Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Dave wrote
But given the TCXO"s sensitivity to temperature changes, I don't
know whether it might be preferable to mount the LTE lite in its own box
without any power supplies in it - perhaps with some thermally insulting
material around the LTE lite so the crystal doesn't experience any fast
temperature changes.
First, mount the LTE in a cast aluminum box (not thin sheet metal,
something with some heft). Use thermally insulating standoffs
(teflon or nylon, with no metal "through" fasteners) to get the board
in the middle of the volume of the box. Use a box a bit larger than
you'd first think, so there is at least 1" of air on all 6 sides of
the LTE board. Do NOT mount any part of the LTE board (connectors,
etc.) directly to the box walls -- use "pigtails" for all
connections. Do NOT use any insulation between the LTE and the box
walls other than the 1"+ of air.
The mounting described above will add substantial thermal capacitance
to the LTE board (good) without adding significant thermal resistance
(bad). For further discussions of this issue, search the list
archives for "thermal capacitance" and "thermal mass."
Now, mount the cast box (plus any thermal mass you add to it -- see
below) so that IT is thermally isolated from the overall enclosure
(or, if it sits out in the open, thermally isolated from anything
solid). The air space in the enclosure isolates the oscillator from
the cast box and the box is sufficiently massive that its temperature
cannot change nearly as fast as ambient. The thermal mass of the
cast box can be adjusted by adding thermal mass to it as desired.
The goal is for the box temperature to change only by changes in
ambient AIR temperature, and the LTE board to change only by changes
in the AIR temperature inside the cast box. This integrates any
changes to the LTE board temperature with a very long time constant,
which allows the GPS discipline to track and cancel the temperature changes.
(If you mount an ovenized oscillator this same way, it integrates any
changes to the OCXO temperature so that the oven control loop can
track and cancel any changes to the crystal temperature.)
You can, of course, improve things even further by making sure the
ambient air temperature surrounding the cast box changes slowly, or
not at all. But the technique described above can be counted on to
reduce thermal effects in most OCXOs or GPSDOs to better (often much
better) than the 1e-13 level unless the ambient temperature changes
MUCH more and MUCH faster than any change we wouild consider normal
for a living space. This is true whether the cast box is mounted out
in the open, or inside an overall enclosure with other electronics.
Best regards,
Charles
In message 20141123153744.bioKftA5@smtp16.mail.yandex.net, Charles Steinmetz
writes:
First, mount the LTE in a cast aluminum box (not thin sheet metal,
something with some heft). [...]
Charles' design has some good points, but I don't agree with it.
What you are trying to do is to low-pass filter any thermal signals
before they reach the LTE or OCXO.
Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.
(For LTE and OCXO it is probably less of a problem that changing
power-disipation will have a outsized effect on the central
temperature.)
Here is a much simpler and likely cheaper way to do it:
Put the LTE or OCXO in a small box of your choice. Even a cardboard
box is fine. A little thermal insulation in the box is OK, but not
too much, the heat must be able to get out.
Find a medium sized cardboard box, something like a cubic feet or so.
Place it where you want your house-standard, with some kind of
thermal insulation under it, two layers of old rug will do fine.
Lay a floor of bricks inside the box.
Build a "wall" of bricks along the outside of the box.
Place the smaller box in the hole in the middle, cut the
corner of a brick to run the cables without too much leakage.
Use a floortile as roof, possibly with a layer of bricks on top.
Close the outher cardboard box with tape to minimize convection.
Congratulations, you now have a cheap and incredibly efficient
thermal low-pas filter, which will allow thermal energy to move in
both directions -- eventually.
The outher cardboard box is not optional, unless you replace it
with some other "mostly air-tight" barrier.
The little bit of insulation the outher cardboard adds are not a
bad idea either, for instance it reduces the effect of sunlight
hits the box at certain times of the day/year.
But you can substitute any geological building material you have
at hand for the bricks, because the trick is that geological building
materials have just the right thermal properties we are looking
for: Decent but not too good thermal conductivity with healthy
dose of thermal mass.
Cinderblocks comes with convenient interior holes premade.
