3 ms·

A temperature drop of 3-5 degrees C is meaningless unless other variables are supplied. For example, how much water was cooled? They tell you how long (3 days)

A temperature drop of 3-5 degrees C is meaningless unless other variables are supplied. For example, how much water was cooled? They tell you how long (3 days) but they don't let you how many panels they used either. Too many 'science' articles these days don't add up.

philipkglass 9y ago
This is just a press release about the actual scientific publication. The abstract provides more information: https://www.nature.com/articles/nenergy2017143 https://www.nature.com/articles/nenergy2017143 Cooling systems consume 15% of electricity generated globally and account for 10% of global greenhouse gas emissions. With demand for cooling expected to grow tenfold by 2050, improving the efficiency of cooling systems is a critical part of the twenty-first-century energy challenge. Building upon recent demonstrations of daytime radiative sky cooling, here we demonstrate fluid cooling panels that harness radiative sky cooling to cool fluids below the air temperature with zero evaporative losses, and use almost no electricity. Over three days of testing, we show that the panels cool water up to 5 ∘C below the ambient air temperature at water flow rates of 0.2 l min−1 m−2, corresponding to an effective heat rejection flux of up to 70 W m−2. We further show through modelling that, when integrated on the condenser side of the cooling system of a two-storey office building in a hot dry climate (Las Vegas, USA), electricity consumption for cooling during the summer could be reduced by 21% (14.3 MWh). And you can read the full article via sci-hub to get all the experimental details.
- kbenson 9y ago
  > the panels cool water up to 5 ∘C below the ambient air temperature at water flow rates of 0.2 l min−1 m−2, corresponding to an effective heat rejection flux of up to 70 W m−2. Can someone translate that into layman terms? The chained negative exponents are somewhat confusing. I would think 70 W m^2 would me square meters, but what's 70 W m^-2? I assume it's not really mappable to dimensions at that point...
  - ar813 9y ago
    Sorry, that's the convention of the journal. It's W/m^2 -- heat rejection per unit area.
    - kbenson 9y ago
      Oh, I get it now. I totally missed that there wasn't a division there. That makes complete sense now that it was pointed out, I'm just not used to seeing stuff in that format apparently. :)
  - syntaxing 9y ago
    Negative exponents means its divided by. For instance s^-1 would be equal to 1/s or more formally known as Hertz. You see this every once in a while in scientific papers. This notation is convenient because it makes it easier to simplify the units.
    - kbenson 9y ago
      Yeah, it's basic algebra. I just wasn't seeing it for some reason, possibly because I only think about converting exponents like that when trying to solve something (usually when helping my daughter with her Algebra homework). Yet another example of context affecting cognition, I guess.
- njarboe 9y ago
  The paper's doi:10.1038/nenergy.2017.143 You don't just get electrical savings. Unlike other AC heat transfer systems, the heat is not pumped into the local surroundings, but is ejected from the Earth.

philipkglass 9y ago

This is just a press release about the actual scientific publication. The abstract provides more information: https://www.nature.com/articles/nenergy2017143 https://www.nature.com/articles/nenergy2017143 Cooling systems consume 15% of electricity generated globally and account for 10% of global greenhouse gas emissions. With demand for cooling expected to grow tenfold by 2050, improving the efficiency of cooling systems is a critical part of the twenty-first-century energy challenge. Building upon recent demonstrations of daytime radiative sky cooling, here we demonstrate fluid cooling panels that harness radiative sky cooling to cool fluids below the air temperature with zero evaporative losses, and use almost no electricity. Over three days of testing, we show that the panels cool water up to 5 ∘C below the ambient air temperature at water flow rates of 0.2 l min−1 m−2, corresponding to an effective heat rejection flux of up to 70 W m−2. We further show through modelling that, when integrated on the condenser side of the cooling system of a two-storey office building in a hot dry climate (Las Vegas, USA), electricity consumption for cooling during the summer could be reduced by 21% (14.3 MWh). And you can read the full article via sci-hub to get all the experimental details.

kbenson 9y ago
> the panels cool water up to 5 ∘C below the ambient air temperature at water flow rates of 0.2 l min−1 m−2, corresponding to an effective heat rejection flux of up to 70 W m−2. Can someone translate that into layman terms? The chained negative exponents are somewhat confusing. I would think 70 W m^2 would me square meters, but what's 70 W m^-2? I assume it's not really mappable to dimensions at that point...
- ar813 9y ago
  Sorry, that's the convention of the journal. It's W/m^2 -- heat rejection per unit area.
  - kbenson 9y ago
    Oh, I get it now. I totally missed that there wasn't a division there. That makes complete sense now that it was pointed out, I'm just not used to seeing stuff in that format apparently. :)
- syntaxing 9y ago
  Negative exponents means its divided by. For instance s^-1 would be equal to 1/s or more formally known as Hertz. You see this every once in a while in scientific papers. This notation is convenient because it makes it easier to simplify the units.
  - kbenson 9y ago
    Yeah, it's basic algebra. I just wasn't seeing it for some reason, possibly because I only think about converting exponents like that when trying to solve something (usually when helping my daughter with her Algebra homework). Yet another example of context affecting cognition, I guess.
njarboe 9y ago
The paper's doi:10.1038/nenergy.2017.143 You don't just get electrical savings. Unlike other AC heat transfer systems, the heat is not pumped into the local surroundings, but is ejected from the Earth.