I'm building a portable cold frame; it's a 2x2 frame about 1.5 feet high, 4 feet long, and 3 feet deep. Sides and top will be covered with double thick polycarbonate sheeting left over from building the greenhouse a few years back. My wife's idea is to put it out in the garden and start some seeds under it to get a jump on the growing season. Garden places sell things like this but want a fortune for them.

The problem is that on a very sunny day, it can get hot enough inside there to cook and kill the growing vegetables. I can put in a small, manually operated vent, but would like to have something automatic, that opens when it gets too hot and closes when it gets cold again. I've googled around but can't find what I need. I'm looking for something about 2 inches square that I can mount though a wall of the construction.

The people on this group have such a wide range of experience that it's possible that someone can give me a link to these devices, if they exist. Thanks for any help you can give.

Paul

On 2/11/2013 2:41 PM, Pavel314 wrote:
I'm building a portable cold frame; it's a 2x2 frame about 1.5 feet
high, 4 feet long, and 3 feet deep. Sides and top will be covered
with double thick polycarbonate sheeting left over from building the
greenhouse a few years back. My wife's idea is to put it out in the
garden and start some seeds under it to get a jump on the growing
season. Garden places sell things like this but want a fortune for
them.

The problem is that on a very sunny day, it can get hot enough inside
there to cook and kill the growing vegetables. I can put in a small,
manually operated vent, but would like to have something automatic,
that opens when it gets too hot and closes when it gets cold again.
I've googled around but can't find what I need. I'm looking for
something about 2 inches square that I can mount though a wall of the
construction.

The people on this group have such a wide range of experience that
it's possible that someone can give me a link to these devices, if
they exist. Thanks for any help you can give.

Paul


Perhaps the bimetallic choke coil from an old carburetor is sensitive
enough for your purposes. Here's a couple of links that may help with
your project. ^_^

http://www.crestmfg.com/

http://incubatorproject.wikispot.org/Bimetallic_Coils

TDD

On 2/11/2013 2:41 PM, Pavel314 wrote:
I'm building a portable cold frame; it's a 2x2 frame about 1.5 feet
high, 4 feet long, and 3 feet deep. Sides and top will be covered with
double thick polycarbonate sheeting left over from building the
greenhouse a few years back. My wife's idea is to put it out in the
garden and start some seeds under it to get a jump on the growing
season. Garden places sell things like this but want a fortune for them.

The problem is that on a very sunny day, it can get hot enough
inside
there to cook and kill the growing vegetables. I can put in a small,
manually operated vent, but would like to have something automatic, that
opens when it gets too hot and closes when it gets cold again. I've
googled around but can't find what I need. I'm looking for something
about 2 inches square that I can mount though a wall of the construction.

The people on this group have such a wide range of experience that
it's possible that someone can give me a link to these devices, if
they exist. Thanks for any help you can give.

Paul

Think you'll need a lot more area than that to do any good...look at one
of these...

http://www.johnnyseeds.com/p-8136-univent-automatic-opener.aspx

--

Try checking out automatic foundation vents....You may have to do some
adapting, but they pretty much do the function that you need.

On Feb 11, 3:25*pm, dpb wrote:
On 2/11/2013 2:41 PM, Pavel314 wrote: I'm building a portable cold frame; it's a 2x2 frame about 1.5 feet

high, 4 feet long, and 3 feet deep. Sides and top will be covered with
double thick polycarbonate sheeting left over from building the
greenhouse a few years back. My wife's idea is to put it out in the
garden and start some seeds under it to get a jump on the growing
season. Garden places sell things like this but want a fortune for them.

The problem is that on a very sunny day, it can get hot enough
inside

there to cook and kill the growing vegetables. I can put in a small,
manually operated vent, but would like to have something automatic, that
opens when it gets too hot and closes when it gets cold again. I've
googled around but can't find what I need. I'm looking for something
about 2 inches square that I can mount though a wall of the construction.



The people on this group have such a wide range of experience that
it's possible that someone can give me a link to these devices, if
they exist. Thanks for any help you can give.

Paul

Think you'll need a lot more area than that to do any good...look at one
of these...

http://www.johnnyseeds.com/p-8136-univent-automatic-opener.aspx

--

That's rather pricy aat $49.

On Feb 11, 4:25*pm, dpb wrote:
On 2/11/2013 2:41 PM, Pavel314 wrote: I'm building a portable cold frame; it's a 2x2 frame about 1.5 feet

high, 4 feet long, and 3 feet deep. Sides and top will be covered with
double thick polycarbonate sheeting left over from building the
greenhouse a few years back. My wife's idea is to put it out in the
garden and start some seeds under it to get a jump on the growing
season. Garden places sell things like this but want a fortune for them.

