pathetic CFM given the size of the roof, as well as very expensive and may or may not be working several years down the road. A 1HP fan becomes significant, sure, but that 12 hrs a day would cost almost as much as the AC!

    In short, these ideas are... well, dumb. They're quite expensive, give next to nothing for gains, and some may seriously damage the house.

    The reality is, once you have good attic insulation, you have almost nothing to gain by these measures. Your losses are 1) sunlight through windows (very very very high!), 2) thermal conduction through windows, 3) outer walls, and 4) air infiltration. Sunlight getting through windows is only a huge problem on south-facing windows.

    Double pane glass in itself insulates against warm outside air, but not against light coming in (sunlight is >1000W/M^2 in the summer!). IIRC there are higher tech glass types which can reflect at least the IR part of the spectrum while still looking like a window. There's also solar screens- which I hate, personally, and ripped them off the house because I couldn't see out of the damn windows and they looked... kinda scary from the outside. Trees are nice!
     
  14. arizonaguide

    arizonaguide New Member

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    Hmmmmm. Well, let me clarify it and make it easy to understand.

    Think of my attic as if it was as well ventilated as my CARPORT.
    My (well ventilated) carport does NOT get up to 170degF. It stays ambient (105-115 in the summer).
    What's the difference? VENTILATION! I WOULD like to have the ventilation that I have in my carport (in theory) in my attic! (or as close to it as I can get)...does that make the "ventilation to ambient air temperature" concept more clear?

    I don't care WHAT type of insulation you have, there will be thermal transfer.
    There is NO PERFECT insulation that completely stops the transfer of HEAT.
    The R-value is an indicator of this, but there is no perfect insulator.

    SO, if you heat the insulation repeatedly and heat it MORE than it gives up at night, then it (like any other material) will eventually become a saturated "HOT thermal mass".

    YES, the A/C may cool the bottom that's in contact with the ceiling, BUT it will be a load to do that. I don't think you realize that the kind of HEAT the asphault shingles absorb and transfer/radiate through the sheathing to the attic air (and thus the insulation).

    YES, the windows are the biggest problem, but I've already addressed that issue as much as I can afford, and NOW it's time to address the HOT ATTIC. And I don't believe it's a dumb, "off the deep end" idea to put $100 into solving the problem with 10-15 new 3" eve-vents and a powered fan. And trying to get that attic somewhere close to ambient (like my carport;) ) should help. I believe that IF I had a cooler attic, it will not only help somewhat with the A/C load...but it will help the life of the materials of the house, AND the belongings that I store up there.
     
    Last edited: Jan 6, 2010
  15. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I would have to disagree on the heat saturation effects of insulation. All of the types of blown in and fiberglass insulation I have had to unfortunately help install does have a surprising amount of mass despite its volume. I have 6 inch R-19 on my boiler system now and it still lets through a fair amount of radiant heat when the boiler is at 180+ F. Small things I have laying on top of it are always warm to the touch even though the paper wrapper itself never feels warm.

    My old thermal dynamics books say mass holds thermal energy regardless of its R value. It just takes higher R values longer to heat up and to cool down.
    If the OP has a ton of insulation in his attic that is still a ton of mass that has more heat in it than the house does. Heat radiates, hot air rises. By reducing the direct heat absorption of the roof and lowering the levels of heat in the attic plus increasing air flow to help cool down the attic is not going to hurt anything.

    Ventilation does not need vast amounts of energy either. A basic 10 inch 40 watt fan still moves a few hundred CFM which over a 12 or more hour period is a far greater volume of air than what fills the house! And it could easily be mounted directly in one of the existing roof vents as well.
    I use one on my dirt floor crawl space under my house all summer to keep the moisture levels down. It really makes a big difference! Just put one in on a thermostat that turns it on whenever the attic temp is over 100 F or so. it will make a difference!
    Uncovering a few of the lower vents at the points furthest from the fan so fresh air can be drawn in will help speed up the process and will keep the fan from pulling too much air out of the house itself.
     
  16. arizonaguide

    arizonaguide New Member

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    YES! The insulation is becoming it's own heated THERMAL MASS

    In fact, it's the same HIGH R-value qualities that make it a good insulator, that prevent the material from giving up the heat it absorbes during the repeated "cooking" days!

    So, I believe what is actually happening is that my insulation is becoming a "hot blanket" across the ceiling...getting repeatedly "heat soaked" itself for days on end, and then NOT giving up much heat due to lack of proper ventilation (and repeated HIGH TEMP saturations).


    Well explained. Thanks TCMTech.

    Oznog, I DO agree with your previous idea of viewing the whole house with an IR Thermometer/camera...and identifying ALL the areas/amounts...as well as identifying EXACTLY how hot those shingles ARE getting! (Hot enough to fry an egg on...I DO know THAT!)

    Thinking "outside the norms" (and figuring out exactly WHAT is going..not just the "accepted" theory) is often called "dumb" or "off the deep end"...BUT that's also called "objective investigation" and "creative problem solving". ;)
    AND, with my SMALL budget...I HAVE to be "creative".
     
    Last edited: Jan 6, 2010
  17. arizonaguide

    arizonaguide New Member

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    Great link, and definately food for thought. Looking further into the whole "chiller" technology for future applications. :)
     
    Last edited: Jan 6, 2010
  18. arizonaguide

    arizonaguide New Member

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    The insulation does NOT magically stay "hot on one side and cold on the other, indefinately"...

