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Old 18-01-2004, 04:32 PM
Trent-Lion
 
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Default Condensation in twinwall polycarbonate channels

I, a rank amateur and non-handy person, am trying to restore an old GH
with aluminum frame. I replaced the glass with twinwall polycarbonate
sheets. The frame has a groove in the bottom where the glass used to
fit and into which I fitted the poly. I could see no way to allow for
drainage at the bottom of the sheets. Both ends of the sheets are
tightly sealed with caulk, and I put more caulk at the bottom, to help
the sheets slide into the frame groove and to seal the juncture of
sheet and frame.

Now most channels of the poly look fine and clear, but a lot of them
stay cloudy from moisture (making for an unsightly appearance), and in
some channels several inches of water has collected at the bottom.

I don't understand why the channels are behaving differently. But more
importantly, am I stuck with this condensation/water problem forever,
because I sealed both ends of the channels with caulk? All I can see to
do to remove the water is drill a small hole at the bottom of the
affected channels and let the water drain out or perhaps pull it out
with a hypodermic syringe. Or perhaps the water will evaporate when hot
weather comes.

The weather in north FL where I am located has varied from the 30s to
about 70 since I installed the sheets. Will the problem get better or
worse when hot weather comes?

Thanks for help.
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Old 18-01-2004, 06:42 PM
David J Bockman
 
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Default Condensation in twinwall polycarbonate channels

The manufacturer, Poly-Tex, recommends *not* sealing the ends of the cut
sheets, for the very reason that you're describing.

Dave

"Trent-Lion" wrote in message
...
I, a rank amateur and non-handy person, am trying to restore an old GH
with aluminum frame. I replaced the glass with twinwall polycarbonate
sheets. The frame has a groove in the bottom where the glass used to
fit and into which I fitted the poly. I could see no way to allow for
drainage at the bottom of the sheets. Both ends of the sheets are
tightly sealed with caulk, and I put more caulk at the bottom, to help
the sheets slide into the frame groove and to seal the juncture of
sheet and frame.

Now most channels of the poly look fine and clear, but a lot of them
stay cloudy from moisture (making for an unsightly appearance), and in
some channels several inches of water has collected at the bottom.

I don't understand why the channels are behaving differently. But more
importantly, am I stuck with this condensation/water problem forever,
because I sealed both ends of the channels with caulk? All I can see to
do to remove the water is drill a small hole at the bottom of the
affected channels and let the water drain out or perhaps pull it out
with a hypodermic syringe. Or perhaps the water will evaporate when hot
weather comes.

The weather in north FL where I am located has varied from the 30s to
about 70 since I installed the sheets. Will the problem get better or
worse when hot weather comes?

Thanks for help.



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Old 18-01-2004, 07:02 PM
C
 
Posts: n/a
Default Condensation in twinwall polycarbonate channels

On Sun, 18 Jan 2004 10:11:59 -0500, Trent-Lion wrote:

I, a rank amateur and non-handy person, am trying to restore an old GH
with aluminum frame. I replaced the glass with twinwall polycarbonate
sheets. The frame has a groove in the bottom where the glass used to fit
and into which I fitted the poly. I could see no way to allow for drainage
at the bottom of the sheets. Both ends of the sheets are tightly sealed
with caulk, and I put more caulk at the bottom, to help the sheets slide
into the frame groove and to seal the juncture of sheet and frame.

Now most channels of the poly look fine and clear, but a lot of them stay
cloudy from moisture (making for an unsightly appearance), and in some
channels several inches of water has collected at the bottom.

I don't understand why the channels are behaving differently. But more
importantly, am I stuck with this condensation/water problem forever,
because I sealed both ends of the channels with caulk? All I can see to do
to remove the water is drill a small hole at the bottom of the affected
channels and let the water drain out or perhaps pull it out with a
hypodermic syringe. Or perhaps the water will evaporate when hot weather
comes.

The weather in north FL where I am located has varied from the 30s to
about 70 since I installed the sheets. Will the problem get better or
worse when hot weather comes?

Thanks for help.



Without knowing your setup, I am not so sure I would have been so eager to
seal the poly panels. Moisture has gotten in several with nowhere to go.
If you can, remove the cloudy panels and let them dry complete. Check
them for hairline cracks. Once dried, you could reseal. Since you are in
an area where temps aren't too extreme, I think you'd be safe not to seal.

You could also check the channels where they go and drill drain holes to
allow for drainage.

Greenhouses aren't necessarily supposed to be airtight. I'm not so sure
you really want to make the entire structure inflexible.


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Old 19-01-2004, 05:33 PM
Trent-Lion
 
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Default Condensation in twinwall polycarbonate channels

It is raining and I can now see that the moisture in my twinwall
chambers is getting in *from the bottom*. Some of the chambers are less
well sealed with caulk than the others, water is gathering in/near the
groove in which the panels sit, and capillary action is taking over
from there, causing columns of water to form and mist to rise off the
columns and up into the chambers.

