Tumble Dryer Heat Recovery

[TwoHorsePower]

I know tumble drying is an awful waste, but in this weather (we're on the rainy side!) it is sometimes a necessary evil.....

We have one of those combined washing machines and driers. It has no vent from which I can extract heat, so where does the heat go? It doesn't seem to heat the room, or at least not that I notice. Does it heat water which it pumps out the drain? Or does it work like a dehumidifier, where the energy ends up in the room, and perhaps i'm just not noticing it?

Any advice gratefully received.

[Countrypaul]

I know our machine uses cold water to condense the warm moisture from the clothes and replaces the water several times if tumbling somthing that requires a lot of drying.

Paul

[nickiniquity]

Most machines have a spray of mains cold water inside a little tank on the intake to the heater fan.  The water is at maybe 16C, and the incoming air from the drum will be around say 50C and completely saturated with moisture from the clothes.  The spray of water drops the temperature of the air, and this causes some of the moisture to condense and drop-out because the amount of water air can hold as a vapour is increases with temperature. 

When the air leaves the condesnser tank, it will have a temperature close to that of the spray water and will in saturated state at this lower temperature.  As the air passes through the heater and is raised back up to 60C or so, its capacity for holding moisture increases (i.e. it is no longer in a saturated state) so it can take up moisture from the clothes.

The condensed moisture from the clothes is washed away with the spray water and pumped out by the machine's drain pump.  The spray water  takes out heat from the change in temperature of the air, and also the latent heat from the water vapour condensing.  This is why the dryer doesn't heat or humidify the room as the heat is lost to the drain. 

Nick