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Final verdict on homemade GRID TIE inverters?

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

  1. arizonaguide

    arizonaguide New Member

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    Good points, Oznog.
    I was thinking much simpler heat recovery than capturing the heat directly from the fluid.

    I was considering capturing heat from the hot air that's vented from the top of the outside coil of the heat pump. In other words, there's a huge fan motor outside that cools the outside (condenser) coil. That resulting hot air, could very easily be passed (with same fan) immediatly through another added exchange coil full of water from the domestic hot water tank...especially if it was closeby and was part of a single unit. That would not change the engineering of the basic AirCond system, yet would recover (some) of the hot air that is currently just being vented to the Arizona sky. :) As with most AirCond systems here, the heat is just exchanged and vented outside with a "heat pump" system.

    As far as the attic is concerned, the attic actually is non insulated, and the insulation sits on the attic floor and insulates the "ceiling" of the house...a "hot attic" if you will.

    So, the solar gain in the hot attic (from dark roof shingles, etc), raises the temperature inside the attic to around 170degF during the hot part of the day! So, I could (literally) just place a 50gal tank in the attic, and have it raised to 170deg without any fancy "collectors" or anything!!! Not that I will do this, but it's just my point that excess heat is not a shortage here in the summer!

    I do plan (instead) to build an actual "collector" system, and at least get solar hot water heating accomplished this year!

    In fact my project(s) THIS summer is to vent that attic better, and paint the roof with some reflective coating, and at least attempt to cool it to "normal" (105-115 in July!) outside ambient air temperature...and then build an OUTSIDE solar collector to heat (supliment) my hot water.

    I was just wishing that I could use some of that tremendous amount of Solar Power (here) and excess heat to develop energy to actually do some cooling!
    But, the only realistic system it seems, would be to use it with a "focused mirror" to develop steam for a turbine generator...and that's not in MY budget.
    That would be at least as expensive as a continuous supply of Photovoltaics/batteries! :) ;)
     
    Last edited: Dec 31, 2009
  2. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Changing from a dark color of roof to a light and reflective color and material like white steel panels will substantially reduce your indoors thermal load on the air conditioning. Also adding more insulation along with the better ventilation to further reduce what radiant attic heat comes down through the ceiling will help also.

    For reducing the air conditioner loads just having it in a shaded location greatly helps its efficiency as well. If your trying to reclaim heat off of the compressor its common for the high pressure discharge line that comes out of the compressor and goes to the condenser coils to have temperatures in excess of 300 F in hot climates and high load conditions. Just adding a simple water jacket heat exchanger over that section of the line from the compressor to the condenser coils can pick up a good deal of heat and also reduce the condenser coils thermal loads as well.
    There are factory made heat exchanger units that can be installed in that line section as well that have far more effective heat transfer capacity and efficiency than a basic home made one.

    Lastly just adding a simple drip system that puts a small amount of water mist or drops onto the condenser coils to help reduce the thermal loading by using simple evaporation can also greatly reduce the energy required for the compressor to do its job.
     
  3. arizonaguide

    arizonaguide New Member

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    Thanks Tcmtech!
    I will look into adding some H2o (evap) capability to the condenser coil. That's pretty easy/inexpensive to do.

    Also a must (this spring) is getting those roof shingles into a lighter color, and working on serious attic ventilation.

    Part of the ventilation problem is that the attic insulation was blown out to the edges, and has covered the eve-vents, thus blocking the natural convection current in the attic. So, part of my energy task is to find an easy way to "clear" the blown insulation from the eves, without actually crawling around the attic (and smashing down all the insulation and losing the R-value). So, I'm thinking some new vent holes in the eves, with some piping up through the insulation...all done from the outside. It's a hip roof, so there's no convenient gable-ends to put new venting...so I have to convect from under the eves to get a good current going. I'm sure all the houses in the neighborhood had the same insulation contractor, and thus share the same (170degF attic!) problem. Cooling that attic by 50-60deg should result in a substantial decrease in A/C energy consumption!!!
     
    Last edited: Jan 1, 2010
  4. dave

    Dave New Member

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  5. smanches

    smanches New Member

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    Never understood eve vents.

