Maps optimize radiative cooling system siting in the US
S. Himmelstein | June 26, 2019The residential and commercial sectors in the U.S. are responsible for about 39% of the total national energy consumption, and 15% of that is allocated for air conditioning applications. Increased adoption of passive 
Annual average values during the daytime. From top left, clockwise: (a) air temperature Ta, (b) water vapor partial pressure Pw, (c) ratio of clear sky periods Rc, and (d) radiative cooling potential qcool, ideal. Source: Carlos Coimbra, University of California San Diegoradiative cooling technologies, such as cool-roof paint coatings and solar panels, can conserve electricity and reduce pressure on power grids.
Optimal placement of these systems depends on local meteorological conditions, so a series of radiative cooling resource maps for the contiguous U.S. was developed by University of California San Diego researchers to determine the best climates for large-scale deployment. Zero shortwave absorptance (maximum reflectance), blackbody longwave emittance and other optical properties were analyzed in the preparation of annual and season-averaged maps. Daytime and nighttime cooling potential were also computed and compared.
The maps presented in the Journal of Renewable and Sustainable Energy show that the southwestern U.S. has the highest annual averaged cooling potential of over 70 W/m2, due to its dry and mostly clear sky meteorological conditions. The lowest potential of around 30 W/m2 is assigned to the southeastern U.S., due to frequent humid or overcast conditions. The annual average cooling potential over the contiguous United States is 50.5 W/m2.
Unfortunately, where it's HOT & DRY is also where the WATER ain't...for a reason.
In reply to #1
'Unfortunately' why?
In reply to #2
The least costly "air cooler" (evaporative) systems require water which is getting more scare by the year.
Use the sun to make DC, convert to AC, run HVAC -- unfortunately -- isn't 100% efficient or even close to it.
In reply to #3
Oh.
That was a litte confuaing as the article was about radiatove cooling. I understand your poiint.
As I understand it, two methods of radiative cooling can be used in the southwest and similar areas:
One could use radiative panels through which a heat transfer fluid is pumped to cool the fluid using the second method above. This cooled fluid would be returned to the conditioned space to absorb additional heat. Essentially this would be an air conditioning system without the need for refrigerant or a compressor. If one used a fluid that was able to absorb heat by boiling and then condense at the external radiators this would reduce or eliminate the need for pumps and further reduce the energy requirements for such a system.
The first system was used in at least one home built in the central valley of California about 40 years ago, using water, and called a pond roof system. It was effective.
JMM
I found this interesting:
Approach to fabricating high-performance cooler with near-ideal emissive spectrum for above-ambient air temperature radiative cooling
https://www.scienced
- via Researcher https://researcher-a
In reply to #6
Thanks for the reference. I read the abstract but didn't pay for the article. It is curious because the stated publication date is over two months in the future. I would be interested in seeing data relating its emissivity over the range, showing it to be very low at the typical temperatures of incoming solar radiation and very high at the longer wavelengths. It certainly looks interesting to the manufacturers of PV cells because high temperature is one of their challenges.
--JMM