T.J. Hebrink
3M Company,
United States
Keywords: passive, radiative, radiation, cooling, film, polymer
Summary:
Nano-layered and nano-particle technologies have been innovated into easy to apply passive cooling films by 3M Company and have demonstrated significant cooling of roof surfaces by both reflecting solar energy and radiating heat away from the roof surfaces. When applied to roofs, our passive cooling films can save energy for buildings, vehicles, and many other applications. These passive cooling films have been measured to reduce roof surface temperatures by 5-15C and reduce net radiant solar loads by 30-200W/m2 depending on what surface they are being applied to. This reduction in solar load provides a reduction in electricity consumed by air conditioning systems. In the case of electric vehicles, a reduction in electricity consumed by air conditioning systems will extend driving range. If the electricity is generated with fossil fuels, the reduction in electricity consumed provides a significant reduction in CO2 emissions. If no air conditioning is being used in the building, or vehicle, passive cooling films can provide improved comfort to people inside those buildings, or vehicles. 3M’s most solar reflective passive cooling films are enabled by multi-layer optical film technologies comprising hundreds of layers of alternating polymers having different refractive indices. Broadband solar mirror films made with our multi-layer optical film technologies reflect 97% of solar energy. However, they have a specular silver mirror appearance which is not attractive to all building and vehicle owners. To overcome barriers to widespread deployment of 3M’s passive cooling film, we then developed diffusely reflective films which have the appearance of white paint but reflect more solar energy than commercially available white paints. When potential customers have been shown our diffusely solar reflective (white) passive cooling, they frequently ask if we have colored versions of passive cooling film. Thus, we have also developed the most solar reflective colored surface ever made. Air conditioning systems have a negative overall impact on the outside air temperature in cities with an Urban Heat problem. By taking heat out of a building, or vehicle, air conditioners heat up the air surrounding the building or vehicle which in turn causes the air conditioners to work even harder and essentially creates a negative feedback loop. By reflecting solar energy and radiating heat to the sky, passive cooling films can remove heat from a city by acting as a radiant heat pump. If passive cooling films are applied to enough surface area in a city, they have potential to mitigate their urban heat problem. Passive cooling energy savings is very dependent on weather conditions which requires sophisticated modeling to calculate energy savings for different locations around the world. Our passive cooling energy savings model is being validated by measurements in North America, South America, Europe, and Asia. In this presentation I will share modeled energy savings and measured energy savings achievable with passive cooling films in a wide variety of hot climates.