i2Cool: Cooling Paint for Buildings

By Dr. Martin Zhu 19 January, 2023

Painting Hong Kong's buildings with iPaint could reduce 580,000 tonnes of carbon emissions. We chat with i2Cool Founder, Dr Zhu to find out more

>50,000 buildings use 90% of HK's total electricity of which ~30% is used by AC systems; using iPant could save 1 billion kWh & reduce 580,000 tonnes of carbon emissions
Found that cooling effect of the surface can be maintained without energy or refrigerant; IEA says global electricity consumption for cooling purposes could increase 50% by 2030
iPaint reflects most of sunlight & thermal heat back into space, reducing outdoor surface temp by 40˚C & indoor temp by 10˚C; saving ~40% of energy for air cooling
Dr. Martin Zhu
Author: Dr. Martin Zhu
Dr. Martin ZHU, a PhD graduate (supervisor: Dr. Edwin TSO) from the School of Energy and Environment, City University of Hong Kong. His research focuses on understanding the fundamentals of heat transfer, energy conversion, and engineered materials. He strives to integrate theory and experiments to create innovative solutions for enhancing phase-changing, air cooling, dehumidifying, thermal management, thermal rectification, micro-droplet manipulation, and energy-efficient building technologies. With solid research background in thermal science, Dr. ZHU and his team successfully developed the electricity-free cooling technology for building energy saving. Incubated by HK Tech 300 program, he founded a startup, i2Cool, to commercialize the cooling technologies. Empowered by the self- developed and ever-improving products, as well as fueled by Dr. ZHU’s highly adaptive and long- term strategies, i2Cool successfully attracted interest from various sectors of society, creating a significant social impact by contributing to the goal of carbon neutrality.
Read more from Dr. Martin Zhu →

i2Cool aims to promote a novel energy-free and environmentally friendly passive radiative cooling paint to save energy and assist in decarbonisation. The PaintTM features sunlight reflectance and thermal emittance, bringing out its all-day sub-ambient cooling capability and energy-saving potential. Given how many buildings there are in Hong Kong, we sat down with Dr Martin Zhu, Founder of i2Cool to learn more about the paint and what it could mean for Hong Kong and reducing emissions.

CWR: Thank you Martin for chatting with us. The 2022 summer hit record-breaking temperatures and Hong Kong was not exempt from high temperatures. Could you tell us about your experience of Hong Kong’s summer?

Dr. Martin Zhu (MZ): As a City with subtropical monsoon climate, Hong Kong is a perfect place to live, yet Hong Kong is also a city which is widely applied with air-conditioning systems, with more than 50,000 buildings that consume 90% of its total electricity, around 30% of which is consumed by air-condition systems.

>50,000 buildings use 90% of HK’s total electricity

It’s a pity that this is contributing to global warming every minute of our lives but we always complaining that the air conditioning is too cold.


CWR: In 2021 you launched your startup, i2Cool. Can you tell us a bit about i2Cool and why you started it?

Dr. MZ: i2Cool is a technology company cultivated by the “HK Tech 300” Entrepreneurship Programme of CityU and the HKSTP Incubation Programme, which was established in June 2021 by PhD graduates and scientists of CityU.

Our team began to research passive radiant refrigeration technology in 2015, and is committed to the commercialization and promotion of non-electric refrigeration technology and more innovative green building energy-saving technologies.

Found from our research that the cooling effect of the surface can be maintained without energy or refrigerant…

…going to be key as IEA says global electricity consumption for cooling purposes could increase by 50% by 2030

After continuous testing and scientific research by the i2Cool team, the advanced powerless refrigeration technology was finally successfully transformed into a technology that can be applied on a large scale. We not only solve the difficulty of large-scale production of products, but also solve the technical obstacles of the construction process, and realizes the cooling effect of the surface of the object that can be maintained below the ambient temperature all day without energy or refrigerant, effectively reducing the energy consumption of buildings from the source and promoting carbon neutrality.

