> Would attaching a heat sink to my shed cool it below the ambient temperature?
To which the answer is obviously no.
Except it's "yes" if you define "ambient temperature" as the temperature inside the shed on a sunny day, and if you put the radiating fins of the heatsink in the cooler outside air, which is the equivalent of what the paper does! You can criticize that this is a poor definition of ambient, but it is the one they use.
No configuration of heat sink + device will decrease the temperature unless we put some "work" into the system. That "work" will be electrical energy of some sort The source is irrelevant. It must be external to the system and it must have a cooling effect. We absolutely need some sort of peltier device (or other refrigeration technology). There is no way around it!
So when I take a shower and then and then see water condensing on the inside of my single pane bathroom window on a cold night, it means there's got to be a hidden Peltier cooler in there somewhere? Or in a more exact comparison, if I have an outdoor greenhouse on a cold but sunny day, and I see water condensing on the inside of the glazing, there's got to be a refrigerator making it happen? No, there just needs to be a temperature differential, and the heat sink acts like a cold window.
At 25C and 100% humidity air can hold about 0.02ml of water. Meaning for every one liter of water you need 50,000 liters of air.
By contrast, this is an appropriate criticism! Yeah, to collect a liter (1 kg) of water at 25C and 50% humidity, you'd need to extract all the water from 100,000 liters of air. And since you aren't going to get all the water out, you it probably needs to process several times that amount. Is this absurd? It probably depends on how much water you need. An Olympic Swimming Pool is 50m x 25m x 2m, so that amount air would give you something between 1 and 25 liters of water depending on your efficiency of extraction.
How do you get this much air over your collector? It looks like a medium bathroom fan (70 cubic feet per minute) seems to move a little over 100,000 liters per hour, so it could move this amount of air in a day. Alternatively, if you wanted to do it without power, you'd probably get more than this amount of air flow with a gentle breeze. Whether it's worth it would depend on how thirsty you are in that desert and what your other options are, but it's still a neat technique!
The world is ambient. Your device is not. You are trying to extract water from the world so your device needs to be lower than ambient.
> So when I take a shower and then and then see water condensing on the inside of my single pane bathroom window on a cold night, it means there's got to be a hidden Peltier cooler in there somewhere? Or in a more exact comparison, if I have an outdoor greenhouse on a cold but sunny day, and I see water condensing on the inside of the glazing, there's got to be a refrigerator making it happen? No, there just needs to be a temperature differential, and the heat sink acts like a cold window.
The hot, moist air from your shower should be considered ambient. Your window is colder than that ambient temperature. Hence the water condenses.
Let me explain further because this is clearly a sticking point.
The air your shower is generating is roughly 40C at 100% humidity. You don't have to put in any work to condense this water on the window because you already put work in to heat it.
"Ah ha!" you say. "They're heating the water vapor up inside the container! Just like my shower!" Except no the two are not equivalent. Heating up 25C air at 100% humidity to 40C would decrease its humidity. I.e. no condensation. Cooling 40C air at 100% humidity to 25C would result in condensation (your shower)! It is a one way process. The source of the water vapor MUST be hotter than the condenser! When your source is the atmosphere that means your condenser has to have a lower temperature than the exterior conditions.
> Except it's "yes" if you define "ambient temperature" as the temperature inside the shed on a sunny day
The temperature is higher in the shed but the humidity is lower! Lowering the temperature of the shed to the outside temperature will not produce condensation!
Edit: Sidenote. Greenhouses generate their own water vapor (transpiration). Their absolute humidity will be higher than the outside.
Edit2: I also want to emphasize that if you're adding water to the system you're doing it wrong. We're trying to harvest water not supply it. Showers and greenhouses are not apt comparisons.
I think you are thinking about this device as if it operates continuously. My understanding is that it 'consumes' the temperature gradient created by the day/night cycle.
Could mean that this would be ineffective in the tropics where the temperature between day and night varies less. And presumably the device may 'stop working' part way through the afternoon if the previous night was too warm relative to daytime temperature.
To which the answer is obviously no.
Except it's "yes" if you define "ambient temperature" as the temperature inside the shed on a sunny day, and if you put the radiating fins of the heatsink in the cooler outside air, which is the equivalent of what the paper does! You can criticize that this is a poor definition of ambient, but it is the one they use.
No configuration of heat sink + device will decrease the temperature unless we put some "work" into the system. That "work" will be electrical energy of some sort The source is irrelevant. It must be external to the system and it must have a cooling effect. We absolutely need some sort of peltier device (or other refrigeration technology). There is no way around it!
So when I take a shower and then and then see water condensing on the inside of my single pane bathroom window on a cold night, it means there's got to be a hidden Peltier cooler in there somewhere? Or in a more exact comparison, if I have an outdoor greenhouse on a cold but sunny day, and I see water condensing on the inside of the glazing, there's got to be a refrigerator making it happen? No, there just needs to be a temperature differential, and the heat sink acts like a cold window.
At 25C and 100% humidity air can hold about 0.02ml of water. Meaning for every one liter of water you need 50,000 liters of air.
By contrast, this is an appropriate criticism! Yeah, to collect a liter (1 kg) of water at 25C and 50% humidity, you'd need to extract all the water from 100,000 liters of air. And since you aren't going to get all the water out, you it probably needs to process several times that amount. Is this absurd? It probably depends on how much water you need. An Olympic Swimming Pool is 50m x 25m x 2m, so that amount air would give you something between 1 and 25 liters of water depending on your efficiency of extraction.
How do you get this much air over your collector? It looks like a medium bathroom fan (70 cubic feet per minute) seems to move a little over 100,000 liters per hour, so it could move this amount of air in a day. Alternatively, if you wanted to do it without power, you'd probably get more than this amount of air flow with a gentle breeze. Whether it's worth it would depend on how thirsty you are in that desert and what your other options are, but it's still a neat technique!