coldest ac

Discussion in 'Health & Life Counseling' started by hat, May 29, 2015.

  1. hat

    hat New Member

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    I had a norpole 12000 btu unit until recently. It worked alright, but it could have been code colder. I got an LG 12k btu unit to replace it, thinking it would be comparable but it didn't quite cut it. Then I took it back for an 8000 btu after some reading about oversized air conditioners not reducing the humidity enough because the compressor doesn't run enough to bring it down... But it feels the same.

    Bottom line is I need the ac of acs, an unholy contraption cold enough to freeze out old man winter himself. It has to be a window unit that will fit in a window that opens 16.5 inches tall and 26 wide.
     
  2. FordGT90Concept

    FordGT90Concept Well-Known Member

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    /me is not an expert.

    12000 BTU is going to be about the limit for that amount of space.

    My Googling turned up with an RCA unit but I have no idea if it will perform better than the two you already tried.


    To be perfectly honest, central air is the way to go. Not cold enough? Put in a bigger AC unit. Probably not an option in your case. My the feels be with you.
     
  3. jmcslob

    jmcslob Well-Known Member

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    Not sure if this helps but I'll suggest it anyways...
    I put a dehumidifier in the basement and a box fan on the 3rd floor as an exhaust fan and a 5000btu on the first and second floors and that works fantastic.

    The key to everything is the dehumidifier...the A.C. Cools dryer air way more effectively and in return you need less A.C..
     
  4. FordGT90Concept

    FordGT90Concept Well-Known Member

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    We have one dehumidifier running 24/7 from spring to fall here. We add a second in the summer. The air conditioner is capable of some dehumidifying but I don't know how much it does. Probably less because it isn't running 24/7 like the dehumidifiers.

    Granted, colder air is incapable of carrying as much moisture so reducing temperature also reduces maximum humidity.
     
    Last edited: May 29, 2015
  5. m4gicfour

    m4gicfour Well-Known Member

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    That's not really how it works.

    http://home.howstuffworks.com/dehumidifier1.htm

    If you want to cool your air, you're likely better off with more AC units. The dehumidifier is wasting energy reheating your air.

    Think of it like this: You've got two heatsinks and a TEC or phase change cooler between them. The dehumidifier pulls the air in across the cold heatsink, which causes the air to cool and lose moisture (condensation). Then the dehumidifier blows that cool air across the hot heatsink to keep itself within operating temperature and also to return the air back to room temp. It's basically like running an AC unit completely indoors, with the hot air staying in the house. (yes, I know there are absorbative dehumidifiers that use dessicants but AFAIK they're uncommon - and you have to heat the dessicant to get the water back out of them once they're saturated, which puts the moisture back in your air)

    The dehumidifier likely has less losses because it's using the same air on hot and cold side (higher delta T - aka difference in temp - makes transferring heat to and from air more efficient. An AC unit seperates the airflow into two loops - indoor and outdoor air; the air passing over the hot coils outside is already hot and the air passing over the cool coils inside is already cool[er], therefore it takes more energy per unit of heat transferred from cold to hot side.) but if your goal is for the air inside to end up colder, well...

    An AC unit dehumidifies in exactly the same manner as a dehumidifier does; by cooling the air. The system is optimized for heat transfer as opposed to collection of water, though so... yeah IDK really what the exact most efficient configuration would be. Likely if you had a specialized AC unit that would switch between cooling (high energy use per heat transfer, inefficient use of hot air on hot coils and cooler air on cool coils in attempt to draw heat out of the cool air) and dehumidifying (cold air passed over hot coils and returned to room, lower energy use per heat transfer - and therefore per moisture removed - but no drop in overall air temp) based on the air temp and relative humidity you could get the best of both worlds but there's so many factors involved it's hard to say, really.

    Especially since I'm not an HVAC engineer.


    EDIT - I figured I'd throw this in here, as it's directly relevant:
    Basically, the reason having your air dehumidified seems to work isn't because the AC works better, but because it FEELS cooler with lower humidity; according to them a dehumidifier uses around half the energy of an "average" AC unit, but since you have to use both to make the dehumidifier have any benefit, it's really going to be a balancing act.
     
