Water misting on evaporator - SEER of evaporator

[ericrocks]

I have an 11 year old YORK split airco system, 3 ton. No TXV valve.

1. I want to increase the efficiency of my HVAC system. I put some 12 water misters around the outdoor condensing coil. Water is supplied via a (compressor signal controlled) valve and water filter to take out most of
impurities. The temperature of the liquid line dropped considerable. But the air temperature coming out of the evaporator coil increased! I made a temperature log of the air temperature coming out of the evaporator coil and
when I activated the water misters, the temperature shot up more than 5 F in a matter of minutes. Superheat increased with >10F
My take on this is that more freon sits in the condensor and provides no longer enough freon to the evaporator coil.

Questions:
- Is it correct that by water misting the condensor, the efficiency goes up, or is this just a scam (e.g. http://www.acmister.com ).
- Can I simply add more freon
- If I would add more freon, will my system more efficient?
- What happens when the subcooling gets too high, can it get too high?
- Would adding a TXV valve improve this working
(A good friend my is a certified HVAC tec, so he can help out.)

2. These day a lot is going on about higher-SEER HVAC systems. My question: what is the main difference between a 13 SEER, 14 SEER, 15 SEER etc. The whole range between 13 SEER and 21 SEER exist.
What is the difference between a 3 ton 13 SEER evaporator coil and a 3 ton 16 SEER evaporator coil?

3. Do you know about some good HVAC books that would cover this type of questions.

[BaldLoonie]

The flow of refrigerant through a fixed meter coil is based on head pressure which is based on outdoor temp. When you lower the outdoor temp considerably by evaporation, you've lowered the head to the point where the indoor coil is starved. A TXV will help, reducing the evaporation will help too.

[icyflame]

What would happen if you changed the control signal from the compressor to... say a pressure switch set at maxium pressure you would have the system run at? :D

[star882]

It's technology that works, but you can't add it to just any A/C. It must be designed with it in mind.
I think you could use some type of thermostatic control to allow it to cool down only on hot days, but I'm not sure.
The old systems run at high temperatures and pressures by design, so chances are, you lowered it to the point where the capiliary tubes cannot pass enough refrigerant. It's more likely to work on a newer system.
Have you tried lowering the amount of water? You will have to tune it just right. If you really care, have a pro install a TXV (automatically adjusts, may need some manual adjust) or CPEV (manual adjustment, rare).

[cem-bsee]

be careful of minerals depositing on fins -- from water! mineral deposits would screw up the heat transfer capacity big time -- I would get a 750x microscope & watch

[alexb]

Does the temp of the liquid line correlate at all to head pressure? My liquid line doesn't even start to get warm until the OD temp is ~90F.

The air from the registers is 2-3F colder when the OD temp is above 90, than it is when the OD temp is lower (~low 80's) or so.

Is my TXV not doing its job properly, or do I not have proper charge? I thought I read that the Am. Standard Alegience product had a 2-speed condenser fan? This way, the fan spins down a bit when the OD temp is lower.

Keeping in mind what the original poster said, and what Loony has said, would it be an interesting experiment to *restrict* airflow thru the condenser **briefly**, to raise the head pressure, and see if it increases deltaT across the evap?

[beenthere]

What Baldie said.

Also, if you cool the condenser down to much, teh liquid will begin to flash before it gets to the evap, which also decreases your cooling ability.

Lower your water volume, and only use it when its 90+ outside.

But you won't increase its eff. by much.

[markwolf]

Where is the water coming from?If you are using domestic water you may be breaking code in your area.Pump & dump is frowned on in many areas.Using something like this could be in violation with department of natural resources regulations.

[hvaccolo]

I had a building with 2- 120 ton split dx systems which were undersized for the building. The on site maintenance guy (who knows enough to be dangerous) installed a foot valve (head pressure reg) on each compressor, which controlled a 3/4" water valve that responded to head pressure. Sprays water on each condenser coil, and drops the supply temp 5 deg. The problem is that the coils are so fouled from the minerals that 5 years later you can't pull any air through them. Also, he never shuts the water off before freeze temps and the pipes always burst.

