Radiative cooling systems
A material may be included in a cooling film or cooling panel to achieve cooling even under direct solar irradiation. The material includes one or more constituent materials and an outer surface configured to interact thermally with the atmosphere and with solar radiation. The material exhibits an emissivity of at least 0.8 in spectral range of 5 μm to 15 μm, an ultraviolet reflectivity of at least 0.5 in the spectral range of 275 nm to 375 nm, an ultraviolet absorptivity of at least 0.75 in the spectral range of 275 nm to 375 nm, or a combination thereof. A cooling film, or cooling panel, may be affixed to an exterior surface of a vehicle, structure, or system to provide cooling even under direct solar irradiance.
1. A material for radiative cooling comprising:
one or more constituent materials; and
an outer surface configured to interact thermally with the atmosphere and with solar radiation, wherein the material has at least one of:
an emissivity of at least 0.8 in spectral range of 5 μm to 15 μm,
an ultraviolet reflectivity of at least 0.5 in the spectral range of 275 nm to 375 nm, or
an ultraviolet absorptivity of at least 0.75 in the spectral range of 275 nm to 375 nm.
2. The material of claim 1 , wherein the material is capable of achieving a cooling rate of 10 W/m2 when exposed to the sky at a 300 K ambient air temperature.
3. The material of claim 1 , wherein the material has a thickness substantially normal to the outer surface.
4. The material of claim 1 , wherein the material is capable of reflecting greater than 93% of the weighted solar spectrum from 300 nm to 4 μm in free-space wavelength.
5. The material of claim 1 , further comprising a plurality of discrete planar layers along a depth dimension.
6. The material of claim 1 , wherein the material is capable of absorbing at least some of the visible spectrum of 400 nm to 900 nm.
7. The material of claim 1 , further comprising lateral structuring of the outer surface to enhance surface wettability for hydrophobic behavior.
8. The material of claim 1 , wherein the one or more constituent materials comprises at least one of ZnO, Si, HfO2, or ZnO2.
9. A cooling assembly comprising:
a panel comprising:
one or more constituent materials;
an outer surface configured to interact thermally with the atmosphere and with solar radiation, wherein the panel having at least one of:
an emissivity of at least 0.8 in spectral range of 5 μm to 15 μm,
an ultraviolet reflectivity of at least 0.5 in the spectral range of 275 nm to 375 nm, or
an ultraviolet absorptivity of at least 0.75 in the spectral range of 275 nm to 375 nm; and
a heat exchanger affixed to the panel to cool a liquid or gas.
10. The cooling assembly of claim 9 , further comprising an enclosure configured to insulate the panel to enable cooling to temperatures further than 3° C. below an ambient air temperature.
11. The cooling assembly of claim 9 , configured to be affixed to a top of a roof to provide durable cooling to an underlying structure or building.
12. The cooling assembly of claim 9 , configured to be affixed to a road transport vehicle to provide durable cooling to the vehicle while stationary or in motion.
13. The cooling assembly of claim 9 , wherein the one or more constituent materials comprises at least one of ZnO, Si, HfO2, or ZnO2.
14. A cooling material configured to facilitate thermally-generated emissions that originate from the material, wherein the material has at least one of:
an emissivity of at least 0.8 in spectral range of 5 μm to 15 μm,
an ultraviolet reflectivity of at least 0.5 in the spectral range of 275 nm to 375 nm, or
an ultraviolet absorptivity of at least 0.75 in the spectral range of 275 nm to 375 nm.
15. The cooling material of claim 14 , further configured to be integrated with a heat exchanger to cool a liquid, gas or solid by conductive or convective heat transfer.
16. The cooling material of claim 14 , further configured to cool refrigerant in a vapor-compression cycle.
17. The cooling material of claim 14 , further configured to achieve a cooling rate greater than 10 W/m2 of net heat rejection at an ambient air temperature during the day or night.
18. The cooling material of claim 14 , further configured to cool a building, structure or vehicle by direct thermal contact with the building, structure or vehicle.
19. The cooling material of claim 14 , further configured to enable free convective cooling to cool heat loads from a temperature above an ambient air temperature to the ambient air temperature.
20. The cooling material of claim 14 , further configured to cool a fluid from the outlet of a component 0.5° C. below or further below an inlet temperature.
21. The cooling material of claim 14 , wherein the cooling material comprises one or more constituent materials, and wherein the one or more constituent materials comprises at least one of ZnO, Si, HfO2, or ZnO2.