What is the panel's opinion on these items, for example the Ventaxia HR25:
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? I quite like the concept, as blowing warm air out of the house seems counterproductive when paying to heat it. They also tend to run continuously in a low-speed mode (feasible because you're not pumping out the heat) which is attractive to help the bathroom dry out after everyone's been through the shower of a morning.
They're not cheap, given I could buy a normal fan for a tenth of the price and connect it to my existing vertical vent rather than drilling the wall. However, since I'll be tiling the wall, it's to some extent a now-or-never choice.
Pete Verdon coughed up some electrons that declared:
It looks quite good, by the data. Extra Low Voltage, 84% recovery and reasonably priced (when compared to whole house units - you could get 3-4 of these for the price of a single whole-house system).
And sold by Screwfix.
I have one shower room that this could work in. Sadly the other is land-locked and cannot accomodate a unit like this. But I wonder if putting one in the hall to provide general background ventilation to the centre of the house with less loss of heat would be a good idea?...
2 to 25 watt consumption sounds a bit low but that's what it says. A plastic heat interchanger is a novel idea. What is the price? I couldn't see it on the site.
Agreed, but I'm not sure what the payback time would be.
One other benefit (I'm theorising) is that throughput is much better than an ordinary fan when the door is closed, because it's not trying to create a vacuum.
I have one (Eclipse, not Ventaxia). I got my soldering iron out and modified it to stop the trickle ventilation, which although commendably quiet, was still intrusive, especially in the middle of the night.
The ordinary humidity-driven operation does that very effectively.
I've looked at the manual for these (from the screwfix site) and a couple of sillyt questions come to mind.
1.) if the units extract the heat from the vented, moist air won't that lead to a lot of water condesing somewhere. Although it would hopefully be outside the vent, wouldn't it just drip down the wall?
2.) It looks like the heat extracted by the heat exchanger is sent back into the room, in close proximity to the fan itself. Wouldn't this just result in the newly heated air just being extracted again - as it's closer to the extractor than the manky stuff?
The heat matrix from a condensing tumble dryer would be *a* place to start - prolly get one down the dump for free.
Now, the matrix in mine is about 20x8x40cm (without measuring).
It wouldn't be hard to couple rectangular ducting to the front and back ends for one flow. The other flow is from side to side so that would be harder and , so it's not very balanced and thus not very efficient.
The other option would be to get busy a reel of 8mm or 10mm copper pipe chopped into short (80cm?) lengths. If it were me, without attempting a serious design at this stage:
Take enough lengths of pipe to be able to bunch to the overall size of a
100mm duct. Have two such bunches interleaved so the pipes from alternate bunches are in direct contact over a distance (maybe 30-40cm). Solder these pipes together in layers to get good thermal contact.
Form the pipes from the 2 bunches into 2 sets of parallel round sets 100m in diameter side by side. Do this at both ends.
Plug the pipe ends (wax maybe), and with suitable retainment, pot the pipe set end in resin. Clean off, remove wax (boiling water) and seal into duct pipe.
Now the biggest 2 problems there are, in my reckoning:
1) How to handle condensation - it needs to be trapped and drained.
2) 8mm pipe is probably too thick walled for this job. The aim is to establish a temperature gradient along the length - thick copper is going to fight that by conducting heat from the hot end to the cold end, defeating the exchanger. Thin walled pipe would help, but thin walled brass is going to be harder to bend and the complex bends involved in my scheme really need something quite soft to make it practical for a man with a simple workshop.
And does anyone have info. about its efficiency even if it does manage to condense?
I was bothered by the statement in the manual that it "provides up to
84% heat recovery from the stale extracted air.".
First, the use of "up to" is often a sign of spin. In what circumstances does it achieve this? What is the figure for typical bathroom and UK external conditions?
Second, does heat recovery from the air include heat recovery from the moisture in the air? I note that the Vent-Axia site refers in places instead to "up to 84% of the temperature differential of out going air". I'm not sure that temperature differential translates into energy efficiency when the outgoing air is moist and the incoming dry. (Many moons ago I might made have made a stab at this but most of my physics has aged like a Lancia Beta.)
I don't think we're talking about a large volume of water.
Mine extracts centrally, from directly above the shower, and blows sideways away from the shower. The (adjustable) dehumidifier switches the fan off usually two or three minutes after the shower stops.
Another possible is just a corrugated metal roofing sheet. Next to no forming needed, the downside is its rather large.
Outgoing moist air will condense as its cooled, hopefully the dripping is designed to miss the wall. Likely it wont when the wind blows, so I'd expect some pretty patterns to grow.
Andy Champ coughed up some electrons that declared:
An excellent point! I "invented" one airway system and just duplicated it (lazy - boo)
In which case, loose bunch inside and parallel in a 150mm duct pipe. Keep copper generally straight.
Put 2 x 45deg adaptors on 150mm at each end, cut hole in sides so that copper tube (still straight) comes out: Adapt final 150mm ends down to 100mm if required.
100mm
--- /-------------------------------\ Cu --------- ============================================================== Fresh air >
------/ \-------------
Bingo - opposing-flow heat-X.
Now, because the 150mm pipe will look like a bulge with a natural sump (OK I'm not doing the ASCII art again - it's upside down), just add a small condensate drain to the bottom of the plastic pipe.
Half the copper, no soldering (well maybe some to assist assembly). Some sort of potting (or soldering) needed to seal the copper pipes when they exit the 150mm.
It's robust, hygenic and can be unplugged for a good wash out from time to time...
large stack of those is made, so there are two separate paths for the air. On entry the hottest air is adjacent to the coldest air on the other side of the aluminium. The aluminium would need to be thick enough to stay flat by itself, and be say about 12 inches square, with two holes as shown.Cooking foil will *not* do! The gaskets (also 12 inches square?) are all the same shape and each one is twisted 90 degrees from the last. They'd need to be made from a waterproof and corrosion resistant material.
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