As temperatures flare around the globe, deep tech startups are working to build sustainable technology that will keep us cool without further heating the planet.

Bloomberg recently featured two HAX companies that have designed solutions to do just that.

MIMiC Systems has designed a solid-state heating and cooling system that uses solid material to transfer thermal energy, thereby requiring no moving parts, making the system maintenance-free and reducing the cost of operation.The setup is fully modular, which means it can be more responsive to the differing temperature needs of individuals in a space. It also eliminates the need for refrigerants completely, according to CEO and co-founder Berardo Matalucci.

Flair is pioneering smart and flexible climate control, selling a smart vent that can redirect air from one part of the house to another, balancing temperatures and avoiding wasted energy. Customers have told the company they’ve saved as much as 30% of their electricity bills by installing the system, according to chief executive officer and co-founder Daniel Myers. The company’s devices are installed in 30,000 homes.

For homes with ductless mini split systems, which make up the bulk of HVAC systems outside the US, Flair sells a smart thermostat that customers can use to control the temperature from anywhere via an app. That could allow these smart thermostat-connected HVAC units to be integrated into the grid and participate in load flexibility programs, per Myers.

Myers told Bloomberg the “fully variable HVAC systems the company’s ‘North star,’ both in terms of providing comfort and being responsive to the needs of the grid.”