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  1. #27
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    Quote Originally Posted by penderway View Post
    If interested, here's a link to further information http://apps1.eere.energy.gov/buildin...rica/27630.pdf
    see page 4

    We can now return this thread to the original post
    We can just agree to disagree, maybe all duct systems do leak some, I agree with that, but my scenario was a duct system with no leaks, just because there probably are not any that don't leak, that does not negate my example. "We can now return this thread to the original post"
    __________________________________________________ _______________________
    Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  2. #28
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    Mechanicsville, Virginia
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    Quote Originally Posted by Mr Bill View Post
    We can just agree to disagree, maybe all duct systems do leak some, I agree with that, but my scenario was a duct system with no leaks, just because there probably are not any that don't leak, that does not negate my example. "We can now return this thread to the original post"
    Quote Originally Posted by Mr Bill View Post
    Close in just the bottom part of the condenser just were the coil is, and run an inside cold air duct to it, make sure you leave the top part open
    If only we could agree that running an inside cold air duct to the outside resembles a duck leak. I don't think this is possible, so I'll accept your offer to agree to disagree.
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  3. #29
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    Feb 2009
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    Tallahassee, FL
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    Since we are back on topic ....with a fixed metering device and high indoor load wouldn't lowering the head pressure that much actually lower delta t? And raise SH. Although evap sat temp would fall further below dew point.

    Seems counteractive to a point.

  4. #30
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    Aug 2004
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    North Richland Hills, Texas
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    Quote Originally Posted by Mr Bill View Post
    But I am right! your only going to return "inside" what you produce "inside" Did you read the whole thread?
    So where is the cold air for your proposed "cold air duct" coming from?
    Just from inside the house, not connected to the HVAC system?

    Either way, you will loose more than you could potentially gain.
    If more government is the answer, then it's a really stupid question.

  5. #31
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    Aug 2001
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    Quote Originally Posted by SBKold View Post
    Since we are back on topic ....with a fixed metering device and high indoor load wouldn't lowering the head pressure that much actually lower delta t? And raise SH. Although evap sat temp would fall further below dew point.

    Seems counteractive to a point.
    Certainly wouldn't want to lower head pressure to a point where it could cause problems, but i don't think there is any chance of that if the water is 55 or higher and the indoor load is normal. With normal evaporator pressures, Delta is determined by relative humidity so it shouldn't change much. The water on the outdoor coil would simulate cooler outdoor temperatures but exactly what OD temp I don't know, so it'd be hard to know what your target superheat is. That would be a problem if trying to troubleshoot the system.

    Cooling the condenser with water would cause the condenser to reject more heat and allow the evaporator to absorb more heat. The compression ratio would be reduced and lower the compressor amperage.

    If the minerals left behind from evaporation didn't destroy the condenser coil, misting would be a good idea.

    I think Glennac's suggestion of condensate water is worth looking into since it shouldn't crud up the coil. My condensate drains right next to my condenser so I'm gonna pipe it to my base pan. It may not do much, but I can't see it doing any harm.
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  6. #32
    Join Date
    Jul 2011
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    Nanaimo,BC, Canada!
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    I have seen many supermarkets use sprinklers on their condensers in hit weather to reduce head pressure. I can tell you first hand that while it may work in the short term, over the long term it destroys the condensers. I've seen 10 yr old 10 fan keeprite condensers with bare tubes due to damage from sprinklers. I cringe every time I see a sprinkler on a condenser.
    If your aim is to sell more equipment.... Go for it.. But your customers will not be too happy

    And for what it's worth... If you remove air from a building it must be made up, other wise you put the building into a negative pressure.. It's the whole principle behind make up air units in commercial kitchens.. 30 Cfm 300 Cfm 3000 Cfm doesn't matter.. If you exhaust it you must make it up... Hence the requirement for new houses requiring a means of making up the air exhausted via bathroom fans, and range hoods..

