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Forums > General > Shooting the breeze... > Pre-cooling outdoor A/C unit?
Author Pre-cooling outdoor A/C unit?
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WA
145 Posts
Posted 27/1/2012, 9:43 pm        Report
Question for any A/C tech regarding pre-cooling outdoor A/C unit. I have 7.2 kW Panasonic Inverter split system and the recent heat wave in Perth got me thinking that I could use a simple evaporative cooler to cool down the outdoor unit. Did a quick search on the net and sure enough there are misting systems on the market that do just that. Most of them look like something I could cobble together by using some PVC lines and misting sprinklers from Bunnings. I also found some reviews on discussion forums that indicate that the water droplets will cause corrosion inside the head unit. Does anybody have any experience with this? Does pre-cooling make any difference? Will the mist / water droplets cause any damage? The A/C is less than year old so I would not want to damage it. Another option I thought of is to buy a small portable evap cooler (Big W sell them for $78) and let it blow cool air on the main unit. This shouldn't cause any dramas with water as it will blow only moist air but will this make any difference? Theoretically on a (very) hot dry day I should get temperature drop around 10 – 12 C assuming I'll get within 75% of Delta-T. But for 78 it sounds too good to be true... Thanks for any info...
WA
12443 Posts
Posted 27/1/2012, 10:42 pm        Report
Like water sprays onto a car intercooler? That works awesome with metho / water about 5:1 (not pure methanol cos it eats the rubber hoses) Just go do it.
WA
2293 Posts
Posted 27/1/2012, 11:59 pm        Report
gs12 said...
Thanks for any info...
Can I ask which side of the house did the outside unit go on and did you stick it against the wall or out from the wall? and how have you found your unit this last week... Changing homes and have evap now but want to get ac cheers
WA
366 Posts
Posted 28/1/2012, 8:54 am        Report
gs12 said...
I also found some reviews on discussion forums that indicate that the water droplets will cause corrosion inside the head unit.
Not sure how... the units are designed to live and run outdoors. (Saw your post on whirlpool as well - bit negative in the answers over there) Intrigued me as well... ours is a 17kw unit and anything to keep that beast using less energy is fine by me.
VIC
1682 Posts
Posted 28/1/2012, 12:11 pm        Report
Does the physics of it work? (did physics at uni but also drank a lot, thermodynamics lectures were at 9am so didn't make many) You pump moisture into the air which then vaporises (this cools the air). If you're running evaporative cooling, then this vapour then disappears off out of your house and subsequently condenses... (giving heat out in doing so). So if you put air with vapour into your air conditioner, then it will condense as it cools (which will heat the air up) This looks like the best option for cooling... and it is FREE http://www.newscientist.com/article/mg21328466.100-buildings-and-clothes-could-melt-to-save-energy.html
WA
3779 Posts
Posted 28/1/2012, 1:09 pm        Report
^^^^ Spraying water on the outside condenser coils will increase the amount of cooling that the aircon puts out for the same input power, but it will slowly corrode the fins and eventually rot them off. It will also coat them with the impurities out of the water so that the unit will become less efficient when you run it in dry mode. The fins on my aircon get a coating of salt on them so once every few years I run it flat out and spray water over the condenser for about 5 to 10 minutes to wash it off. It makes some super cold air in this mode. All the workings of the compressor unit and associated electronics are usually in a sealed side section and are not affected by the water spray. They have to be because the same unit run in reverse cycle (heating mode) has to be able to work flat out in the pouring rain. The fan motor will get wet but the bearings are sealed and should last for about 5 years. If you ran the air through an evaporative cooler before it got sucked through the outside unit, that should mostly eliminate the fin contamination and corrosion issues because the contaminants should stay behind on the evaporative filters. However, this wouldn't be as effective as running the water directly onto the fins as it introduces another heat transfer stage, and every stage is inefficient. When the water is run directly on the fins, the heat conduction from the evaporation process is directly onto the fins, which is where it is needed. Only a small flow of water is required for this, but it needs to be sufficient so that all the condenser unit is wet. You would probably need about 100 litres an hour to do this. All things considered, for the amount of trouble and expense it is to set up a something like this, it is probably not worth the mess and effort unless you really like fiddling with this sort of stuff. About 30 years ago we had one running for about 10 years with water running directly onto the fins and it worked very well. It was an old aircon which used to trip out on hot days when it was needed most so since we had irrigation water close by we ran a small feeder line onto the condenser. It eventually clagged up all the fins and probably corroded through the gas pipes because it eventually stopped cooling, but for the many years that it worked it was the ducks nuts. Since the aircon was considered on it's last legs anyway it was no great loss when it finally died, but I haven't put the same system on the new aircon.
