[namibj]

Doesn't need to be a heatpump dryer, just needs to be ventless.

E.g. the 20+ year old common German dryer that runs the clothes air closed-loop, first through the clothes, then to a heat exchanger with drainage geometry (typically feeding into a tray you have to pull out and pour out after each cycle), then across an electric heater, circulation fan, and back to the clothes. A second fan blows room air across the heat exchanger; the dryer action relies on the clothes being much warmer than room temperature such that the desired relative humidity of/at the clothes doesn't survive the cold from the room temperature.

[masterj]

Yeah, modern heat pump dryers are just nice and have cycle times more in line with North American expectations, but you’re right that alternatives have been around a long time!