Dual stage evaporative cooling water setup

[ckdistills]

Here's my take on combining evaporative cooling with a water/air heat exchanger to recirculate a small amount of cooling water. Many thanks to the various threads here over the years with air cooling, evaporative cooling, and radiator cooling that got me started down this path. Can't say that this is cost effective but it sure was fun to plan & build and, living in a drought prone area, it makes me feel good using a minimal amount of water.

I'm recirculating 10 gallons of water and could use less but I want some buffer to shut it down if things go south. Plus I need enough water to cover the pump with some more to gift the evaporative gods.

Test 1
80 F cooling water - ambient is around there too. Fairly humid, reducing evaporative performance.
Boiler input 3,000 watts. Distillate is 80 F (same as cooling water). Cooling water stayed at 80 F. I think the humidity was too high to drop it under ambient. Briefly went up to 3500 watts and the cooling water started to rise, back down to 3000 and it dropped back to ambient.

Test 2
Spirit run. Low wattage (800 - 1,100) until into tails. Ended at 2,650 watts into the boiler for the last 1.5 hours of the run. Cooling water 70 F in the reservoir. Ambient 79 F. Earlier in the run with less power, reservoir water was low 60's (ambient was lower too).

Need to clean up my wiring but I'm really happy with this performance. And it would be easy to add another to double performance. Oh and those fans pull 16 watts each. 32 watts of fan, plus the pump, is dumping 3000 watts of heat out of the cooling water.

[Wildcats]

Looks like that will save you in water. Hope it works out good for you. I like when people think outside the box. Nicely done sir.

[shadylane]

Can't say that this is cost effective but it sure was fun to plan & build

That almost sounds logical.
I'll hold your beer and watch.

[LWTCS]

Nice,,,,I think?
Are you able to put together a napkin diagram?
PI&D on a wipey?

[ckdistills]

Nice,,,,I think?
Are you able to put together a napkin diagram?
PI&D on a wipey?

Here's a quick diagram. The hot condenser water goes into the radiator (1st stage), then into the PVC where it drips down through the evaporative cooler pad (2nd stage). The fans pull air through the evap pads, chilling both the water and the air. The chilled air then goes through the radiator.

Credit also to BamaBill (many others here but his is the closet inspiration to this) and this Youtube channel, specifically this video for the two stage 'aha' moment.

[GrumbleStill]

Nice one ckd. Beats the daylights out of my wet towel on a clothes horse

Are you able to share specs / links for the key components like the cooling media, fans and radiator?

Also, and just out of pure nerd interest, have you checked temps across the different parts of the setup to see where you’re getting the most cooling?

Have fun & stay safe.

[ckdistills]

Are you able to share specs / links for the key components like the cooling media, fans and radiator?

Sure thing - it adds up if you don't already have some of this.
Fans are 12v high static pressure, 223 CFM each:
Transmission cooler radiator:
Cooler pad, there are way less expensive versions if you can find the right size:

Also, and just out of pure nerd interest, have you checked temps across the different parts of the setup to see where you’re getting the most cooling?

Temps are hard to measure as the fans are pulling water to the inside of the media so my IR thermometer is measuring the media itself rather than the water. But from touch, the water coming down the media is the coldest. The radiator temps are weird - sometimes it measures warmer on the output than the input and it's never much of a gradient. Not sure what to make of that.

Full nerd post to come with CFM to cooler pad size ratios with theoretical BTU performance.

[Yummyrum]

Thanks for sharing ckdistills .

I wonder about the fans . Do they get wet with all the moist air pulling through them ? More a long time reliability thing I’m thinking.

[LWTCS]

Thanks for sharing ckdistills .

I wonder about the fans . Do they get wet with all the moist air pulling through them ? More a long time reliability thing I’m thinking.

Thinking a belt driven fan might be best for long term service life?

[ckdistills]

Radiators and air cooling can cool water to ambient temperature. An evaporative cooler can cool to ambient in high humidity or below ambient in medium / low humidity.

