Has anyone ever set up a solar thermal system to essentially run backwards for Night Sky Radiation Cooling (NSRC)?
I have read a little about it on the internet, but I was curious if anyone has experience with it.
I am interested in alternative methods of cooling, and this is something that is of interest to me. I had John Yellott as a professor at ASU, who was a very early solar pioneer, developed the Skytherm system with Harold Hays for passive rooftop cooling in the desert, and built a lithium bromide A/C system for his home in Phoenix.
I live in the Chicago area, so I know this is probably not the solution I would use here due to a lack of really clear night time sky, but as an architect I occasionally do work in other climates and want to understand this in more detail for possible use on an appropriate project.
The system I have heard about is an unglazed solar panel set facing straight up into the night time sky, and running water through the panels at night to cool the water. I don’t know if this is a marginal strategy or one that could really work.
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Kevin, thank you for the response. I would agree it would be a dedicated system, as the sloped angle of the collector would be a big problem, I think, for night time radiant cooling. And as you point out, the glazing would be a big efficiency problem.
I did track down an article online that sounded good (http://www.plumbingengineer.com/jan_09/solar.php) but just seeing if anyone has ever tried this or knows someone who has. I am also interested in a solar assisted lithium bromide system. I believe I heard that a company was starting to manufacture one, but it was no currently on the market.
Steve Baer at Zomeworks has done a lot of research on this issue. They have a product, Cool Cell, that uses night sky radiational cooling to lower the temperature of a fluid used to cool batteries in an insulated box. (The application is for remote battery boxes used in PV systems in hot climates.)
More info here: http://zomeworks.com/products/cool-cell/introduction
I am always amazed at how simple, passive and elegant Steve Baer's products are. In the same article link you gave, there is a link to 'Cool Cell Architectural Climate Control'.
I haven't read through it yet, but after glancing at it quickly, this appears to be in line with what I am thinking. While roof ponds would work (probably only in desert climates where it was originally developed), why have movable insulation when you can move the fluid back and forth at the right time of the day? I will look through Zomeworks .pdf on this.
An unglazed solar collector could do a decent job of cooling off a storage tank at night. But then you wouldn't have any hot water for your showers in the morning. That means a hybrid system is impractical.
Using a glazed collector for a hybrid system is also impractical, because a glazed collector is a poor heat rejector.
Now, a dedicated air conditioning/heat rejection system using NSRC may be worth exploring, but you would need a fairly large storage tank, so it starts getting expensive.
My guess is that a standard high efficiency compression cycle A/C unit will get the job done for a lower life cycle cost. Interesting idea, though.
After reviewing the article in Plumbing Engineer, the main result of the research is that the temperature of the water will be the mean of the night air temperature and the wet bulb temperature. On very cloudy nights, the water will be closer to the night air temperature.
This tells me that a swamp cooler is a much better solution, because it puts out air that is closer to the wet bulb temperature. And it works during cloudy conditions and even in the daytime.
Kevin, thanks for the summary. I am going to keep my eyes open for alternative cooling methods for various climatic regions.