    Put in some good gable vents with a solar powered fan on one end. Best way to vacate an attic.
     
  6. magickaldan

    magickaldan New Member

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    On the AC evap cooling here's the best way to do it. It's done on all the commercial buildings with AC units on the roof around here. Except most of the units are designed for it with Head pressure switches etc. Take some half inch pipe (copper would be the best), and drill a line of the smallest holes you can around 5 inches or so apart, and do this for each side of the condenser, then take 2 valves one valve will be your flow adjustment and the other will be the shut off. Then hook up to a water hose and your ready to go. Only thing to remember is don't run it under 95* outside and don't obstruct the fan on top or the coils with any heat exchanger you will cause more harm then good. Too much cooling of the condenser and you can ice up your evaporator inside the house.
     
  7. arizonaguide

    arizonaguide New Member

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    Agreed, if I had some gable ends. But, it's a hip roof, so I'm forced to use the eves.
     
  8. magickaldan

    magickaldan New Member

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    Might consider putting some powered vents on the peak.
     
  9. Oznog

    Oznog Active Member

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    Not really. Get an IR thermometer and check the ceiling temp. IF you have good insulation the ceiling may not be measurably hotter than the rest of the room, and there is little to gain. If there is a problem, the best fix is more insulation. If you look around on "bulk pickup" trash day, people will throw away cubic meters of fiberglass sometimes. As long as it's not gotten wet, it's great stuff!

    Cooling the attic has one primary benefit, and that's that the roofing material will last substantially longer.

    Solar-powered roof fans do not provide much ventilation, and certainly not enough to justify their high cost.

    What DOES work is gable vents (which you should already have) and apex vents- which are kind of a new thing and you may not have. Those are the vent all along the very peak of the roof. The type of convection those create with the gable vents is very impressive and is very effective at cooling the heated plywood roof decking. Apex vents are not very expensive, and not that hard to install, but unlikely to be worth it on an old roof. When actually replacing a roof, by all means, build in apex vents.

    Roof PAINT will probably degrade the shingles in the long run, save nothing in power, and the paint alone will cost a bundle.
     
    Last edited: Jan 2, 2010
  10. Oznog

    Oznog Active Member

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    I ran some calcs on that before. It is unlikely to work on an condenser not designed for it. Long story... but no, it probably won't have much benefit, and the amount of water required to be effective is quite significant, and creates a significant legionella hazard. More of a problem, it may damage the condenser with minerals or algae growth.
     
    Last edited: Jan 2, 2010
  11. arizonaguide

    arizonaguide New Member

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    Yes, after pricing the solar roof vents I quickly decided that was crazy! $300-500 is rediculous!!!

    And pricing the roof coating was a bit of a shock also. I wonder if some "colored primer" like KILZ would be just as good? I know I've heard that the color shouldn't matter, (and that Black is no different than white) but I know for a fact that I can walk up on a hot summer day and my white car is cool to the touch, and anything dark is very hot. The roof shingles get so hot that you could fry an egg on them, and yet the white siding right next to them are (relatively)cool to the touch. There HAS to be an inexpensive way to coat these.

    The Roof is a HIP roof, so there are no gable ends to put a low-level vent. I could place a vent low on the hip (as shown in BLUE) or more eve vents (also shown in BLUE). I already have 2 normal (unpowered) PEAK vents (RED) that get turned in the breeze...but I believe that a "powered" vent would really help...when combined with more eve ventilation, and a light color on the shingles. The attic heats to 170degF, and thus the insulation heats up also all the way down to the ceiling...and that HAS to result in increased A/C load!

    [​IMG]
     
    Last edited: Jan 3, 2010
  12. magickaldan

    magickaldan New Member

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    It's a tried and true method, just requires some more maintenance. Really depends on the humidity of your surrounding air to be effective and quality of your water supply. You want to do it in 60% or less humidity the lower the better. If done correctly no water should be pooling on the ground, it should all evaporate, for one you have a massive amount of heat going through those coils on a 100+F Day way more than the Fan can cool adequately by itself. And coils get dirty all the time nothing a good cleaning can't fix and in my opinion coils should be cleaned at least once every cooling season to get rid of the dirt. And Ideally you would want a Certified HVAC technician to install it, for one you really need a head pressure switch and a electronic water valve that will turn on automatically after the pressure reaches a certain level, and shut the water off when it reaches normal pressures.
     
