What is the panel's opinion on these items, for example the Ventaxia
HR25: http://www.vent-axia.com/products/vacas/hr25.asp ? 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

Pete Verdon coughed up some electrons that declared:

What is the panel's opinion on these items, for example the Ventaxia
HR25: http://www.vent-axia.com/products/vacas/hr25.asp ? 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

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?...

Cheers

Tim

On Jan 30, 12:37 pm, Pete Verdon
d wrote:
What is the panel's opinion on these items, for example the Ventaxia
HR25:http://www.vent-axia.com/products/vacas/hr25.asp?

I have always wondered why these are not more common.
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.

Matty F coughed up some electrons that declared:

On Jan 30, 12:37 pm, Pete Verdon
d wrote:
What is the panel's opinion on these items, for example the Ventaxia
HR25:http://www.vent-axia.com/products/vacas/hr25.asp?

I have always wondered why these are not more common.
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.

£185 on Screwfix

In uk.d-i-y, Pete Verdon wrote:
What is the panel's opinion on these items, for example the Ventaxia
HR25: http://www.vent-axia.com/products/vacas/hr25.asp ? I quite like
the concept, as blowing warm air out of the house seems
counterproductive when paying to heat it.

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.

They also tend to run continuously in a low-speed mode (feasible
because you're not pumping out the heat)

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.

which is attractive to help the bathroom dry out after everyone's been
through the shower of a morning.

The ordinary humidity-driven operation does that very effectively.

--
Mike Barnes

On Jan 30, 8:37 pm, Tim S wrote:
Matty F coughed up some electrons that declared:

On Jan 30, 12:37 pm, Pete Verdon
d wrote:
What is the panel's opinion on these items, for example the Ventaxia
HR25:http://www.vent-axia.com/products/vacas/hr25.asp?

I have always wondered why these are not more common.
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.

£185 on Screwfix

How hard can it be to make a heat exchanger and attach a cheap fan to
it? This is uk.d-i-y after all

On Thu, 29 Jan 2009 23:37:41 +0000, Pete Verdon wrote:
What is the panel's opinion on these items, for example the Ventaxia
HR25: http://www.vent-axia.com/products/vacas/hr25.asp ? 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

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?

Matty F wibbled:


How hard can it be to make a heat exchanger and attach a cheap fan to
it? This is uk.d-i-y after all



That is a very good question.

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.

Anyone got any better ideas?

Cheers

Tim

On Jan 30, 11:23 pm, Tim S wrote:
Matty F wibbled:

How hard can it be to make a heat exchanger and attach a cheap fan to
it? This is uk.d-i-y after all

The other option would be to get busy a reel of 8mm or 10mm copper pipe
chopped into short (80cm?) lengths.

I was thinking of a large stack of sheets of thick aluminium foil with
gaskets around the edge. That could be taken apart for cleaning if
necessary.

Matty F wibbled:

On Jan 30, 11:23 pm, Tim S wrote:
Matty F wibbled:

How hard can it be to make a heat exchanger and attach a cheap fan to
it? This is uk.d-i-y after all

The other option would be to get busy a reel of 8mm or 10mm copper pipe
chopped into short (80cm?) lengths.

I was thinking of a large stack of sheets of thick aluminium foil with
gaskets around the edge. That could be taken apart for cleaning if
necessary.

Sheets would be better from a physics POV. What I can't visualise is how
you're going to form these sheets so as to have 4 ports?

Care to expand?

Cheers

Tim

On 30 Jan, 09:44, Matty F wrote:

How hard can it be to make a heat exchanger

Turbocharged truck intercooler is the usual choice.

If you want air/water, look at aerospace scrap (more compact layout
than cars).

1.) if the units extract the heat from the vented, moist air won't
that lead to a lot of water condensing somewhere. Although it would
hopefully be outside the vent, wouldn't it just drip down the wall?

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.)




--
Robin

In uk.d-i-y, pete wrote:
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?

I don't think we're talking about a large volume of water.

