New research has been published in the journal ACS Applied Energy Materials, conducted by scientists from the Nanjing University of Science and Technology in Japan, on a conceptual design of an adaptive radiative cooling system to provide sustainable indoor heat management. The proposed system will help to reduce the carbon footprint of domestic heating, a significant cause of power use.

Many materials explored are hindered by complicated manufacturing processes. Image credit: Creative Commons

Many materials explored are hindered by complicated manufacturing processes. Image credit: Creative Commons

Effective heat regulation is vital for the comfort of inhabitants in regions around the globe. If a dwelling is cold in the winter, but too hot in the summer months, the health of occupants can be impacted, and inefficient heat regulation systems can cost homeowners large sums of money through heat loss in colder months and the need for fans and air conditioning to regulate sweltering heat in the summer months.

Along with power costs and the dangers of unregulated heat to human health, domestic heating systems are a key cause of overburdened power grids during peak demand. Moreover, generating the huge amount of power needed by numerous dwellings drives climate change due to the increased need for fossil fuels to provide energy.

While strategies such as insulation and double glazing can reduce heat loss in winter months, thereby keeping dwellings warmer without the need for expending energy, it is more difficult to keep homes cool during the summer months without using powered devices such as air conditioning units. The need for a heat regulation system that uses low power and can operate efficiently in both hot and cold climates has facilitated an increased research focus in the fields of engineering and materials science.

Radiative Systems

Radiative systems have garnered growing research interest due to their advantages in regulating indoor temperatures without the power demands of devices such as air conditioning units or heating systems. Near-black radiators have been thoroughly investigated in recent years for night-time radiative cooling, but daytime cooling systems are more challenging due to the negating effect of solar radiation.

Rapid advances in the materials industry with the development of nanomaterials and micro-scale technologies have rekindled interest in daytime radiative cooling systems. Initial successes were achieved using integrated photonic structures, with subsequent materials reported including porous polymer coatings.

Despite significant research progress, radiative daytime cooling systems are still static, and are undesirable in colder climates and time periods where cooling is undesirable and power demands are consequently higher.

Dynamic radiative systems are therefore more desirable, and research has focused on the design of materials for these systems in recent years. Thermochromic materials such as perovskites, hydrogels, vanadium dioxide, and liquid crystals have been explored and have shown promise. Additionally, adaptive photonic structures have proven to be an interesting research direction.

However, many materials explored are hindered by complicated manufacturing processes and low performance in terms of being switchable. Dynamic silicone membranes have emerged recently, which offer the advantages of switchable transparency and reflectance, but these materials need external intervention to work properly, complicating their design. Manufacturing a simple, efficient switchable radiative system has thus far proven challenging.

The Research

The authors have reported research into the development of an innovative switchable radiative heat regulation system for domestic dwellings that addresses the challenges associated with both conventional heat regulation systems and previously reported radiative systems.

The proposed conceptual system comprises two parts; a temperature-responsive part, and a radiative cooling coating. Thus, with the dual design, the device achieves adaptive and dynamic radiative cooling. Highly efficient, a reflectance value of 96% is achieved in solar bands, whereas in the atmospheric transference window, 95% infrared emission is achieved due to the radiative cooling coating.

The temperature-responsive part functions as a thermal switch and is constructed of springs made from nickel-titanium alloy. In the ON state, heat can easily transfer to the coating due to low thermal resistance. In the OFF state, heat escape is blocked due to high thermal resistance. Thus, due to this controllable heat transfer between the two parts, the system achieves adaptive switchable radiative heat control for indoor spaces.

The authors compared a building model using the proposed system to one where the system was not installed, demonstrating the suitability of the switchable radiative system. Results indicated that the novel system can perform as an adaptive radiative cooling regulator. Moreover, the system requires no external intervention, providing a route to a passive radiative cooling system, requiring no power input, creating a highly sustainable indoor heat regulation solution for both hot and cold climates.

Source: AZO Materials