[alexb]

Greetings;

I'd really be interested in a professional opinion to what's below. Please get as technical as you can w/o breaking Site Rules. I need someone to tell me if my new system is set up properly. If you can't answer me, just indicate that.
__________________________________________________

Does the temp of the liquid line correlate at all to head pressure? My liquid line doesn't even start to get warm until the OD temp is ~90F.

The air from the registers is 2-3F colder when the OD temp is above 90, than it is when the OD temp is lower (~low 80's) or so.

Is my TXV not doing its job properly, or do I not have proper charge? I thought I read that the Am. Standard Alegience product had a 2-speed condenser fan? This way, the fan spins down a bit when the OD temp is lower.

Keeping in mind what the original poster said, and what Loony has said, would it be an interesting experiment to *restrict* airflow thru the condenser **briefly**, to raise the head pressure, and see if it increases deltaT across the evap?

[jir]

My little brain is struggling to understand what the OP said:

1. I want to increase the efficiency of my HVAC system. I put some 12 water misters around the outdoor condensing coil. Water is supplied via a (compressor signal controlled) valve and water filter to take out most of
impurities. The temperature of the liquid line dropped considerable. But the air temperature coming out of the evaporator coil increased! I made a temperature log of the air temperature coming out of the evaporator coil and
when I activated the water misters, the temperature shot up more than 5 F in a matter of minutes.

Say the net effect of the misters is to drop the outside air temp from 100 to 95 degrees. When all the effects of the sudden changes in air temp finish damping out, what's the difference between how the system runs as compared to a day when the "un-misted" air temp is 95 degrees?

Any insights, anyone?

[Mr Bill]

Originally posted by BaldLoonie
The flow of refrigerant through a fixed meter coil is based on head pressure which is based on outdoor temp. When you lower the outdoor temp considerably by evaporation, you've lowered the head to the point where the indoor coil is starved. A TXV will help, reducing the evaporation will help too.

You right on here! I have never seen this work but I have seen many try and even if he does filter the water do you realize what water over a warm condenser 24/7 will eventually do to your condenser coil, I have seen the after effects when changing out the old condenser the coil looks rotten. If you had a system designed for this with maybe a stainless condenser coil I could see were it might work long term.

[icyflame]

"I want to increase the efficiency of my HVAC system. I put some 12 water misters around the outdoor condensing coil."


Why 12? Did it come as a set? Can you use just one or two?

[jeffnette]

Whers is Bob Brown when you need him!

[ericrocks]

I want to thank everybody for their contributions/thoughts.

I started this 'project' on my old airco system (11 year old). Even if the condensor is wasted after a couple of years because of mineral depositing, well so be it.
The goal was to have a somewhat higher SEER unit at low or no cost.
The potential is there, look at the numbers.
Outdoor temperature: 99F

- Measurements before misting:
Suction P: 62.5 psi - Liquid P: 260 psi
Temperature of Suction line: 62.5F
Temperature of Liquid line: 103F
Power consuption unit: 4.5 Kw

- Measurements during misting (after 5 minutes):
Suction P: 69 psi - Liquid P: 220 psi
Temperature of Suction line: 77F !!!
Temperature of Liquid line: 98F
Power consuption unit: 4.1 Kw

So there is a 10% reduction in power consumption. But look at the suction line temperature. I did not measure the air temperature coming out of the registers inside (only one thermometer), but believe me, it goes up. This results in a longer running cycle of the compressor (more than 10% longer). Bottom line: MORE power consumption instead od less!

I used 12 misters to cover all 4 sides of the condensor. I bought 3 boxes of 4 misters each at Lowes. With less misters the power reduction and superheat increase is simply less.

