It has been too long since I posted here...There are 2 or 3 articles that I started but did not finish yet. Rather than start another well-researched post, I just wanted to quickly jot my thoughts down.
Setup
The other day, I finally started to address some of the concerns around my family house. The south facing side of the house (my in-laws room, and the room of my 2 sons) gets really hot in the afternoon. I do want the room to be cooler, but I also don't want to increase the use of the AC which is associated increased GHG. So the question was:
How do I increase comfort level without increasing AC use?
The answer is something I applied to the previous house we owned. Since up to 50% of thermal temperature gain comes through the windows, it is to increase the shade to those windows via solar screens. Our house does have white internal shutters that do block a lot of light and heat coming into the rest of the room. But direct sun light heats up the windows themselves which then radiate the heat into the room. Convection air currents touching the windows also helps to spread the heat into those rooms. Therefore, it is still beneficial to somehow cover up those windows. All those rooms now feel a lot more comfortable. Let's see what the effect will be on the electric bill.
But then I started wondering:
How I can further reduce heat build-up in the house?
The garage is also south-facing and has an HOA-compliant dark-brown facade which is amazing in soaking up all the midday and afternoon heat. The 2 bedrooms above may get warmer by heat that creeps into the little cracks. So how I can I reduce heat gain there? There are radiant barriers that can be applied to garage doors. Reach has such a product. But this technology is now quite old now, and I started wondering if there is anything new on the market that performs better?
This led me down a rabbit whole. Let me just quickly put some links here:
https://pubmed.ncbi.nlm.nih.gov/25428501/
https://pubs.acs.org/doi/10.1021/nl4004283
https://pubmed.ncbi.nlm.nih.gov/31323830/
https://www.osapublishing.org/abstract.cfm?uri=CLEO_QELS-2016-FTh3B.1
https://www.osapublishing.org/viewmedia.cfm?uri=CLEO_QELS-2016-FTh3B.1&seq=0
https://science.sciencemag.org/content/349/6245/298
https://www.researchgate.net/publication/268878079_Passive_radiative_cooling_below_ambient_air_temperature_under_direct_sunlight
https://www.skycoolsystems.com/
So what did I find?
In ancient times, the Shahs in Iran were able to freeze water in the desert at night that they could use to cool special housing structures during the day using a phenomenon called radiative cooling. Basically, a thin layer of water insulated on all sides can radiate heat in the form of infrared light into space on clear nights. Interestingly, the light spectrum from 8-13 nm falls in the window of the spectrum that only gets minimally absorbed by the atmosphere.
I found that this phenomenon could also work during the day. Silver, silicon oxide (glass), hafnium oxide layers can be constructed to radiate light in the spectrum mentioned above leading to even temperature reductions of up to 12 C under real-world conditions compared to ambient temperatures. Nature has also found solutions to survive in hot desert climates. Saharan silver ants have special hair structures that exibit similar properties as the reflective layers above. Can these structures somehow be replicated to create more efficient radiative cooling surfaces?
There is even a new start-up company in the Bay area, called Skycool Systems that seeks to exploit this mechanism to make ACs more efficient, or solar panels more efficient by reducing their temperatures.
Very cool technology. Too bad we can't buy any of that yet.
Comments
Post a Comment