    There is a GRADIENT of temperature from one side to the other.

    HOT SIDE|||||<- gradient of warm ranges ->||||||COOL (A/C) SIDE

    Insulation slows the transfer of heat, and heat transfers in 3 ways:
    1. Conduction
    2. Convection
    3. Radiation
    YES, heat rises, but to my understanding it also "naturally" conducts (and convects) from Hot areas to cold areas. Radiation is somewhat "directional".
    ALL of these are taking place in my attic/ceiling.

    Right now (without good ventilation and reflective roofing) the average temp of the attic in the summer is around 150degF, even while the outside ambient temp is only 105!!!! I know this for a fact, because I HAVE tracked it for a couple days in JULY. The A/C will cool the inside of the house, but it has to run almost constantly to do it.

    If I turn the air conditioning OFF completely, and leave the house for a week in JULY, I GUARANTEE YOU that the insulation will HEAT SOAK in the warm attic air, and will become a giant THERMAL MASS!!! (somewhere around the 150degF temperature "average" of the attic).

    It WOULD take hours (maybe days!) to cool it back down. It would be a "heat saturated" THERMAL MASS.

    THAT is effectively what is happening after REPEATED days of 150deg "averages". The A/C can't fully keep up with the warming of the insulation at those extreme temps...AND the insulation is actually holding MUCH of it's OWN absorbed heat WELL into the night and into the next day. The next day a little MORE of this takes place. Eventually...I believe the insulation is close to "saturation" in spite of A/C going on below it.

    The attic peaks at 170 during the hot part of the day, and cools to around 120 at night. This HAS to create a WARM ceiling in the house, and increase the A/C load. Better ventilation (and reflective roofing) should help keep the attic air closer to outside ambient. AND MAYBE (just maybe) help keep the attic insulation (and my other belongings in the attic!) from getting cooked in the ARIZONA summer heat.

    The REAL trick is how to solve this in the couple hundred $$$ range, rather than the thousands. So, I'm thinking PVC pipe vents (screened on the ends), a powered vent fan, and some type of (inexpensive!?) light color/reflective roof coating.

    Anyone have any ideas for a good light colored roof coating for asphault shingles?
     
    Last edited: Jan 6, 2010
  19. Oznog

    Oznog Active Member

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    I'm just not sure what you're saying. Sure the attic has thermal mass! Some in the wood and shingles, some in the FG. But that's not "saturation". Presuming the house hasn't been left with the AC on, there is no equilibrium. The insulation is cold on bottom and hot on top with a gradient in between. The warm attic will continue to warm the house after the sun goes down- but there's still a (hopefully) huge R-value separating the ceiling and attic heat. If not, add insulation!

    There's nothing wrong with attic ventilation. Ventilation is great. But, it's no substitute for insulation. And again soffit vents plus ridge vents are the super-effective solutions. 40W fan? Sure, it'll have some effect, about 120CFM. But the passive vents start up a wicked convection all on their own, no power needed. The fan of course needs an intake vent, and there's a question of where the air's coming from if you've already got gable vents. It might be flowing in the gable vent on one side and out a powered gable vent on the other, which is not productive. Or if you have a big gable vent and a smaller fan in the middle, there's less resistance to drawing in air from around the gable vent than through the soffit vents, meaning it'll simply recirculate some of the air it just exhausted which again is counterproductive.

    Other misc notes- anything added to the back of the plywood roof decking can likely build up moisture and cause premature roof damage (costs thousands). Any creative ideas about painting shingles is likely to reduce their life, and may trap moisture underneath that again damages the roof decking. Plus most paints will peel off in the sun before too long, and cost a ton for that many sq feet.

    That's why the soffit+ridge vent solution got adopted so widely: it works and doesn't screw other stuff up. And that's also why insulation is adopted as the #1 line of defense: it also works.
     
  20. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I have the quieter and lower power version of this one. EBM PAPST|W2E208-BA86-51|Axial Fan | Newark.com
    I think mine has a 350 CFM 46 watt rating.


    Given my house is 14 X 70 and both main floor and sub floor are roughly ten feet combined so that gives me a volume of around 9800 cubic feet. At 350 CFM I get a full air exchange about once every half hour.
     
    Last edited: Jan 6, 2010
  21. arizonaguide

    arizonaguide New Member

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    We basically agree. Problem is, I just blew in an additional 8" on top of the 12" that was there already...and can't afford more.
    AND, with close to 20" already, I'm not sure that's the problem.

    I believe that the problem NOW is that the eve vents being blocked do NOT allow the attic (and related insulation) to stay cool to normal (ambient) temperatures. I believe that the insulation mass RETAINS a little more heat each day...eventually becoming a (almost?) "heat saturated" thermal MASS itself...that the AC can't keep up with.

    YES, this is just my educated guess. (based on temp readings over a few days in JULY!)

    So, now it's VENTILATION time. AND try to find some cost effective coating that will work on asphault shingles.

    Perhaps IF I just COVER the roof with SOLAR HOT WATER COLLECTORS for STEAM POWERED ELECTRICITY...that will provide the "shade" to the asphault shingles that I need! ;)
     
    Last edited: Jan 6, 2010

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