Misting the home a/c condenser

[Kestas]

My house a/c has trouble keeping up with demand. It'll take forever to drop a few degrees when it's below 80°F inside the house. We've never had is so hot for so long since I bought this house 21 years ago.

I set up the garden hose to a fine mist on the outside of the condenser to help it shed heat. I'm pretty sure it'll help move the heat along. I was wondering if this will also help with efficiency and energy use.

 

[eljefino]

I read somewhere (here?) that window ac units deliberately splash condensate against the condensor for this purpose. Mine makes an obnoxious noise that sounds like this going on.

My parents had an ancient central air conditioner that had an open loop water system; it dumped tepid water either in a utility sink or out a garden sprinkler spigot. Presumably the water was part of a heat exchanger.

 

[LineArrayNut]

i used to spray an outside heat pump to help in summer. it was effective. you can feel the fan get NOTICEABLY cooler. almost all outside air coolers use this principle. my added water cost at the time was free. my electricity was not... but it ran all day at over 100 degrees F to cool to 76. with a mist it was ~70%.

 

[JHZR2]

Originally Posted By: Kestas
My house a/c has trouble keeping up with demand. It'll take forever to drop a few degrees when it's below 80°F inside the house. We've never had is so hot for so long since I bought this house 21 years ago.

I set up the garden hose to a fine mist on the outside of the condenser to help it shed heat. I'm pretty sure it'll help move the heat along. I was wondering if this will also help with efficiency and energy use.


What heat transfer is more efficient, to air or liquid?

Does phase change or air pull more latent heat from a surface?

You know the answers well, but its a thought exercise for others if they care to do so

I bet youll see an improvement.

 

[azjake]

Maybe you should have someone come out and check your A/C. Could be a refrigerant leak. Also if it's always had a hard time keeping the home cool it may be the unit is too small for the size of your house.

Part of an A/C tuneup includes cleaning the fins with soap and water to help them shed heat better. Over a year's time dirt can accumulate in there making the fins less efficient.

 

[JHZR2]

Originally Posted By: azjake
Maybe you should have someone come out and check your A/C. Could be a refrigerant leak. Also if it's always had a hard time keeping the home cool it may be the unit is too small for the size of your house.

Part of an A/C tuneup includes cleaning the fins with soap and water to help them shed heat better. Over a year's time dirt can accumulate in there making the fins less efficient.


Agre on both cases, but for someone living in MI, not TX or FL, I'd prefer to suffer a bit in this heat wave and have a good undersized/right sized system for the rest of the time.

 

[Shannow]

Your sealed condenser needs a temperature differential between it and ambient to get the heat shifted...it can only work in the dry bulb region.

Cooling towers, like those at the mall, work partially by transferring heat to the air (dry bulb), but then score points by utilising the latent heat of the coolant, and being able to operate in the range between the dry bulb and wet bulb temperatures.

So yes, your unit will be more efficient with water cooling.

Two ways of doing it, are to mist the coils, or to mist the air going into the coils.

having just enough water to get the water to evaporate off the coils is the go, with enough excess to wash off the salts as they deposit.

 

[Drew99GT]

Originally Posted By: eljefino
I read somewhere (here?) that window ac units deliberately splash condensate against the condensor for this purpose.


I was wondering about that. It's ridiculously humid here and my window unit doesn't have a hole to drain water that's condensed in the evaporator to drain it out of the base of the unit. Instead, the water level rises in the base of the unit to where the condensor fan will splash the water around; presumably to spray water on the condenser.

In fact, I was looking at it this afternoon and contemplating drilling a hole so the water would drain out but I thought the water splashing on the condenser would help heat transfer.

http://ask.metafilter.com/126530/water-mist-to-improve-AC-function

"Some window units are designed so the fan spatters water onto the fins of the condenser, but this is water that has been condensed from the air on the cold side of the AC, so it is effectively distilled and mineral free."

I know in my car if it's very hot out and I drive through a little shower, the A/C gets noticeably colder.

 

[wander2039]

Originally Posted By: Kestas
My house a/c has trouble keeping up with demand. It'll take forever to drop a few degrees when it's below 80°F inside the house. We've never had is so hot for so long since I bought this house 21 years ago.

I set up the garden hose to a fine mist on the outside of the condenser to help it shed heat. I'm pretty sure it'll help move the heat along. I was wondering if this will also help with efficiency and energy use.


Have you had your unit checked lately? Had mine checked yesterday and it was only a little bit low on freon but did that little bit ever make a difference. It still runs quite a bit which the tech says is completely normal with these temps. Have to factor in your water bill also.. the water up here is high IMO. I've watered ours down a few times truthfully didn't notice a difference.

 

[Rick in PA]

I think it's a good idea. I believe newer air conditioners will splash the condenser condensate on the evaporator to improve efficiency (as a plus, it IS cold water, OK, I'm not an expert...)

By coincidence, I was just reading in Popular Science where a fireman developed a cooling mister to cool down overheated fire fighters. It's a cap he modified by installing a half dozen mister nozzles from Home Depot. They install the cap on one of the ports on the side of a pumper truck and it provides a cooling mist for any overheated fire fighters. It only uses a couple of gallons of water per hour. I thought that was pretty darn clever, that's engineering!

Home Depot (or equivalent) some PVC pipes & fitting, some mister nozzles, and you're good-to-go. Sounds like a fun little project. The only concern I'd have would be mineral build-up on the condenser, but that shouldn't be a problem with occasional use.

 

[KrisZ]

Originally Posted By: Kestas
My house a/c has trouble keeping up with demand. It'll take forever to drop a few degrees when it's below 80°F inside the house. We've never had is so hot for so long since I bought this house 21 years ago.

