On a scavenging trip to Santa Fe, to gather solar hot water panels, I ran across this solar wall or Trombe Wall. The south face of the house is fully glazed with insulated glass. The idea here is to collect the solar gain in a dense mass behind the glazing. In this case it’s a concrete wall painted black for maximum heat absorption. The solar wall charges up during the day and radiates heat to the inside space like a radiator. This particular model has no air vents, but often there are air vents that transport hot air into the living space via convection. High mass material such as concrete or cob leaks heat easily to the outdoors. Since the mass is behind glass it’s protected from the outdoor temperature swings.
This would work well with cob too, making a cob wall a lot more energy efficient in cold climates.
Another benefit of using a trombe wall with cob is you wouldn’t ever need to re-plaster it!