Hi all,
I am interested in replacing our current “hole in the wall” ventilation in our bathroom with a ‘single room heat recovery ventilator’ - the type that would just fit through the wall, using the current hole, with little modification. I am wondering if anyone has any experience of these? I have only found one supplier that seems to be doing them for about £250, which seems quite pricy. Can anyone recommend any other suppliers/ types?

I also had a thought that I might be able to run this off a fairly small and simple 12V solar charged battery (the bathroom is upstairs and the bat could sit above in the loft)? Any advice on either fronts most welcome. Thanks,
Samantha

Thanks Tony, from what I know I agree with the expense! But why would condensation collect in it? From what I know, they are mounted in a similar way to a regular extractor fan- on a very slight slope so condensation drips out? Or is this only the case for some designs, or have I overlooked something completely?

I was thinking of condensation being a problem if you made a diy heat exchanger.

I have done several in doctors waiting rooms.

i have installed both baxi and vent-axia types, both ok, but v-a quieter, easy to install and settings adjustable. mine are both 12v but with mains connections.

Thanks everyone,

Thoughts so far on the three I have looked at (am i missing any others?):

The Silavent Energex -
Price: £70 – but need to check – I think this is the single speed version, and the dual speed could be quite a bit more pricy?
Motor: 12V AC.
Extraction rates: Low 22m³/h
High 70m³/h
Power consumption: Low 15W
High 40W
dBA 15 - 35
Input: 240V AC or 12V AC S.E.L.V.
Notes: Seems to be the cheapest, though I still need to track down a supplier and check. Website does not provide very good data to compare the efficiency of the heat exchanger. Sounds like the humidity controller does not work well and is not adjustable.
Link: http://www.silavent.co.uk/products/heat_recovery/energex-technical.asp


Kair Heat Recovery Ventilator
Price: £330
Motor: 12V AC
Extraction rates: Low 19m³/h
High 38m³/h
Power consumption: Low 9W
High 46W
dBA 21 - 45
Input: 240V AC which is transformed down to 12V AC in the separate humidistat control box.
Notes: The most expensive – though it seems like a good idea to have a separate/remote humidistat/control, so it is not measuring the humidity right next to the extractor fan (incoming and outgoing air).
Link: http://www.kiltox.co.uk/products/hrv.htm



Vent-axia HR25
Price: £227
Motor: 24V DC
Extraction rates: Low 15.7m³/h
High 54.6m³/h
Power consumption: Low 1.9W
High 24.1W
dBA 17 - 49
Input: 240V AC and possibly 24V DC
Notes: Seems to be the most power efficient, and hopefully will take a 24V DC battery input (am enquiring now). Middle price (though still expensive). Humidity control is adjustable, and can override with manual control (I think – can anyone confirm?). Might be the best option for us as we are keen on powering it with solar – would be no loss of energy from any step down transforming or inverters.
Link: http://www.vent-axia.com/products/vacas/hr25.asp

Make sure that the fan has the appropriate IP rating for the zone that it will be located in the bathroom.

From the spec I've read the 'upto 86%' referred to the amount of heat being recovered - e.g. if the exhaust air temp was 25C then the incoming air would be heated by upto 21.5C. I think the key word, though, is 'upto'.

" From the spec I've read the 'upto 86%' referred to the amount of heat being recovered - e.g. if the exhaust air temp was 25C then the incoming air would be heated by upto 21.5C. I think the key word, though, is 'upto". I think this is over simplistic, it all depends on the outside temperature. For instance if the outside temperature is -5 deg C, then the excess of heat in the internal air is 25 +5 = 30 deg C. So recovering 86% would give us 25.8, subtracting the -5, would give an incoming air temperature of 20.8, a small error compared to your method. If the outside temperature was +5, then the excess would be 20 so the incoming air temp would be 20 X .86 +5 = 22.2 deg.
What I suspect is that the 86% recovery is at a very modest temperature differential, in to out of say 5 degs. When the differential increases above this, because of the thermal resistance of the plastic heat exchanger and its limited size, the hot air can't transfer its heat to the incoming (cold) air at one end and at the other end the cold air can't pick up heat from the exausted (hot) air. Its a shame that the efficiiency is not stated at a working temperature diffential of some thing that is relevant, say a internal 20 deg, external zero deg C, or 20 deg C. This also catches any potential icing problems.
One other point is that the water content in the air carries an appreciable amount of heat energy, so cooling wet air releases more "heat" then cooling dry air. This added heat due to the water content is called latent heat. The heat in the air alone is called sensible heat. So a good spec would quote sensible heat recovery and latent heat recovery. Think of the moisture content of the shower room air!
Frank

A well designed heat exchanger (with perfectly dry air) could in principle approach 100% efficiency.

Have a look at: http://en.wikipedia.org/wiki/Countercurrent_exchange

I suspect the 86% figure might have something to do with latent heat? Not sure, though. Maybe they just pulled it out of the air.

Easybuilder if this is so then why don't they just say 86% and not up to?
I would have thought that the unit could be represented by a "perfect" heat exchanger with a lossy heat path bypassing it, like a bit of none heat insulator ( solid bar of metal). The lossy bit will have a loss directly proportional to temperature. I see the problem with the "perfect" heat exchanger, at the units higher speeds a lot of the air will not touch the sides of the heat exchanger medium and so will go whistling through carrying its heat with it. Or conversley will come in like a jet engine and not pick any heat up!
Frank

Perhaps the main purpose of bathroom ventilation is to remove moisture in the air. If so, wouldn't a dehumidifier do the job just as well with the added advantage of 0% heat loss?

Posted By: timbrennanPerhaps the main purpose of bathroom ventilation is to remove moisture in the air.

There's other toxic gases which sometimes need removing from bathrooms ;)

Paul in Montreal.

Has this situation changed at all? I'm looking into getting an extractor with heat recovery but am unsure if it's a good idea after reading around the forum, anyone out there with experiences of living with one?

We need a new extractor for the bathroom the very draughty little Victorian house we're living in during the self-build. The units above would probably be overkill, but does anyone know of an extractor to use intermittently with an overrun timer that doesn't leak too much when not working and has some heat recovery when it is?