    That's my 2 cents..

  7. #33
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    Aug 2009
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    I'm pretty sure he was joking about ducting inside air to the condenser - perpetual motion machine and all - so I'll mostly ignore those comments. Now, some other comments made here I do think should be discussed:

    The lowering head pressure having a negative impact: This is about what has the greater impact. If dropping condenser head pressure by evaporative cooling is going to make cooling worse, then why is capacity on every equipment spec sheet higher when OSA is 70F than when it is 100F? Yes, lowering head pressure with a fixed orifice is going to have less impact than lowering head pressure on a fully metered system - but it is still going to move more BTU's for less kW's.

    The use of condensate: This would only work to an extent. If you are removing more moisture from the inside air than it takes to evaporate off that moisture in the outside coil, there is something seriously wrong with the envelope. That said, if you WERE to have an evaporative system, it would certainly make sense to dump indoor coil condensate to it's sump to reduce potable water usage.

    Wasting water to save electricity: I'm pretty sure if you looked into how much water is actually evaporated per ton of cooling, and compared that to how much water is used at your local power plant to generate the kW, you'll see that the magnitudes are WELL in the favor of evaporative cooling SAVING water.

    Lime deposits/scale: For starters, this is only a problem if the water is deposited and evaporated on the coil itself. If the water only ever comes in contact with surfaces designed for it (evaporative cooler pads, for instance), then this is a null point. Also, it greatly depends on the water quality. If the residence already has a water softener, and you put soft water to the system, it will have virtually NO effect. I have an evaporative cooler for my garage, supplied with softened water. It drains down periodically, automatically, and it never shows any signs of scale or deposits on the pads (and they are a few years old). Yes, soft water ends up costing more, because of water usage for regeneration, and salt costs, but it is FAR cheaper than the electrical load it would take to move those BTU's.

    The 'RIGHT' way to do it: An evaporative cooler, fed with soft water, to a condenser coil that does not get wetted, on a system with a TXV, will result in quite a bit of energy savings, for very little water usage. Unfortunately, most residential manufacturers do not publish performance numbers for various conditions - luckily, many water source manufacturers do, so I can use those for a reference point on the benefits of a colder condenser. For example, we can look at a WaterFurnace matched system (UB030). Their specs are done with an indoor EAT of 80db/67wb.

    Code:
    	Evap			Cond	Water	Water
    EWT	BTU/hr	kW	kW/ton	BTU/hr	(lb/hr)	(gal/hr)
    100F	33,300	2.33	0.839	41,250	42.5	5.10
    90F	34,800	2.16	0.745	42,170	43.5	5.22
    80F	36,200	1.98	0.656	42,956	44.3	5.32
    70F	37,700	1.82	0.579	43,910	45.3	5.44
    
    NOTES: 	Condenser BTU/hr calculated by Evap BTU/hr + kW (converted to BTU/hr)
    	Water usage assuming 100% evaporative cooling, 0% conductive cooling (worst case water usage)
    So, assuming a 100db/60wb outside temp, this 3 ton unit would have the following approx. operating costs:
    Code:
    		ElecUse	Elec$	WtrUse	Wtr$	Total$
    dry condenser:	2.33kW	$0.56	------	$0.00	$0.56
    evap condenser:	1.82kW	$0.44	5.44	$0.02	$0.46
    
    NOTES:	Elec Costs @ $0.24/kWh
    	Water Costs @ 0.004/gal
    CONCLUSION: Dropping condenser temp from 100F to 70F results in a savings of about 18% on an hour of operation and that hour of operation cools 13% more BTU. That sounds significant to me.

  8. #34
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    You should not spray water on to the coil, it should be sprayed, in the opposite direction to the air flow, to drop the air entering temp, and not localized cooling on the coil block (where droplets hits ,and TDS drops out and causes mineralization).
    On small compressors, the head pressure is driving force for power usage, and thus COP and cooling performance.
    But to drop your head to give greater capacity, then a new equilibrium has to be reach on the evaporator, which normally means a drop in SST (suction pressure). A refrig system is a circular system, so any change will change the rest of the system.

