AC Evaporative Cooling - Page 2

GaryGary · 09-09-12, 09:01 AM

Hi,
Here is another approach that is closely related to your approach for helping out your AC from Chad. I just put it up on BIS this morning: Increasing AC Efficiency Using Evaporative Cooling of Condenser Coil

Also got an email from a person whose AC unit was sitting in the sun. After some experimentation with various kinds of shading devices he settled on taking sheet of plywood, and cutting a circular hole that matches the diameter of the fan discharge. He just places the plywood over the AC outside unit with some supports -- it shades the unit from direct sun. No doubt, not as effective as the water cooling, but probably helps a bit and is very simple.

I was kind of surprised at the mineral levels for rain water -- it picks these minerals up from the air on the way down? Or?

Gary

Homeless · 07-13-13, 03:12 PM

So what were the results on this ? Does it work ?

I read the posts rather hastily, so i might have skipped over something.

I live in an apartment, so i am never on this site, but my job has these huge industrial A/C units on the roof that i thought might be a good candidate to have some system like this.

Rather than create an entirely new post, i thought i would ask here if this sort of thing works. I have an A/C repair friend that guesses that they do not work, but im not so sure he has tried them before.

He states that you would spend more on the water than you would save from having the A/C misted.

Thanks guys !

warmwxrules · 07-13-13, 04:25 PM

My window AC unit uses the water that collects in it to increase the efficiency or so that is how i understand...during very humid weather you can feel the spray come out of it outside (from the fan)... There are no drip holes in these so a lot of water builds up in them...it also starts to stink after a few days (outside)...

A place i worked at (very large) at one point was using hoses to cool their ac units outside. I remember them using a lot of water. Never found out how effective it was...i'm pretty sure they ended up replacing those units (this was years ago). The problem with that place was they were located in direct sunlight all day (no shade) surrounded by black top and brick walls..horrible spot for AC...

jeff5may · 07-14-13, 12:00 PM

Ben,

This approach has been tested to death by the HVAC industry and works like magic. The best approach is to fill the entire bottom pan of the condenser unit with your evaporator condensate. The unit should be level and the water is just gravity fed from the drain line. At pan overflow, the bottom coil of your condenser should be submerged in water. This way, you have sufficient thermal mass in the water to subcool your liquid leaving the condenser to a temp close to indoor temperature. No moving parts, no sweating liquid line, you get good dT in the top of the condenser, and design airflow out of your outdoor unit. Typical savings are 5 to 10 percent (more savings the hotter it is outside).

Window air conditioners take this approach a step further by slinging the condensate with the outdoor fan when the drain pan is close to full. Well- designed units do not weep any overflow when outdoor temps are high and dry. With your unit, a thin swamp cooler pad wrapped around a portion of the bottom of the unit would help the water to maintain more intimate contact with the condenser coil.

Simply spraying mist onto the coil does not allow the water to linger long enough to absorb as much heat as it can. The mist briefly passes through the condenser and is exhausted without completely evaporating. What you want ideally is for the hot runs (multiple flow paths from compressor side) to see raw outdoor air at max velocity. This keeps your unit in its design range for head pressure, very important if you are running a cap-tube evaporator. Once the hot runs merge, the hot refrigerant is "tempered" and somewhat condensed. This is where the cool water can do its best. Liquid-to liquid contact doesn't take very much dT to move massive heat compared to air-source (dx) coils. What happens when the condensing "foam/fog" hits the water-cooled zone? the mixture is immediately condensed, essentially "sucking" the head pressure downwards. In window units, the subcooled section is snaked back up the coil face on the intake side. The liquid reboils somewhat, cooling the air stream through the condenser upstream from the hot coils. Back down at the bottom (on its way out), the liquid is again subcooled by the pan water before it leaves the condenser.

Recycling your condensate water captures and reuses the latent heat you have removed from indoors to cool your hot outdoor unit, sort of a double-whammy. Also, you will have no need for a water supply or elaborate plumbing. If you want to evap cool, run a solar or mag-drive fountain pump that draws water from your drain pan. You could even power the pump with a little battery-powered fan rigged up as a generator where your flow control is situated now. Drip or spray onto pad (which ultimately should touch your dx coil to allow water to wick in between the fins) when the pan has ample water to submerge bottom of coil. Pump will not prime until there is sufficient water in pan, thus maintaining self-regulation.