I would say, for the time being the water misting myth is BUSTED. Shame on these companies that want to sell you these misters and promiss impressive cost reductions.


Nobody said anything about the difference between a 13 SEER evaporator and e.g. a 16 SEER evaporator. Is this classified material?
Everbody always says that the indoor and outdoor units need to match to get the specified SEER value. So there must be (should be) a difference.

Also, what is the difference between al the different SEER systems. What need to be changes to a 14 SEER system to get a 15 SEER?

All remarks are welcome. Let's all learn is little so we can make better buying decisions later.

[ericrocks]

I'm sorry typo:

Suction pressure before misting: 80 psi (not 62.5)

[Mr Bill]

Originally posted by ericrocks

- Measurements before misting:
Suction P: 62.5 psi - Liquid P: 260 psi
Temperature of Suction line: 62.5F


How can that suction be? that is about a 35 degree coil temp that suction line should have been a lot colder than that.

[Mr Bill]

Originally posted by ericrocks
I'm sorry typo:

Suction pressure before misting: 80 psi (not 62.5)

Guess I posted to soon I knew that could not be right. :

[jdenyer]

Keep in mind that as you lower the temp at the condenser as caused by misting, the greater the superheat. You are doing this on a fixed metering device, so the only thing that you are really doing is reducing the capacity of the unit. As the condenser gets hotter the high side pressure goes up, forcing more liquid through the metering device and increasing capacity. With higher superheat you are no longer using as much of the evap coil as you could be. While it appears that you are saving about 400 watts the unit will run longer. Your electric usage will end up the same at the end of the day, and you will have a higher water bill to go with it. Believe me you are not saving anything by doing this. Also having a superheat that is to high is not a good thing, that compressor needs to see that cool gas coming back to keep the motor windings cool. Please unhook your little experiment and run the unit the way it was designed, you will save in the long run.

[Mr Bill]

Originally posted by jdenyer
Please unhook your little experiment and run the unit the way it was designed, you will save in the long run. http://www.MyOnlineImages.com/Members/mrbillpro/images/4_9_3.gif

[jdenyer]

Oh my, I didn't read ericrocks post closely enough and upon second glance see that he mentioned about the unit running longer. He was just trying to dis-prove a myth. My apologies to you. It wasn't until I saw Mrbillpro's post of the crying smiley dude with my quote and assumed that he was calling me a crybaby, of course he was right, it probably did sound like that, it really sounded like that after I reread the post:D Again I do apologize, I really need to read posts more closely:D

[Mr Bill]

Originally posted by jdenyer
It wasn't until I saw Mrbillpro's post of the crying smiley dude with my quote and assumed that he was calling me a crybaby, of course he was right,

My intentions of the crying dude was that his experiment did not work, just a general cry because it did not work, nothing sarcastic or personal to any poster.

[jdenyer]

Hey I'm 2 for 2 today:D Oh well I still feel bad for running my mouth without fully reading the post and my apology still stands.

[ericrocks]

Well, I don't give up that easily...
I should have said "I would say, for the time being the water misting myth is busted WITH MY SYSTEM CONFIGURATION", meaning:
- my freon charge set for a air-cooled system
- no TXV

I think that adding freon would help. But it is expensive and doing so would force me to continuously use water misting, the system would be grossly overcharged without misting
A TXV might solve the superheat problem (or at least partially). When the superheat goes up the valve opens up some more and lets more freon in the evaporator.

Next spring I check with my friend the HVAC specialist if he can add a TXV at a reasonable cost.

