Using a heat exchanger to increase latent heat extraction – GreenBuildingAdvisor

This is a follow-up to a discussion from an article that was recently posted about dehumidifiers — https://www.greenbuildingadvisor.com/article/dehumidifying-with-portable-unit-vs-ducted-system?  *– and a discussion in the comments. I wanted to break that discussion into a new thread because it’s really a separate topic, and posts in the Q&A seem to get more and better comments.

I feel greatly indebted to Charlie Sullivan, who turned me on to the idea of using a heat exchanger in combination with a regular air conditioner to make a dehumidifier with very high latent heat removal. If you look at posts #8 through #11 in the comments, I expound on the idea in great detail, and I came to the conclusion that doing so would use about 75% less electricity for the same level of dehumidification as a standalone dehumidifier, or even a conventional whole-house dehumidifier.

The idea is that the output of an air conditioner is run through a heat exchanger, where air entering the air conditioner is cooled and air leaving is warmed. If the heat exchanger were 100% efficient the air would leave at exactly the same temperature as it entered at, there would be no sensible cooling. When the air was cooled, moisture in it would condense out, so there would be the same level of latent cooling as a similar-sized air conditioner would develop. 

This is such  dramatic improvement over conventional dehumidifiers that I’m wondering if there is a catch that I’m not seeing. 

Thoughts?

*(Ironically the article was a “Q&A Spotlight,” where questions here get expanded into full articles. So we’ve gone full circle!)