Its ability to cool below ambient depends significantly on both the ambient temperature and the relative humidity. There are various charts online, including this one: https://www.captiveaire.com/CATALOGCONT ... T_TEMP.ASP

We can also calculate the theoretical watts or BTU's that can be expected from a cooler.
1 watt = 3.41 BTU's.
It takes 8700 BTU's to evaporate 1 gallon of water.
For my 3500 watt/hr heating element, I need to be able to evaporate 1.37 gallons/hr.

Evaporation rate in GPH for an evaporative cooler is (CFM * dT * eff) / 8700.
CFM - cubic feet / minute of airflow through the medium
dT is the dry bulb - wet bulb temperature delta. The higher the humidity, the smaller the delta. This is hard to measure, I'm using 20 or 30 for my calcs.
eff is the efficiency of the medium. 75% is often listed for this type of media.

So to evaporate 1.37 gallons of water, we need ~530 CFM.

That Dura-Cool pad is rated for 6500 CFM given its 33" x 160" size. That's 177 cfm / ft^2. For 530 CFM, we need 3 ft^2 of it.

Building a PVC frame around two of those fans is nearly exactly 12" x 6". A height of at least 12" gives us 3 ft^2.

Those fans are each rated to 223 CFM, so a total of ~450 or 80 CFM less than I theoretically need. I also have the radiator to pre-cool the water so I decided to try it anyway as a proof of concept, figuring I could add another one if needed (first without the radiator as that doubles the price).

I'll be curious to see how this works in different seasons and temperatures. I added the radiator partly as a hedge against lower evaporative performance when it's cold. When it's cold getting water under ambient is less important so it becomes about having enough air flow and surface area to dump the heat. 

[ckdistills]

Thanks for sharing ckdistills .

I wonder about the fans . Do they get wet with all the moist air pulling through them ? More a long time reliability thing I’m thinking.

They don't get wet to the touch but I'm sure the humidity will affect service life. Though when I first put it together they were pulling actual water through the fans - you could hear the blades hitting water droplets. Reducing water flow through the media fixed that.

Given how infrequently this will be running, I'm not sure how much service life reduction matters. TBD for sure.

[ckdistills]

Thinking a belt driven fan might be best for long term service life?

Interesting! Also conducive to a large fan that pushes high CFM. I intentionally went the small fan route to keep my footprint small but we'll see about reliability.

[ecir54]

sweet, a mini cooling tower. A variable speed for the fans would be nice to tune it. the delta t split will tell you how efficient it is, nice job!!!

[GrumbleStill]

Thanks heaps for sharing all the links and specs! Very much appreciated

Thinking cap now on

[ckdistills]

sweet, a mini cooling tower. A variable speed for the fans would be nice to tune it. the delta t split will tell you how efficient it is, nice job!!!

Thanks! And can you expand on the delta t split?

There actually is a DC speed controller - though there isn't much difference between enough voltage to turn on and full voltage.

[ckdistills]

Thanks heaps for sharing all the links and specs! Very much appreciated

Thinking cap now on

Nice, look forward to seeing what you come up with. Make it better!

[ecir54]

sweet, a mini cooling tower. A variable speed for the fans would be nice to tune it. the delta t split will tell you how efficient it is, nice job!!!

Thanks! And can you expand on the delta t split?

There actually is a DC speed controller - though there isn't much difference between enough voltage to turn on and full voltage.

the split or temperature difference between the supply and return of the water. If you could get a 10-14 degree split that would be awesome.

[ckdistills]

Quick update from 1 stripping run yesterday and 3 today. I ran them at 3 kw, 5 gallon charges into my 7.75 gallon boiler. One today was flirting with puking so I dropped it to 2.75 kw. I topped up water between the 2nd and 3rd run today, probably unnecessary as I still had several inches of water above the pump.

the split or temperature difference between the supply and return of the water. If you could get a 10-14 degree split that would be awesome.