[jim baughman]

I want to try to hit on something that the other guys have not mentioned...the principles of your AC system. Technicians understand the properties and states of refrigerants as they pass through the system, but that is bit too much for the average person to know. Basically, the function is to remove latent heat from inside your home via the evap coil, then transfer that heat to the outside by means of the condenser coil. Maybe this will give you a general idea:
If the outside air is 90F and the condenser coil is running at 120F then that basically allows the heat to be removed from your house. However, if you lower the temperature of the condenser to 95F with the water, then you have lessened the capacity of the system. Make sense? If the condenser runs cooler than the outside air, there is NO heat being removed at all. To cure your problem easily...simply install an outdoor temp sensor into the controls of the water sprayer system that will only allow it to run when the outside air reaches in excess of 100F. If it runs before then it will actually reduce the capacity...and of course how often does your outside temp reach that high? In general, depending on the enviroment where you live, this is not practical. As mentioned above, the water over time will possibly damage the coils due to the additives and minerals. This type of system was intended for use in areas where the temperature can reach 115F and the condenser would reach such high pressures that the compressor would shut off.

[wendel]

With all due respect, Jim, a condenser coil does not operate at one temperature. If you measured the temperature at the compressor output (coil input) and also at the condenser coil output, you'll notice a significant difference. No heat exchanger is 100% efficient but helping the condenser coil to remove heat will improve performance, assuming other components are adjusted to the new operating parameters. That's why the high SEER condensers have more coil surface area and more fpi... better heat transfer, just like misting (heat transfer through evaopration).

[ericrocks]

Jim, I'm afraid you're off and not even a little bit.
The house is cooled by boiling of the liquid refriggerant in the evaporator coil. With R22 and 70psi it boils around 34F, so plenty of opportunity to cool the air over the evaporator.
Thermodynamically speaking, what happens is that the enthalpy of the R22 increases going from liquid to vapor. The total amount of enthalpy can be increased by lowering the temperature of the liquid refrigerant.
If you were right, the efficiency of a split-airco system would increase with the outdoor temperature. Believe me, that's not the case.

[docholiday]

The problem with this whole set up is it's half thought through. If you are going to supliment the heat rejection with water, then you would have to also reduce the airflow through the coil. Possibly reengineering the fan and blade combination. You still need a head pressure with the proper subcooling so you simply cannot reduce the head pressure and hope there are no consequenses.

As far as a 16 SEER coil goes, there are severl things that go into getting efficiencies that high. Very often you may have an outdoor ECM motor, you would definately have one inside. If you increase the outdoor coil without increasing the indoor coil size, you risk other problems such as loss of capacity and reliability.

Bottom line is if you want a 16 SEER system, buy one or invest in a 4 year meachnical engineering degree and have at it.

[dayne]

Interesting project you have going here...any chance you could post a pic of the misters in action :)

[icyflame]

Originally posted by jim baughman
If the outside air is 90F and the condenser coil is running at 120F then that basically allows the heat to be removed from your house....However, if you lower the temperature of the condenser to 95F with the water, then you have lessened the capacity of the system. Make sense? If the condenser runs cooler than the outside air, there is NO heat being removed at all.


Jim, I misread you post and was going to question you on a point, Sorry.. I think you said it right I need to quit playing with the dog while I'm reading these post! :D

[Edited by icyflame on 08-24-2006 at 10:03 PM]

[perel]

Originally posted by star882
If you really care, have a pro install a TXV (automatically adjusts, may need some manual adjust) or CPEV (manual adjustment, rare).
Why is this making me think of Payson's ADJUSTABLE SUPERHEAT (http://hvac-talk.com/vbb/showthread.php?threadid=104531) metering device? :D

Seriously, it was very interesting to see some hard numbers on this.

[dallasbill]

Originally posted by jeffnette
Whers is Bob Brown when you need him!
He's over here now http://ths.gardenweb.com/forums/load/hvac/msg0821152323993.html?12

...giving two posts of "advice."

[xersw]

Ive heard it all now.