Aerated concrete blocks are also a candidate material but
don't make it too thick since it insulates quite well, and
paint the surface to bind the dust.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
NIST did something similar for their WWWV site, where they used bottled
water in its staple packaging to build a thermal mass. They measured how
their atomic clocks and rig behaved before and after, and could see the
difference. Very neat way of using off the (store)shelf components for a
test.
Another aspect is to think about what kind of heating/coolling you have.
If it can act more as a proportional system rather than bang-bang
regulations, it won't produce as drastic swings for you.
Cheers,
Magnus
On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:
In message 20141123153744.bioKftA5@smtp16.mail.yandex.net, Charles Steinmetz
writes:
First, mount the LTE in a cast aluminum box (not thin sheet metal,
something with some heft). [...]
Charles' design has some good points, but I don't agree with it.
What you are trying to do is to low-pass filter any thermal signals
before they reach the LTE or OCXO.
Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.
(For LTE and OCXO it is probably less of a problem that changing
power-disipation will have a outsized effect on the central
temperature.)
Here is a much simpler and likely cheaper way to do it:
Put the LTE or OCXO in a small box of your choice. Even a cardboard
box is fine. A little thermal insulation in the box is OK, but not
too much, the heat must be able to get out.
Find a medium sized cardboard box, something like a cubic feet or so.
Place it where you want your house-standard, with some kind of
thermal insulation under it, two layers of old rug will do fine.
Lay a floor of bricks inside the box.
Build a "wall" of bricks along the outside of the box.
Place the smaller box in the hole in the middle, cut the
corner of a brick to run the cables without too much leakage.
Use a floortile as roof, possibly with a layer of bricks on top.
Close the outher cardboard box with tape to minimize convection.
Congratulations, you now have a cheap and incredibly efficient
thermal low-pas filter, which will allow thermal energy to move in
both directions -- eventually.
The outher cardboard box is not optional, unless you replace it
with some other "mostly air-tight" barrier.
The little bit of insulation the outher cardboard adds are not a
bad idea either, for instance it reduces the effect of sunlight
hits the box at certain times of the day/year.
But you can substitute any geological building material you have
at hand for the bricks, because the trick is that geological building
materials have just the right thermal properties we are looking
for: Decent but not too good thermal conductivity with healthy
dose of thermal mass.
Cinderblocks comes with convenient interior holes premade.
Aerated concrete blocks are also a candidate material but
don't make it too thick since it insulates quite well, and
paint the surface to bind the dust.
All:
I am enjoying this thread. These are all very interesting ideas.
Hoping to power up my first unit later today....
I'm putting my LTE-Lite in the recommended HAMMOND box. That takes care
of the box with air. I was then considering proportional heating of the
surface of the box, like I did long ago with some GUNNPLEXERS -- seemed
to work pretty well. Then this whole assembly goes inside two or four
inches of the foam insulation.
Now, the question becomes, to what temperature to heat it? With a
crystal, I'd plot /f/ vs. /T/, and look for minimum slope. How to do
that with LTE-Lite -- plot /efc/ vs /T/ and look for either center of
range or minimum slope??
Thoughts?
Jim
wb4gcs@amsat.org
On 11/23/2014 9:03 AM, Magnus Danielson wrote:
NIST did something similar for their WWWV site, where they used
bottled water in its staple packaging to build a thermal mass. They
measured how their atomic clocks and rig behaved before and after, and
could see the difference. Very neat way of using off the (store)shelf
components for a test.
Another aspect is to think about what kind of heating/coolling you
have. If it can act more as a proportional system rather than
bang-bang regulations, it won't produce as drastic swings for you.
Cheers,
Magnus
On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:
In message 20141123153744.bioKftA5@smtp16.mail.yandex.net, Charles
Steinmetz
writes:
First, mount the LTE in a cast aluminum box (not thin sheet metal,
something with some heft). [...]
Charles' design has some good points, but I don't agree with it.
What you are trying to do is to low-pass filter any thermal signals
before they reach the LTE or OCXO.
Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.
(For LTE and OCXO it is probably less of a problem that changing
power-disipation will have a outsized effect on the central
temperature.)
