Devices and methods for concentrated radiative cooling
Devices and methods for concentrated radiative cooling using radiative cooling coatings in combination with mid-infrared reflectors. Concentrated radiative cooling (CRC) devices include an object to be cooled that is coated with a radiative cooling material and a mid-infrared (mid-IR) reflector configured to reflect thermal energy radiated from a surface of the object to deep space. The object may be nested in a mid-IR reflective trough such that substantially an entirety of the object's surface area contributes to radiative cooling. The radiative cooling material may be a coating such as a paint or film that is applied directly to the object's exterior surfaces to reduce thermal resistances. The radiative cooling coating is configured to lose thermal energy from the object by means of exhibiting high emissivity for wavelengths of 8 to 13 micrometers, and in some arrangements of 5 to 30 micrometers.
1 . An air conditioning system comprising:
an air conditioner;
a pre-cooling coil comprising a heat exchanger operatively connected to the air conditioner to supply pre-cooled return air to the air conditioner; and
a preconditioning heat exchanger operatively connected to the pre-cooling coil to supply chilled water to the heat exchanger of the pre-cooling coil to pre-cool the return air,
wherein the preconditioning heat exchanger comprises a water loop that flows through a concentrated radiative cooling device, the concentrated radiative cooling device comprising:
a pipe forming a portion of the water loop to be cooled, the pipe having exterior surfaces configured to be exposed to sunlight from first directions;
a radiative cooling coating on the exterior surfaces of the pipe, the radiative cooling coating configured to lose thermal energy from the pipe, the radiative cooling coating comprising a solar-reflective infrared-emissive paint that contains nanoparticles, is free of a polymeric matrix, and does not contain a metallic component, the radiative cooling coating exhibiting high emissivity for wavelengths of 8 to 13 micrometers and high reflectance for the solar spectrum wavelengths of 0.3 to 3 micrometers, wherein the radiative cooling coating is configured to radiate the thermal energy from a first of the exterior surfaces in the first directions and a second of the exterior surfaces in second directions that are different from the first directions; and
an elongated reflector having a concave cross-sectional V-shape with an opening opposite a rounded valley of the concave cross-sectional V-shape, wherein the pipe is nested within the opening and the opening is not covered, wherein the concave-cross-sectional V-shape defines a surface configured to reflect the thermal energy radiated from the radiative cooling coating on the second of the exterior surfaces and redirect the thermal energy in the first directions, and wherein the elongated reflector has a high reflectance for wavelengths of 5 to 30 micrometers; and
a temperature sensor configured to sense temperature of the pre-cooled return air from the heat exchanger of the pre-cooling coil, wherein the air conditioner is configured to turn on if the temperature of the pre-cooled return air is higher than a set point and to turn off if the temperature of the pre-cooled return air is lower than the set point.
2 . The air conditioning system of claim 1 , wherein the elongated reflector has a high reflectance for wavelengths of 8 to 13 micrometers.
3 . The air conditioning system of claim 1 , wherein the elongated reflector is formed of aluminum.
4 . The air conditioning system of claim 1 , wherein the pipe has a serpentine path and the elongated reflector follows along the serpentine path of the pipe.
5 . The air conditioning system of claim 4 , wherein the pipe is nested within the cross-sectional V-shape of the elongated reflector along the serpentine path to block adjacent radiating surfaces of the pipe from exchanging with one-another and provide convective shielding.
6 . A cooling system comprising the air conditioning system of claim 1 , the cooling system comprising:
an environment;
wherein the air conditioning system is configured to receive thermal energy from the environment to cool the environment or surface.
7 . The cooling system of claim 6 , wherein the environment is an interior of a building.
8 . The cooling system of claim 6 , wherein the thermal energy received by the air conditioning system from the environment or surface originates as waste heat generated by information technology (IT) equipment.
9 . The device of claim 1 , wherein the nanoparticles are BaSO 4 .
10 . A method of using the device of claim 1 , the method comprising:
orienting the pipe such that the first of the exterior surfaces faces skyward toward deep space and the second of the exterior surfaces faces away from deep space; and
using the elongated reflector to reflect and redirect the thermal energy radiated from the second of the exterior surfaces skyward toward deep space.