[star882]

Originally posted by perel

Originally posted by star882
If you really care, have a pro install a TXV (automatically adjusts, may need some manual adjust) or CPEV (manual adjustment, rare).
Why is this making me think of Payson's ADJUSTABLE SUPERHEAT (http://hvac-talk.com/vbb/showthread.php?threadid=104531) metering device? :D

Seriously, it was very interesting to see some hard numbers on this.
You can actually buy proper CPEVs. In the following link, one is used to optimize a CPU cooling unit.
http://www.xtremesystems.org/forums/showthread.php?t=88368&highlight=cpev
There are even electronic expansion valves (EEVs) which are basically TXVs with the sensing bulb and diaphragm replaced with a linear servo motor. When combined with the proper control computer and sensors, it can be very well optimized under many conditions. The computer (usually a tiny Jessica Simpson "computer-on-a-chip" SoC) reads the sensors and adjusts the voltage to the EEV to make it change refrigerant flow.
In an 8 way Britney "supercomputer" with R410a, an inverter drive scroll compressor, and 8 EEVs (one for each CPU), startup is very fast (since the EEVs can optimize for fast pull down and the compressor can run at full speed) and yet it has no problem with low load conditions (EEVs start closing to avoid floodback and compressor slows down in response to reduced load). If there is an unbalanced load, it still operates correctly as the EEVs are independent. The system actually has a 200MHz Jessica Simpson CPU and about 6MB of firmware to manage all the functions. I have worked on that machine a few days ago and it has been running nonstop at full design load (Folding@home) for over half a year. Very clever piece of modern engineering.

[justbud38134]

be careful of minerals depositing on fins -- from water! mineral deposits would screw up the heat transfer capacity big time -- I would get a 750x microscope & watch
I bought a cool-n-save unit for kicks to see if I'd:) have any problems. Initally, I did'nt like the way the water sprayed because it was too heavy on the condenser so I bought some different nozzles for it with a finer spray pattern and now it works great. I have been watching for build up on my coil and have found none. Been running about 3 months. The unit does have a filter in line plus memphis water is almost mineral free anyway. I'd call it a success!!! Utility bill is down about 33% from last year too!!!:)

[Shophound]

I want to try to hit on something that the other guys have not mentioned...the principles of your AC system. Technicians understand the properties and states of refrigerants as they pass through the system, but that is bit too much for the average person to know. Basically, the function is to remove latent heat from inside your home via the evap coil, then transfer that heat to the outside by means of the condenser coil. Maybe this will give you a general idea:
If the outside air is 90F and the condenser coil is running at 120F then that basically allows the heat to be removed from your house. However, if you lower the temperature of the condenser to 95F with the water, then you have lessened the capacity of the system. Make sense? If the condenser runs cooler than the outside air, there is NO heat being removed at all. To cure your problem easily...simply install an outdoor temp sensor into the controls of the water sprayer system that will only allow it to run when the outside air reaches in excess of 100F. If it runs before then it will actually reduce the capacity...and of course how often does your outside temp reach that high? In general, depending on the enviroment where you live, this is not practical. As mentioned above, the water over time will possibly damage the coils due to the additives and minerals. This type of system was intended for use in areas where the temperature can reach 115F and the condenser would reach such high pressures that the compressor would shut off.

For all who stated that system capacity drops due to head pressure being artificially reduced by misting system...you are right on target. :cool:

Only thing I might add to that is the importance of the pressure difference across the piston...lowering head pressure reduces the delta P. Compressor is still pumping at same speed but lower head pressure means less refer volume and velocity going to and through piston...lower mass flow through evap resulting in not as many pounds per minute circulated through evap to meet heat load imposed on coil.

For Jim's reply, there will still be an exchange of heat even if the condensing temperature is being artificially reduced via the misting system. The misting itself imposes an evaporative cooling factor, and for that to occur there must be a transfer of heat to evaporate the water droplets. If the outdoor wet bulb is low enough the wet bulb depression (WBD) can be significant...up till recent days in the Dallas area the WBD has been lousy, with wet bulb temps running in the mid to upper seventies. Not much to be gained from having misters piss on a condenser coil during those conditions except that the tap water is maybe a little cooler than the ambient air.

