You can do radiant cooling with an air-to-water heat pump just as you can with an air-to-air or water-to-water heat pump.
The main issue is managing humidity so that the dewpoint stays below the emitter temperature.
The main issue is managing humidity so that the dewpoint stays below the emitter temperature.
The downside of course is that its not going to make your already +40°C room into a flu-inducing +18°C one. Its more of a tool to offset a 2°C, maybe 4°C in extreme cases indoor temperature rise. Which is likely more than plenty for many airtight & insulated houses.
And indeed, managing humidity is hard. If this sounds at all interesting to the reader, definitely research whether this is applicable in your situation/area at all.