If I can ever get the moisture out, by drilling small holes and sucking
the water out with a hypodermic or however, I can perhaps seal it all
up so no more can get in.

Thanks for comments received.

In article , Trent-Lion
wrote:

I, a rank amateur and non-handy person, am trying to restore an old GH
with aluminum frame. I replaced the glass with twinwall polycarbonate
sheets. The frame has a groove in the bottom where the glass used to
fit and into which I fitted the poly. I could see no way to allow for
drainage at the bottom of the sheets. Both ends of the sheets are
tightly sealed with caulk, and I put more caulk at the bottom, to help
the sheets slide into the frame groove and to seal the juncture of
sheet and frame.

Now most channels of the poly look fine and clear, but a lot of them
stay cloudy from moisture (making for an unsightly appearance), and in
some channels several inches of water has collected at the bottom.

I don't understand why the channels are behaving differently. But more
importantly, am I stuck with this condensation/water problem forever,
because I sealed both ends of the channels with caulk? All I can see to
do to remove the water is drill a small hole at the bottom of the
affected channels and let the water drain out or perhaps pull it out
with a hypodermic syringe. Or perhaps the water will evaporate when hot
weather comes.

The weather in north FL where I am located has varied from the 30s to
about 70 since I installed the sheets. Will the problem get better or
worse when hot weather comes?

Thanks for help.

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Old 19-01-2004, 07:54 PM
C
 
Posts: n/a
Default Condensation in twinwall polycarbonate channels

On Mon, 19 Jan 2004 11:11:05 -0500, Trent-Lion wrote:

If I can ever get the moisture out, by drilling small holes and sucking
the water out with a hypodermic or however, I can perhaps seal it all up
so no more can get in.


Small vent holes near the top of each fogged channel would help. I'd put
the holes on the inside surface, that which is away from the weather. The
vents holes would allow trapped moisture a way to escape. The holes would
not need to be any wider than 1/32 or 1/16", I would think. It's worth
trying on one panel before committing to all of them.


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Old 19-01-2004, 07:54 PM
C
 
Posts: n/a
Default Condensation in twinwall polycarbonate channels

On Mon, 19 Jan 2004 11:11:05 -0500, Trent-Lion wrote:

If I can ever get the moisture out, by drilling small holes and sucking
the water out with a hypodermic or however, I can perhaps seal it all up
so no more can get in.


Small vent holes near the top of each fogged channel would help. I'd put
the holes on the inside surface, that which is away from the weather. The
vents holes would allow trapped moisture a way to escape. The holes would
not need to be any wider than 1/32 or 1/16", I would think. It's worth
trying on one panel before committing to all of them.
  #7   Report Post  
Old 19-01-2004, 08:11 PM
C
 
Posts: n/a
Default Condensation in twinwall polycarbonate channels

On Mon, 19 Jan 2004 11:11:05 -0500, Trent-Lion wrote:

If I can ever get the moisture out, by drilling small holes and sucking
the water out with a hypodermic or however, I can perhaps seal it all up
so no more can get in.


Small vent holes near the top of each fogged channel would help. I'd put
the holes on the inside surface, that which is away from the weather. The
vents holes would allow trapped moisture a way to escape. The holes would
not need to be any wider than 1/32 or 1/16", I would think. It's worth
trying on one panel before committing to all of them.
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Old 20-01-2004, 02:13 PM
Dwight Sipler
 
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Default Condensation in twinwall polycarbonate channels

C wrote:

Small vent holes near the top of each fogged channel would help. I'd put
the holes on the inside surface, that which is away from the weather. The
vents holes would allow trapped moisture a way to escape. The holes would
not need to be any wider than 1/32 or 1/16", I would think. It's worth
trying on one panel before committing to all of them.




When I put up my twinwall polycarbonate panels the manufacturer
recommended that the bottom of the panels be left open and the top be
sealed. This prevents air convection through the panels (decreasing
their insulation properties) while allowing moisture to get out through
the bottom. Sealing the panels can be done either with caulk or with
tape. The aluminium tape is weather resistant and will last a lot longer
than something like duct tape (which has about a 2-month lifetime in
sunlight).

In practice, there are times when moisture collects in the channels, but
the next sunny day clears it out.

If the caulk in the original poster's installation is too thick to
remove or if it is still unsightly after attempts at removal, you could
cut of an inch or two of the bottom of the panel and install a baseboard
(on the inside of the panel).

If you opt for the vent hole approach, I would put the holes at the
bottom, just above the caulk (or maybe even through it), so that they
could also act as a drain in the event that a large quantity of
condensate forms in the channels.
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Old 20-01-2004, 05:32 PM
C
 
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Default Condensation in twinwall polycarbonate channels

On Tue, 20 Jan 2004 08:10:44 -0500, Dwight Sipler wrote:

C wrote:

Small vent holes near the top of each fogged channel would help. I'd
put the holes on the inside surface, that which is away from the
weather. The vents holes would allow trapped moisture a way to escape.
The holes would not need to be any wider than 1/32 or 1/16", I would
think. It's worth trying on one panel before committing to all of them.