WA
3779 Posts
Posted 28/1/2012, 1:23 pm        Report
ginger pom said...
Does the physics of it work? (did physics at uni but also drank a lot, thermodynamics lectures were at 9am so didn't make many) You pump moisture into the air which then vaporises (this cools the air). If you're running evaporative cooling, then this vapour then disappears off out of your house and subsequently condenses... (giving heat out in doing so). So if you put air with vapour into your air conditioner, then it will condense as it cools (which will heat the air up)
Yes the physics work, because the air with the vapour in it only passes over the outside condenser unit, not the inside evaporator unit, so the vapour is never condensed until it finally ends up in a cloud somewhere and rains on someone. If you also ran the same air over the inside unit it would do as you say and part of the advantage would be lost but most house aircons just recycle the inside air.
WA
145 Posts
Posted 28/1/2012, 1:27 pm        Report
Does the physics of it work?
It works on the same principle as evap cooler, you lower the temperature by evaporation, theoretically (depending on ambient temperature and humidity) up to 15C. This colder moist air then cools the coils. It's explained in detail here: http://www.coldmistcooling.com.au/item/66-air-conditioning-condensor-pre-cooling.html This page has a video showing residential application: http://www.cloudmister.com/p-148-ac-pre-cool-mist-system-residential-free-shipping.aspx I'm fairly certain the misting would work, as in lower the head end temperature and energy use too. I saw some posts on Whirlpool where people say they hose down the unit when it cuts out on a hot day. I tried that with a garden hose and misting nozzle (one off can't hurt it right?) and the unit runs quiter and it drops the output temperature by around 10 C. BUT I would be quite concerned about the water directly entering the unit on long term basis. I don't think the mist entirely evaporates before hitting the coils (rain doesn't worry me since it doesn't last long) and causing corrosion and mineral build up. So apart from my little test, I'm not going to do this to my 10 month old A/C. I might still get the little evap cooler from BIG W - there should be no water droplets in the air stream.
Can I ask which side of the house did the outside unit go on and did you stick it against the wall or out from the wall? and how have you found your unit this last week...
Ours is installed on SE wall, under a car port, and it does not get any direct sunlight. I often see outdoor units in full sun - I think this will increase the temperature and the compressor will have to work lot harder (increase in running cost). There is about 20 cm between the wall and the unit (installed by professional installer). It was running fine even during the hottest days last week (had 42 C). We also have a ducted evap in the house, which we still use a lot but it is pretty much useless on hot days like these. The refrigerated AC makes the house lot more comfortable, should have bought it lot earlier.
SA
137 Posts
Posted 28/1/2012, 4:38 pm        Report
I quite often throw a jug of water in the back of my in the window unit the installations instructions actually suggest it and it has a drip tray for over flow
WA
175 Posts
Posted 28/1/2012, 6:00 pm        Report
GreenGriff said...
I quite often throw a jug of water in the back of my in the window unit the installations instructions actually suggest it and it has a drip tray for over flow
Do you want to try that again...... in english?
QLD
5277 Posts
Posted 28/1/2012, 6:51 pm        Report
GreenGriff said...