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?

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.

--
Mike Barnes

Tim S wrote:
Matty F wibbled:

On Jan 30, 11:23 pm, Tim S wrote:
Matty F wibbled:

How hard can it be to make a heat exchanger and attach a cheap fan to
it? This is uk.d-i-y after all

The other option would be to get busy a reel of 8mm or 10mm copper pipe
chopped into short (80cm?) lengths.

I was thinking of a large stack of sheets of thick aluminium foil with
gaskets around the edge. That could be taken apart for cleaning if
necessary.

Sheets would be better from a physics POV. What I can't visualise is how
you're going to form these sheets so as to have 4 ports?

Care to expand?

Cheers

Tim

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.


NT

Tim S wrote:

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.

Why two bunches? Think of something like a steam loco boiler, with air
one way in the tubes, and air the other way outside.

Andy

Andy Champ coughed up some electrons that declared:

Tim S wrote:

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.

Why two bunches? Think of something like a steam loco boiler, with air
one way in the tubes, and air the other way outside.

Andy

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
================================================== ============
--- ---/ \-------- ---------
/------------------------\
/ 150mm \
/ \ Stale 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...

I think you're onto something here!

Tim

On Jan 30, 11:49 pm, Tim S wrote:
Matty F wibbled:

I was thinking of a large stack of sheets of thick aluminium foil with
gaskets around the edge. That could be taken apart for cleaning if
necessary.

Sheets would be better from a physics POV. What I can't visualise is how
you're going to form these sheets so as to have 4 ports?

Care to expand?

Rather than drawing them I'm making some trial gaskets. I've run out
of materials temporarily!

On 30 Jan, 09:52, pete wrote:
On Thu, 29 Jan 2009 23:37:41 +0000, Pete Verdon wrote:
What is the panel's opinion on these items, for example the Ventaxia
HR25:http://www.vent-axia.com/products/vacas/hr25.asp? 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

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?

Vent Axia state:
"Condensation : The outlet should be via drain holes in the lower part
of the external grille."


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?

On Jan 30, 11:49 pm, Tim S wrote:
Matty F wibbled:

I was thinking of a large stack of sheets of thick aluminium foil with
gaskets around the edge. That could be taken apart for cleaning if
necessary.

Sheets would be better from a physics POV. What I can't visualise is how
you're going to form these sheets so as to have 4 ports?

Care to expand?

Here's a photo to show the principle.
http://i44.tinypic.com/2btfh1.jpg

A 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.

pete formulated on Friday :
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?

Yes, ventilation should always be cross flow - two opposite ends.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Matty F coughed up some electrons that declared:

Here's a photo to show the principle.
http://i44.tinypic.com/2btfh1.jpg

A 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.

Ah - I see. That looks like it will turn into something that will be easy to
make due to many identical simple parts.

Do I understand it correctly: the air goes down one of the triangular
sections and fans into every alternate layer, coming out in the opposite
diagonal corner? The other air path is the other two diagonals and between
the layers of foil used by the first airway?

If so, the only comment I would dare to offer is that you're running the air
past two fairly sharp 90 degree bends, so you might need beefier fans?

For the foil, what about brass sheet? It would be fairly stiff for a given
thickness and resistant to corrosion.

I don't know about the gaskets - maybe square solid brass tube soldered, or
solid square plastic section cemented together - both with a bit of rubber
glued on one face and clamped with through-studs?

This sounds interesting - please let me (us) know how it develops.

Cheers

Tim

Pete Verdon wrote:

What is the panel's opinion on these items, for example the Ventaxia
HR25: http://www.vent-axia.com/products/vacas/hr25.asp ? 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.

I am in two minds about these. Typically when responding to a shower, it
seems that a humidistat controlled fan will work just as well and in
some ways better...

Yes a ordinary fan will throw away some heat, however that is quite
often desired after a shower to return the room to some semblance of
normal temperature rather than it remaining super heated from the shower.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Jan 31, 12:52 pm, Tim S wrote:
Matty F coughed up some electrons that declared:

Here's a photo to show the principle.
http://i44.tinypic.com/2btfh1.jpg

A 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.