    Last edited: May 29, 2015
  6. Magibeg

    Magibeg Active Member

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    I feel this thread needs some science!!

    Realistically your AC is going to pull moisture from the air anyway so I'm not going to get into the humidifier discussion here. Instead I'm going to talk about why it sounds like you'll never have an AC unit to suite your needs, it's all about power.

    Even though the units say they are both 12,000BTU units, it is complete lies. Assuming you are plugging the units into a regular wall socket and somehow you obtain 100% energy efficiency you can only pull 1800 watts from a 15amp outlet at 120v. Unfortunately 12,000 BTU is slightly over 3500 watts of power, so it would trip the breaker. Even if you had a 20amp socket you're still only good for 2400 watts or 8189 BTU's. And that is full on maxing the circuit with nothing else connected to it for a sustained amount of time.

    Instead of hunting for a more powerful AC unit you should be trying to figure out ways of preventing heat from getting in to begin with.
     
  7. Peter1986c

    Peter1986c Artist formerly known as Chevalr1c

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    Yep. Insulation, keeping windows on the sunny side closed, etc.
     
  8. FordGT90Concept

    FordGT90Concept Well-Known Member

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    Or specify which kind of outlet is powering it. 220v should net more cooling capacity.

    But yeah, insulation is vital, especially windows. If your windows aren't double or triple paned, start saving up to replace them. They'll save you a lot of money.
     
    Last edited: May 30, 2015
  9. m4gicfour

    m4gicfour Well-Known Member

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    AH! Refreshing Science!
    [​IMG]

    Except that you're not actually converting electricity into heat energy (molecular vibration, if I remember my highschool physics). Those watts are spent running the compressor (electrical into mechanical energy); whatever portion of those ~1800w available is being used is all spent compressing the refrigerant through the condenser (well, that, a control circuit, and a couple fans). Heat is absorbed when the compressed refrigerant is allowed to expand in the evaporator and then released as the refrigerant is forced to condense into a liquid in the condenser by the compressor. The heat transfer from the cold to hot side is being done by the intrinsic qualities of the refrigerant and the laws of physics, heat is not being converted to or from electricity - only transported (again, with exception of a certain amount of electricity wasted as additional heat due to inefficiencies in the electrical components and friction).

    It could plausibly transfer 12K BTU. You'd be correct if you were talking about an electric heater, where the electricity is being converted directly into heat via resistance. I will, however, be the first to admit that my own understanding of the principles involved is - shall we say, incomplete?

    A phase change system like an AC unit is just a type of heat pump. Wikipedia states
    http://en.wikipedia.org/wiki/Heat_pump

    Agreed 100% with the rest of what you're saying, though any actual structural modifications will almost always have a higher up-front cost, the payoff is in increased perceived performance and long-term energy savings.
     
    Last edited: May 30, 2015
  10. Magibeg

    Magibeg Active Member

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    Thank you very much for the correction!
     
  11. hat

    hat New Member

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    Well, I don't have a 220v outlet. Not much way for heat to be getting in... hardly any windows. I live in an apartment that basically looks like a large one story house. The part I live in was added on later, not part of the original structure. There's only 2 windows, one in the kitchen which is sealed, and one in the living room which the air is in. This is all one big open area in the front of the apartment. I'm mostly concerned with keeping the living room cool.
     
  12. hat

    hat New Member

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    One thing potentially killing me is the fact that the air sits on the sunny side of the place. I'm sure it doesn't run as well as it could with the sun staring at it all day. Not sure how to solve this problem, though.
     
  13. m4gicfour

    m4gicfour Well-Known Member

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    You're welcome. Please do me the same courtesy if our positions should ever be switched.

    Thanks for making a comment I had to go doublecheck my facts on before replying. It's nice to have to think a bit :p


    If you can build some kind of awning that would shade the AC unit (taking care not to starve it of air or come in contact with the unit itself) you *might* get a bit better performance out of it, if it's normally in direct sunlight. It's hard to say. The hotter the exhaust coils are, the less effective the system will be and direct sunlight will definitely impart some heat but the casing of the AC unit itself might shield it enough, I just don't know.