I quite often throw a jug of water in the back of my in the window unit the installations instructions actually suggest it and it has a drip tray for over flow
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SA
137 Posts
Posted 28/1/2012, 7:31 pm        Report
gee talk about picky I quite often throw a jug of water in the back of my(in the window Air conditioner unit). The installation instructions actually suggest it, and it has a drip tray for over flow And yes OP Bundy bear is my best friend
WA
366 Posts
Posted 28/1/2012, 7:55 pm        Report
So being outside and playing a bit of slip & slide with my boy I decided to try the approach of misting water near the AC - I gave the whole unit a wash out (then did a few runs on the slide ) and then misted water in front of it (to cut down on the water going in). After about 30 secs the unit switched down from full power which it had been running at all day. Checked the kwh drawn and its also dropped but just over 1kwh. My AC is in a crappy spot, SW cnr between the fence and house - one side of the inlet draws hot air off the sun heated brickwork. (Dont ask the neighbour what she thinks about it... its louder at her bedroom window than next to the unit due to the way the sound reflects off the roof and walls and steel fence)
WA
175 Posts
Posted 28/1/2012, 9:56 pm        Report
GreenGriff said...
gee talk about picky I quite often throw a jug of water in the back of my(in the window Air conditioner unit). The installation instructions actually suggest it, and it has a drip tray for over flow And yes OP Bundy bear is my best friend
Sorry mate, my head hurt trying to understand that the first time you posted it.... I am not a residential refrigeration tradie but am an automotive refrigeration mechanic. We quite often spray water on to the vehicles condensors on hot days when testing systems to simulate air flow across the condensor. I would not however, start spraying my residential system with water, as I have seen the mother board inside the system and no mater how well it is sealed I would not want to tempt fate and introduce corrosion to the electronics of the system. Further, consistent water cooling of the condensor (as I understand) would prematurely corrode the condensor unit as well. In order to water cool the condensor you would have to spray the inside of the condensor unit (closest to the wall) then the water would draw the the condensor, covering the fan motor in moisture. No doubt they are sealed for outdoor applications but, do you really want to test its sealing ability?
Posted 28/1/2012, 10:13 pm        Report
I've got the solution: Duct some cold air from inside the house out to the radiator. There I fixed it!
Kazakhstan
2967 Posts
Posted 28/1/2012, 10:21 pm        Report
air-cons his air-conditioner....
Make sure you have substantial RCD's and circuit breakers before trying the above points. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Im sure if manufacturers could provide a more efficient system off cooling it would of been covered. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items. Water and power do not mix.Do-not under any circumstances throw water over electrical items.
WA
1106 Posts
Posted 29/1/2012, 7:59 pm        Report
Water and power do not mix.Do-not under any circumstances throw water over electrical items If it doesn't mix nothing will happen if you throw water over electrical items Actually water and electrecity do mix all too well. How to prove? Put "live" extension cord into puddle of water, stand with 1 foot in puddle and hold water pipe. Unless the water is pure you will either get a "tingle" (die?)or you will trip the power off
Kazakhstan
2967 Posts
Posted 29/1/2012, 8:20 pm        Report
No sweat !!!!
NSW
691 Posts
Posted 30/1/2012, 5:10 am        Report
Test pilot 1 said...
Water and power do not mix.Do-not under any circumstances throw water over electrical items If it doesn't mix nothing will happen if you throw water over electrical items Actually water and electrecity do mix all too well. How to prove? Put "live" extension cord into puddle of water, stand with 1 foot in puddle and hold water pipe. Unless the water is pure you will either get a "tingle" (die?)or you will trip the power off
Is that why they call you the test pilot?
WA
2293 Posts
Posted 30/1/2012, 9:03 am        Report
Test pilot 1 said...
Water and power do not mix.Do-not under any circumstances throw water over electrical items If it doesn't mix nothing will happen if you throw water over electrical items Actually water and electrecity do mix all too well. How to prove? Put "live" extension cord into puddle of water, stand with 1 foot in puddle and hold water pipe. Unless the water is pure you will either get a "tingle" (die?)or you will trip the power off
I use to clean a hotel in the city ..... many many many years ago..... and a guy bared the wires of a cord and stuck his hands into a basin of water... Not a pretty sight to knock on the door and come into ...nore did it smell that good...
 
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