Thermal diffusivity and thermal effusivity are related but distinct thermophysical properties. Thermal diffusivity measures the rate of heat diffusion within a material, while thermal effusivity characterizes the ability of a material to exchange heat with its surroundings. Both properties are important in understanding heat transfer phenomena in buildings and HVAC systems. For example, thermal diffusivity influences the thermal response of building materials, while thermal effusivity affects the performance of heat exchangers and radiative cooling systems.