I wanted to test this but wasn't able to get reliable temperature readings from my IR thermometer. I think the CSST and aluminum or brass fittings are too reflective to get a reliable reading. It said the output and input were both around 73 F, which from feeling them I knew wasn't true. And my water hose is partially transparent so can't take readings from it either. The output was noticeably warmer. Here's what I do know from today's 3 back to back runs:

Highest ambient temp during run: 73 F
Humidity (from weather report not measured): 75%
Highest reservoir temp: 73 F (though I didn't measure this often)
Highest distillate temp: 95 F
Cooling water input temp: assuming 73 F
Cooling water output temp: noticeably warmer than input, close but not as warm as the distillate
Cooling water flow rate: 0.9 gallons/minute

I'd like to play with the flow rate and see how low I can go. My guess is that going much lower won't work very well as there needs to be enough water going through the evaporative medium to wet out the medium.

Edit: corrected gallons/hour to gallons/minute

[Chauncey]

Super cool. Hehe see what I did there? Really though I had been thinking about something along these lines for a while but never saw it thru. We need more stuff like this, and you definitely seem to know your stuff man. Keep up the good work and keep on posting.

I assume the apparatus warms the room up a bit eh?

[Salt Must Flow]

It seems to me that all you would need is a thermometer probe (or thermowell) on the output of the radiator and a thermometer probe in the reservoir. That would tell you exactly what the radiator is doing vs the reservoir temp. The reservoir temp would likely read the exact same temp as if you had a thermowell on the input of the radiator so that would probably be redundant, an unnecessary expense and wasted effort.

The only way I can think of to test exactly what the evaporative medium is doing vs the temp of the output of the radiator, is to have a separate vessel (let's say a cookie sheet) to collect that water into with another temp probe. Allow it to collect only enough water to overflow into the reservoir. Forget those IR thermometers. They're not accurate for this use as you've already experienced. Personally I prefer digital thermometers, ideally with temp alarms settings if you are trying to adjust water flow rates in order to stay within a certain temp range. This is the one I've been using for years. I'm not saying it's the best, the cheapest or anything, it's just the one I've been using for lots of uses and has worked great for me. I use it on the output of my condensers to adjust my flow rates to make sure they stay within a certain temp range.

[ckdistills]

Super cool. Hehe see what I did there? Really though I had been thinking about something along these lines for a while but never saw it thru. We need more stuff like this, and you definitely seem to know your stuff man. Keep up the good work and keep on posting.

I assume the apparatus warms the room up a bit eh?

Appreciate it! To be honest it's a combination of reading and thinking way too much. It's always rewarding to move from the planning to doing stage and this one particularly has worked out better than I thought it would

I run my water lines through a window so all the heat dissipation (and humidity) is outside. I can hear the fans run and have a flow rate gauge on the condenser so I will know if the pump or fans fail.

[ckdistills]

The only way I can think of to test exactly what the evaporative medium is doing vs the temp of the output of the radiator, is to have a separate vessel (let's say a cookie sheet) to collect that water into with another temp probe.

Yea, that could work but I probably won't go through the trouble. While it would be neat to calculate efficiency, grabbing the input and output hoses to feel the temp gradient and ensure the input isn't warm works for now.

[Smog]

I run the returns from the reflux and the condenser shotguns through a 3 tons AC evaporator out of an old air handler. The output from the evaporator is dumping into a pail where the 2 small 12v pumps are pumping up the cooler water to the reflux and condenser.

[ckdistills]

Figured it was time for an update on this setup now that I've used it for dozens of runs over the last nearly year and a half.

Durability:
I've had a couple of failures, in the last run one of the two fans in the evaporative cooler didn't come on. Didn't seem to affect performance so it may have had more airflow than necessary before. I also had to replace the pump awhile back. I'm using inexpensive pond pumps, imagine that is affecting durability. It has not been babied - it's stored uncovered outside and often with water left in the reservoir for longer than I care to admit. Sometimes water flow slows down and then I back flush it with high pressure mains.

Performance:
It still works! Distillate does come off hot on stripping runs over 3000 watts. I usually run at or a bit under 3kw. This is worse in the summer. Spirit runs at lower power are fine.

I'd like to get the distillate temperature down when stripping but haven't put much effort in yet. Given that one fan works just as well as two, more evaporative pad is where I'd start. I like the small footprint so I'd start by making it taller.

[quadra]

Keep your eyes open for a centerfugal or squirrel cage type fan, they are more effective at developing the pressure your system needs. Inductor fans from dead direct vented furnaces or hot water heaters are a good source.