Here is a much simpler and likely cheaper way to do it:
Put the LTE or OCXO in a small box of your choice. Even a cardboard
box is fine. A little thermal insulation in the box is OK, but not
too much, the heat must be able to get out.
Find a medium sized cardboard box, something like a cubic feet or so.
Place it where you want your house-standard, with some kind of
thermal insulation under it, two layers of old rug will do fine.
Lay a floor of bricks inside the box.
Build a "wall" of bricks along the outside of the box.
Place the smaller box in the hole in the middle, cut the
corner of a brick to run the cables without too much leakage.
Use a floortile as roof, possibly with a layer of bricks on top.
Close the outher cardboard box with tape to minimize convection.
Congratulations, you now have a cheap and incredibly efficient
thermal low-pas filter, which will allow thermal energy to move in
both directions -- eventually.
The outher cardboard box is not optional, unless you replace it
with some other "mostly air-tight" barrier.
The little bit of insulation the outher cardboard adds are not a
bad idea either, for instance it reduces the effect of sunlight
hits the box at certain times of the day/year.
But you can substitute any geological building material you have
at hand for the bricks, because the trick is that geological building
materials have just the right thermal properties we are looking
for: Decent but not too good thermal conductivity with healthy
dose of thermal mass.
Cinderblocks comes with convenient interior holes premade.
Aerated concrete blocks are also a candidate material but
don't make it too thick since it insulates quite well, and
paint the surface to bind the dust.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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This email has been checked for viruses by Avast antivirus software.
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Hi
If you have a basement in your house / building
—and —
it’s dry and reasonably draft free (no garage doors opening up from time to time)
— and —
At least one side / corner is well buried in the ground
— and —
You can get at that corner / side.
Move your thermal baffle gizmo up against that wall, move it into that corner. There is a lot more mass in the foundation of a building than anything you would want to lug around for a project. You still need to handle the issues on at least half the surface, that should be less trouble than doing the whole thing.
There is another subtle advantage to this approach. The standard is out of the way. It’s not in the middle of the lab. It does not get bumped. It does not get sparked (unless you have full ESD protection in the lab …). It’s less likely to have random power cycle events due to cords being accidentally pulled. Even second order stuff related to ground loops from connecting and disconnecting cables may be reduced. “Just leave it alone” is much easier to do when the gizmo is surrounded by a pile of bricks.
With a GPSDO, you don’t care (much) about the environmental swings from week to week or month to month. The GPS will take care of that. What you care about are the hour to hour or minute to minute movements. Those are the ones that the filter on an OCXO based unit will struggle with. Hotter in the summer / colder in the winter is not as big a deal as “cold when I come in / hot after I turn everything on”.
One practical hint if you do try this:
Put a cheap plastic bag around the gizmo and tape it up. It discourages the bug colonies. I have empirical evidence that this is a good idea ...
Bob
On Nov 23, 2014, at 9:03 AM, Magnus Danielson magnus@rubidium.dyndns.org wrote:
NIST did something similar for their WWWV site, where they used bottled water in its staple packaging to build a thermal mass. They measured how their atomic clocks and rig behaved before and after, and could see the difference. Very neat way of using off the (store)shelf components for a test.
Another aspect is to think about what kind of heating/coolling you have. If it can act more as a proportional system rather than bang-bang regulations, it won't produce as drastic swings for you.
Cheers,
Magnus
On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:
In message 20141123153744.bioKftA5@smtp16.mail.yandex.net, Charles Steinmetz
writes:
First, mount the LTE in a cast aluminum box (not thin sheet metal,
something with some heft). [...]
Charles' design has some good points, but I don't agree with it.
What you are trying to do is to low-pass filter any thermal signals
before they reach the LTE or OCXO.
Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.
(For LTE and OCXO it is probably less of a problem that changing
power-disipation will have a outsized effect on the central
temperature.)
Here is a much simpler and likely cheaper way to do it:
Put the LTE or OCXO in a small box of your choice. Even a cardboard
box is fine. A little thermal insulation in the box is OK, but not
too much, the heat must be able to get out.