The problem is that on a very sunny day, it can get hot enough
inside

there to cook and kill the growing vegetables. I can put in a small,
manually operated vent, but would like to have something automatic, that
opens when it gets too hot and closes when it gets cold again. I've
googled around but can't find what I need. I'm looking for something
about 2 inches square that I can mount though a wall of the construction.



The people on this group have such a wide range of experience that
it's possible that someone can give me a link to these devices, if
they exist. Thanks for any help you can give.

Paul

Think you'll need a lot more area than that to do any good...look at one
of these...

That's what I was thinking. A passive 2" square vent
doesn't sound very big. And with a flap of some kind,
etc, the effective area is further reduced.






http://www.johnnyseeds.com/p-8136-univent-automatic-opener.aspx

--

On Monday, February 11, 2013 7:37:48 PM UTC-5, Richard Heath wrote:
Try checking out automatic foundation vents....You may have to do some adapting, but they pretty much do the function that you need.

That's the sort of thing I'm after but they're a bit large for this application. I was looking for something smaller. We're going to try a manual vent, one on each end to allow cross-ventilation. Since my wife goes out every morning and evening to adjust the greenhouse heater anyway, she can just add this task to the list.

Paul

Pavel314 wrote:
On Monday, February 11, 2013 7:37:48 PM UTC-5, Richard Heath wrote:
Try checking out automatic foundation vents....You may have to do
some adapting, but they pretty much do the function that you need.

That's the sort of thing I'm after but they're a bit large for this
application. I was looking for something smaller. We're going to try
a manual vent, one on each end to allow cross-ventilation. Since my
wife goes out every morning and evening to adjust the greenhouse
heater anyway, she can just add this task to the list.


A small thermostat controlled fan should do the job nicely.
Temp gets high, fan turns on. An old bathroon exhaust fan would have flaps in it
to stop air flow when not on.

On 02/11/2013 06:02 PM, wrote:
On Feb 11, 4:25 pm, dpb wrote:

Think you'll need a lot more area than that to do any good...look at one
of these...

That's what I was thinking. A passive 2" square vent
doesn't sound very big. And with a flap of some kind,
etc, the effective area is further reduced.

My thoughts on a 2"x2" opening would involve increasing the size to
4"x4" (or even 6"x6") and installing a little computer fan into a frame
to fit. It would be trivial to built a thermostat to turn the fan on
with a thermister and a small signal transistor and a couple of
resistors, or you could go the lazy route and use a prebuilt electronic
thermostat.

You would, of course, need to supply a source of low-voltage to the cold
frame if you decided to go this route, but it would have the benefit of
being automated.

Jon

On 2/12/2013 11:01 AM, Jon Danniken wrote:
On 02/11/2013 06:02 PM, wrote:
On Feb 11, 4:25 pm, dpb wrote:

Think you'll need a lot more area than that to do any good...look at one
of these...

That's what I was thinking. A passive 2" square vent
doesn't sound very big. And with a flap of some kind,
etc, the effective area is further reduced.

My thoughts on a 2"x2" opening would involve increasing the size to
4"x4" (or even 6"x6") and installing a little computer fan into a frame
to fit. It would be trivial to built a thermostat to turn the fan on
with a thermister and a small signal transistor and a couple of
resistors, or you could go the lazy route and use a prebuilt electronic
thermostat.

You would, of course, need to supply a source of low-voltage to the cold
frame if you decided to go this route, but it would have the benefit of
being automated.

Jon


Why not one of those solar powered vents you can buy fits the top part
of a car window? The things are inexpensive enough to play around with
then take apart, modify and use the parts to build whatever you like. ^_^

http://www.amazon.com/Solar-Powered-...061073-5857430

http://tinyurl.com/bc6k2go

TDD

On 02/12/2013 09:18 AM, The Daring Dufas wrote:
On 2/12/2013 11:01 AM, Jon Danniken wrote:

My thoughts on a 2"x2" opening would involve increasing the size to
4"x4" (or even 6"x6") and installing a little computer fan into a frame
to fit. It would be trivial to built a thermostat to turn the fan on
with a thermister and a small signal transistor and a couple of
resistors, or you could go the lazy route and use a prebuilt electronic
thermostat.

You would, of course, need to supply a source of low-voltage to the cold
frame if you decided to go this route, but it would have the benefit of
being automated.

Jon


Why not one of those solar powered vents you can buy fits the top part
of a car window? The things are inexpensive enough to play around with
then take apart, modify and use the parts to build whatever you like. ^_^

http://www.amazon.com/Solar-Powered-...061073-5857430


http://tinyurl.com/bc6k2go

Hey, even better, as you wouldn't need to supply power or do any
designing, and since it is the sun that is causing the overheating,
you'll always have sunlight for the solar cell.

