recycling damp bathroom ait into the house

[simon m]

we have a B&B and some 6 bedrooms exhaust their power showers steamy air into the atmosphere via individual extractor fans connected to a

4inch pipe in the attic to a mushroom vent. Since we have the builders in doing a load of work up there, I wonder is there a unit I could mount in the attic so that rather than vent this lovely hot air (these are BIG showers) we could send it out into the corridors for communal heating? Obviously the air would need dehumidifying, and the unit would be needed to redirected to outside in summer when we get hot weather (hard to imagine in this snow). Ideally we'd run the unit on a timer/humidistat to save my electric bills.

Any pointers to such a beast would be much appreciated!

Simon

[Tim W]

simon m wibbled on Wednesday 13 January 2010 11:31

If the showers contain a loo, you won't want to be doing this.

But, the normal solution is called a "whole house heat recovery unit" (that should google for you). 4 ports, 2 fans. On pair of ports link your inside vents to an external exhaust. The other pair (isolated from the air flow of the 1st set) sucks air in from outside, warms it using the heat from the 1st airpath and the delivers it where you want.

Not cheap, but in your scenario of lots of heating and lots of showers going on, it might add up.

[dennis]

Something like

[TMC]

so what does it do with all the moisture?

What happens when the sun is not warming the roofspace that being most of the time when wnidows need to be closed to keep the heat in

I get the impresssion that it would be raining in my loft if I had one of these

Tony

[Owain]

The moist air goes to the outside. There is a heat exchanger between the moist outgoing air and the fresh incoming air.

The incoming fresh air is warmed by the moist outgoing air, not sun in the roofspace.

Unless I've misunderstood both your question and the function of the unit.

Owain

[TMC]

Had another look got it wrong the first time

seems that it draws cold air out of the loft and pumps it into the house

Then the pressure created pushes the damp out from around the door and window frames

should work well with my open fireplace then ?

Am I missing something here?

[Tim W]

TMC wibbled on Wednesday 13 January 2010 13:03

Looking at the diagram, it looks like they want you to believe it draws warm air (solar heating of roof) out of the loft, filters it and pumps it into the house. Cole air comes in from outside to replenish the loft and the waste air in the house escapes via normal ventilation routes.

I can't see it being any use whatsoever in winter (as you say, it's just going to suck cold air in, unless your loft runs warm due to lack of loft floor insulation).

In summer, the last thing you want is hot air being blown into the house.

It won't send wet air from the shower into the loft though, unless there are significant air leaks between the shower room and the loft.

This is what I was thinking of:

the OP googles, this subject has been on here, a year or two back IIRC. The possibility of building a DIY unit was discussed too.

[NT]

If there are just showers in there you wont want to do it either.

Pretty cheap to make your own, its only a counterflow heat exchanger. I'd recycle the hall air unless you specifically need a lot more fresh.

NT

[TMC]

Hi

As there is no outside vent in the diagram my first assumption was that the moist air would vent into the loft - not a good idea

Closer viewing of the diagram does not show any intake of moist air into the unit hence my second post

As described it looks like it would only be beneficial if the loft was warmer than the house in winter and cooler than the house in summer which is not a likely scenario

Tony

[dennis]

Having just got back from work I wish i had looked closer at the diagram.. its cr@p and not a proper system like it looked at first glance.. so no I don't recommend it at all.

[simon m]

many thanks all, all the pointers were good and I didn't realise there were so many options for a fairly small building. I've printed all this out for the builder and he's off to investigate.

Thanks again, sometimes it's just knowing the keywords to search for that sets the hare off to google land!

Simon

[JimK]

mmm anyone have a link to either someone who's done it DIY or somewhere that sells the hardest bits (heat exchanger?)

Cheers JimK

[NT]

One ubercheap and efficient design uses ali foil zigzagged over a frame. The lid needs to be easily removable, as the foil will need replacing every couple of years.

NT

[JimK]

I know I'm a Yorkshireman but even I can see some merit in making something that lasts longer than 2 years! :>))

any pointers to something betterer and more longer lasting?

Cheers JimK

[Onetap]

Oh dear.

NT's 'cheap-to-make-your-own' schemes have much enthusiasm behind them but are untempered by hard experience.

You should filter both air streams. You don't have to, the plate heat exchanger acts as a fairly good filter having very narrow airpaths; bit of a bugger to clean them, though.

The moist extract air stream forms condensation under some conditions and should be connected to a drain. The extract air path also needs to be inclined towards the drain tray and you need to restrict the velocity or droplets will blow into the discharge duct.

There should be a by-pass route around the heat exchanger, for when you don't want to recycle heat into the incoming air.

I think it would be a major PITA to make your own, unless you manufacture AHUs for a living. I have experience.

[NT]

I would think its more deposition than condensation.

NT

[Onetap]

This lot make them.

you can see, commercial stuff at commercial prices. My last contact with them was in 1991, I think, so the name didn't come to mind immediately.

That project was for multiple bathrooms with extract running 24/7 in a care home. The OP would have problems connecting multiple pressurized extract ducts into a system if he doesn't want air from one room being blown out into another. You'd need some shut-off dampers if you don't want continuous extract. It is usual to have one common extract fan so ducts are at negative pressure.

[Onetap]

You may do, but that is because you really don't have a clue.

[JimK]

mmmmm - any thoughts on the domestic versions that are about - for maybe one bathroom rather than the OPs multiples?

Cheers JimK

[NT]

There isnt a lot of temp difference between the bathroom and an internal corridor

NT