Find a medium sized cardboard box, something like a cubic feet or so.
Place it where you want your house-standard, with some kind of
thermal insulation under it, two layers of old rug will do fine.
Lay a floor of bricks inside the box.
Build a "wall" of bricks along the outside of the box.
Place the smaller box in the hole in the middle, cut the
corner of a brick to run the cables without too much leakage.
Use a floortile as roof, possibly with a layer of bricks on top.
Close the outher cardboard box with tape to minimize convection.
Congratulations, you now have a cheap and incredibly efficient
thermal low-pas filter, which will allow thermal energy to move in
both directions -- eventually.
The outher cardboard box is not optional, unless you replace it
with some other "mostly air-tight" barrier.
The little bit of insulation the outher cardboard adds are not a
bad idea either, for instance it reduces the effect of sunlight
hits the box at certain times of the day/year.
But you can substitute any geological building material you have
at hand for the bricks, because the trick is that geological building
materials have just the right thermal properties we are looking
for: Decent but not too good thermal conductivity with healthy
dose of thermal mass.
Cinderblocks comes with convenient interior holes premade.
Aerated concrete blocks are also a candidate material but
don't make it too thick since it insulates quite well, and
paint the surface to bind the dust.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Poul-Henning wrote:
Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.
I have been using the technique for 30+ years, including with many
OCXOs (which, obviously, generate significant heat) and have never
observed any problems of that nature at the 1e-13 level. I did
consider the possibility when I first started doing it, and tested
two potential fixes: (i) putting a fan inside the box to homogenize
the internal temperature, and (ii) filling the air space inside the
box with irregular solid shapes to break up the convection
pattern. I tested both methods extensively with instrumented
sources, in many variations (fan speeds and orientations, mass and
porosity of passive internal shapes), and did not find any difference
at the 1e-13 level. I have occasionally used an internal fan just on
theoretical grounds, but I have never measured any practical difference.
Thinking about it, this does not seem too surprising -- one would
expect any convection to settle into a stable pattern and thus not to
cause any temperature changes over time (once it is warm and
settled). Whether this explains my results or some other effect
predominates (for example, convection may move enough air in the
limited space to achieve substantial isothermy), I have confirmed to
my satisfaction that it is simply not a factor in practice at the
levels we are concerned with.
If you test the "cast aluminum box" method and find that your results
do not accord with mine, please publish them and we can discuss what
might account for the observed differences and how the method could
be improved. Until then, you are just posting speculative musings on
the subject based on no data, which does not seem helpful.
And good luck fitting a cubic foot box with a surround of bricks into
a 3U rack cabinet, or any other relocatable (much less,
semi-portable) enclosure.
Best regards,
Charles
In message C9E99C83-AAA9-4D50-9729-B86A79AF2DBA@n1k.org, Bob Camp writes:
At least one side / corner is well buried in the ground
But be aware that such a corner may be dry only when empty.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
In message 20141123174632.kVK4sk45@smtp18.mail.yandex.net, Charles Steinmetz
writes:
And good luck fitting a cubic foot box with a surround of bricks into
a 3U rack cabinet, or any other relocatable (much less,semi-portable)
enclosure.
I didn't say it doesn't work, I said that I don't agree with it ;-)
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Hi
What you have in the LTE is a TCXO rather than a bare crystal or an OCXO. It’s got a compensation circuit that corrects the FT curve of the crystal. The net result is likely a 5th or higher order curve when you plot frequency over temperature. Every TCXO off that production line will have a different curve. You would need a full characterization of that curve for your specific TCXO to pick an optimum point.
With a GPSDO, taking care of the long term drift is not what you are after. The GPS does that. If the GPSDO is TCXO based, the the loop filter is going to be pretty fast. That is not a knock on the LTE part, it’s just physics. An OCXO part is a different beast. Each has their strong points. Don’t try to run the OCXO off batteries for a week … With a fast filter, temperature variations at the “per hour” level are not likely an issue.
Once you get to the point that drafts are worked out, and that temperature change is slowed down, you are done. No need for anything more complex.
