The energy consumption of building for heating and cooling accounts for about 15% of total energy consumption. Currently, many promising methods with minimum carbon footprint have been proposed for energy saving of buildings. Solar thermal energy has been one of the major energy sources to realize zero energy buildings for a sustainable future. The high efficiency and low cost make it particularly attractive to reduce the energy consumption for hot water and space heating. On the other hand, the radiative cooling uses the rest of the sky, i.e. the deep space, as the cold source to generate cooling that can offset the usage of refrigeration and space cooling. Both technologies show rapid and promising improvement in the past decade, which calls for new engineering and design principles to further maximize the energy saving for buildings. While they harvest renewable heating/cooling energy to supplement the space heating/cooling energy consumption, these approaches are static and monofunctional, which can only reduce energy consumption in certain conditions and climate zones. Having the capability to achieve both highly efficient cooling and heating in a limited roof area and to accomplish energy saving in various weather and climate conditions remains a challenge. Here, we demonstrate the dual-mode device that can switch between radiation cooling and solar heating for building energy saving. The device consists of dual-function thin film materials and a pair of electric motors for actuation. As the motor switches the material between solar heating and radiative cooling, thermal contact resistance becomes the key factor to determine the utilization of the harvested heating/cooling energy. The issue was overcome by designing the material triboelectricity and applying an external voltage to adhere to the thin film to the heat exchanger via Maxwell pressure. Field testing of the heating/cooling performance shows a 2X improvement after electrostaticity engineering. By optimizing the heating/cooling power and heat transfer pathways, the device can achieve up to 71.6 W/m^2^ of cooling power density and up to 643.4 W/m^2^ of heating power density (over 93% of solar energy utilized) because of the suppression of thermal contact resistance and surface morphology and optical property engineering. Finally, to demonstrate the universal benefit of the dual-mode building envelopes, we perform building energy simulation for all the climate zones in the U.S. The results show our dual-mode device, if widely deployed, can save 45.8% of the heating, ventilation and air conditioning (HVAC) energy, which is 2.46 times higher than cooling-only and 1.43 times higher than heating-only approaches.


Switchable Smart Radiative Heating and Cooling Building Envelopes

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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