More significantly, a recent study by the International Energy Agency (IEA) projects that barring improvements in energy efficiency, global electricity consumption for cooling purposes could increase by as much as 50% by 2030. Besides, traditional AC systems feature the use of refrigerants which contribute to ozone layer depletion and the greenhouse effect. To reduce the massive energy consumption of traditional AC systems and mitigate the cascading effects of climate change, more energy-efficient and environmentally friendly cooling strategies are urgently needed.

The first product of i2Cool is the daytime passive radiative cooling paint, called iPaint

i2Cool aims to develop and employ innovative technologies for energy saving and environmental protection. The first product of i2Cool is the daytime passive radiative cooling paint, called iPaint. i2Cool will focus on the development and commercialization of the iPaint, including improvement of the practicality and large-scale fabrication.

Many governmental departments and private property developers are interested in and willing to use the iPaint on their buildings. Moreover, in the long term, i2Cool will develop more products for energy saving, namely smart windows and AI control of air conditioning systems.

CWR: How exactly does paint cool buildings and reduce energy consumption? Do you think we should be focusing on improving the external material of buildings rather than improving energy efficiency internally to decarbonize?

Dr. MZ: The electricity-free cooling technology (i.e. passive radiative cooling technology, iPaint) can make the surface of the object reflect most of the sunlight, and at the same time can effectively emit thermal heat into outer space in the mid-infrared wavelength. It can reduce the surface temperature by 40 ˚C and indoor air temperature by 10 ˚C, saving around 40% energy consumption for air cooling.

iPaint can make the object’s surface reflect most of the sunlight & thermal heat back into space…

…reducing the outdoor surface temp by 40˚C, indoor temp by 10˚C; saving ~40% of energy consumption for air cooling

The technology can spontaneously provide cooling effect for the applied objects throughout 24-7 operation by blocking incoming solar thermal radiation and radiatively dissipating heat to cold outer space through mid-infrared (MIR) wavelength range. This product uses polymer with high MIR emission as matrix and embeds spherical ceramic particles. Selected particle and polymer have ideal intrinsic electromagnetic properties that absorb negligible solar irradiation.

The microsized particle enhances Mie scattering throughout solar spectrum and therefore effectively prevent heating by sunlight. The optimized particle size, on the other hand, strengthen phonon polariton resonances that enhanced thermal emission in MIR range. Besides, the MIR emission is effective in outdoor environment. Therefore, the application of iPaint focuses on building external materials.

CWR: Realistically, how much emissions can we cut if we painted more buildings in Hong Kong in passive radiative cooling paint? What is stopping Hong Kong’s buildings from being painted in all white?

In HK would save 1bn kWh & reduce 580k tonnes of emissions annually

Dr. MZ: Assuming that all buildings in Hong Kong have applied with iPaint, around 1 billion kWh can be saved annually, reducing 580,000 tons of carbon emission and significantly promoting carbon neutrality. Major issues are appearance. That’s why we are now promoting iPaint Rainbow that has multiple colour options.

CWR: Have you found interest in the marketplace? What are some of the projects you’ve undertaken? What challenges have you faced?

Dr. MZ: Yes, we have. Buildings, outdoor facilities, refrigeration supply chain are our interests. We have demonstrated the cooling performance of the iPaint on the rooftop of InnoTCE belonging to HKSAR Civil Engineering and Development Department (CEDD) in Tung Chung, and we also cooperate with more than 20 local companies in Hong Kong (such as Gas Company, AMPD, Tradeport, etc.), real estate developers (Henderson, Chinachem, Sun Hung Kai, Hang Lung, etc.), government and public entities (DSD, ASD, HAD, HA, URA, etc.) to implement the application projects. One of the biggest challenges is appearance issues. Customers may need different colour options and that’s why we developed the second generation of cooling paint called iPaint Rainbow to fulfill their needs.