    Without knowing how the place was built, it's tough to say where to start; if you don't own your home you may not be able to do much anyway. The walls may not be insulated well (quantity) or they may not have been insulated properly (quality), old or low-quality windows and doors let through a disgusting amount of heat in both directions. You might not have sufficient insulation in the attic-space or any crawlspaces, even just the color of the exterior can make a decent difference on how much heat the home absorbs (Dark colors absorb sunlight, lighter colors reflect more of it - white being best for summer). There's not a whole lot you can do about any of those without investing serious cash, and either having the landlord's permission or owning it yourself.

    For something you *could* do, but with unfortunately lesser results (though depending how badly the place is leaking or not right now, could still be substantial):

    Look for drafts (air leaks) around exterior doors and windows and plug them. Easiest and most effective way is to pry the casing around the interior side of the leaky door or window off and fill the gap between the window jamb and the rough framing of the wall with a window and door foam like THIS stuff.
    [​IMG]

    See the gap between the window itself and the rough studs?
    [​IMG]
    This is normally filled (usually poorly) with scraps of fibreglass insulation in older houses and sometimes is filled with *nothing*.

    Follow the directions and don't overfill the cavity as it expands significantly for an hour or so after applied. Try not to get it on *anything* you don't want it to be permanent on, trust me it's a bastard to clean up. Give it a day and night and then cut excess off with a sharp utility knife (cured foam cuts fairly easily but that knife does need to be deadly sharp or it will want to tear), then replace the casings with a brad nailer. Should be able to get one from any rental place that rents tools if you don't own or have access to one. There are pneumatic (compressed air-operated) or battery powered units out there. The battery powered units are nice because you don't need an air compressor but they're MUCH heavier as it uses a flywheel mechanism to get enough force to drive the nail.

    If your doors or windows don't seal properly, replace the weather stripping or adjust hinges as required. Next would be to cover any window that gets sun with tin-foil or other reflective material, then use something like THIS to trap air in the windowframe and seperate it from the room circulation air as a kind of poor-man's insulation (it's meant for winter but it works in summer too, though you won't be able to open the window until you take it back off - think of it like shrink-wrapping the window). Better would be to replace old windows with new high efficiency ones but that's expensive and downright impossible if you don't own the home.

    Also make sure that there's no air leakage around that AC unit in the window. If it's one of those jobs with the accordian-like plastic thing that expands sideways to plug the window hole, you might try putting your hand by or on that and seeing if it feels warm/hot during the hot part of the day. If so, you could buy some rigid foam insulation (something like this and use it to block that space instead. If you have really crappy windows you could also cut a square that fits tightly in the inside of the jamb to block out some more heat. The 3/4" or 1" thick stuff would be plenty (and far better than those accordion deals) . They come in several different values and sizes (R-4, r-14, r-20 etc, 4'x8', 2'x8', etc.) The R-value is it's resistance to heat transfer and will be based on what specific type of foam it is and how thick the product is (for example, say; a 2x8' extruded polystyrene sheet, 3/4" thick with value of R-4). You should be able to buy in single sheets, some places might even let you take some scrap if you ask nicely.

    ....and it sounds silly, but if you've got a lawn to water, let the sprinkler hit the roof of your room (and exterior walls, if you're sure the weatherproofing is good). It'll give you a few degrees of relief on the hottest parts of the building while your sprinkler(s) run, but the building will heat back up quick so it's not a great strategy - and they say you shouldn't water your lawn during the hottest part of the day anyway, but maybe help cool the place down after the sun goes away to save a few bucks on AC?.

    I'm sure there's other things I haven't thought of to improve efficiency, but you're really fairly limited if you don't want or aren't able to do fairly major renovations.
     
  14. Steevo

    Steevo Well-Known Member

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    We stopped fiberglass packing the window gaps on new homes when we started wrapping the inside with tyvek, and instead used latex foam, it cleans up easier, and won't cause the windows to warp, and as well will NOT trap water or moisture. Fiberglass needs air pockets to keep the Tdelta, as the glass alone is a very poor insulator, especially when broken up during stuffing, and instead allows for water to condense and mold and mildew to grow. Latex foam wicks moisture from any area that it might pool into so that it has a much larger surface to evaporate from.
     
