Air conditioner - exhaust heat storage in summer (sodium acetate)
Heat retrievement in winter.
basic idea : no air vent for elimination of heat for stand-alone air conditioner appliances but storage of heat in swappable cartridges.
Utilization of physical state changes in a chemical substance solving/melting for heat storage and crystallization for heat retrieval. Possible substances are sodium acetate trihydrate CH3COONa · 3 H2O range [60°C ... 70°C] or salt mixture of magnesium nitrate hexahydrate with lithium nitrate Mg(NO3)2 · 6 H2O+LiNO3 range [70°C ... 80°C] as used in car industry.
Reusable Cartridges could be "charged" in summer to store the unwanted heat, and used in winter to get most of the heat back. There is no prototype, it is just an idea for designing an air conditioner to be more economical.