When I put up my twinwall polycarbonate panels the manufacturer
recommended that the bottom of the panels be left open and the top be
sealed. This prevents air convection through the panels (decreasing their
insulation properties) while allowing moisture to get out through the
bottom. Sealing the panels can be done either with caulk or with tape. The
aluminium tape is weather resistant and will last a lot longer than
something like duct tape (which has about a 2-month lifetime in sunlight).

In practice, there are times when moisture collects in the channels, but
the next sunny day clears it out.

If the caulk in the original poster's installation is too thick to remove
or if it is still unsightly after attempts at removal, you could cut of an
inch or two of the bottom of the panel and install a baseboard (on the
inside of the panel).

If you opt for the vent hole approach, I would put the holes at the
bottom, just above the caulk (or maybe even through it), so that they
could also act as a drain in the event that a large quantity of condensate
forms in the channels.



I was thinking the top because heated air rises thus evacuating more
quickly. I doubt whether minute holes in the panels will affect their
insulation properites to any noticeable extent. The original poster's
outdoor temps were not so bad. There is still plenty of air trapped in
the panels to insulate.
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Old 20-01-2004, 06:32 PM
Dwight Sipler
 
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Default Condensation in twinwall polycarbonate channels

C wrote:

...I was thinking the top because heated air rises thus evacuating more
quickly. I doubt whether minute holes in the panels will affect their
insulation properites to any noticeable extent. The original poster's
outdoor temps were not so bad. There is still plenty of air trapped in
the panels to insulate.



The faster you get the air out of the channels, the less effective they
will be for insulation. If this is not a problem in your area, it might
help to put them high. Water vapor has a lower density than air, (H2O
has a molecular weight of 18, compared to 28 for Nitrogen) so it might
tend to rise. However, if the holes are very small, you will not get
much leakage, since you need to resupply the air in the channel to keep
the pressure constant. A 1/16" hole will allow the air to exit the
channel, but very very slowly. Two 1/16" holes will increase the flow.
Placing one hole high and one low will increase the flow further, since
it will then be driven by convective forces.

Again, based on empirical observation on one greenhouse, Sealing the top
and leaving the channel fully open at the bottom keeps the condensation
in the channels to a minimum. I have not seen a greenhouse yet that
solved the problem conpletely, but I don't travel around the country
looking at greenhouses, so my observations are limited to New England.

Of course, if your area's temperatures are moderate, you probably don't
need twinwall anyway and could make do with single layer polycarbonate
or fiberglass.


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Old 20-01-2004, 08:52 PM
C
 
Posts: n/a
Default Condensation in twinwall polycarbonate channels

On Tue, 20 Jan 2004 12:31:04 -0500, Dwight Sipler wrote:

The faster you get the air out of the channels, the less effective they
will be for insulation. If this is not a problem in your area, it might
help to put them high. Water vapor has a lower density than air, (H2O has
a molecular weight of 18, compared to 28 for Nitrogen) so it might tend to
rise. However, if the holes are very small, you will not get much leakage,
since you need to resupply the air in the channel to keep the pressure
constant. A 1/16" hole will allow the air to exit the channel, but very
very slowly. Two 1/16" holes will increase the flow. Placing one hole high
and one low will increase the flow further, since it will then be driven
by convective forces.

Again, based on empirical observation on one greenhouse, Sealing the top
and leaving the channel fully open at the bottom keeps the condensation in
the channels to a minimum. I have not seen a greenhouse yet that solved
the problem conpletely, but I don't travel around the country looking at
greenhouses, so my observations are limited to New England.

Of course, if your area's temperatures are moderate, you probably don't
need twinwall anyway and could make do with single layer polycarbonate or
fiberglass.


Note that the original poster is from northern Florida. I think we are
picking nits here. As moisture laden air heats up, it rises.



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Old 20-01-2004, 09:33 PM
Dwight Sipler
 
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Default Condensation in twinwall polycarbonate channels

Xref: kermit rec.gardens:262579

C wrote:

Note that the original poster is from northern Florida. I think we are
picking nits here. As moisture laden air heats up, it rises.




So noted. However, others are reading these posts so I thought I'd make
it more general.
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Old 20-01-2004, 09:48 PM
Dwight Sipler
 
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Default Condensation in twinwall polycarbonate channels

Xref: kermit rec.gardens:262579

C wrote:

Note that the original poster is from northern Florida. I think we are
picking nits here. As moisture laden air heats up, it rises.




So noted. However, others are reading these posts so I thought I'd make
it more general.
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Old 21-01-2004, 01:32 AM
C
 
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Default Condensation in twinwall polycarbonate channels

On Tue, 20 Jan 2004 15:08:12 -0500, Dwight Sipler wrote:

C wrote:

Note that the original poster is from northern Florida. I think we are
picking nits here. As moisture laden air heats up, it rises.




So noted. However, others are reading these posts so I thought I'd make it
more general.


Your posts are fine. I don't mean anything by mine.

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