MN Renovator · 07-14-13, 12:56 PM

"Window air conditioners take this approach a step further by slinging the condensate when the drain pan is close to full. Well- designed units do not weep any overflow when outdoor temps are high and dry. With your unit, a thin swamp cooler pad wrapped around a portion of the bottom of the unit would help the water to maintain more intimate contact with the condenser coil. Simply spraying mist onto the coil does not allow the water to linger long enough to absorb as much heat as it can. The mist briefly passes through the condenser and is exhausted without completely evaporating."

I'm not trying to derail the thread or anything but I noticed that my window AC has the copper line sitting in the pan water and it has plenty of green oxidization on it. I'm assuming that since it is copper and the water is essentially distilled since its condensate that it should be safe. Is that true?

jeff5may · 07-14-13, 01:13 PM

MN,

This is true. The copper develops a patina that protects the underlying base metal. This copper oxide actually helps heat transfer as well. Aluminum and stainless steel do the same thing, forming a haze to protect themselves from the elements.

Servicetech · 11-09-13, 08:51 AM

Quote:

Originally Posted by MN Renovator

I asked a local HVAC guy about the water mist systems and he said he thought it would corrode the coils to have water sprayed on them. Then he suggested I feel the temperature coming out of a supply register after the a/c was running for awhile. Then spray the condenser down with water and go back inside and feel the air again. I did that, the air was coming out noticeably warmer. I'm not sure why and it doesn't make sense to me. I searched some Youtube videos of those misting systems and the comments from those in the HVAC industry seemed to imply that they were a bad idea for the corrosion aspects as well as if you get the condenser too cold you could freeze up the evaporator and which would cause the refrigerant to slug the compressor.

I originally thought the idea was more about spraying colder underground temperature water that was below ambient air temp on them more than the evaporative cooling idea.

I'm not trying to discourage you, just unsure about the whole idea myself. I thought of trying it since my A/C is 26 years old, 8.5 SEER, and has a small condenser coil so I might see a bigger improvement and the risk is less since its might need replacement soon anyway. ..but that decision is hard because my upcoming electric bill will be about 300kwh($45) and I don't keep the house that cool anyway, even with the record outdoor temps we've had here.

With fixed orfice systems the head pressure loss with cause warmer tempatures at the vent. On a TXV system the vent tempatures will drop with a cooler condenser.

Servicetech · 11-09-13, 09:06 AM

Freus has already done most of the work on a larger basis. System does get great efficiency but isn't without it's issues. Homewoners don't want to maintain them or pay to have them maintained is the biggest issue. Water cooled condensers are more common in commercial enviroments where the energy savings are larger and they have the staff to maintain them.

07-14-13, 12:00 PM	#14
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Ben, This approach has been tested to death by the HVAC industry and works like magic. The best approach is to fill the entire bottom pan of the condenser unit with your evaporator condensate. The unit should be level and the water is just gravity fed from the drain line. At pan overflow, the bottom coil of your condenser should be submerged in water. This way, you have sufficient thermal mass in the water to subcool your liquid leaving the condenser to a temp close to indoor temperature. No moving parts, no sweating liquid line, you get good dT in the top of the condenser, and design airflow out of your outdoor unit. Typical savings are 5 to 10 percent (more savings the hotter it is outside). Window air conditioners take this approach a step further by slinging the condensate with the outdoor fan when the drain pan is close to full. Well- designed units do not weep any overflow when outdoor temps are high and dry. With your unit, a thin swamp cooler pad wrapped around a portion of the bottom of the unit would help the water to maintain more intimate contact with the condenser coil. Simply spraying mist onto the coil does not allow the water to linger long enough to absorb as much heat as it can. The mist briefly passes through the condenser and is exhausted without completely evaporating. What you want ideally is for the hot runs (multiple flow paths from compressor side) to see raw outdoor air at max velocity. This keeps your unit in its design range for head pressure, very important if you are running a cap-tube evaporator. Once the hot runs merge, the hot refrigerant is "tempered" and somewhat condensed. This is where the cool water can do its best. Liquid-to liquid contact doesn't take very much dT to move massive heat compared to air-source (dx) coils. What happens when the condensing "foam/fog" hits the water-cooled zone? the mixture is immediately condensed, essentially "sucking" the head pressure downwards. In window units, the subcooled section is snaked back up the coil face on the intake side. The liquid reboils somewhat, cooling the air stream through the condenser upstream from the hot coils. Back down at the bottom (on its way out), the liquid is again subcooled by the pan water before it leaves the condenser. Recycling your condensate water captures and reuses the latent heat you have removed from indoors to cool your hot outdoor unit, sort of a double-whammy. Also, you will have no need for a water supply or elaborate plumbing. If you want to evap cool, run a solar or mag-drive fountain pump that draws water from your drain pan. You could even power the pump with a little battery-powered fan rigged up as a generator where your flow control is situated now. Drip or spray onto pad (which ultimately should touch your dx coil to allow water to wick in between the fins) when the pan has ample water to submerge bottom of coil. Pump will not prime until there is sufficient water in pan, thus maintaining self-regulation. Last edited by jeff5may; 07-14-13 at 02:42 PM.. Reason: more details

