A/C Condenser Evaporative Cooling Assist

[dclark1946]

I am wondering if any company offers an evaporative cooler designed to reduce RV A/C condenser inlet air temp to assist in 95+ deg temps? I designed such a system (inspired by some mechanical engineers I worked with) for our residential central A/C back in the late 70's when the condensing units had coils only on one side making the design much simpler. I had the system in place during the torrid 1980 TX heat wave when peak temps reached 113 deg. The system functioned as a nearly constant condenser inlet temperature regulator. As the temperature increased during the day the relative humidity decreased and the evaporative cooling delta t increased so for outside ambient air temp of 113 deg the condenser inlet air temp was 85. This reduced compressor hgh side pressure and consequently lowered current draw. Our unit cycled nicely even in those extreme temps.

The main complication for RV A/C applications to me is the condensing air inlet being on both sides of the unit requiring some ducting of the evaporative cooler's output air or maybe an enclosure over the whole unit except for the back for the condenser's air exhaust with a single duct feeding the cooled air to the enclosure. Maybe just block off the side inlets and feed the cooled air into the units cover.

Based on Coleman's Evaluating RV A/C performance document, you would expect compressor current draw to increase 1A over LRA for every 5 deg above 95 and also decrease the same amount for every 5 deg below 95 so there would be benefits for reducing power consumption.

I would welcome any thoughts/feedback.

[pianotuna]

dclark1946 wrote:

I thought you were referring to the rooftop RV evaporative cooler where you would keep a window open for proper operation. The reason your cooler did not work is because it kept raising the interior humidity level to the point that very little evaporative cooling could occur. These coolers only work when you have a continued fresh supply of outside air.

I'm aware of the need to have a way to exhaust air when running a roof top evaporative cooler.

The input air was at 27 C, the output air was about 4 C cooler, at 23 C. The physical temperature in the RV rose as the out door temperature peaked at 31 C. I did take humidity readings--but I failed to record them.

I'm comfortable up to 25 c (77 f). The recirculating air evaporative cooler I purchased was not able to maintain the RV at 25 C, even though the makers rating was for 500 square feet when my RV is 241 square feet.

[red31]

dclark1946 wrote:
These coolers only work when you have a continued fresh supply of outside air.

and big A fan, w tx bbq slamming screen door comes to mind, with roof top evap the front door was screened with a heavy duty spring

[dclark1946]

pianotuna wrote:

dclark1946 wrote:

pianotuna wrote:
Chum lee,

Where I live--I do on occasion run a humidifier in my RV. But never in the summer. Our relative humidity goes from 4% to 84% on a yearly basis.

Even with our relatively low humidity I found the swamp cooler I bought, rated for 500 square feet, did just about nothing for the 241 square feet in my class C.

Here is the one I was referencing: https://www.turbokool.net/product-p/2b-0001-turbokool-swamp-cooler.htm

They don't share the picture--how odd of them.

Did you open a window to allow the outside air pulled into the evaporative cooler to push the trailer air outside? These systems are commonly used for interior cooling in dry climates where the cooling is greater and increase in interior humidity is a desired benefit. We used evaporative cooling in Dallas when I was a kid with cooler pads in three windows and a centrally located attic fan that pulled outside air through the wet pads and exhausted interior air out through the attic.

Hi,

The unit I purchased is a "stand alone" device that recirculates the air in the room. It did lower the temperature of the out put air--but there was too little cooling going on to keep up with the sun--even thought I had purchased something that was supposed to be good for double the area I was attempting to cool.

I thought you were referring to the rooftop RV evaporative cooler where you would keep a window open for proper operation. The reason your cooler did not work is because it kept raising the interior humidity level to the point that very little evaporative cooling could occur. These coolers only work when you have a continued fresh supply of outside air.

[dclark1946]

Chum lee wrote:

dclark1946 wrote:
Chum lee,

The evaporative cooling system I am proposing raises the humdity only of the outside air passing through the condenser unless the RV A/C is not sealed properly and allows leakage between outside and interior (conditioned) air. It should function like the home central A/C system I referred to in my original post. Not only does the humidified cooled air benefit the condenser because of the lower temperature but the denser humid cool air is more efficient in removing heat from the condenser coils.

I understand what you are doing and I agree with you. It will work. However, how much time have you spent traveling/living in an RV? Most who have realize that water is always at a premium when they are out and about. (boondocking/camping/fishing/hunting/etc.) If you prefer to stay in an RV park, generally, water/electricity/sewage are no big deal. IMO, you are trying to solve a problem that doesn't exist.

I don't know what else to say to you other than "live and learn."

Chum lee

Apparently you have not comprehended my posts with regard to where I would use the A/C assist. I listed two different specific scenarios at home where this would be most beneficial for us. We have been camping in travel trailers since 1999 and have traveled thousands of miles. We typically do not camp at locations where the daytime temperature is expected to be above mid 90's although we often stay at a commercial campground overnight (where there have been upper 90 deg daytime temps ) heading to a cooler more scenic final destination where we will dry camp and not require A/C. However on a North Texas RV website there have been multiple posts by those trying to camp in recent NT 100+ deg weather who find their RV A/C is not up to the task of maintaining comfortable temp. I think these campers might also benefit from such a system and since they are camping mostly either in state parks or commercial camp grounds water supply should not be an issue.

