It's actually a regenerative heat exchanger: https://en.wikipedia.org/wiki/Regenerative_heat_exchanger.

The person you are replying to was discussing "exchanging heat across a continuous length along opposing flows", which is countercurrent exchange. Regenerative exchange is, at least to my understanding, more of a cyclical store and release process.

Yes, which is what OpenERV is. I can understand why they might have thought I was talking about their system, my wording was a bit ambiguous there. So it doesn't hurt that they cleared that up :)