Ah - I see. That looks like it will turn into something that will be easy to
make due to many identical simple parts.

Do I understand it correctly: the air goes down one of the triangular
sections and fans into every alternate layer, coming out in the opposite
diagonal corner? The other air path is the other two diagonals and between
the layers of foil used by the first airway?

The air doesn't fan into every alternate layer, it just goes to the
next single alternate layer.
The air uses the triangular sections just to skip past only two sheets
of aluminium. So the hot air goes past each alternate layer one at a
time, heating up the cold air
http://i42.tinypic.com/156var9.jpg

The cold air passes through triangular sections that are not shown in
the diagram.

If so, the only comment I would dare to offer is that you're running the air
past two fairly sharp 90 degree bends, so you might need beefier fans?

I'd suggest the air is going past more than 100 sharp bends.
Sure, but make the device as large as you want. I think it should have
two fans, and the inlet and outlet be widely separated in the room.

For the foil, what about brass sheet? It would be fairly stiff for a given
thickness and resistant to corrosion.

I imagine that brass would cost a lot more than aluminium.
Almost anything would do as long as it is stiff, the thinner the
better, and preferably a good conductor of heat.

I don't know about the gaskets - maybe square solid brass tube soldered, or
solid square plastic section cemented together - both with a bit of rubber
glued on one face and clamped with through-studs?

The gaskets don't have to be perfectly air-tight. I'd just assemble
the sheets and gaskets together and put them in a box that squashes
them all together. Then they are easily taken apart for cleaning.

This sounds interesting - please let me (us) know how it develops.

On Jan 31, 1:10 pm, wrote:
On 30 Jan,
Tim S wrote:

For the foil, what about brass sheet? It would be fairly stiff for a given
thickness and resistant to corrosion.

With the (small) thickness involved, would polythene sheet be conductive
enough? It would be strong and corrosion sresistant.

I have suggested that the sheets have to be very stiff, but if it's
supported along the edge by the triangular transfer channels,
something more flexible (i.e. conductive and cheap) would do.

Matty F coughed up some electrons that declared:

On Jan 31, 12:52 pm, Tim S wrote:
Matty F coughed up some electrons that declared:

Here's a photo to show the principle.
http://i44.tinypic.com/2btfh1.jpg

A 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.

Ah - I see. That looks like it will turn into something that will be easy
to make due to many identical simple parts.

Do I understand it correctly: the air goes down one of the triangular
sections and fans into every alternate layer, coming out in the opposite
diagonal corner? The other air path is the other two diagonals and
between the layers of foil used by the first airway?

The air doesn't fan into every alternate layer, it just goes to the
next single alternate layer.
The air uses the triangular sections just to skip past only two sheets
of aluminium. So the hot air goes past each alternate layer one at a
time, heating up the cold air
http://i42.tinypic.com/156var9.jpg

The cold air passes through triangular sections that are not shown in
the diagram.

OK - so like one really long air path then - but swap the directions of one
of the airflows on your diagram; you've got hot air and cold air coming in
together - so you'd get warm air back into the room and warm air at the
same temperature being blown outside. Sure that was just a drawing typo.

If so, the only comment I would dare to offer is that you're running the
air past two fairly sharp 90 degree bends, so you might need beefier
fans?

I'd suggest the air is going past more than 100 sharp bends.
Sure, but make the device as large as you want. I think it should have
two fans, and the inlet and outlet be widely separated in the room.

Yes - you'd need two fans whichever way you do it - though you may be able
to get a single motor double blower unit (probably cost more that 2 fans
though)

For the foil, what about brass sheet? It would be fairly stiff for a
given thickness and resistant to corrosion.

I imagine that brass would cost a lot more than aluminium.
Almost anything would do as long as it is stiff, the thinner the
better, and preferably a good conductor of heat.

