I noticed this when I had nickel-titanium glasses frames maybe 20 years ago. If I folded them in half at the bridge they would get hot, I could then conduct the heat away with my fingers, then, releasing the tension, the bridge would get very cold. Just like a refrigerant, but solid.

I did wonder at the time if they could replace the refrigerant in fridges with this but figured they would eventually fail from repeated bending.

Spartan article. I was curious about the efficiency. Seems like it's theorized as high as 30, but practically is more in line with 20 year old heat pumps? Lots of articles about simulations.

> COP of 3.7

https://www.nature.com/articles/s41467-023-43611-6 (2023)

> Using elastocaloric systems, these efficiencies can be increased by a multiple. Elastocaloric materials show COPs of up to over 30, and current technology demonstrators achieve simulative efficiencies of over 9.

https://analyticalscience.wiley.com/content/article-do/elast... (2023)

Looking for articles by the interviewee, Google Scholar only lists six. This one has a COP study:

https://asmedigitalcollection.asme.org/SMASIS/proceedings-ab...

The 20 COP is at temp. diff of around 3 K. At 20 K diff, the COP seems to land around 3-4.

> "The efficiency of elastocaloric materials is more than ten times higher than today’s air conditioning or heating systems – they will require significantly less electricity,” said Motzki.

Please also explain what's wrong with existing technologies that makes NiTi relevant in residential buildings. Current numbers don't seem to say what you're saying.

I could see this being really useful in e.g. space exploration where you don't want liquids slushing around, or risk leaking gas.

A necessary part of a heat pump is a way to move the heat away from where it was collected, so that you can either reject it (if you are cooling) or pump it into a space (if you are heating).

How do you do that with a solid metal? Do you have a complicated setup of hot room air blowing over the metal to absorb some heat, and then pump outside air through the same cavity to take away that heat? That sounds mediocre, as air is a pretty crummy working fluid for heat pumping.