There do appear to be quite a few poorly-made units out there, though;
this model is more expensive, but seems to have better reviews:

http://www.amazon.com/Round-Solar-Bo...sim_sbs_auto_2

Jon

On 2/12/2013 12:18 PM, Jon Danniken wrote:
On 02/12/2013 09:18 AM, The Daring Dufas wrote:
On 2/12/2013 11:01 AM, Jon Danniken wrote:

My thoughts on a 2"x2" opening would involve increasing the size to
4"x4" (or even 6"x6") and installing a little computer fan into a frame
to fit. It would be trivial to built a thermostat to turn the fan on
with a thermister and a small signal transistor and a couple of
resistors, or you could go the lazy route and use a prebuilt electronic
thermostat.

You would, of course, need to supply a source of low-voltage to the cold
frame if you decided to go this route, but it would have the benefit of
being automated.

Jon


Why not one of those solar powered vents you can buy fits the top part
of a car window? The things are inexpensive enough to play around with
then take apart, modify and use the parts to build whatever you like. ^_^

http://www.amazon.com/Solar-Powered-...061073-5857430



http://tinyurl.com/bc6k2go

Hey, even better, as you wouldn't need to supply power or do any
designing, and since it is the sun that is causing the overheating,
you'll always have sunlight for the solar cell.

There do appear to be quite a few poorly-made units out there, though;
this model is more expensive, but seems to have better reviews:

http://www.amazon.com/Round-Solar-Bo...sim_sbs_auto_2


Jon


I remember finding one of those solar window vents at a thrift store and
it was a dollar. I'll cruse the thrift stores for items I can take
apart to experiment with and it costs very little to come up with parts
for projects. ^_^

TDD

On 2/11/2013 12:41 PM, Pavel314 wrote:
I'm building a portable cold frame; it's a 2x2 frame about 1.5 feet high, 4 feet long, and 3 feet deep. Sides and top will be covered with double thick polycarbonate sheeting left over from building the greenhouse a few years back. My wife's idea is to put it out in the garden and start some seeds under it to get a jump on the growing season. Garden places sell things like this but want a fortune for them.

The problem is that on a very sunny day, it can get hot enough inside there to cook and kill the growing vegetables. I can put in a small, manually operated vent, but would like to have something automatic, that opens when it gets too hot and closes when it gets cold again. I've googled around but can't find what I need. I'm looking for something about 2 inches square that I can mount though a wall of the construction.

The people on this group have such a wide range of experience that it's possible that someone can give me a link to these devices, if they exist. Thanks for any help you can give.

Paul

Think about this...
If you poke a chimney pipe thru the top, can you get enough convection
to do the deed?
Now, imagine an S-curve in the chimney so the air travels down before
going up...where down may be a very small distance.

By judicious use of white and black paint, can you create a system
where there's insufficient convection to get past the down section
unless there's sun on the pipe?? Maybe even paint the sides
of the pipe differently
so the angle of the sun is part of the equation?

I know zip about photosynthesis, but can you build a system that lets
visible light thru, but blocks the IR?

On 02/12/2013 10:27 AM, The Daring Dufas wrote:
On 2/12/2013 12:18 PM, Jon Danniken wrote:

Hey, even better, as you wouldn't need to supply power or do any
designing, and since it is the sun that is causing the overheating,
you'll always have sunlight for the solar cell.

There do appear to be quite a few poorly-made units out there, though;
this model is more expensive, but seems to have better reviews:

http://www.amazon.com/Round-Solar-Bo...sim_sbs_auto_2



Jon


I remember finding one of those solar window vents at a thrift store and
it was a dollar. I'll cruse the thrift stores for items I can take
apart to experiment with and it costs very little to come up with parts
for projects. ^_^

Heck yeah! If it's only a dollar, you can probably replace whatever the
most "breakable" thing is on the unit, and reuse the rest of the kit as
a project.

Jon

On 2/13/2013 11:32 AM, Jon Danniken wrote:
On 02/12/2013 10:27 AM, The Daring Dufas wrote:
On 2/12/2013 12:18 PM, Jon Danniken wrote:

Hey, even better, as you wouldn't need to supply power or do any
designing, and since it is the sun that is causing the overheating,
you'll always have sunlight for the solar cell.

There do appear to be quite a few poorly-made units out there, though;
this model is more expensive, but seems to have better reviews:

http://www.amazon.com/Round-Solar-Bo...sim_sbs_auto_2




Jon


I remember finding one of those solar window vents at a thrift store and
it was a dollar. I'll cruse the thrift stores for items I can take
apart to experiment with and it costs very little to come up with parts
for projects. ^_^

Heck yeah! If it's only a dollar, you can probably replace whatever the
most "breakable" thing is on the unit, and reuse the rest of the kit as
a project.

Jon


One time I was looking through a bin in the toy section of items that
hadn't been put out yet and I found a prosthetic breast. When the gal
working there saw it she freaked and took it. I was disappointed that
they wouldn't let me buy it because I wanted to hollow it out and put
it over a mouse to make a "Computer Hooter". A soft GUI pointing device
that is cushioned and easy on the hand. ^_^

TDD