Portable dehumidifier/heat pumps

[Luckypants]

Got my daughter one to help dry her paddling kit in the winter. It works very well, but better to have the 'drying room' heated as well, so the air picks up more moisture before being dried by the de-humidifier. It is an expensive thing to dry out your kit this way.

[yorkie_chris]

I know how they work, Im surprised they are unimpressed. Sounds like they haven't done their sums right.

Any dehumidifier heats the room! Where do you think the energy goes.

What I really want to do is a CHP system with a battery bank and heat pump but no chance of that on a rented property.

OK, you're the expert.

[yorkie_chris]

Originally Posted by yorkie_chris

...they can act as heat pumps. I presume this is just by being air conditioning in reverse and they expel the cold air out of the window. But this doesn't seem thermodynamically sound to me.

Turns out I was wrong on that.

The ones which can act as heat pumps use 2 pipes and circulate the cold outside air through the cold coils at the back of machine.

The spec on them seems to indicate a CoP of about 3 which would make it cheaper than gas. That seems optimistic so it will probably work out cheaper to use the central heating for heat.

[dizzyblonde]

Aren't dehumidifiers expensive to run, like having a kettle permanently running?Surely Be better off drying your kit in that massive DRY garage you have there, where there's plenty of air running through than a room very much smaller and prone to damp.

[tigersaw]

I thought ground source heat pumps were supposed to use compressed gas, and by taking 1 degree out of a large area they could heat a small area by 10 degrees or whatever, like a fridge in reverse?

[yorkie_chris]

Originally Posted by tigersaw

I thought ground source heat pumps were supposed to use compressed gas, and by taking 1 degree out of a large area they could heat a small area by 10 degrees or whatever, like a fridge in reverse?

They do.

A lot of them use an intermediate "loop" of antifreeze or whatever to transfer the heat from the ground to the cold side of the machine where the working fluid is (same stuff as air-con gas)

Basically on the cold coils, heat is caused to flow to the low temperature (outside)... then when you compress the gas (inside the house, effectively) it heats up the hot coils, and the heat you collected outside is transferred to the house (into the central heating circuit or whatever).

The performance is heavily dependant on the temperature of the hot and cold sides... the bigger the difference the lower the performance. That's why ground source is supposedly better, the ground stays warmer than the air. Hence my confusion at small clangers post that people hate the ground source ones.

[johnnyrod]

The amount of heat to shift for heating is much larger than just for dehumidifying. Yes COP of around 3 is correct so the potential is there for cheap heat, but these aren't simple systems so if you **** up the sizing calcs you may as well not even get started. Yes they are like a fridge in reverse, or air con, or whatever you want to call it. Go to the refrigeration engineer forum if you want hard facts, there are some good guys on there.

Micro CHP would be nice, still a bit pricey for the home, but maybe next time I need a boiler they'll have come down to something sensible.