Cooling with 55 degree water?

[mike90045]

.....How do they actually calculate how many BTU is actually coming out of the front of an air conditioner? 

I don't know, but you could measure your bucket temp, run the unit for 5 min, then remeasure, and subtract the watts added by the motor heat, and that's how much heat you moved.

At some point, the freon can't move more heat, regardless of the size of the creek you stick the condenser in .

[DanG]

When you note the conditioned air is colder that will be setting you up for problems if you get ice on the evaporator - the additional back-end cooling the water gives will need extracting on the front end by increasing air volume. Beware changing the layout since the condenser fan also cools the compressor that is hopefully internally overtemperature protected with a self resetting temp switch. The fans usually share a motor so removing the rear one may increase the front-end air stirring but not by much.

[BioHazard]

Interesting...I thought the compressor was mainly cooled by the refrigerant it's pumping? Maybe I could wrap it in copper tubing and water cool it....

Good point about needing more air flow if the evap is colder, I've experienced that freezing over many times in the winter when I use this air conditioner as a dehumidifier. 

[BioHazard]

Some more questions about pumping head losses:

If I have a submersible pump let's say 10 feet deep, does the "head" start at the water level, 10 feet above the pump, or does it start all the way down at the pump?

Also, using an inline sort of pump, does it make any difference whether it is pulling or pushing water? In other words, if I had 10 feet of suction, and 40 foot of head, would that be any different than zero suction and 50 feet of head?

[mbryner]

Head height is the difference between static water at start and static water at end.   Example, think about a drilled well:  the "head" is measured from the static water level in the well casing, not from how deep you set the pump in the water.   Therefore, you would measure the difference in water level at your creek to your outflow.   Yes, you have to include the suction of water from below in you calcs of head height.   Weight of water is still weight of water for the pump to overcome, whether it is pulling or pushing.   The real problems are that you can only suck water from so far down before you get cavitation/vacuum from the weight of the water, and that pumps aren't built to suck water from more than a few feet below.   And remember, the pump is running dry if you are sucking for a while before building up enough suction so water flows through it.   Keep the pump as low as possible.   

If you're dealing w/ a pressurized closed loop filled w/ water, all you have to deal with is the resistance of the pipe per foot x length of the loop, as someone mentioned earlier.

[BioHazard]

Alright, I got some more testing done tonight. I have two identical 5200 BTU window air conditioners. One of them has the condenser in a bucket as mentioned above and the other is unmodified.

Plugged them both in side by side with a kill-a-watt. The air cooled A/C was burning about 480 watts, while the water cooled was closer to 390 watts. (with the fan still attached) The colder the water on the "hot" side, the less electricity it used.

I don't understand how that works. Can somebody explain this? I would think the motor should be pumping away at the same rate it always does?

It also easily heats 20+ gallons of water to over 100 degrees in a few minutes. I see an air conditioner powered shower in my future....

Looks like my creek flow has dropped significantly since the rain stopped, I hope it doesn't stop flowing all together. Tonight I was able to pump the entire creek dry with a 1/2hp sump pump....

[billswan]

I don't understand how that works. Can somebody explain this? I would think the motor should be pumping away at the same rate it always does?

Bio

I am no expert but I will take a shot at explaining it.

If you would have a way of attaching a high side pressure gauge to both units I think the high side pressure  on the water cooled unit will be much lower and that is why the compressor runs at lower amp draw.
If the water was allowed to get very hot the amp load would come up and match the air cooled unit.
Water holds a lot of BTU's and is very efficient at absorbing it. Wish I could remember all those scientific terms I learned in school.

Interesting test, now can you get the fan that moves the air through the condenser off the shaft and retest?

Billswan

[Carlb]

Did you test both units with the kill a watt meter before running the test to see if the draw was the same on both?

Did the output temp on the water cooled unit get colder?

[mbryner]

Water holds a lot of BTU's and is very efficient at absorbing it. Wish I could remember all those scientific terms I learned in school.

Hey, finally something that relates to my training (I have a Biophysics major and Chemisty minor):   I think you're looking for the term "specific heat" and "heat capacity".     

• Specific heat of air:  1.01 (J/G degree C)
• Specific heat of water:   4.179 (J/G degree C)

[BioHazard]

Interesting test, now can you get the fan that moves the air through the condenser off the shaft and retest?

Yeah, I'll try to do that tonight. Interestingly the fan motor is labeled "20 watts" but when the A/C is on fan only mode it draws 45w.

Did you test both units with the kill a watt meter before running the test to see if the draw was the same on both?

Did the output temp on the water cooled unit get colder?

I didn't test the power consumption before modifying, I wish I had. They are identical units though, both with about 3-4 years of heavy use on them.

The evaporator was colder on the water cooled machine, I can't remember the numbers now I'll try and post them later.

[WGB]

Water holds a lot of BTU's and is very efficient at absorbing it. Wish I could remember all those scientific terms I learned in school.

Hey, finally something that relates to my training (I have a Biophysics major and Chemisty minor):   I think you're looking for the term "specific heat" and "heat capacity".     

• Specific heat of air:  1.01 (J/G degree C)
• Specific heat of water:   4.179 (J/G degree C)

Also latent heat!
The added heat added to or released as something goes from solid to liquid, liquid to gas or back again .
Sublimation from liquid to a gas.

http://en.wikipedia.org/wiki/Latent_heat

[BioHazard]

Alright, working with this thing is getting a bit akward with the condensor haning out the back. If I move it anymore I'm afraid I'll kink the lines.

I can either surround the condensor with some sort of water jacket(??) or, I was thinking about just removing the condensor and replacing it with a coil of copper tubing. Would that work, just a simple coil of 1/4" tubing dunked in water? Obviously I'd have to recharge the unit if I did that...

[Carlb]

If you are going to remove the condenser to add the copper tubing, Why not just use the copper tubing to re-locate the existing condenser?

[BioHazard]

If you are going to remove the condenser to add the copper tubing, Why not just use the copper tubing to re-locate the existing condenser?

I could, although it would be a lot easier to build a heat exchanger if the condenser is nothing more than a coil of tubing. The original one is made for air, and I've already bent a bunch of fins...

[RogerAS]

Grain of salt warning:

If you leave the coil as is and remove that fan you could just spill water over it and use a metal gutter to route the hot waste water anywhere, even down a zig zag of other gutters into a pool. Reuse the same water with a small pump. Big volume of reserve water and you're set.

The coil should work just fine for a long time in that sort of mode, made for air or not. The heat exchange is working now with water, why mess with that end of it?

R