2016 ASHRAE Winter Conference

The IIR Congress is organized every four years and gathers refrigeration researchers from all over the world. The 24^th Congress program included over 700 talks in 122 technical sessions and 14 workshops covering technologies from low-temperature liquefaction to refrigerated storage to heat pumping and energy recovery. Refrigeration, air conditioning, and heat pumping topics dominated. The presentation highlights the latest research and engineering results, and coinciding and diverging technical opinions.  The audience will learn about the state of the art of these technologies and promising technical solutions for ‘improving the quality of life while preserving the earth.'

We explore possible low-GWP refrigerants by defining optimal thermodynamic properties and comparing those to properties estimated for a database of millions of compounds. We find that the optimal characteristics are quite rare; additional fluids are eliminated because they are unstable or toxic. We then estimate the cycle performance of the remaining candidates and apply efficiency as an additional screening criterion. The result is a handful of low-GWP candidates, and even these present tradeoffs. We argue that these represent all the viable candidates for single-component, medium- and high-pressure refrigerants—in other words, we have hit the limits of what chemistry allows.

Over last twenty years microchannel heat exchangers (MHX) have dramatically increased their presence in energy conversion systems: from aircraft and automotive applications and expanding to residential and industrial refrigeration and air-conditioning. This presentation presents major issues impacting application of MHX as evaporators: 1) condensate retention/removal, 2) frosting/defrosting and 3) refrigerant distribution.  The physics of the issues are discussed along with directions for mitigating them. Particular attention is given to refrigerant distribution and potential of Flash Gas Bypass to improve it.  In addition, quantification of vapor flow reversal in MHX tubes is presented along with system improvements obtained by its removal.

It seems to be clear that heat pumps have a unique role in the energy system of the future. Barely any other energy technology can provide net primary energy savings, economic benefits to the users and reduced climate impact at the same time. The benefit of heat pumps are achieved in several ways; by system integration capabilities tying together different parts of an energy system for enhanced overall energy efficiency, by storage of heat to offset peaks and, if efficient enough, providing the most efficient way to heat buildings from a net primary energy perspective.