Development of temperature-responsive dynamic-emissivity phase change material for all-season building energy savings

• Fabry-Perot resonator enables emissivity modulation of phase change materials. • Composite phase change materials achieve up to 23.5 % of building energy savings. • Colored composite materials are developed to meet application preferences. Phase change material (PCM) applied on building envelope (e.g., roof, wall) has been proved to be effective for reducing both cooling and heating energy use. Recently, preliminary studies have applied high-emissivity radiative cooling material on PCM for enhancing cooling performance. However, since emissivity of the cooling material is static, it leads to a fast indoor heat dissipation rate at cold ambient and thus results in increased building heating loads. To this end, this study develops a dynamic-emissivity PCM that synchronizes adaptive emissivity regulation with PCM’s latent heat characteristics, thereby reducing both building cooling and heating loads. This composite material integrates a temperature-responsive Fabry-Perot resonator with PCM using facile and cost-effective method (mainly spin coating). The composite PCM can achieve low emissivity for heating in cold environment and high emissivity for cooling in hot environment in response to ambient temperature change, which matches the latent heat absorption and release of PCM for improving thermal performance. Outdoor experiments show that the composite PCM can reduce and increase the indoor temperature by more than 3.5 °C at hot ambient and 1.5 °C at cold ambient respectively in comparison with conventional PCM. Numerical simulations demonstrate the developed material can achieve 10.5–23.5 % year-round energy savings across diverse Chinese climate regions. At last, the color design of the composite material is also conducted to cater for users’ preferences. This work paves new way to develop advanced PCM for all-season building energy savings.