  15. m4gicfour

    m4gicfour Well-Known Member

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    (r) No shit. (r)

    Notice how I said "on older homes"? I said that part on purpose. :p

    All he's said is that the part he lives in was added on after. We have no idea when the place was built, for all we know there could be sawdust in the walls for insulation, or it could be paper-wrapped and lath'd with *nothing* in the walls but air for insulation if it's old enough. Even on brand new construction, it's downright criminal how much people get away with when they know the inspector's already been around. You always want the contractor that's going to work to his own high quality standards regardless, but somehow I doubt hat commisioned the structure himself.

    Fiberglass is what fiberglass is. I install the stuff for a living, I know all about its limitations and the reasons it's not used for that anymore. I wasn't advocating it's use, I was saying that's the shit that you're likely to find if you've got air leakage around windows and doors.

    As far as foams, I've used a good chunk of those professionally too since, you know, that's what's used for that purpose these days. The two relevant to the discussion at hand would be the Latex and Polyurethane (Window & Door formulations only).

    Latex foam is... a mixed bag. It's easy to install. It's easy to tool. It's easy to clean. It's also rediculously mechanically fragile which means it's not great if you've got any amount of expansion or movement in your building, which most older buildings do - and to be fair, a chunk of newer ones too. It's open-cell which means that it's water permeable so it's not a weather seal of any sort. "Wicks moisture" is another way of saying it absorbs it; it's basically a sponge. It's also usually water-based so if it sees any moisture before it's 1000000% cured, it washes away like nothing. That said, it's a still damn sight better than fibreglass packing. It's just not the best seal you can get - that whole "won't trap water" thing - if it's installed incorrectly and the weatherproofing is defective or compromised then it will still allow the moisture to get out through the inside of the wall - unlike a PU foam - which isn't neccessarily a good thing. The idea is to install the foam so that it completes the vapor barrier to the window without leaving any space at the exterior so water never has anywhere to *be* trapped even if the exterior waterproofing is compromised around the window. Latex is a poor vapor barrier, though from what I've seen of renovations, the latex around the windows is likely the least of his worries as far as vapor barrier goes.


    I can't say what the DOW Great Stuff W&D is formulated of beyond being a type of PU, as it's a proprietary blend and they don't list specifics. It's not your standard "low expansion" PU foam. I've seen "low expansion" PU push studs apart that had 6" spikes holding them. This stuff won't even come close to that. It's better than other brands' Window & Door PU foams I've used as well. It really really is low-pressure. Not quite as low as the latex stuff, but reasonable. It's stretchy when cured and won't crumble like latex. It's a good seal. It's got its downsides too, obviously; you've got to get the first bead right at the back (exterior) so there's no room for moisture to be trapped behind the building envelope but outside the foam seal as it's not water permeable (it's supposedly closed-cell) like most PU foams, then if you decide to fill the cavity right up, you've got to make sure each bead is right back against the previous one so there's no gaps - not that water should ever be able to get past your initial seal bead, but good practice. It also won't bulge or distort the jamb and sill unless you go full retard and try to fill a 6" deep cavity x 54" long window all at once (and even then usually not - what it will do is hold an already warped jamb in it's warped shape once it cures, and I've seen more windows than not come from the factory with warped jambs - especially the vinyl windows) - but if you filled the space right up then you'd have foam all over your walls anyway as it oozes out during curing expansion. It's good stuff, but it's not magic. Go figure.


    For a DIY'er, you may be right, latex might be the way to go. I'd still use a W&D PU myself.
     
    Last edited: Jun 2, 2015
  16. Steevo

    Steevo Well-Known Member

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    Damn you and your wurds n stuff. I hope Tim Hortons coffee burns you, and you choke on a kinder egg. :D

    I was tired.
     
  17. m4gicfour

    m4gicfour Well-Known Member

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    Yeah, I know, I'm bad for the textwall thing. It's not intentional; just that brevity is not my forte.

    You were tired, and I was being intentionally snarky (for the first sentence or two anyway). I mean, come on! This is GN! If we can't all be a little bit of a dick to amuse ourselves then why are any of us even here?


    What was this thread about again?
    [​IMG]
     

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