Pete @ www.GymRatZ.co.uk presented the following explanation :
Andy Hall wrote:

For the heating case, the heat is moved from outside to inside.

Ah ha... I see. the electricity is being used purely to extract heat from one
side, shift it to the other then release it.

Yes, basically a heat pump.

Is it possible for a aircon unit to remove moisture from the air while
pumping the heat back into the room?

Not usually. To draw moisture out of the room, the need to blow the
room air across the chilled fins. Many a/c units have heat, cool and
dehumidfy settings. In cool and dehumidify they collect water in a drip
tray along the bottom, which then has to drain out by gravity or pumped
up and out using a small condensate pump.

Just that we have an upsidedown house with the bedrooms/bathroom partially
underground so virtually no way of getting any through ventilation. and the
steam from the shower doesn't vent very well from the bathroom as the only
window is at ground level and the extractor fan struggles to remove moist air
as the bathroom is 4m x 3m.


I wonder if there is such a thing as a wall mounted de-humidifier for such
situations.

There are plenty of small, free standing models about and they are very
effective - though I not looked for permanently wall mounted ones. Like
an a/c, they drip the collected moisture into a tray then into a
holding tank which needs to be emptied regularly. Some can be run to a
permanent drain with no need to empty them, providing gravity can be
used - otherwise I suppose a condensate pump would do the job.

Some of the older de-humidifiers had to be manually turned on and off -
much better is an automatic type, you set a knob on the front to the
humidity level you want and it runs has needed. Some optionally include
a small heater to provide heat and yet others can be set to just blow
air through a filter to help purify the air.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk