A comparative assessment of space-conditioning technologies

Highlights: • Thermodynamic comparison of 14 space-conditioning cycles conducted. • Coefficient of performance, exergetic efficiency, and power density compared. • Performance assessed in cooling and heating modes. • Vapor compression still outperforms all technologies in cooling mode. • Vapor absorption shows highest performance in the heating mode. With recent technological developments, many space-conditioning technologies have undergone significant breakthroughs. This investigation provides an updated quantitative comparison of 14 air-source heat pump technologies for residential or commercial space conditioning. These technologies are subdivided into three categories based on the working material, which can be solid-state, two-phase, or gaseous. Thermodynamic models are implemented for each technology and three figures of merit – primary-energy-based COP, exergetic efficiency, and power density – are calculated for cooling and heating mode operation. Solid-state technologies (thermoelectrics, thermionics, elastocaloric, magnetocaloric, and electrocaloric), two-phase technologies (vapor absorption, adsorption, ejector heat pump, membrane heat pump, and conventional vapor compression), and gas cycles (Stirling, Brayton, Bernoulli, vortex tube, and thermoacoustics) are analyzed on a common basis, with proper accounting of realistic thermal resistances and estimates of component requirements, rather than just computing idealized performance. Vapor compression outperforms all the not-in-kind technologies in cooling mode; however, in heating mode, vapor absorption with the ammonia-water working pair outperforms vapor compression by ~ 4.3%, 50.2%, and 49.3% when comparing primary energy COP, exergetic efficiency, and power density, respectively. Elastocaloric and thermoelectric devices demonstrate high power density in heating mode, exceeding that of vapor compression by 83.3% and 46.1%, respectively.