Bob
On Nov 23, 2014, at 9:30 AM, Jim Sanford wb4gcs@wb4gcs.org wrote:
All:
I am enjoying this thread. These are all very interesting ideas.
Hoping to power up my first unit later today....
I'm putting my LTE-Lite in the recommended HAMMOND box. That takes care of the box with air. I was then considering proportional heating of the surface of the box, like I did long ago with some GUNNPLEXERS -- seemed to work pretty well. Then this whole assembly goes inside two or four inches of the foam insulation.
Now, the question becomes, to what temperature to heat it? With a crystal, I'd plot /f/ vs. /T/, and look for minimum slope. How to do that with LTE-Lite -- plot /efc/ vs /T/ and look for either center of range or minimum slope??
Thoughts?
Jim
wb4gcs@amsat.org
On 11/23/2014 9:03 AM, Magnus Danielson wrote:
NIST did something similar for their WWWV site, where they used bottled water in its staple packaging to build a thermal mass. They measured how their atomic clocks and rig behaved before and after, and could see the difference. Very neat way of using off the (store)shelf components for a test.
Another aspect is to think about what kind of heating/coolling you have. If it can act more as a proportional system rather than bang-bang regulations, it won't produce as drastic swings for you.
Cheers,
Magnus
On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote:
In message 20141123153744.bioKftA5@smtp16.mail.yandex.net, Charles Steinmetz
writes:
First, mount the LTE in a cast aluminum box (not thin sheet metal,
something with some heft). [...]
Charles' design has some good points, but I don't agree with it.
What you are trying to do is to low-pass filter any thermal signals
before they reach the LTE or OCXO.
Charles' design works great from the outside, but doesn't do anything
with respect to the thermal energy expended by the encapsulated
device themselves, which will cause convection in the inner box.
(For LTE and OCXO it is probably less of a problem that changing
power-disipation will have a outsized effect on the central
temperature.)
Here is a much simpler and likely cheaper way to do it:
Put the LTE or OCXO in a small box of your choice. Even a cardboard
box is fine. A little thermal insulation in the box is OK, but not
too much, the heat must be able to get out.
Find a medium sized cardboard box, something like a cubic feet or so.
Place it where you want your house-standard, with some kind of
thermal insulation under it, two layers of old rug will do fine.
Lay a floor of bricks inside the box.
Build a "wall" of bricks along the outside of the box.
Place the smaller box in the hole in the middle, cut the
corner of a brick to run the cables without too much leakage.
Use a floortile as roof, possibly with a layer of bricks on top.
Close the outher cardboard box with tape to minimize convection.
Congratulations, you now have a cheap and incredibly efficient
thermal low-pas filter, which will allow thermal energy to move in
both directions -- eventually.
The outher cardboard box is not optional, unless you replace it
with some other "mostly air-tight" barrier.
The little bit of insulation the outher cardboard adds are not a
bad idea either, for instance it reduces the effect of sunlight
hits the box at certain times of the day/year.
But you can substitute any geological building material you have
at hand for the bricks, because the trick is that geological building
materials have just the right thermal properties we are looking
for: Decent but not too good thermal conductivity with healthy
dose of thermal mass.
Cinderblocks comes with convenient interior holes premade.
Aerated concrete blocks are also a candidate material but
don't make it too thick since it insulates quite well, and
paint the surface to bind the dust.
time-nuts mailing list -- time-nuts@febo.com
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I am scratching my head here.
From what I see the LTE is a good unit but does swim around a bit. The
conclusion I might get from this thread is that lots of insulation will fix
that.
I suspect not.
The LTE in use down at 2.8 e-10 according to its output.
I have put it in a small cardboard box with free standing air and some
Styrofoam.
Because thats what turned up in the basement.
I have added heat to it. It sits on top the Lucent box thats on. :-)
It still swims around. It moves forward and backwards stays steady. Random.
Certainly not terrible. I just think as neat as bricks may be it would not
help allot.
The top of the thread is excellant about checking the TCXO output Z.
