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Engineering360: "Maps optimize radiative cooling system siting in the US"

06/26/2019 1:43 PM

Read Engineering360 article: Maps optimize radiative cooling system siting in the US.

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#1

Re: Maps optimize radiative cooling system siting in the US

06/26/2019 2:25 PM

Unfortunately, where it's HOT & DRY is also where the WATER ain't...for a reason.

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#2
In reply to #1

Re: Maps optimize radiative cooling system siting in the US

06/26/2019 7:42 PM

'Unfortunately' why?

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#3
In reply to #2

Re: Maps optimize radiative cooling system siting in the US

06/26/2019 8:04 PM

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.

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#4
In reply to #3

Re: Maps optimize radiative cooling system siting in the US

06/27/2019 6:27 PM

Oh.

That was a litte confuaing as the article was about radiatove cooling. I understand your poiint.

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#5

Re: Maps optimize radiative cooling system siting in the US

06/29/2019 11:24 PM

As I understand it, two methods of radiative cooling can be used in the southwest and similar areas:

  • using movable insulation to cover a structure of high thermal mass and high emissivity so it is retarding the heat gain during the day and then moving the insulation away so it can radiate the stored heat to the night sky during the night
  • having a surface that is shielded against direct solar gain and is effectively exposed to the clear sky; this surface would again have to have a high emissivity, but would not be required to be with a high thermal mass.

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

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#6

Re: Maps optimize radiative cooling system siting in the US

07/03/2019 11:55 AM

I found this interesting:

Approach to fabricating high-performance cooler with near-ideal emissive spectrum for above-ambient air temperature radiative cooling
https://www.sciencedirect.com/science/article/pii/S0927024819303423?dgcid=rss_sd_all
- via Researcher https://researcher-app.com (@ResearcherApp)

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#7
In reply to #6

Re: Maps optimize radiative cooling system siting in the US

07/03/2019 6:02 PM

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

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