I don't know about the gaskets - maybe square solid brass tube soldered,
or solid square plastic section cemented together - both with a bit of
rubber glued on one face and clamped with through-studs?

The gaskets don't have to be perfectly air-tight. I'd just assemble
the sheets and gaskets together and put them in a box that squashes
them all together. Then they are easily taken apart for cleaning.

This sounds interesting - please let me (us) know how it develops.

Harry Bloomfield writes:

pete formulated on Friday :
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?

Yes, ventilation should always be cross flow - two
opposite ends.

Well, that would probably be better, but the flow of air in
the room won't be so simple as to result in the "newly
heated air just being extracted again - as it's closer to
the extractor than the manky stuff". The unit sucks on one
side and blows out of the other, so there'll be a tendency
for the air in the room to circulate (likely to work best in
a cylindrical room (!), and a squarish one is going to do
better than an oblong one). There'll be mixing, but in the
bath/shower room I've seen with one of these units (HR25H)
installed, it seemed to work pretty well. Note that
"seemed" is just that; the owners were happy with it because
there was nolonger a condensation problem, but no double
blind controlled experiments were performed ;-)

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2009-01-30)

Matty F wrote:

The air doesn't fan into every alternate layer, it just goes to the
next single alternate layer.
The air uses the triangular sections just to skip past only two sheets
of aluminium. So the hot air goes past each alternate layer one at a
time, heating up the cold air
http://i42.tinypic.com/156var9.jpg

The cold air passes through triangular sections that are not shown in
the diagram.

I think you need one of your airflows reversed to get cross flow
operation - it would greatly enhance the efficiency.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Pete Verdon wrote:
What is the panel's opinion on these items, for example the Ventaxia
HR25: http://www.vent-axia.com/products/vacas/hr25.asp ? 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.

Once upon a time in the early 80s we bought a new built house that had
double glazing to the south side but single to the north, (and blown in
cavity insulation).

Surprise, surprise, we had major condensation problems. Initially, though
money was tight, I purchased a dehumidifier - the name escapes me but it was
the major one that didn't become the "Hoover". Initially I placed this on
the landing which resolved the condensation issues upstairs. Having resolved
that, I thought I'd use it downstairs for a couple of days to at least
prevent further condensation of the N facing windows. To my surprise, we
kept the upstairs clear of condensation. Removing it from the hall to the
kitchen, I found that we resolved all our condensation problems. Yes, we did
have open windows in the kitchen whilst cooking. However, despite four
humans emanating moisture upstairs and generating moisture in the bathroom,
the principal source was (and still is) the kitchen.

YMMV

Clot wrote:
Pete Verdon wrote:
What is the panel's opinion on these items, for example the Ventaxia
HR25: http://www.vent-axia.com/products/vacas/hr25.asp ? 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.

Once upon a time in the early 80s we bought a new built house that had
double glazing to the south side but single to the north, (and blown
in cavity insulation).

Surprise, surprise, we had major condensation problems. Initially,
though money was tight, I purchased a dehumidifier - the name escapes
me but it was the major one that didn't become the "Hoover".
Initially I placed this on the landing which resolved the
condensation issues upstairs. Having resolved that, I thought I'd use
it downstairs for a couple of days to at least prevent further
condensation of the N facing windows. To my surprise, we kept the
upstairs clear of condensation. Removing it from the hall to the
kitchen, I found that we resolved all our condensation problems. Yes,
we did have open windows in the kitchen whilst cooking. However,
despite four humans emanating moisture upstairs and generating
moisture in the bathroom, the principal source was (and still is) the
kitchen.
YMMV

I meant to add that the power used is significant and that the heat
generated is retained within the house.

On Jan 31, 8:44 pm, Tim S wrote:

OK - so like one really long air path then - but swap the directions of one
of the airflows on your diagram; you've got hot air and cold air coming in
together - so you'd get warm air back into the room and warm air at the
same temperature being blown outside. Sure that was just a drawing typo.

