From the rain. They have a built-in reservoir at the bottom, and use a little bit of electricity to pump the water up. And then water is collected back at the bottom etc
Yeah so if you’ve had two months of 35+ degree days and only a couple mm of rain it does nothing but soak up more heat. Like the above commenter said, there are probably places in a sweet spot for this, but it also wouldn’t work in many places. They even addressed your point about rain directly.
I might be wrong, but I remember seeing some numbers and your toilet would use more water than a similar system, so I still think it might be worth it (unless you use compost toilet with no water, then the comparison goes kaput). Let me try to find the source
Anyone please feel free to correct any misconceptions I might have had below, if you have more examples, let me know too:
Keep in mind that stuff like this is expected to vary a lot depending on design, temperatures, solar irradiance, humidity, shapes, water flow, wind speed, wind direction, drag, etc
For comparison, misting systems, which can be a popular
technique to improve outdoor comfort in public spaces, might use around 0.8 l/h per misting nozzle
Another experimental study using porous ceramic water containers measured cooling capacity approaching 225 W/m² of exposed wet ceramic surface under hot and dry conditions (30–35°C air, 35–50% RH).
Considering latent heat of vaporization of water is about 675 Wh/kg at 30°C, it would give us an evaporation rate of around 0.333 and 0.415 l/h for the previous 2 studies respectively
If we consider that, on average, a healthy adult goes between 4-10 times per day to the toilet and that each time you flush, you can use between 4 to 22 liters of water depending on the efficiency of your toilet… yeah, I think we can agree we might have a bigger problem with water usage somewhere else
Summary of water usage below assuming the system is up 24 hours per day, which was not the case in all above examples
—
Liters per 24h
Study 1
9.6 - 26.4
Misting nozzle
26.4
26-36 °C / RH 72%
18.9
30-35 °C / RH 35-50%
8
45 °C / RH 50%
10
Water Efficient toilet
16 - 40
Old inefficient toilet
88 - 220
So if you haven’t already, and if you can, change your toilet with more efficient option. Bonus points if you get a bidet
TLDR: You are more likely to waste more water going to the toilet than having a passive evaporative cooling wall
From the rain. They have a built-in reservoir at the bottom, and use a little bit of electricity to pump the water up. And then water is collected back at the bottom etc
Yeah so if you’ve had two months of 35+ degree days and only a couple mm of rain it does nothing but soak up more heat. Like the above commenter said, there are probably places in a sweet spot for this, but it also wouldn’t work in many places. They even addressed your point about rain directly.
I might be wrong, but I remember seeing some numbers and your toilet would use more water than a similar system, so I still think it might be worth it (unless you use compost toilet with no water, then the comparison goes kaput). Let me try to find the source
Find it?
Anyone please feel free to correct any misconceptions I might have had below, if you have more examples, let me know too:
Keep in mind that stuff like this is expected to vary a lot depending on design, temperatures, solar irradiance, humidity, shapes, water flow, wind speed, wind direction, drag, etc
Based on “Design integration of novel porous ceramic evaporative cooling systems”, their design had a water consumption ranging from 0.4 to 0.8 l/h/m² (liter per hour per square meter of surface area) (whereas predicted data from simulation was around 0.4 to 1.1 l/h)
For comparison, misting systems, which can be a popular technique to improve outdoor comfort in public spaces, might use around 0.8 l/h per misting nozzle
On another study, “Experimental study of cooling effects of a passive evaporative cooling wall constructed of porous ceramics with high water soaking-up ability” DOI, shows an evaporation rate of 20.7 kg/day for an area of 1.1m², converting to l/h/m², it is around 0.784 l/h, where it had max-min air temperatures at 36.4 and 26.2 °C, relative humidity (RH) at 72% and mean wind speed at 0.6 m/s
Another experimental study using porous ceramic water containers measured cooling capacity approaching 225 W/m² of exposed wet ceramic surface under hot and dry conditions (30–35°C air, 35–50% RH).
Computer modelling and experimental investigation of building integrated sub-wet bulb temperature evaporative cooling system DOI
A separate study, from the same author at different conditions, with air temperatures up to 45°C and RH up to 50%, found up to 280 W/m²:
Investigation of an Evaporative Cooler for Buildings in Hot and Dry Climates DOI
Considering latent heat of vaporization of water is about 675 Wh/kg at 30°C, it would give us an evaporation rate of around 0.333 and 0.415 l/h for the previous 2 studies respectively
If we consider that, on average, a healthy adult goes between 4-10 times per day to the toilet and that each time you flush, you can use between 4 to 22 liters of water depending on the efficiency of your toilet… yeah, I think we can agree we might have a bigger problem with water usage somewhere else
Summary of water usage below assuming the system is up 24 hours per day, which was not the case in all above examples
So if you haven’t already, and if you can, change your toilet with more efficient option. Bonus points if you get a bidet
TLDR: You are more likely to waste more water going to the toilet than having a passive evaporative cooling wall
Solid effort cheers