[pianotuna]

dclark1946 wrote:

pianotuna wrote:
Chum lee,

Where I live--I do on occasion run a humidifier in my RV. But never in the summer. Our relative humidity goes from 4% to 84% on a yearly basis.

Even with our relatively low humidity I found the swamp cooler I bought, rated for 500 square feet, did just about nothing for the 241 square feet in my class C.

Here is the one I was referencing: https://www.turbokool.net/product-p/2b-0001-turbokool-swamp-cooler.htm

They don't share the picture--how odd of them.

Did you open a window to allow the outside air pulled into the evaporative cooler to push the trailer air outside? These systems are commonly used for interior cooling in dry climates where the cooling is greater and increase in interior humidity is a desired benefit. We used evaporative cooling in Dallas when I was a kid with cooler pads in three windows and a centrally located attic fan that pulled outside air through the wet pads and exhausted interior air out through the attic.

Hi,

The unit I purchased is a "stand alone" device that recirculates the air in the room. It did lower the temperature of the out put air--but there was too little cooling going on to keep up with the sun--even thought I had purchased something that was supposed to be good for double the area I was attempting to cool.

[Chum_lee]

dclark1946 wrote:
Chum lee,

The evaporative cooling system I am proposing raises the humdity only of the outside air passing through the condenser unless the RV A/C is not sealed properly and allows leakage between outside and interior (conditioned) air. It should function like the home central A/C system I referred to in my original post. Not only does the humidified cooled air benefit the condenser because of the lower temperature but the denser humid cool air is more efficient in removing heat from the condenser coils.

I understand what you are doing and I agree with you. It will work. However, how much time have you spent traveling/living in an RV? Most who have realize that water is always at a premium when they are out and about. (boondocking/camping/fishing/hunting/etc.) If you prefer to stay in an RV park, generally, water/electricity/sewage are no big deal. IMO, you are trying to solve a problem that doesn't exist.

I don't know what else to say to you other than "live and learn."

Chum lee

[dclark1946]

pianotuna wrote:
Chum lee,

Where I live--I do on occasion run a humidifier in my RV. But never in the summer. Our relative humidity goes from 4% to 84% on a yearly basis.

Even with our relatively low humidity I found the swamp cooler I bought, rated for 500 square feet, did just about nothing for the 241 square feet in my class C.

Here is the one I was referencing: https://www.turbokool.net/product-p/2b-0001-turbokool-swamp-cooler.htm

They don't share the picture--how odd of them.

Did you open a window to allow the outside air pulled into the evaporative cooler to push the trailer air outside? These systems are commonly used for interior cooling in dry climates where the cooling is greater and increase in interior humidity is a desired benefit. We used evaporative cooling in Dallas when I was a kid with cooler pads in three windows and a centrally located attic fan that pulled outside air through the wet pads and exhausted interior air out through the attic.

[dclark1946]

Chum lee,

The evaporative cooling system I am proposing raises the humdity only of the outside air passing through the condenser unless the RV A/C is not sealed properly and allows leakage between outside and interior (conditioned) air. It should function like the home central A/C system I referred to in my original post. Not only does the humidified cooled air benefit the condenser because of the lower temperature but the denser humid cool air is more efficient in removing heat from the condenser coils.

[pianotuna]

Chum lee,

Where I live--I do on occasion run a humidifier in my RV. But never in the summer. Our relative humidity goes from 4% to 84% on a yearly basis.

Even with our relatively low humidity I found the swamp cooler I bought, rated for 500 square feet, did just about nothing for the 241 square feet in my class C.

Here is the one I was referencing: https://www.turbokool.net/product-p/2b-0001-turbokool-swamp-cooler.htm

They don't allow sharing the picture--how odd of them.

[Chum_lee]

pianotuna wrote:

Chum lee wrote:


Key words: Home (residential) system, not motorhome. (there is a difference) Hey look, bang your head against the wall. Make evaporative cooling work in a motorhome and you could be the next Bill Gates, Elon Musk, etc. Good luck to you!

Chum lee

Chum Lee,

There is, or was, a commercially available evaporatetive cooler designed for use in an RV. However, it was about the same price as a regular roof top unit.

Hi Don: IMO, there's no reason why you couldn't put an evaporative cooling system on any MH. They WORK. BUT only in hot dry climates (0-20% relative humidity) where you have a readily available supply of fresh water. (like 10 gallons per day) In my Class A MH with an 80 gallon fresh water tank, that simply doesn't work. (especially while boondocking in the deserts SW) Now if I'm staying in an RV park with full hookups, I just use the regular rooftop AC unit which works fine. I'm not interested in adding the complexity of an evaporative cooling system to an HVAC system that already works fine without it. IMO, excessive moisture inside a motorhome is always a bad idea. If you look at the RV industry, in general, they seem to agree with me. (well more accurately, ego set aside, I agree with them)

I've been designing/building things for over 50 years now. Evaporative cooling systems are an economical solution and definitely have their place. IMO, a motorhome is NOT one of them.

