Andy Burns <
usenet@andyburns.uk> wrote:
Mike Halmarack wrote:
Been given advice to add powered extractors in bathroom and kitchen.
the idea of using expensive electricity to heat rooms, and then using
more expensive electricity to blow that heat out into the outside
world is daunting.
I don't know whether single-room MVHR is effective (cost-wise or humidity-wise)?
They claim to recover about 75% of the heat. That means you can run them in trickle mode without losing too much, which is important in a bathroom where
it might get uncomfortably cold if a regular fan were venting to the wintry outside.
Extractor fans that blow out need the air replacing from somewhere. If you don't open a window it'll come from inside the house somehow, which will
likely mean cold air will come in via air leaks. You might not feel the bathroom being cold unless the bathroom itself leaks, but some other spot
will get colder because of it.
Dehumidifiers will reduce moisture, but they won't do anything for air
quality - cooking, 'toilet smells', pet/human odours, gas hob. The
advantage of MVHR is you're simultaneously pulling in fresh outside air
instead of recirculating stale inside air.
Single room MVHR are a bit expensive for what they are. I have a used one
of these to play with:
https://www.i-sells.co.uk/product/vent-axia-lo-carbon-tempra-single-room-heat-recovery-unit/
The actual heat exchanger (available as a spare) is a tube of plastic
straws. That connects with a double sided fan - one side of the fan blows
air down the straws, the other side sucks air in from the side of the tube which is connected to the space between the straws, resulting in opposite directions air passing each other across the surface of the straws.
The trouble is the fan is loud (perhaps because it's used, but I don't think so) and I need to work out how to quieten it down, which is awkward. There
are some hacks here:
https://www.earth.org.uk/MHRV-Vent-Axia-Lo-Carbon-Tempra-P-REVIEW.html https://homefarmparham.co.uk/HomeFarmHouse/fittings/Vent-Axia/VentAxiaTempraMods.html
It's a custom 24V PWM fan controlled by a little control board with a PIC
micro that does timer, humidity, etc, and if you get the non-SELV version a 240V->24V PSU board. The uplift on the humidity/timer/etc version is ridiculously pricy for such a simple board - a standard PWM fan controller might do it, or an Arduino.
But even at lowest PWM it's not quiet enough for me. The other option is
just to DIY an equivalent, perhaps with a matrix of copper tubes like a
steam loco boiler. But I need to work out how to do a tangential/cross-flow fan (pulls air across the fan blades like a water wheel) as that doesn't
seem to be a thing you can easily buy in a flat form factor, only a long cylinder.
Theo
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