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.

[C_Schomer]

Our rv ACs and existing compressors would benefit GREATLY with larger coils and more airflow to bring the DTs down and that would automatically increase efficiency... N.R.E. The evap. would bring the sensible load down better and not so much the latent load. But, we only get cheapo engineering/design in our rv junk. Craig

[dclark1946]

PatJ wrote:
I like the idea and would love anything that would make RV AC more effective or efficient, and wish you the best of luck overcoming the issues with using water to assist the condenser in an RV.

In the meantime, it seems to me the effort is best spent just using a much larger condenser and much larger condenser fan for increased efficiency. Of course then we would need a variable speed condenser fan and compressor to keep the pressures in check, maybe an electronic TXV, and a computer to run the whole thing. This is starting to sound like a modern mini-split!.

Most current RV roof air conditioners use 1960s/1970s window banger technology. They could make a rooftop RV air conditioner with a very superior performance and efficiency to what's available now, but it would be $4500 instead of $800. You and I may buy one for that, but unfortunately we are the minority RV buyer at the moment.

We do have the Coleman Mach 3 PS 13.5 which has a higher efficiency compressor (scroll I think) and larger condenser compared to their standard 13.5 Mach 3. Currently only have 15A service in our back yard where our trailer is parked and that works well except in the middle 9f Aug. in full sunlight.

[dclark1946]

PatJ wrote:
I like the idea and would love anything that would make RV AC more effective or efficient, and wish you the best of luck overcoming the issues with using water to assist the condenser in an RV.

In the meantime, it seems to me the effort is best spent just using a much larger condenser and much larger condenser fan for increased efficiency. Of course then we would need a variable speed condenser fan and compressor to keep the pressures in check, maybe an electronic TXV, and a computer to run the whole thing. This is starting to sound like a modern mini-split!.

Most current RV roof air conditioners use 1960s/1970s window banger technology. They could make a rooftop RV air conditioner with a very superior performance and efficiency to what's available now, but it would be $4500 instead of $800. You and I may buy one for that, but unfortunately we are the minority RV buyer at the moment.

We do have the Coleman Mach 3 PS 13.5 which has a higher efficiency compressor (scroll I think) and larger condenser compared to their standard 13.5 Mach 3. Currently only have 15A service in our back yard where our trailer is parked and that works well except in the middle 9f Aug. in full sunlight.

[time2roll]

whjco wrote:
We have a 34' Cherokee with a 15k BTU Dometic AC unit. We've had it in high humidity 98 degree weather in Alabama and it keeps up just fine. There may be some issue with the AC unit or, if it's ducted, it might have a leak that's blowing cold air into the attic area.

I think 90% have this issue. Some worse than others.

[PatJ]

I like the idea and would love anything that would make RV AC more effective or efficient, and wish you the best of luck overcoming the issues with using water to assist the condenser in an RV.

In the meantime, it seems to me the effort is best spent just using a much larger condenser and much larger condenser fan for increased efficiency. Of course then we would need a variable speed condenser fan and compressor to keep the pressures in check, maybe an electronic TXV, and a computer to run the whole thing. This is starting to sound like a modern mini-split!.

Most current RV roof air conditioners use 1960s/1970s window banger technology. They could make a rooftop RV air conditioner with a very superior performance and efficiency to what's available now, but it would be $4500 instead of $800. You and I may buy one for that, but unfortunately we are the minority RV buyer at the moment.

[whjco]

We have a 34' Cherokee with a 15k BTU Dometic AC unit. We've had it in high humidity 98 degree weather in Alabama and it keeps up just fine. There may be some issue with the AC unit or, if it's ducted, it might have a leak that's blowing cold air into the attic area.

[dclark1946]

Craig,

Thanks for you comments on the commercial application of evaporative cooling to assist A/C operation. I found it informative.

[C_Schomer]

In the 70s and 80s I added sub coolers... water cooled exchangers and Penn head pressure control valves in the liquid lines of condensing units that were in hot equipment rooms and overworked ACs and that worked terrific to increase NRE - net refrigeration effect.
I remember seeing swamp cooler frames and pads that could be added to the face of condenser coil's and it dripped water over the pads just like a swamp cooler and cooled the air before it went thru the cond. coil. I thought that was a great idea but I was working at a plant with well over 100 RTUs and I had a bunch of large ones, up to 80 tons, with horizontal coils and swamper pads wouldn't have works. We had excellent water with very low hardness and I ran lawn sprinklers under those coils until I could add liquid line subcoolers, cooled with plant chilled water, to them.
I've been thinking about adding something to my home condensing unit. Swamper pads require staying on top of the maintenance. If the water were to stop, there would be a big air restriction in front of the coil, but the liquid line subcooler with a Penn control valve is fully automatic and will maintain a preset liquid line temperature no matter what the conditions are. Also, there's no negative effect if the water stops.
I also added a water subcooler to my recovery machine and it cut recovery time to a fraction of the time. Craig

[dclark1946]

pianotuna wrote:

dclark1946 wrote:

I don't understand how any kind of evaporative cooler can function to lower temperature in a closed environment regardless of where it is located. The cooling process adds moisture to the air raising the interior humidity and if it is just recirculating it keeps adding more humidity to the air reducing the cooling. To me it seems somewhat similar to operating a window A/C unit totally inside your closed RV with the cooled evaporator air and heated condenser air both being blown into your RV.

