cold wall design
Launderess its all about 2 things - efficiency and low cost.
My fridge is a Haier 220 litre 2 door. It was the cheapest 2 door on the Aussie market at the time (about 10 years ago) yet was super efficient by the standards of the time, though there are fully frost free models of larger size that use less power on the market now.
It has a manual defrost freezer of about 30 litres above a (cold rear wall) fridge of about 190 litres. It has been great for us.
the freezer is well insulated and has good hefty door seals. It only needs defrosting maybe once a year or 18 months.
The freezer evaporator is just a tube that circulates refrigerant around the freezer cavity - you only see the plastic walls of the freezer, the tubes are tucked behind. The refrigerant tube then passes to the back wall of the fridge compartment, again tucked behind the plastic rear wall of the fridge compartment. The tube zigzags down behind the plastic back wall, creating a cold surface area of the entire inner back wall of the fridge. The plastic is moulded to form a gutter at the bottom which drains to a catch pot on top of the fridge compressor and the condensed water evaporates away when the compressor is running.
When the compressor runs, the freezer chills first, then the refrigerant gas passes down behind the back wall of the fridge, creating a "passive evaporator" at the back of the fridge cavity before returning to the compressor. The back wall gets a light frost on it when the compressor is running but once the fridge is down to temperature and the compressor click off, the fridge temperature is still above freezing and the evaporator is only lightly frosted, the fine frost layer passively defrosts, needing no defrost elements or fans.
The simple way to think of it is that you are actively chilling the freezer compartment and getting almost "free" refrigeration of the fridge compartment simply by running the refrigerant gas down the back wall of the fridge compartment before it goes back to the compressor.
It is a very efficient system because you are getting your fridge cooled almost for free from the cold gases leaving the freezer evaporator, and because it is a very cheap to manufacture system with no fans, defrost elements, ducting, flaps, false walls and so on.
It needs to be precisely engineered to ensure that both compartments are kept within design temperature when there is only 1 thermostat, it only measures fridge temperature and it is assumed (designed in) that the freezer will be down to temp before the fridge thermostat is satisfied and shuts off. This in turn depends on the fridge being kept in a room that is warm enough to keep the thermostat cycling on often enough to keep the freezer down to temp. If the unit is installed in an unheated basement in a US Midwestern winter, the room is likely to be so cold that the fridge thermostat only rarely comes on, which would have the freezer warming up too much before the compressor came on again. That is my guess why these types of fridge aren't common in the USA.
I know that's a lotta words but that's the simplified version. Well, you asked...
