residential a/c efficiency help for dummies

[rdronk]

I'm an HVAC dummy...help.

The unit that sits outside of my house with the big fan it it...is that the condenser (compressor)? Anyway, it's surrounded by radiator fins and the large fan draws outside air across these fins and exhausts out the top. I'm guessing the air flow across the fins cools some fluid - freon?

Anyway, today its over 100 deg F outside so the air being drawn in is already hot. If I set up a water misting system so that it wets down the fins, will this "help" my a/c system?

Thanks everyone for your help!

 

[quark]

Rdronk!

That is pretty high temperature for a condenser. (That is condenser you are talking about and it will extract heat from freon gas and makes it liquid which is called a phase change) Certainly the cooler the air temperature the better the efficiency. Try putting water elsewhere before condenser instead of forming water film on condenser fins. But before that check your wet bulb temperature.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[butelja]

It may help greatly in the short term.

However, if you continually spray water on it, a couple of problems will likely occur. The first is increased dust, fiber, etc. accumulation on the coil. This will block airflow, but can be easily removed. The second is if you have hard water, you can form mineral scale on the condensor. This will insulate the coil and prevent heat trasfer. It will also be very difficult to remove by any means that won't also damage the coil.

Your best bet is probably to use the garden hose to clean the coil well, removing any dust, lint, or vegetation on it, but don't leave a continuous spray on it.

 

[ChasBean1]

rdronk, the above posts are both right if you are having a problem with the system tripping because it's too hot. Water will help immediately becuase it will provide the cooling that the fan is trying to do. If the system controls right you should see the fan slow or shut off after spraying down the coils for a while. Regardless, you're not a "dummy!" Your thoughts are accurate. I'd just be interested to know why you need to hose the system down(?) So long as the system still operates, the refrigerant charge is right, and the low side (cooling) refrigerant pressure is the same, it should work fine... Feel free to repost if you'd like to discuss the nature of the problem more. Tx, -CB

p.s. - afterthought - refrigerant type plays a role also. 110°F might be plenty cool to operate condensers for some types of units...

 

[madddog]

My problem is that my system was not sized for the added heat load of a townhouse end unit. All systems were sized as a middle unit with other units on both sides, two "cool" walls on each side. Since my unit is an end unit I have only one "cool" wall and one HOT wall. My system runs a total of 12-16 hours a day in hot weather.

I want to spray "conditioned" water on the coil intermittantly regulated by monitoring the evaporation. Once sprayed for a defined duration the temp should cycle form high to a low and then begin rising at which point I will spray the coil again.

As you mentioned the wetbulb temp will determine how much of a temp dip occurs and the duration of the dip.

The conditioned water will come from a reverse osmosis device to remove all comtaminants. Yes from time to time I will have to clean the coil from the inside.

Does anyone see a kink in my logic?

 

[quark]

I would not prefer spraying water on the condenser coil. The permeate from RO system is costlier. We here generally use evaporative air coolers as a cheeper option in low humidity areas. A mat is placed infront of a fan in an enclosure. This mat is wetted continuously and the air when comes into contact with the wet mat gets cooled down. (The mat is made up of some natural herbs which smell good and keeps one cool.

This sort of arrangement is much cheeper.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[dieselman]

The "kink" is that your system is not designed for this water spray. The vast majority of home units are equipped with air cooled condensing units as you describe. Although it may have helped if you gave your location, I would, off the top of my head, say that a 12/24 hour run time with ambients over 100F is pretty good design - almost guarantees good dehumidification. On the other hand, 16/24 is pushing the envelope a little.

Regards

 

[Energia]

If you are willing to spend money a good option will be to install a auxiliary water cooled condenser. There are some in the markets used to heatup pools. (although in the

http://www I

have only found one good one made in Australia). But, I agree with the rest the air cool condenser coil is designed for air not water. If you persist on the idea, then protect the coil fins with coating such as Adsil (

http://www.adsil.com).

Spraying water will definitly work but will lower the life of the coil.

 

Hey maybe try some shade like some large shrubs on either side just if any thing keep them 24" away from the unit

 

[walkes]

Just a comment/question. Won't the RO water have a tendency to leech minerals from the metal (finned elements on the coils). Generally when conveying RO water one would use stainless steel pipe or plastic pipe to avoid such problems. You will probably cause more damage to your system with the RO water.

 

[RJVAN]

If I understand the condenser configuration, the air is drawn through the cooling coil and then up through the fan. By spraying water on the coil, you'll get moist air and some droplets continually pulled through the fan's motor. While the fan/motor unit is protected from rain water from above, I wonder if there is protection from water from below.

Typically in evaporative condensers, the air is forced in from below the coil, and excess water is caught in a pan.

Also, as mentioned previously, I would be extremely cautious about the build up of dirt & mineral scale.

 

[ClydeMule]

rdronk:

Your logic is correct, but unfortunately all of you efforts probably won't make your townhouse noticeably cooler. Nominal Capacity of A/C compressors are rated at a 45 F evap temp and a 130 F condensing temp. The 130 F condensing temperature corrsponds to a 100 of 105 F design ambient air entering the condenser. A decrease in condensing temp increases compressor capacity, and power consumption. However, that is only when you consider the compressor by itself. Residential A/C systems are designed for low first cost, there isn't a whole lot of wiggle room in the system sizing. To make a longer story longer, you may reduce the condensing temp, but because of the sizing of the rest of the system, you won't significantly increase the capacity of your system. You probably will draw less power, but at the cost of water, and the a forementioned risk of wrecking the coils and fan. Evaporative cooling pads can "precool" the air, but they also give you a static pressure drop penalty that will reduce the airflow. Unless you have super low wet bulb temp, the benefits are canceled out by the cost (I have tried this, only worked on a system I built in Las Vegas).

BTW- The unit outside is called a "condensing unit" (compressor/condenser package.)

If your the curious type, try what you were thinking of anyway. Maybe it will help a bit. Makes for an interesting afternoon.


Clyde the Mule

 

[prodeng]

One other thing you need to know: The refrigerant tubes on the condenser are probably copper. RO water pits copper over time and a refrigerant leak in your condenser would definitely defeat your purpose. A one time spray, as Clyde mentioned shouldn't hurt it, but I would avoid continuous use as you had proposed. RO water seeks to regain minerals to balance itself out - if it comes from metal, it obviously means there is less metal there than when you started. That's where the pitting comes in over time.