Regards
Paul
WB8TSL
On Sun, Nov 23, 2014 at 9:55 AM, Poul-Henning Kamp phk@phk.freebsd.dk
wrote:
In message 20141123174632.kVK4sk45@smtp18.mail.yandex.net, Charles
Steinmetz
writes:
And good luck fitting a cubic foot box with a surround of bricks into
a 3U rack cabinet, or any other relocatable (much less,semi-portable)
enclosure.
I didn't say it doesn't work, I said that I don't agree with it ;-)
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
Hi
Yup, that’s another good reason for the plastic bag :)
If moisture might be an issue in your area, cover up the corner for a while in the rainy season to check for that problem before the project begins. Depending on the bag is not a real good idea.
Bob
On Nov 23, 2014, at 9:50 AM, Poul-Henning Kamp phk@phk.freebsd.dk wrote:
In message C9E99C83-AAA9-4D50-9729-B86A79AF2DBA@n1k.org, Bob Camp writes:
At least one side / corner is well buried in the ground
But be aware that such a corner may be dry only when empty.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
The short-term performance is 10x worse if you don't shield the TCXO from air, even if the ambient air is "still". I suggested Said sell the product with some sort of engineered shield in place. Instead each of us will solve the problem in our own way; which is ok for a dev kit.
For plots and photos showing performance with, and without, and with insulation see:
http://leapsecond.com/pages/LTE-Lite/
The difference is dramatic, especially if you are used to working with OCXO where this sort of effect does not occur.
The insulation may be found in convenient rolls at many local stores. I used TP, which for this application is an acronym for Thermal Paper.
/tvb
On 23 Nov 2014 14:45, "Bob Camp" kb8tq@n1k.org wrote:
Hi
If you have a basement in your house / building
I do not.
—and —
it’s dry and reasonably draft free (no garage doors opening up from time
to time)
My lab is a room which is part of the garage! Just about everything is
against me with this method, BUT you do give me an idea...
You got me thinking about the possibility of actually mounting the TCXO
burried in the ground! The temperature of that is not going to change
very rapidly.
FWIW, I know a guy that did work as an air conditioning engineer,, but now
works for a company selling geothermal heating. He installs ground source
heat pumps for the geothermal energy. He says that they actually work
quite poorly in many cases. In a couple of years the temperature of the
ground falls as the heat is extracted faster than it replenishes. So the
efficiency falls off. I don't think that the TCXO would heat the ground
faster than it dissipates away.
Of course there would be some practical issues burying the TCXO, but those
would not be insurmountable ones. I have no idea what depth might be
needed.
My wife thinks thinks I am a nutcase - that would only confirm it to her!
Dave, G8WRB
In message CANX10hB0KdrnaAYzGvM1gkDUJ7gkLth0AcdxCZG894hxbUScFQ@mail.gmail.com
, "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
He installs ground source
heat pumps for the geothermal energy. He says that they actually work
quite poorly in many cases.
There is a BIG difference between geothermal and ground heating.
Geothermal means you drill at least 50m (Iceland) or more likely
half a kilometer down, in order to harvest water at near boiling
point from the Earths geological heat-sources (mostly uranium decay).
Extracting more energy than available just means the temperature
drops temporarily. It will increase again once you reduce the
pump rate.
Horizontal ground heat means that you are harvesting sunshine
accumulated in the top one meter of the soil. Much of the energy
is harvested from freezing the water around the pipe thus pulling
out the relatively high melting energy of water.
If you extract more energy than you deposit sunshine, you end
up freezing a larger and larger volume of water/soil around
the pipe and your compressor will eat a lot of electricity.
In practice it looks like this:
http://ing.dk/artikel/varmepumpe-mareridt-jordslange-var-dybfrossen-i-maj-113176
(The two pictures show the same pipe, with and without frozen ground.)
Finally there is vertial ground heat where you drill down only about
40-80 meter, tapping heat mostly from ground water resources. Most
places the ground water doesn't move fast enough to deliver the amounts
of energy extracted, and over time the source returns unusably low
temperature and must be abandonned. Typically after 25-30 years.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
On 23 Nov 2014 17:49, "Poul-Henning Kamp" phk@phk.freebsd.dk wrote:
In message <
, "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
He installs ground source
heat pumps for the geothermal energy. He says that they actually work
quite poorly in many cases.