CWR: As heat intensifies so will extreme weather. Do you have any concern regarding the weather eroding the cooling paint on buildings?

Dr. MZ: From the third-party experimental results, iPaint keeps its perfect results including its energy saving performance, stable mechanical performance, prevention from light pollution, etc., under different climate conditions. Also iPaint is very easy to apply and maintain its excellent performance. We are trying to get more resources for cooperation, and hope to provide a series of whole process services from R&D, production, application, energy management, etc., in order to get the most out of our product.

iPaint produces ‘perfect results’ under different climate conditions

But it has to be said that it requires very strong human resources and team to support our idea, however, recruiting people is very difficult for startups, and we keep trying for more and more good partners as part of staff.

CWR: Do you have any plans to expand your product internationally? Share with us your new year’s resolution and i2Cool’s next steps forward?

Dr. MZ: Firstly, iPaint will be sold not only in mainland China, Hong Kong, and Taiwan, but also in ASEAN countries such as Singapore, Thailand, the Philippines and Indonesia. It will also cooperate with customers from Saudi Arabia, Germany, Canada and the United States. In the future, we will continue to expand the sales area and application field of our products, to cover 224 countries or regions in the world.

Secondly, i2Cool Limited is now in the midst of attempting to diversify their products by integrating the passive radiative cooling technology into materials with different textures and features. For instance, iPaint 2 is a new i2Cool product not only inheriting the splendid passive radiative cooling effect from the first generation but also developing into different colors, so that the customers can choose their favorite color.

We are expanding in Asia & eventually want to be global…

…also expanding products incl. different colour paints

Furthermore, iPaint 3 will also be launched later by i2Cool to possess the features of changing colors and self-adaptability with an aim to performing cooling in summer and warming in winter, which is best fit the weather in North China and Europe. Apart from iPaint, an intelligent thermos-responsive energy-efficient thermochromic smart window is developed by i2Cool Limited to enhance energy saving in buildings, and also a novel iTextile with passive radiative cooling function to produce energy-efficient daily necessities, such as umbrella, mask and clothing.

i2Cool Limited continues participating in various local, Asian and International competitions proactively to promote passive radiative cooling technology and approach different potential investors for further R&D of innovative products.

For air conditioning energy saving, i2Cool research team developed AI artificial intelligence air conditioning control system, which is an automatic control strategy that can be real-time monitoring and continuous optimization. The scheme is stable and reliable. It can optimize the working efficiency and reduce the energy consumption of air conditioning units by monitoring environmental variables such as air flow, temperature, humidity and even density. The solution ensures that the chillers operate at their most efficient state throughout the year while maintaining indoor environmental quality.

Further readings

  • A Conversation with Antonio Ng on Carbon Sequestering Cement – Concrete = 11% of global emissions. Frustrated about not moving the needle on emissions, Antonio Ng, former architect & now FORMWORK IO CEO, walks us through his carbon sequestering cement start-up in HK
  • Cement’s Role In A Carbon-Neutral Future – Energy Innovation’s Jeffrey Rissman shares how to achieve carbon-neutral for cement production by 2050 with the help of carbonation & potentially becoming a carbon-squestering process
  • Green Roofs: Increasing Hong Kong’s Resilience – You’ve probably heard of green roofs but what about purple roofs? Dr. Anna Zakrisson, VP at GRD, highlights the various benefits of these roofs from tackling heat, flooding & a clear ROI
  • Nature as Leverage: Design Approach For Climate Change – Despite the massive climate challenges, Martin Probst, Associate Director at MLA+, remains optimistic thanks to a new design thinking methodology – ‘Nature as Leverage’ – and showcases 3 example projects in the GBA
  • Archireef: 3D-printed Clay Reef Tiles – Home to more hard coral species than the Caribbean, Hong Kong reefs need protecting. We sit down with CEO & Co-founder of Archireef, Vriko Yu, to hear how their 3D printed clay tiles save reefs with a 95% survivorship rate

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