    Last edited: Jan 3, 2010
  13. magickaldan

    magickaldan New Member

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    Check this website out it has some great info on Attic Vents and how many you should have etc. Attic Ventilation | Balancing Attic Air Circulation | Roof Vents
    Click Here
     
  14. arizonaguide

    arizonaguide New Member

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    GREAT LINK! Thanks, MKaldan :) Yup! It's gotta be done this spring. I can't go through another summer with a 170deg attic!
    Now, to figure out how to coat the shingles with some type of decent "light color/reflective coating" without spending thousands.
     
    Last edited: Jan 3, 2010
  15. summitville

    summitville Member

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    Three things that I have on my Hip Roofs are:
    1) Ridge Vents
    2) Rafter Vents
    3) Vented Eaves

    Ridge Vents run 90% of the length of each & every Ridge.
    Ridge Vents allow the hottest air to exit directly out of the attic at the ridge of the roof.
    This then pulls in cooler air via the the Rafter Vents.
    Rafter Vents allow you to insulate the entire attic floor all the way to the eave but still allow cool air to enter from the eave.
    Installing Rafter Vents : ENERGY STAR

    I am maintaining a 60 Degree temperature differential (10 outside vs. 72 inside) at half your cost.
    You are maintaining a 30 Degree temp differential (75 inside vs. 105 outside) at twice my cost.
    I realize that cooling is more difficult than heating but not that much since it also gets to 95 here.

    If you can't do a vertical well for geothermal then I would consider Horizontal Coils - Get a quote.
    Especially, if you have a friend that can dig the trenches for you.

    Also, look for these thin breathable lightweight aluminized panels that you lay over your attic insulation.
    It will reflect 90% of the radiant heat energy from your roof back towards the roof and away for your insulation.
    Do NOT pay to have installed - DIY.

    1) Insulating your attic floor to the eaves and adding Rafter Vents.
    2) Adding refelective aluminized panels
    3) Adding Ridge Vents (or Wind Powered Roof Vents)
    4) Conversion to geothermal (with free hot water)
    5) All Windows Double Pane, Argon Filled, Low E & UV Block (Federal Tax Credits?)

    Also, I read some where that there is a White "Rubberized" Paint that you apply with a paint roller to your roof shingles to significantly reduce the absorbed radiant heat energy.

    Doing all this could cut your energy bills in half for a savings of $1,800 per year?
    That seems very reasonable compared to a $6,000 Solar Panel that will only save you $300 per year.
     
  16. arizonaguide

    arizonaguide New Member

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    Wow! Another GREAT link! Those rafter vents may be the solution to my vent problem.
    I will also look into that reflective aluminum. That may be cheaper than the outside reflective coating.
    Thanks, Summitville. You seem to have done a lot of the same research.
    GOOD stuff!
     
  17. Oznog

    Oznog Active Member

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    Note that any attempt to ventilate the attic will actually reduce the energy efficiency in winter. However, attic insulation will improve efficiency in both summer and winter.

    Again, insulation is the primary strategy for efficiency. Roof ventilation- cooling the attic- is the primary strategy for improving the life of the roofing material. The efficiency gains of improving ventilation are very limited unless you have poor attic insulation- in which case the cheapest and most effective solution is simply to add insulation.

    Once your attic has like R-30 batts, very little of your cooling OR heating is wasted through heat seepage from the attic and another 10F, 20F cooler attic isn't gonna change anything (and if anything, makes it worse in the winter). In short this is a waste of time and money. The vast majority of your heat is gonna be through walls and especially windows and air infiltration around windows and doors and losses in the ducts.

