Air conditioning technology is dominated by ‘vapor compression’ machines that circulate refrigerants. Although refrigerants account for only 1-2% of GHG emissions, researchers are exploring all ways to reduce GHGs. While some investigate more benign refrigerants, one research agenda proposes to eliminate vapor compression technologies altogether. Goetzler (2014) surveyed the potential of seventeen such technologies.
DOE’s Fantastic Five
Five rose to the top in terms of DOE’s selection criteria. Those criteria appeared to prefer ideas that are promising but underfunded. Although these five have promise, currently they are costly, complex, and immature in their technological and market development:
- Thermoelastic — Astonishingly, if you bend certain “shape memory alloys”, the microscopic structure changes (akin to water changing to ice), causing release of a large amount of heat.
- Membrane Heat Pumps combine two effects: water permeable membranes with the cooling effect of evaporation (when evaporating water robs heat from nearby air).
- Evaporative Liquid Desiccant A/C joins two familiar processes. A desiccant, latent-cooling stage is followed by an evaporative cooling stage. This combined process is suitable for both dry and humid climates.
- Magnetocaloric – Some rare materials contain magnetic dipoles that are readily aligned by a magnetic field. When the field is relaxed, surrounding particles bounce the dipoles back to random positions, transferring molecular motion (heat) to the dipoles, and causing overall cooling of the surrounding material.
- Vuilleumier Heat Pump – A heat source such as natural gas drives linked pistons that alternately compress or expand helium in separate hot and cold cylinders. Expansion of the compressed helium can cool.
The table summary below was collated from Goetzler:
The five technologies lack refrigerants that contribute to climate change. That does not mean each is free of any impact. All electric and gas powered devices have impacts — so the cooling or heating efficiency is important.
 Goetzler, William etal. (2014). “Energy Savings Potential and RD&D Opportunities for Non-Vapor-Compression HVAC Technologies.” Retrieved from DOE website: http://energy.gov/sites/prod/files/2014/03/f12/Non-Vapor%20Compression%20HVAC%20Report.pdf