Well, I didn't think that through, you are probably right.
As I see it, this kind of device would be useful to slowly change the
air in a room - replacing the CO2 with oxygen and getting rid of water
vapour, at an extremely low running cost, perhaps only a few percent
of the cost of other devices such as dehumidifiers and air
conditioners.
I'm not at all concerned about the size of the device. Cheapness and
ease of build is the most important. And it must be able to be cleaned
easily, unlike ones with thin pipes.
The next task is to invent a good cheap way of making the gaskets.
If they were rigid enough, cheap plastic sheet could be used.

Matty F coughed up some electrons that declared:

On Jan 31, 8:44 pm, Tim S wrote:

OK - so like one really long air path then - but swap the directions of
one of the airflows on your diagram; you've got hot air and cold air
coming in together - so you'd get warm air back into the room and warm
air at the same temperature being blown outside. Sure that was just a
drawing typo.

Well, I didn't think that through, you are probably right.

Hi Matty

Thus is one of those times I'm prepared to say I'm absolutely right.

What you want for max efficiency is to have the last of the cooled exhaust
air meet the coldest incoming air, to suck the last joules out of it.

And conversely, you want to finish heating the new incoming air at the end
of its flow with the first and hottest of the exhaust air. It's the same
principle as that shower water reheater driang thingy in the Wiki.

As I see it, this kind of device would be useful to slowly change the
air in a room - replacing the CO2 with oxygen and getting rid of water
vapour, at an extremely low running cost, perhaps only a few percent
of the cost of other devices such as dehumidifiers and air
conditioners.
I'm not at all concerned about the size of the device. Cheapness and
ease of build is the most important. And it must be able to be cleaned
easily, unlike ones with thin pipes.
The next task is to invent a good cheap way of making the gaskets.
If they were rigid enough, cheap plastic sheet could be used.

This will be interesting. I was thinking, if you leave some temperature
probe holes in all 4 ports, one could take 4 readings and directly measure
the efficiency (mass airflow speed assumed constant).

Good luck!

Cheers

Tim

Tim S wrote:
Matty F wibbled:

How hard can it be to make a heat exchanger and attach a cheap fan to
it? This is uk.d-i-y after all



That is a very good question.

The heat matrix from a condensing tumble dryer would be *a* place to start -
prolly get one down the dump for free.

I bought one of these fans a few weeks ago, and will fit it soon. The heat
exchanger is remarkable similar to the one in the tumble dryer.

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 unit I have has a fan at each end - not sure if they are both blowing or
both sucking, but one deals with the air out, and the other with the air in. I
believe it is not supposed to be balanced, creating a slight +ve or -ve pressure.

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.

The whole unit is in a 6" plastic pipe, which is sloped slightly downwards
towards the outside. Condensation then drips out.

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.

Anyone got any better ideas?

Cheers

Tim

pete wrote:
...
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?

Yes, it drips outside. Make sure the tube the unit is in slopes slightly
downwards towards the outside.

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?

It is all about direction - the inlet directs the air into the middle of the
room, while the outlets suck it from alongside the wall. I expect the air will
be pretty well mixed by the time incoming air gets sucked back out again.

The manual in mine also says not to locate it where the incoming air can blow
the humid air away, e.g. don't direct it towards the cooker. It needs to be
directed to some out point in the room so it then flows past the cooker on the
way back out again.

-- JJ

John Rumm wrote:
Pete Verdon wrote:

What is the panel's opinion on these items, for example the Ventaxia
HR25: http://www.vent-axia.com/products/vacas/hr25.asp ? 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.

I am in two minds about these. Typically when responding to a shower, it
seems that a humidistat controlled fan will work just as well and in
some ways better...

Be in two minds no longer: they generally do have a humidistat too, and boost
their output accordingly. All all that heat - you've paid for it. It is a bit of
a shame to throw it all outside.

Yes a ordinary fan will throw away some heat, however that is quite
often desired after a shower to return the room to some semblance of
normal temperature rather than it remaining super heated from the shower.