There is a BIG difference between geothermal and ground heating.
Geothermal means you drill at least 50m (Iceland) or more likely
half a kilometer down, in order to harvest water at near boiling
point from the Earths geological heat-sources (mostly uranium decay).
Sorry. What he installs is pipes in the ground in residential or
industrial sites. Basically he says they work initially, but performance
drops dramatically over a couple of years.
If you extract more energy than you deposit sunshine, you end
up freezing a larger and larger volume of water/soil around
the pipe and your compressor will eat a lot of electricity.
That is what he was saying.
Dave.
In message CANX10hCaoB-5GYsbR7sdXwL7DYH7QUBMhXWmi9xDRcF3mDM7_Q@mail.gmail.com
, "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
Geothermal means you drill at least 50m (Iceland) or more likely
half a kilometer down, in order to harvest water at near boiling
point from the Earths geological heat-sources (mostly uranium decay).
Sorry. What he installs is pipes in the ground in residential or
industrial sites. Basically he says they work initially, but performance
drops dramatically over a couple of years.
That is not "geothermal" then, and yes, a LOT of those systems are
badly underdimensioned.
I've been researching this topic intensively because my new house
will be heated that way.
My conclusion, based on reading a lot of reports, is that there
is no credible way to predict the performance. The wetter your
soil the better, but that's about it.
I'm going to overprovision by a factor two to be on the safe side,
afterall it only costs EUR7 for each extra meter of pipe.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Schomandl -- the company which made the first indirect synthesizers in
the sixties in the past century -- used buried crystal oscillators as
standard frequency source, 12meter deep in the companies yard in the
Belfort Strasse in Munich, Bavaria Germany, ...Rohde& Schwarz also had
buried oscillators. I have one in California, where, the temperature at
10m deep is 15,784C° around the year, and measuring the frequency off
set between wwvb's harmonic and the buried oscillator originally tuned
to cca 3MHz, to the natural serial resonance of the crystal, by counting
the beat -- to a harmonic of wwvb, cca 4217Hz , 364 358 801 pulses per
day, as of Nov 2014, counter resets by wwvb daily, daily changes max ± 8
pulses, are to see, but a yearly decrement of 15 to 8 pulses per year,
less per year in the last time is observable the "system down there"is
running since 1991.
73
KJ6UHN
Alex
On 11/23/2014 8:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
On 23 Nov 2014 14:45, "Bob Camp" kb8tq@n1k.org wrote:
Hi
If you have a basement in your house / building
I do not.
—and —
it’s dry and reasonably draft free (no garage doors opening up from time
to time)
My lab is a room which is part of the garage! Just about everything is
against me with this method, BUT you do give me an idea...
You got me thinking about the possibility of actually mounting the TCXO
burried in the ground! The temperature of that is not going to change
very rapidly.
FWIW, I know a guy that did work as an air conditioning engineer,, but now
works for a company selling geothermal heating. He installs ground source
heat pumps for the geothermal energy. He says that they actually work
quite poorly in many cases. In a couple of years the temperature of the
ground falls as the heat is extracted faster than it replenishes. So the
efficiency falls off. I don't think that the TCXO would heat the ground
faster than it dissipates away.
Of course there would be some practical issues burying the TCXO, but those
would not be insurmountable ones. I have no idea what depth might be
needed.
My wife thinks thinks I am a nutcase - that would only confirm it to her!
Dave, G8WRB
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by us in central California, we get 1kW/h square meter average around
the year, the south even more, el Cajon will have today +29C° in the
afternoon as of 23 of November 2014
73
Alex
On 11/23/2014 9:49 AM, Poul-Henning Kamp wrote:
In message CANX10hB0KdrnaAYzGvM1gkDUJ7gkLth0AcdxCZG894hxbUScFQ@mail.gmail.com
, "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
He installs ground source
heat pumps for the geothermal energy. He says that they actually work
quite poorly in many cases.
There is a BIG difference between geothermal and ground heating.
