AC Evaporative Cooling

benpope · 07-11-12, 02:14 PM

With the high temperatures and low humidity over the last few weeks, Central Arkansas has started to feel more like West Texas. The typical summer here sees temperatures in the high 90s with humidity around 85%. In the past three weeks, temperatures have been over 100 and humidity about 25%. My AC use has gone from high to really high, but the “dry heat” poses an opportunity that I didn’t have before: evaporative cooling. I’m not going to install a swamp cooler yet (we’ll see what sort of tricks climate change has in store) but, I can use evaporation to help my AC run more efficiently.

This chart shows temperature reduction of an evaporative cooler based on air temperature and relative humidity. As you can see, cooling efficiency goes down as humidity goes up, so they would be more aptly called desert coolers than swamp coolers. I think the chart is based on a cooling pad that is about 80% efficient. Spraying directly onto the coils is going to be less efficient, say 30 to 50%, so instead of seeing a 20 degree drop when air temp is 105 and RH is 25%, I may see a 10 degree drop, not as good but it will still be helpful. Overall, I guess that a mister on the AC may save 10% on the electric use, but I am going to test to see.

I was inspired by two things: a new drip irrigation system that I installed over the past month and a picture of a commercial AC mister. The commercial model uses a valve with a paddle to start water flow to three misters when the AC fan turns on. I immediately thought of the spare toilet fill valve sitting in my shed. Turned upside down, it would turn on when the float was up. Direct the water to a mister or series of them and I would be in business.

A regular fill valve won’t work—they require a lot more force to turn off than provided by gravity alone. So, I took a trip to the local Home Despot and found this flapperless fill valve. I turned it upside down and gravity was enough to turn off the valve. $50 later I had a valve, a new length of drip irrigation pipe, several 3 gph misters, and an assortment of connectors to get everything to work together. $20 was for the ½ inch irrigation pipe, much of which I will use to expand my drip irrigation setup.

Summary of jury-rigged install:

I unhooked the flapper arm and business portion of the valve and rotated it 180 degrees. I had to cut off a bit of plastic intended to prevent this.
Attached the water supply to valve with a length of ½ inch irrigation pipe, a barb fitting, and a compression fitting.
Remove the cap from the valve outlet and silicone into place a length of ½ inch irrigation pipe.
Zip tie the contraption to the AC housing.
Punch a hole in the pipe and attach irrigation mister. I am starting with one and will later test with two and three.

This took me much longer than it should because I didn’t realize that a ½ inch compression fitting is different from a regular ½ inch connection. Now I know.

Initial tests were promising. The fan blew the valve arm up and water flowed to the mister. Then the valve went down but water continued to flow.I think it is a problem with the vacuum breaker, but I am not sure. The valve works in the same way as a normal toilet valve. Thoughts on this?

Then my jury rigging chickens came home to roost. It sprung a leak. Then another. I shut it down, took everything apart, cleaned and applied new silicone to all of the connections.

Everything will be dry now, so I will take a look this evening, take some pictures, and continue the saga tomorrow.

Once everything is up and working I will test it by running the AC and timing how long it runs to drop indoor temperature from 78 to 76 in the heat of the day.

07-11-12, 02:14 PM	#1
benpope Helper EcoRenovator Join Date: Jan 2010 Location: Little Rock, AR Posts: 95 Thanks: 16 Thanked 13 Times in 12 Posts	AC Evaporative Cooling With the high temperatures and low humidity over the last few weeks, Central Arkansas has started to feel more like West Texas. The typical summer here sees temperatures in the high 90s with humidity around 85%. In the past three weeks, temperatures have been over 100 and humidity about 25%. My AC use has gone from high to really high, but the “dry heat” poses an opportunity that I didn’t have before: evaporative cooling. I’m not going to install a swamp cooler yet (we’ll see what sort of tricks climate change has in store) but, I can use evaporation to help my AC run more efficiently. This chart shows temperature reduction of an evaporative cooler based on air temperature and relative humidity. As you can see, cooling efficiency goes down as humidity goes up, so they would be more aptly called desert coolers than swamp coolers. I think the chart is based on a cooling pad that is about 80% efficient. Spraying directly onto the coils is going to be less efficient, say 30 to 50%, so instead of seeing a 20 degree drop when air temp is 105 and RH is 25%, I may see a 10 degree drop, not as good but it will still be helpful. Overall, I guess that a mister on the AC may save 10% on the electric use, but I am going to test to see. I was inspired by two things: a new drip irrigation system that I installed over the past month and a picture of a commercial AC mister. The commercial model uses a valve with a paddle to start water flow to three misters when the AC fan turns on. I immediately thought of the spare toilet fill valve sitting in my shed. Turned upside down, it would turn on when the float was up. Direct the water to a mister or series of them and I would be in business. A regular fill valve won’t work—they require a lot more force to turn off than provided by gravity alone. So, I took a trip to the local Home Despot and found this flapperless fill valve. I turned it upside down and gravity was enough to turn off the valve. $50 later I had a valve, a new length of drip irrigation pipe, several 3 gph misters, and an assortment of connectors to get everything to work together. $20 was for the ½ inch irrigation pipe, much of which I will use to expand my drip irrigation setup. Summary of jury-rigged install: I unhooked the flapper arm and business portion of the valve and rotated it 180 degrees. I had to cut off a bit of plastic intended to prevent this. Attached the water supply to valve with a length of ½ inch irrigation pipe, a barb fitting, and a compression fitting. Remove the cap from the valve outlet and silicone into place a length of ½ inch irrigation pipe. Zip tie the contraption to the AC housing. Punch a hole in the pipe and attach irrigation mister. I am starting with one and will later test with two and three. This took me much longer than it should because I didn’t realize that a ½ inch compression fitting is different from a regular ½ inch connection. Now I know. Initial tests were promising. The fan blew the valve arm up and water flowed to the mister. Then the valve went down but water continued to flow.I think it is a problem with the vacuum breaker, but I am not sure. The valve works in the same way as a normal toilet valve. Thoughts on this? Then my jury rigging chickens came home to roost. It sprung a leak. Then another. I shut it down, took everything apart, cleaned and applied new silicone to all of the connections. Everything will be dry now, so I will take a look this evening, take some pictures, and continue the saga tomorrow. Once everything is up and working I will test it by running the AC and timing how long it runs to drop indoor temperature from 78 to 76 in the heat of the day.