One of the replies above pondered what would happen regarding efficiency if the air entering condenser conditions on a 100 degree day, for example, were reduced via the misting system to, say, 85 degrees...would there be a gain in efficiency? There are a few things to consider for this scenario:

First, the effect of reduced head pressure for fixed restrictor systems has already been covered.
Second, concurrent with the first bullet above, the heat load being imposed upon the house has not changed.
Third, with reduced mass flow due to first bullet conditions (reduced head pressure), the refrigerant can't carry enough heat out of the house to match heat gain to the house.
Fourth, if one were to bother crunching the numbers for compression ratios with ericrock's data, one might say, "Well, with the misters the compression ratio is better! Why would you still think efficiency is reduced?" In this case, the lower compression ratio is due to reduced head pressure through a fixed orifice metering device, which translates to lower suction pressure. Less volume of refrigerant being circulated certainly is not offset by a lower compression ratio!A TXV might work better in eric's scenario, but a TXV alone will give eric better performance than farting around with misters on a system not designed for such a thing. Get a TXV, get the condenser and evap coils clean as a whistle, along with blower wheel (if they are not already), get the ductwork sealed as tight as possible (including supply register boots) on both supply and return sides, reduce infiltration into house, improve insulation...redirect the misters toward your patio or deck!

[Shophound]

I bought a cool-n-save unit for kicks to see if I'd:) have any problems. Initally, I did'nt like the way the water sprayed because it was too heavy on the condenser so I bought some different nozzles for it with a finer spray pattern and now it works great. I have been watching for build up on my coil and have found none. Been running about 3 months. The unit does have a filter in line plus memphis water is almost mineral free anyway. I'd call it a success!!! Utility bill is down about 33% from last year too!!!:)

Electrical savings offset by increase in water bill?

You may think you're not seeing a build-up of minerals on your coils...it is in between the fins and on the tube surfaces where the true story will be told...must be one hell of a good filter if you're not seeing build-up.

I'd have to say after my preceding post that if you are seeing reduced electric usage, it is because compressor is pulling less power, but I can't see how your system has become more efficient at dumping heat. It's probably running a bit longer but using less juice to do it...seems like a savings but again you're spinning your water meter to do it.

If you want the full monty, rip out the air cooled condenser and get a cooling tower installed and you'll see rockin' good head pressures on very hot days. You'll just have to ante up for proper chemical treatment, is all. :D

[Airmechanical]

I have an 11 year old YORK split airco system, 3 ton. No TXV valve.1. I want to increase the efficiency of my HVAC system. I put some 12 water misters around the outdoor condensing coil. Water is supplied via a (compressor signal controlled) valve and water filter to take out most of
impurities. The temperature of the liquid line dropped considerable. But the air temperature coming out of the evaporator coil increased! I made a temperature log of the air temperature coming out of the evaporator coil and
when I activated the water misters, the temperature shot up more than 5 F in a matter of minutes. Superheat increased with >10FMy take on this is that more freon sits in the condensor and provides no longer enough freon to the evaporator coil.Questions:- Is it correct that by water misting the condensor, the efficiency goes up, or is this just a scam - Can I simply add more freon - If I would add more freon, will my system more efficient?
- What happens when the subcooling gets too high, can it get too high?
- Would adding a TXV valve improve this working(A good friend my is a certified HVAC tec, so he can help out.)2. These day a lot is going on about higher-SEER HVAC systems. My question: what is the main difference between a 13 SEER, 14 SEER, 15 SEER etc. The whole range between 13 SEER and 21 SEER exist.What is the difference between a 3 ton 13 SEER evaporator coil and a 3 ton 16 SEER evaporator coil? 3. Do you know about some good HVAC books that would cover this type of questions.


hmmm. another wheel reinventer!:(



.