Then you don't understand that when water evaporates the temperature is lowered.

It is NOT at all similar to a window A/C operating inside.

I must be doing a terrible job of communicating on this post. I was trying to use an analogy with the window unit substituting temperature for humidity. I fully understand that when water evaporates the air is cooled. The lower the relative humidity the greater the cooling. I used that principle in the A/C assist evaporative cooler I designed, built and used successfully for years. However when the air is cooled by evaporation the air moisture content is increased. If you keep recycling the air through the evaporative cooler in a closed environment (no outside air brought in) the relative humidity will continue to increase and the evaporation process will give you less and less cooling. I hope I have explained it clearly.

[pianotuna]

dclark1946 wrote:

I don't understand how any kind of evaporative cooler can function to lower temperature in a closed environment regardless of where it is located. The cooling process adds moisture to the air raising the interior humidity and if it is just recirculating it keeps adding more humidity to the air reducing the cooling. To me it seems somewhat similar to operating a window A/C unit totally inside your closed RV with the cooled evaporator air and heated condenser air both being blown into your RV.

Then you don't understand that when water evaporates the temperature is lowered.

It is NOT at all similar to a window A/C operating inside.

[Chum_lee]

dclark1946 wrote:
Chum lee,

I get it that you understand the technical concept of evaporative cooling to assist the A/C by significantly reducing condenser temperature. Your responses however seem to suggest that this is an impractical solution looking for a suitable problem. I have already demonstrated to myself how well it works on a home residential system under extreme temp conditions. I would agree that under normal camping conditions there is no need to assist an RV A/C. It is the extreme high ambient temperature conditions that I routinely run into every year (as do others camping in Jul/ Aug here in TX) where the heat load exceeds the A/C BTU capacity (which unfortunately is decreasing as temps go above 95) that would benefit.

Yes. Your idea is a good one but only within the narrow range of the application you want to use it for. IMO, most people want simple broad range solutions that work well ALL THE TIME because they are lazy (I am too) and don't want to be bothered with endless complicated technical issues. I encourage you to continue your education, work hard, build your experience, find solutions, and figure out a way to make them work.

Chum lee

[dclark1946]

Chum lee,

I get it that you understand the technical concept of evaporative cooling to assist the A/C by significantly reducing condenser temperature. Your responses however seem to suggest that this is an impractical solution looking for a suitable problem. I have already demonstrated to myself how well it works on a home residential system under extreme temp conditions. I would agree that under normal camping conditions there is no need to assist an RV A/C. It is the extreme high ambient temperature conditions that I routinely run into every year (as do others camping in Jul/ Aug here in TX) where the heat load exceeds the A/C BTU capacity (which unfortunately is decreasing as temps go above 95) that would benefit.

[Chum_lee]

dclark1946 wrote:

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.

Yes, I do understand what you are doing. You are using an evaporative cooler to precool the air that flows across the condenser coils hoping to improve the efficiency of the AC compressor/evaporator coils. Correct? This IS NOT a new idea. It does work, but only in hot/dry climates where you take advantage of the high heat of vaporization of water and you have a readily available water source. When/if the relative humidity gets above +-30%, the system efficiency drops off sharply.

There are many currently available commercial misting systems that do the same thing without the evaporator pads/housing/pumps/sumps/etc.

Have you thought about what happens to the evaporative cooler sump water when you travel in the RV? Where does it spill off to?
(Accelerating/turning/braking on super elevated/off camber/inclined/potholed roadways) Depending on your final design you may have to drain the sump so it doesn't slosh around in the pan while driving. Most evaporative coolers are designed for stationary fixed applications. In the 50's and 60's you could buy an aftermarket evaporative cooling system for automobiles. They mounted in a partially open window and THEY WORKED while travelling at speed on the highway, but you rarely see them any more. Why do you think that is? (hint: modern automotive HVAC systems rendered them obsolete and inconvenient)

Chum lee

[dclark1946]

pianotuna wrote:

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.

I don't understand how any kind of evaporative cooler can function to lower temperature in a closed environment regardless of where it is located. The cooling process adds moisture to the air raising the interior humidity and if it is just recirculating it keeps adding more humidity to the air reducing the cooling. To me it seems somewhat similar to operating a window A/C unit totally inside your closed RV with the cooled evaporator air and heated condenser air both being blown into your RV. Except in this case you would dehumidfy the air but not see any net cooling because the heat you absorbed in the A/C evaporator would be pumped right back into the RV via the condenser.