  9. #35
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    Quote Originally Posted by barbar View Post
    You should not spray water on to the coil, it should be sprayed, in the opposite direction to the air flow, to drop the air entering temp, and not localized cooling on the coil block (where droplets hits ,and TDS drops out and causes mineralization).
    Not only spraying away, as the amount of blowback will vary based on relative humidity of the incoming air - too much risk of non-evaporated droplets making it to the coil. This is why a physical media should be used to ensure moisture is not carried over the the coil (typical swamp cooler pads are effective in this purpose).
    Quote Originally Posted by barbar View Post
    On small compressors, the head pressure is driving force for power usage, and thus COP and cooling performance.
    But to drop your head to give greater capacity, then a new equilibrium has to be reach on the evaporator, which normally means a drop in SST (suction pressure). A refrig system is a circular system, so any change will change the rest of the system.
    This is why a fixed metering device limits the effectiveness of this approach.. However, with a decent enough system size and TXV, the system will be able to maximize efficiency through varied temperature ranges. Some could argue that it is easier to properly charge/tune a system if the condenser temp only varies 10-20 degrees, than an air cooled system which can vary by up to 50F.

  10. #36
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    Dec 2011
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    Quote Originally Posted by CraziFuzzy View Post
    Not only spraying away, as the amount of blowback will vary based on relative humidity of the incoming air - too much risk of non-evaporated droplets making it to the coil. This is why a physical media should be used to ensure moisture is not carried over the the coil (typical swamp cooler pads are effective in this purpose).
    This is why a fixed metering device limits the effectiveness of this approach.. However, with a decent enough system size and TXV, the system will be able to maximize efficiency through varied temperature ranges. Some could argue that it is easier to properly charge/tune a system if the condenser temp only varies 10-20 degrees, than an air cooled system which can vary by up to 50F.
    I agree some form of impingement device is best, as long as it has little effect on the air flow ( pressure drop of the medium), i use a very fine mist some 300mm (12inch) away from the coil (plus the velocity of the spray, so a envelope of mist around 500mm from the coil), there is very little blow back , but can not guarantee zero (but to date not seen a problem "touching wood as i am writing". Also the spray is only used when required.

    In NZ we are tight arses, so our head variants can be well above 50F. (no heat masters, and normally very basic control of cond fan, (with one fan normally non controlled)

    Just trying a new source of EEVs (liquid chillers normally), seem to handle the pressure difference across the range better. (was looking at the sporlan double port, but can not get them here)

  11. #37
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    Oct 2002
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    1,394
    Water treatment companies charge big bucks to keep minerals from plaquing condenser tubes and tower drift eliminators from large AC installations. There is a reason why it is a large, profitable industry.

  12. #38
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    Aug 2009
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    Maine
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    Usually water is on a meter also, and around here there is also a sewerage charge added in. Just my 2 cents,

    Quote Originally Posted by mark beiser View Post
    If you can come up with a system that will evaporate 100% of the water before it hits the condenser coil, it would be of benefit on very hot days.

    If the water mist is hitting the condenser coil, any energy savings you experience will be nullified by the need to replace the condenser coil, or whole outdoor unit, in a few years.

  13. #39
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    Quote Originally Posted by lytning View Post
    Usually water is on a meter also, and around here there is also a sewerage charge added in. Just my 2 cents,
    Yes, I guess if it would help that much with the efficiency and economy of the total system the mfg. would install a soaker hose option, with a fitting to attach the hose, and have a solenoid valve that operates off the contactor. I still think the best idea might be, to just run the liquid line inside the armaflex/rubberflex and tie it up tight against the suction line, from the condenser to the evaporator coil.
    __________________________________________________ _______________________
    Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

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