Geothermal means you drill at least 50m (Iceland) or more likely
half a kilometer down, in order to harvest water at near boiling
point from the Earths geological heat-sources (mostly uranium decay).
Extracting more energy than available just means the temperature
drops temporarily. It will increase again once you reduce the
pump rate.
Horizontal ground heat means that you are harvesting sunshine
accumulated in the top one meter of the soil. Much of the energy
is harvested from freezing the water around the pipe thus pulling
out the relatively high melting energy of water.
If you extract more energy than you deposit sunshine, you end
up freezing a larger and larger volume of water/soil around
the pipe and your compressor will eat a lot of electricity.
In practice it looks like this:
http://ing.dk/artikel/varmepumpe-mareridt-jordslange-var-dybfrossen-i-maj-113176
(The two pictures show the same pipe, with and without frozen ground.)
Finally there is vertial ground heat where you drill down only about
40-80 meter, tapping heat mostly from ground water resources. Most
places the ground water doesn't move fast enough to deliver the amounts
of energy extracted, and over time the source returns unusably low
temperature and must be abandonned. Typically after 25-30 years.
I've read about die-hard microwave hams burying their master oscillators
for a long time . . . .
On 11/23/2014 11:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
On 23 Nov 2014 14:45, "Bob Camp" kb8tq@n1k.org wrote:
Hi
If you have a basement in your house / building
I do not.
—and —
it’s dry and reasonably draft free (no garage doors opening up from time
to time)
My lab is a room which is part of the garage! Just about everything is
against me with this method, BUT you do give me an idea...
You got me thinking about the possibility of actually mounting the TCXO
burried in the ground! The temperature of that is not going to change
very rapidly.
FWIW, I know a guy that did work as an air conditioning engineer,, but now
works for a company selling geothermal heating. He installs ground source
heat pumps for the geothermal energy. He says that they actually work
quite poorly in many cases. In a couple of years the temperature of the
ground falls as the heat is extracted faster than it replenishes. So the
efficiency falls off. I don't think that the TCXO would heat the ground
faster than it dissipates away.
Of course there would be some practical issues burying the TCXO, but those
would not be insurmountable ones. I have no idea what depth might be
needed.
My wife thinks thinks I am a nutcase - that would only confirm it to her!
Dave, G8WRB
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Interesting comment about the geothermal.
I have to take continuing education courses in order to maintain my PE;
one was in geothermal.
Intuitively, great for cooling, even (especially!) in Florida.
Intuitively, not so hot for heating, especially in PA, and especially
with the price of natural gas plummeting.
The guy who services our conventional AC and gas furnace was not very
enthused, when I told him I was considering geothermal for the next
cooling unit. He got a little more enthused when he found out I already
have more pipe in the ground than I'd need (ft per ton of cooling
capacity) and a several thousand gallon in-ground tank. Still not
excited about it. I really appreciate your new data point.
Shortly, I'll post response to all replies to my original post on this
topic. For now, the bury it option might actually have use here.
Jim
On 11/23/2014 11:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
On 23 Nov 2014 14:45, "Bob Camp" kb8tq@n1k.org wrote:
Hi
If you have a basement in your house / building
I do not.
—and —
it’s dry and reasonably draft free (no garage doors opening up from time
to time)
My lab is a room which is part of the garage! Just about everything is
against me with this method, BUT you do give me an idea...
You got me thinking about the possibility of actually mounting the TCXO
burried in the ground! The temperature of that is not going to change
very rapidly.
FWIW, I know a guy that did work as an air conditioning engineer,, but now
works for a company selling geothermal heating. He installs ground source
heat pumps for the geothermal energy. He says that they actually work
quite poorly in many cases. In a couple of years the temperature of the
ground falls as the heat is extracted faster than it replenishes. So the
efficiency falls off. I don't think that the TCXO would heat the ground
faster than it dissipates away.
Of course there would be some practical issues burying the TCXO, but those
would not be insurmountable ones. I have no idea what depth might be
needed.
My wife thinks thinks I am a nutcase - that would only confirm it to her!
Dave, G8WRB
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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