I set up the garden hose to a fine mist on the outside of the condenser to help it shed heat. I'm pretty sure it'll help move the heat along. I was wondering if this will also help with efficiency and energy use.


Water will help, but from the sound of it, your system is sized properly. Ideally the system should be sized so that it continuously runs at the hottest day of the season to keep the set temp, which is usually 75*F. That means that it will have a hard time knocking down the temperature, as the system will be almost at its max. capacity.
Your best bet is to get the interior temperature down to your liking during night when there is no heat gain and let the system maintain that temp. throughout the day.

Edit:
If your system has a hard time knoking down the temperature during night, then an AC pro should take a look at it.

 

[JimPghPA]

Originally Posted By: azjake
Maybe you should have someone come out and check your A/C. Could be a refrigerant leak. Also if it's always had a hard time keeping the home cool it may be the unit is too small for the size of your house.

Part of an A/C tuneup includes cleaning the fins with soap and water to help them shed heat better. Over a year's time dirt can accumulate in there making the fins less efficient.


Remove any plants that grow near the outside AC unit so you have maximum air flow. Look for any fins that are bend on the condenser and straighten them. Turn off the breaker and then hose off the condenser to get rid of dirt.

Misting will improve the heat transfer of the condenser. It also reduces high side pressure, therefor the compressor does not have to work as hard because there is less pressure difference between the high side and the low side. When the compressor does not have to work as hard it uses less electric power, therefore it cost less to run.

If you only have to mist for something like 12 days of temperature > 100 Fahrenheit then it is probably cost effective. But if you have to mist every day you use the AC then you have to consider how much the water cost, including sewerage if your bill ties sewerage charge to water use.

Along with looking to see if the AC is the proper size another question may be: “Is the house properly insulated?” If not, adding insulation would have both a summer and winter benefit.

 

[JimPghPA]

You could shut down unused zones during hot days, such as bed rooms, as long as you remember to bring them back on about an hour before use.

 

[oggb]

I was thinking about this earlier today - setting up a system that automatically used a fogger nozzle/nozzles (like some cars use for intercoolers or meth injection) and set it on a timer to spray the condenser coils of a unit every so often during the hottest parts of the day.

 

[gathermewool]

Water evaporation from the condenser coils will produce more heat transfer via the latent heat of evaporation of the water; greater than the SENSIBLE, convective heat transfer of the coil-to-air.

If your AC system is only recently under-performing, then you need to determine whether you have a leak. Does the evap freeze up on humid days?

 

[JimPghPA]

Years ago I worked for an energy research company that did several projects with refrigeration. One of the projects was on a farm that had many cows and a few horses. The milk had to be cooled quickly when it was taken from the cows, and then the cows had to be washed down with warm water. There was a system that made a large room of ice that had pipes running through it for the milk for the fast cooling. The heat removed from the making of the ice was originally dumped to the air. To reduce the operating cost of the farm we put in a system that would dump the heat into water to pre-heat the water that was then heated the rest of the way by the existing water heater. If the pre-heat tank was too hot there was still an air condenser with a fan to dump the heat. Unfortunately when this new system was put in, a new condenser with a new fan was also installed. One of the horses (a male) some how figured out that if it wet on the condenser the fan would blow and do a good job of distributing its scent. Kind of a way for that horse to claim more area. Horse urine chemically ate away the metal of the condenser and in a short time the system lost its refrigerant when the condenser went bad because it was eaten away.

So If you mist on a regular basis, If the water contains minerals that would eat the metal, or build up on the metal and clog it, the misting may not be a good idea. Think of how much minerals build up on humidifier pads. Would you want a condenser clogged up and looking like a worn out humidifier pad?

 

[JHZR2]

Originally Posted By: JimPghPA


So If you mist on a regular basis, If the water contains minerals that would eat the metal, or build up on the metal and clog it, the misting may not be a good idea. Think of how much minerals build up on humidifier pads. Would you want a condenser clogged up and looking like a worn out humidifier pad?



I have to imagine that it would be a minimal difference. After all, think about auto systems that get caked with all kinds of junk... yet still work.

What about rain water? Acid rain? all must have similar effect. For someone pulling high mineral content water in NM and using it in the heat all year, IMO the considerations would be much different than someone setting it up in the far north like the OP, where the need for this Id imagine would really be beneficial but for a few days a year...

Still your comments are most interesting.

 

[larryn]

most well or city water contains minerals that will be deposited on the fins of your condenser causing poor heat transfer and or corrosion. This will ruin a condenser coil in a short time,or require it to be watered to run even under light loads.The temp.drop across an evap. is 20F{80F in 60Fout]as room cools discharge temp. drops.Water coming off of the evap. is mineral free. and can be used to cool the condenser with out harm.

 

[doitmyself]

Originally Posted By: larryn
most well or city water contains minerals that will be deposited on the fins of your condenser causing poor heat transfer and or corrosion. This will ruin a condenser coil in a short time,or require it to be watered to run even under light loads.The temp.drop across an evap. is 20F{80F in 60Fout]as room cools discharge temp. drops.Water coming off of the evap. is mineral free. and can be used to cool the condenser with out harm.


^^^^This! I manage evaporative greenhouse coolers and mineral build up is managed with chemical injection. Arizonians use similar "swamp coolers".

Lets not forget that Kestas is talking about record breaking plus 100f days here. Normally we rarely get a half dozen days over 90F annually.

 

[Kestas]

I'm confident my a/c unit is in decent shape. I just had a spark of an idea to boost the output because I use the same technique when servicing automotive a/c in the driveway, and when my car overheated in Death Valley. Also, thermal transfer is some 13 times greater with water than with air.

Nighttime cooling is not a problem.

As far as mineral buildup, thanks for the heads up. But my imperfect system also washes away the excess water and probably any mineral buildup.