    Also note that AC systems can be radically more efficient nowadays. They can go as high as SEER-21! If your AC was made in the 80's, then it's probably got a SEER of about 8. IF it's working up to spec, which it's probably not. By replacing an old AC system with the best-of-the-best, and the system's engineered by a real pro, you can literally get the same cooling on 1/4 the electricity. That's the lion's share of savings right there. But most "good" systems installed now are like SEER 13 or 14. Which will probably only cut the cost in half... oh darn. ONLY half?

    Also ductwork can lose a lot of your heat/cold as well. In the 80's and 90's they used a "flex duct" which had plastic on the inside, a supporting spring, fiberglass insulation, and a plastic moisture barrier on the outside. Well, the plastic was totally defective and distintegrates all on its own. The fiberglass, carrying very cold air, can collect moisture which turns the R-value to crap. Only costs like $50 or so to buy a new duct with a metallized radiant-barrier exterior, which won't decay and the reflective metallization radiant-barrier is VERY effective at reflecting attic heat and avoiding radiating out duct heat.

    It's worth looking up the difference between convection heat conduction and infra-red radiation. In a hot attic- or out of a hot duct- the radiation is very significant, but not many are familiar with how IR radiation works.
     
    Last edited: Jan 3, 2010
  18. Oznog

    Oznog Active Member

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    You can't just hose off limescale deposits from misting, unfortunately. It's hard and insoluble and only a light amount is needed to reduce the cooling fin efficiency. Mist does not result in "distilled" water, all the minerals are conveyed in the droplets and generally deposit out when converted from droplets to vapor. Very little will manifest as a deposit on the misting head. Droplets are millions of molecules held together with surface tension which will contain all the minerals present in the tap water, vapor is always single molecules of H2O suspended in air. Vapor cannot hold any calcium or iron or whatever's in the water, calcium and iron is insoluble in air. So wherever it converts from mist to vapor is where the cooling happens and also where the minerals get left. That'll probably be around the fan and condenser, and only at the misting nozzle to a lesser extent.

    A gallon of H2O provides about 8700 BTU of cooling when it evaporates. A 2000sq ft house rejects about 48000BTU. But the problem here is that a properly functioning condenser will already cool the return line to close to ambient. Now if you had ONE condenser which cools the coolant down to near-ambient, blowing all 48000BTU out right there, then a second evaporatively cooled condenser which gets it slightly cooler than ambient, little water is required and the gains are significant and you don't need that much water.

    However, in attempting to cool a single properly working condenser with mist, you'll need enough mist to cool not only absorb all 48000BTU but get it cooler than ambient. Because it was ALREADY getting it near ambient without your help. That requires a lot of water. Unfortunately, water is often quite expensive in many places which are very hot. So don't dismiss the cost of H2O, it'll actually rapidly overwhelm the gains in electrical usage in my calcs.
     
    Last edited: Jan 3, 2010
  19. arizonaguide

    arizonaguide New Member

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    Now there's some serious food for thought. You are right about venting possibly loosing efficiency in the winter, and I am counting on the difference being whether or not I turn on the powered attic vent fan. My strategy will be to turn the fan on for 1hr each day (timer) immediatly after sunset to at least help cool it down for nighttime, and pre-cool the insulation saturation for the next day's use. Part of the problem is that we try to also use a small area the attic for storage, and I don't like it cranking to 170deg! So, reflecting as much away as I can with a roof coating, then ventilating the air better, should bring it closer to ambient.

    The walls ARE poorly insulated here (1960's Arizona construction), but I don't have a practical solution for that.
     
    Last edited: Jan 4, 2010
  20. Mr RB

    Mr RB Well-Known Member

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    What about spraying water on the roof tiles themselves? Some cheap garden sprinkler systems and a small electric pump. And a large rainwater tank to recycle any runoff.
     
  21. smanches

    smanches New Member

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    Vent the attic well. You can always plug up vents for the winter. The problem is that the attic will hold that heat all night long, and it WILL leak into the house. I live in Oregon and have this same problem during the summer months, so I can't imagine the issue you have. Foot and a half of blown in fiberglass in the attic, but that attic would keep the AC running until at least midnight on hot days before I ventilated it better.
     

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