Chum lee

[pianotuna]

Chum lee wrote:


Key words: Home (residential) system, not motorhome. (there is a difference) Hey look, bang your head against the wall. Make evaporative cooling work in a motorhome and you could be the next Bill Gates, Elon Musk, etc. Good luck to you!

Chum lee

Chum Lee,

There is, or was, a commercially available evaporatetive cooler designed for use in an RV. However, it was about the same price as a regular roof top unit.

[dclark1946]

Chum,
Yes which is why I am soliciting inputs to see if anyone else has adapted this approach to an RV A/C system. I have two specific scenarios where I would use this. Every summer we prep our trailer for trip to the mountains. Usually temps are in upper 90's to mid 100's and we are operating our A/C to assist the RV fridge during a 2-3 day prep period. The trailer sits in full sun so the A/C is at its limits and runs nearly continuously during the hot part to maintain 83 deg. The other scenario is in case of a neighborhood power outage during a heatwave. In this case we plan on moving to our trailer since it is parked in our back yard and can easily power it and A/C with a pair of EU 2000's.

[Chum_lee]

dclark1946 wrote:

Chum lee wrote:

dclark1946 wrote:

Chum lee wrote:
Yep, it works, but only in hot dry climates when you have a relatively pure inexhaustible water source. Try that in the desert in any MH. Come on guys, you have ask yourself WHY ALL the major HVAC manufacturers DO NOT do this for their factory installations. It's all you 100 mpg carburetor, fuel additive, free energy, Banks chip tuning, tweaky guys who want to talk endlessly about these things. (with NO long term substantiated evidence)

Chum lee

The quality of the water is not an issue since you are not spraying water on the condenser coils. You are pulling hot ambient air over a wet pad and part of the pad moisture evaporates which cools the air before it passes over the condenser coils. The water that does not evaporate returns to the reservoir and is pumped back up to the top of the pad. You only have to replace the water that evaporates from the pad. In the example I gave in Dallas we had 113 deg air temp one summer and the air leaving the Aspen pad was 85 deg. That dropped the compressor high side pressure and reduces the power consumption. For a 95 deg day the electrical consumption was reduced about 14%. Even better I was not losing BTU capacity as the temp went above 95.

Well, we'll have to disagree on that. Eventually the dissolved solid content of the water precipitates out on the pads, (or someplace else) unless you flush the system regularly. That's why you have to replace the pads. Lived in the deserts SW for years. This is no news. I suggest you take/pass a college level general chemistry class. Not a sales/marketing class.

Chum lee

Theoretically you are correct however we have a significant amount of minerals in our Dallas water supply and from a practical standpoint it was not an issue. I operated our evaporative cooling home central A/C assist for about 6 years each full cooling season and replaced the pad at the beginning of each season and the cooling remained effective over the season.

If you recall, the earlier residential central A/C systems condensers were water cooled. The heated water was pumped to a redwood cooling tower which sprayed the water downward at the top of the tower and the water dripped down the wood tower slats partially evaporating and cooling the water which was then collecting at the bottom of the reservoir and then pumped back to the condensor. These systems were more efficient compared to the air cooled systems introduced later. The major issue with the cooling towers was algae buildup requiring periodic draining and flushing and addition of chemicals to minimize algae growth.

With regard to taking a college level chemistry class, I have a MS in electrical engineering so yes I have completed college level chemistry. I was inspired to investigate this technique to improve residential A/C efficiency after discussing this with mechanical engineers that worked on the same government DOD program I did. They were building their own version of this type of cooling system.

Key words: Home (residential) system, not motorhome. (there is a difference) Hey look, bang your head against the wall. Make evaporative cooling work in a motorhome and you could be the next Bill Gates, Elon Musk, etc. Good luck to you!

Chum lee

[red31]

dclark1946 wrote:
Your calcium filter work pretty good for you. Which one did you use?

Not sure it did much as the misters clogged regularly, cleaned with striped bread twist tie wire or replace w/ new or vinegar soaked, inline calcuim inhibitor for outside misting

Calcium inhibitor

[dclark1946]

red31 wrote:

dclark1946 wrote:

I decided to not pursue the misting approach partially due to the issues you mentioned as well as mineral buildup on the condenser coils. I would however be interested in any test data you can share with/without misters vs temp.

I used 1/2" PVC coupler with brass mister, 24v irrigation valve powered via outside compressor unit, wall mounted thermostat to come on over 90F, inline calcium filter. Final config (Mr. Mister) was PVC on the ground ~12" from unit with 2 misters per 3 sides. Measured rotation of electric meter with mist was 10% longer for one revolution. Misters clogged often, 20+y/o freon unit, replaced that winter. IIRC, 10F drop in exit air temp.

Nice piece of engineering. The devil is in the details. I used the watt hour meter revolutions over 10 minutes to compare power consumed with/without cooling before committing to designing and building my home system. Your calcium filter work pretty good for you? Which one did you use?