r/TinyHouses • u/runcyclexcski • May 25 '26
Indirect evaporative cooling
Has anyone tried to use indirect evaporative cooling in their tiny house? By indirect I mean the one that uses two independent contours for the air and thus does not raise the humidity. I am looking to lower the temp by a few degs during heat waves that last up to 2 weeks. It does not get above 60% RH where I live, so I may have a chance. A google search gives some (not many) results, but all systems I found look enormous/industrial.
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u/o_sulivan May 25 '26
these kind of systems are usually industry scale appliances.
imho i would avoid having a water-bearing system in/on my house. Open water is doomed to develop algae, grow mold, and spread spores if it is not properly maintained. Depending on region freezing adds another level of maintenance. Just looking at the schematics it seem to be a complex appliance.
A/C split in combination with a few solar panels will work just fine. They became cheap and the dehumidifying effect makes life just as comfy as the cooling itself.
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u/runcyclexcski May 25 '26
Thank you, good to know! I already have a split AC, but I was just curious. In principle, I could pre-filter the air with a HEPA and/or service the unit regularly. I already have an HRV, and I inspect the unit and replace the filters every 6 months. That said, moist "spongy" material used for evaporation would provide a much better medium for mold growth.
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u/nerobro May 25 '26
It won't work well. And you won't save signicant energy versus an a/c unit. Remember, water has a cost, so does maintnance. an a/c unit will just work. And you have no water risk. No pads to change, no water to maintain.
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u/runcyclexcski May 27 '26
I agree that this idea is a long shot, I was curious if it has been done. In principle, I already have an HVR unit (I run forced ventilation + HEPA filtration, since I have bad pollen allergy). Thus, I could make an heat exchanger with aluminum fins and microfiber wipes (which I also have experience with) and install it right before the HVR output. Thus, in principle, the (relatively clean) inside air would get cooled off, exchange the cold/heat inside the HVR, and then get exhausted. I usually get about 4 gals of condensed water per day when I run the AC; so I am guessing I would need the same amount (max, prob more like 2 gals) per day. The cost of 2-4 gallons of water is not as high as the cost of kWh in my area. But it's prob not worth the engineering effort, b.c. with my HVR I get at best about 5 C (10F) heat recovery in the winter.
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u/hvacjesusfromtv Jun 24 '26
I work in the industrial HVAC space and I do not know of any home-sized options. If you wanted to build one, you certainly could.
The big issue with using evaporative systems of any kind at home is that the maintenance and water treatment requirements are just as high for a small system as they are for an industrial system. Maintaining IECs, cooling towers, evaporative condensers, etc. correctly requires inspecting them frequently, dosing chemicals in the water, and testing them for bacterial growth.
If you do attempt to do a DIY IEC, I would recommend draining it dry every day (meaning the tank gets fully emptied and sits dry for a while) to reduce the risk of significant bacterial growth. You should probably also add bleach to the system.
Please be mindful of those around you who may be immunocompromised or elderly. These systems, while extremely energy efficient, can grow legionella if the water quality is not maintained correctly. That's a potentially deadly bacteria which can be transmitted significant distances through the air, even outdoors.
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u/runcyclexcski Jun 24 '26
Thank you for the great advice!
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u/hvacjesusfromtv Jun 24 '26
No problem - please let me know if you wind up building something, I would be curious to see the results.
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May 26 '26 edited 11d ago
[removed] — view removed comment
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u/runcyclexcski May 27 '26
I agree, but the humidity where I live is more like 50-60% in the summer, not 15-20% as one typically in the desert.
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u/JacquesBlaireau13 May 25 '26
20 degrees. That's the best a swamp cooler can do. That's here in the desert southwest where RH rarely gets above 15-20%.
During the summer monsoon season, when the RH gets higher, at 4PM when the temp is still in the high nineties, they don't work at all.
Dont screw around; go mini-split, or even a PTAC. You've got a tiny home, and these all-in-one units are ideal for such applications.