09-09-12, 09:01 AM	#11
GaryGary Apprentice EcoRenovator Join Date: Nov 2008 Location: SW Montana Posts: 139 Thanks: 1 Thanked 21 Times in 15 Posts	Hi, Here is another approach that is closely related to your approach for helping out your AC from Chad. I just put it up on BIS this morning: Increasing AC Efficiency Using Evaporative Cooling of Condenser Coil Also got an email from a person whose AC unit was sitting in the sun. After some experimentation with various kinds of shading devices he settled on taking sheet of plywood, and cutting a circular hole that matches the diameter of the fan discharge. He just places the plywood over the AC outside unit with some supports -- it shades the unit from direct sun. No doubt, not as effective as the water cooling, but probably helps a bit and is very simple. I was kind of surprised at the mineral levels for rain water -- it picks these minerals up from the air on the way down? Or? Gary

07-13-13, 03:12 PM	#12
Homeless Helper EcoRenovator Join Date: Mar 2009 Location: Austin, Texas Posts: 42 Thanks: 2 Thanked 0 Times in 0 Posts	So what were the results on this ? Does it work ? I read the posts rather hastily, so i might have skipped over something. I live in an apartment, so i am never on this site, but my job has these huge industrial A/C units on the roof that i thought might be a good candidate to have some system like this. Rather than create an entirely new post, i thought i would ask here if this sort of thing works. I have an A/C repair friend that guesses that they do not work, but im not so sure he has tried them before. He states that you would spend more on the water than you would save from having the A/C misted. Thanks guys !

07-13-13, 04:25 PM	#13
warmwxrules Helper EcoRenovator Join Date: Nov 2011 Location: La Crosse, WI Posts: 78 Thanks: 0 Thanked 3 Times in 3 Posts	My window AC unit uses the water that collects in it to increase the efficiency or so that is how i understand...during very humid weather you can feel the spray come out of it outside (from the fan)... There are no drip holes in these so a lot of water builds up in them...it also starts to stink after a few days (outside)... A place i worked at (very large) at one point was using hoses to cool their ac units outside. I remember them using a lot of water. Never found out how effective it was...i'm pretty sure they ended up replacing those units (this was years ago). The problem with that place was they were located in direct sunlight all day (no shade) surrounded by black top and brick walls..horrible spot for AC...

07-14-13, 12:56 PM	#15
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	"Window air conditioners take this approach a step further by slinging the condensate when the drain pan is close to full. Well- designed units do not weep any overflow when outdoor temps are high and dry. With your unit, a thin swamp cooler pad wrapped around a portion of the bottom of the unit would help the water to maintain more intimate contact with the condenser coil. Simply spraying mist onto the coil does not allow the water to linger long enough to absorb as much heat as it can. The mist briefly passes through the condenser and is exhausted without completely evaporating." I'm not trying to derail the thread or anything but I noticed that my window AC has the copper line sitting in the pan water and it has plenty of green oxidization on it. I'm assuming that since it is copper and the water is essentially distilled since its condensate that it should be safe. Is that true?

07-14-13, 01:13 PM	#16
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	MN, This is true. The copper develops a patina that protects the underlying base metal. This copper oxide actually helps heat transfer as well. Aluminum and stainless steel do the same thing, forming a haze to protect themselves from the elements.

11-09-13, 09:06 AM	#18
Servicetech Apprentice EcoRenovator Join Date: Nov 2013 Location: Moore Oklahoma Posts: 267 Thanks: 108 Thanked 23 Times in 21 Posts	Freus has already done most of the work on a larger basis. System does get great efficiency but isn't without it's issues. Homewoners don't want to maintain them or pay to have them maintained is the biggest issue. Water cooled condensers are more common in commercial enviroments where the energy savings are larger and they have the staff to maintain them.