[mark beiser]

I have only ever seen one Cool-n-Save ever. I saw it on a >100º day last year on a "not cooling well in the afternoon" call.

It was on about a 5 year old system with a TXV. With it misting water, the systems actual cooling capacity was more than 10º lower than with the water turned off.

It did indeed reduce the kw usage of the system by more than it reduced the systems capacity, but unless you started with an oversized system, you kinda need that capacity...

I think if it was misting in such a way that all of the water evaporated before hitting the coil, thus lowering the temperature of the air before it enters the coil, it could be worthwhile in extreme conditions.
Misting directly onto an air cooled condenser coil has always been, and will remain, a bad idea, for a variety of reasons.

[hvacrmedic]

For all who stated that system capacity drops due to head pressure being artificially reduced by misting system...you are right on target. :cool:

Only thing I might add to that is the importance of the pressure difference across the piston...lowering head pressure reduces the delta P. Compressor is still pumping at same speed but lower head pressure means less refer volume and velocity going to and through piston...lower mass flow through evap resulting in not as many pounds per minute circulated through evap to meet heat load imposed on coil.

For Jim's reply, there will still be an exchange of heat even if the condensing temperature is being artificially reduced via the misting system. The misting itself imposes an evaporative cooling factor, and for that to occur there must be a transfer of heat to evaporate the water droplets. If the outdoor wet bulb is low enough the wet bulb depression (WBD) can be significant...up till recent days in the Dallas area the WBD has been lousy, with wet bulb temps running in the mid to upper seventies. Not much to be gained from having misters piss on a condenser coil during those conditions except that the tap water is maybe a little cooler than the ambient air.

One of the replies above pondered what would happen regarding efficiency if the air entering condenser conditions on a 100 degree day, for example, were reduced via the misting system to, say, 85 degrees...would there be a gain in efficiency? There are a few things to consider for this scenario:

First, the effect of reduced head pressure for fixed restrictor systems has already been covered.
Second, concurrent with the first bullet above, the heat load being imposed upon the house has not changed.
Third, with reduced mass flow due to first bullet conditions (reduced head pressure), the refrigerant can't carry enough heat out of the house to match heat gain to the house.
Fourth, if one were to bother crunching the numbers for compression ratios with ericrock's data, one might say, "Well, with the misters the compression ratio is better! Why would you still think efficiency is reduced?" In this case, the lower compression ratio is due to reduced head pressure through a fixed orifice metering device, which translates to lower suction pressure. Less volume of refrigerant being circulated certainly is not offset by a lower compression ratio!A TXV might work better in eric's scenario, but a TXV alone will give eric better performance than farting around with misters on a system not designed for such a thing. Get a TXV, get the condenser and evap coils clean as a whistle, along with blower wheel (if they are not already), get the ductwork sealed as tight as possible (including supply register boots) on both supply and return sides, reduce infiltration into house, improve insulation...redirect the misters toward your patio or deck!

Most of your points are incorrect from an empirical perspective You might want to take a look at some actual performance charts, which should clear it up for you. In every one that I've looked at, capacity increases with decreasing ambient. There is more to capacity than mass flow. Take into account the reduction in flash gas, and you might find the added capacity there. Part of the evaporator heat load is the liquid entering the evap.

The only thing to be careful of with these misting systems is corrosion and "over doing it". That is, head pressure can be dropped too low, if outdoor RH is low, in which case I'd recommend a low head pressure cutout for the device, set to a saturated discharge temp of somewhere around 85º. The evap pressure has to be kept high enough to prevent freezing, which is the main problem that I ran into with the things back in the 1980's when the guy came through selling them to every gullible individual who would buy one. He sold quite a few, and I disconnected a good percentage of them. TXV systems didn't suffer freeze-up problems from them, but they did eventually cause condenser coil corrosion. I haven't seen one now in several years, so the other techs in town must've taken care of the rest.