I don't think the fact that the bathroom is hot has ever been an issue
(certainly is not an issue to me). It is always the condensation that you are
trying to deal with.

-- Jason

Clot wrote:
...
Surprise, surprise, we had major condensation problems. Initially,
though money was tight, I purchased a dehumidifier - the name escapes
me but it was the major one that didn't become the "Hoover".
Initially I placed this on the landing which resolved the
condensation issues upstairs. Having resolved that, I thought I'd use
it downstairs for a couple of days to at least prevent further
condensation of the N facing windows. To my surprise, we kept the
upstairs clear of condensation. Removing it from the hall to the
kitchen, I found that we resolved all our condensation problems. Yes,
we did have open windows in the kitchen whilst cooking. However,
despite four humans emanating moisture upstairs and generating
moisture in the bathroom, the principal source was (and still is) the
kitchen.
YMMV

I meant to add that the power used is significant and that the heat
generated is retained within the house.

That's why I wonder about the energy ratings of condenser dryers. It always
seems to be lower, because it uses more energy running the fan. On the plus
side, the heat stays in the house, so energy rating of individual items needs to
be looked at in terms of the bigger picture.

-- Jason

On Feb 2, 12:34 am, Tim S wrote:

Thus is one of those times I'm prepared to say I'm absolutely right.

What you want for max efficiency is to have the last of the cooled exhaust
air meet the coldest incoming air, to suck the last joules out of it.

And conversely, you want to finish heating the new incoming air at the end
of its flow with the first and hottest of the exhaust air. It's the same
principle as that shower water reheater driang thingy in the Wiki.

I don't doubt you for a moment. I was trying to solve the hard
problems of using cheap materials and ease of construction and
maintenance, leaving the simple decisions for later. The direction of
flow could be decided on later. For an efficient exchanger, clearly
it's best to heat the last of the incoming air using the hottest air
from the room.
I have avoided looking at existing heat exchangers so as not to
constrain my thinking. It's now time to see how others do it. But why
do they charge so damn much for them?

A heat exchanger is of interest because of its huge potential for
other people around the world, but is not necessary for me.
I live in an excellent climate. I put an electric heater on for a few
weeks in winter and sometimes turn a fan on in summer and don't need
an air conditioner. There's no real incentive to get or make anything
that reduces my heating bill. I'm busy on a number of other large
projects at the moment.

Matty F coughed up some electrons that declared:


I have avoided looking at existing heat exchangers so as not to
constrain my thinking.

Good plan

It's now time to see how others do it. But why
do they charge so damn much for them?

I do wonder. Perhaps 185 for a one off purchase of a self contained unit is
below the pain potential of many people - but the good whole house units
can cost amounts that are on their way to 1k. There they don't have any
real constrains of form factor or size - they need a big case, 2 big fans
and a heat exchanger and 4 ports.

A heat exchanger is of interest because of its huge potential for
other people around the world, but is not necessary for me.

It's of massive interest to me which is why I'm rather glad you mentioned
it. I was already looking at commercial solutions. I like my fresh air - I
can't stand this stupid modern obsession with building draught free
buildings - I am certain (with no real empirical proof though) that being
shut up in a box with no air makes everyone in my family more diseased in
winter.

The design of my new bathroom (landlocked) and shower room (glass block tile
windows) requires mechanical ventilation - so I could be very partial to a
system where I can blow loads of fresh air into my house all the time
without my gas bill going totally mental.

I live in an excellent climate. I put an electric heater on for a few
weeks in winter and sometimes turn a fan on in summer and don't need
an air conditioner. There's no real incentive to get or make anything
that reduces my heating bill. I'm busy on a number of other large
projects at the moment.

Lucky you! Where BTW, if you don't mind the question?

Cheers

Tim

On Feb 2, 12:52 pm, Tim S wrote:
Matty F coughed up some electrons that declared:

I live in an excellent climate. I put an electric heater on for a few
weeks in winter and sometimes turn a fan on in summer and don't need
an air conditioner. There's no real incentive to get or make anything
that reduces my heating bill. I'm busy on a number of other large
projects at the moment.

Lucky you! Where BTW, if you don't mind the question?

Auckland New Zealand. Av temperature 8 to 23 degrees:
http://www.bbc.co.uk/weather/world/c...ml?tt=TT003100

Tim S writes:

Matty F coughed up some electrons that declared:
It's now time to see how others do it. But why
do they charge so damn much for them?

I do wonder. Perhaps 185 for a one off purchase of a self contained unit is
below the pain potential of many people - but the good whole house units
can cost amounts that are on their way to 1k.

£180 is somewhat past my pain threshold, but it's just about
at the point where it's worthwhile doing, but since I want
to install the thing in a bathroom I'm clobbered with Part P
so have either to pay an electrician something like £200 to
install it or £100+ for building control approval and still
pay an electrician to test it :-(.

But as far as the price of the units is concerned it's just
that so few people currently install them. They're not
intrinsically expensive to make, but with only a handful of
people thinking it's worth doing, the manufacturers have to
charge a lot to make a profit (cover costs of tooling,
stocking etc) and can charge an extra margin because the
people who do want to do it have little choice. And of
course, so long as they're so much more expensive than a
simple extractor, the simple extractors are what people go
for. So a DIY design would be a good thing for the people
who can d-i-y (but not so good for people who can't and want
the price of units to come down)

Given the building regs requirement for mechanical
ventilation in bathrooms, I reckon the best way to kick them
into high volume production would be to change the regs so
they reqiure (some form of) HRV in bathrooms for new build.

The other thing that bugs me is having to have a socking
great hole to the outside when there's a gas cooker in a
room. Sure, it's really important that there's fresh air
coming in for such things, but providing that through a heat
exchanger would make a huge difference to the comfort levels
of a flat in Scotland. AFAIK, that's not allowed, but maybe
I should ask that question in a separate thread?

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2009-01-31)

Matty F writes:

On Jan 31, 8:44 pm, Tim S wrote:

OK - so like one really long air path then

As I see it, this kind of device would be useful to slowly change the
air in a room - replacing the CO2 with oxygen and getting rid of water
vapour, at an extremely low running cost,

It would be useful to do some experiments. My worry with
your design is that the frictional losses would mean that
the fan would have to work very hard. I suspect that the
commercial designs just have a single straightish path with
plates on top of one another.

Here's a rather hurried drawing:
http://homepage.ntlworld.com/jon.fairbairn/counterflow.png
So you'd have a pile of flat rectangular plates separated by
gaskets alternating between the red dashed and the blue
solid pattern. The thing would have to be longer than the
proportions implied by the drawing, I think. You could make
it so the cross-section was the same size as computer case
fans (or some other readily available size of fan with a
rectangular mounting). Since it's nearly a straight through
path, you could just stick the whole assembly (bar the
fans!) in soapy water to wash it out.

perhaps only a few percent of the cost of other devices
such as dehumidifiers and air conditioners.

I think that's true, if you consider the Vent-Axia HR25's
power consumption.

I'm not at all concerned about the size of the
device. Cheapness and ease of build is the most
important. And it must be able to be cleaned easily,
unlike ones with thin pipes. The next task is to invent a
good cheap way of making the gaskets. If they were rigid
enough, cheap plastic sheet could be used.

I was thinking of rectangular cross-section aluminium rod
with thin rubber sheet top and bottom to make the seal, but
I don't know what the optimum distance between the
heat-exchanger plates would be, so maybe the thickness of
the rubber sheet would make enough gap (see
http://www.technix-rubber.com/prodtype.asp?strParents=&CAT_ID=104&numRecordPosit ion=1
for possible sheet). Or maybe use ordinary epdm rubber
draught strip (M-seal) to make the gaskets -- that would be
an easy experiment, but would require the plates to be quite
stiff.

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2009-01-31)