In message C1109A57B22F4DAB86B0BB172981F264@Alta, "David J Taylor" writes:

You can do much better with an old fridge and a small waterpump to
circulate water in the cooling loop.

--
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.

And since this is time-nuts: Measuring humidity accurately is tricky.
According to people who have tested them, commercial electronic humidity
sensors, when tested in a lab, have never come anywhere close to the
accuracy claimed in the data sheet. The best you can hope for is
consistent readings, not absolute accuracy.

The exception is the "cold mirror" type of sensor, which measures the
dewpoint by cooling a mirror and bouncing a light off it to sense the
temperature where dew condenses on it. Those are expensive, and they
require maintenance to keep the mirror clean.

BTW some of us are more sensitive to humidity than others. I can't tell
you the RH of a room, but I can tell you when it's too dry for comfort.
I want it as close to 50% as I can get it without growing mold on the
walls. Some "experts" claim that 30% is good enough for anyone, but
they're wrong.

On 10/27/16 6:30 AM, Poul-Henning Kamp wrote:

I tried that first...

Advantage is that the mass of the water (serving as a thermal transfer
medium) is much greater than that of air.  You wind up with kilos of
water at a relatively constant temperature.

Disadvantages:

1. It leaks
2. It grows stuff (even with additives to prevent it)
3. you've increased the number of thermal transfers: refrigerator coils
   to air to water to air to contents of box.  Both of the air:water
   transfers are not particularly efficient in a "cobbled together in the
   garage" sort of scenario.

I think your suggestion of just adding (solid) mass to the system is
better - the advice to people with wine cellars is to fill empty slots
with bottles filled with wine (actually, the advice is to buy more wine,
so your cellar doesn't have any empty slots.. but if that's not
possible, fill the empties with water, recork and stow them)

The challenge with a refrigerator as chiller is that getting decent
coupling from the cooler coils to the water is tough: you're pretty much
restricted to air as the transfer medium.  In a "real chiller" they put
the evaporator coils in the water so there's good thermal contact.
Refrigerators/freezers aren't made for this - I tried 3 different
approaches of varying complexity:

1. Put a 5 gallon plastic bucket of water in the refrigerator - the
   bucket of water does get cold, but--- it also evaporates inside the
   refrigerator, and the water condenses on the coils, freezes, and then
   eventually is lost to the air when the unit is defrosted.

2. Put an array of copper tubing in close contact with the cold plate in
   the freezer, weighted down by bricks to make close contact - well, let's
   just say I found all sorts of interesting galvanic reactions can occur,
   even at low temperatures - the other problem is that if the circulation
   rate slows, the water in the loop can freeze, and once it starts to
   freeze, it has positive feedback - the flow rate slows even more, and
   pretty quickly, you have tubes full of frozen coolant.  - it is a good
   thing I was doing this in the garage.

3. trying to make a cold plate by using two sheets of aluminum, some
   aluminum spacers, plenty of silicone, and some hose barbs is a lot of
   work, and doesn't seem to work much better.

I think one problem is that the refrigerator/freezer control system is
designed to work off two sensors: one is a air temperature sensor and
the other is a sensor on the actual evaporator unit (basically, if it
gets too cold, it shuts off the compressor to prevent low pressure
damage).  The "design point" for all of this is also probably not
optimum for moving heat out of your equipment closet.

And that's just the challenge on "improvised water chiller"

Then you have the other "water to air heat exchanger".. serpentine
tubing would seem to be the best way, but it turns out that this is
non-trivial to design so that you get even flow rates in multiple loops,
if you have multiple paths. And, arranging the tubing effectively is
hard. There's also all the fabrication/leakage/hose connection issues.
I tried making serpentines out of copper and aluminum tubing that would
be part of the shelf on which the bottles are piled.  That cools the
bottom bottles nicely, but the thermal transfer among the bottles is slow.

The best approach to "get cold to all bottles" (or, more correctly, take
heat from warm bottles" is to have a fan to circulate air among the
stacked and racked bottles.  Well, once you are rigging up a fan to push
air through cold tubing (a re-purposed car heating core - more
fabrication of adapters from one tubing size to another - I had a big
box of hose clamps, between size adapters, and pieces of hose of all
sizes).  Remember that this is all wet at one point or another, either
from leaks or condensation, so stuff corrodes, rusts, etc.

Yep - a $99 window airconditioner bought on sale (about this time of
year is good, in the Northern Hemisphere) worked just fine.  Plumbing
air is a lot easier than plumbing water or glycol coolant.  You won't
get down to <10C because window air conditioners aren't refrigerators -
the choice of refrigerant and internal components and set point range
isn't compatible with that (and putting a small heater on the AC's temp
sensor, which is in the return air flow to the evaporator did not allow
me to "bias" the set point)

However, for a time-cave - I think it would work great  - cheap
airconditioner, large thermal mass buffer, well stirred air.  Concrete
blocks with holes and have the air blow through that would make a fine
low pass filter - keeping the humidity "reasonable" is probably
straightforward - most of time-nuts stuff isn't humidity sensitive - as
long as it's "non-condensing".  You'd just want to watch and make sure
that you don't have cold air blowing on a metal surface intermittently -
I worked in a screen room (solid walls) that had the AC blowing on the
walls.. when the AC cycled off, the walls instantly started to sweat as
our respiratory moisture condensed on what was now the coldest thing in
the room.

Hi

Ok, take this with a bit of caution ….

Your “time cave” does not have a specific spec on temperature or on humidity.
You get to pick a number for either one. Anything in the “non condensing” (let’s
call it < 80%) range for humidity is likely ok. Temperature up to 40C is probably
ok for any gear that I can think of. As long as you never go in and out of the
cave, comfort in the cave is a non-issue.

If I load up the cave with gear that runs up the electric bill, the cave will self
heat to some degree. How much it self heats is unclear. The number will be highly
dependent on your situation. Based on things like racks full of gear in out of the
way places, it’s a good bet that it will be 10 to 20 C above the temperature in the
rest of the basement.

Assuming the humidity in the basement is under control (if not, fix that), all I need
to do for humidity in the closet is to exchange air with the basement. Since the
volume isn’t very large and (hopefully) the water flow is modest …. a small fan
should take care of that.

If the closet is bound by the outside (buried) wall and the basement, both should be well
controlled temperatures.  If I plug everything in and let it run, the heat rise in August should
be the heat rise in February. Let’s say that’s a 20C rise. The basement is at 20 C and
the closet is at 40C. Maybe its more, If it’s less,  you need to buy more stuff:)

All I need to do is knock the 40C down to 35C with a small amount of “cooling” to
keep things under control. My “humidity” fan might do that. If not, a very simple
water based heat exchanger with a controlled fan will do the job. You need some sort
of fan(s) in the closet anyway. Without them you will never get the gradients under
control. A pump, 10’ of tubing and two heat exchangers are not a lot of money. There
also isn’t a lot to break if you do it right.

Why do it this way? No compressors to mess up the local power line and break
every X years (the fridge in the kitchen died Sunday ….. they do break). No super
cold surfaces to mess up humidity. No crazy heat flows to create clod drafts and
fast transients in the closet temperature.

The obvious downside is that you do go in the closet. When you do, everything
goes a bit off. My guess is that you are actually better off letting it recover slowly
than you are trying to move it back in under 10 minutes …. who knows. One solution
to that would be to sub-divide the closet. The gear to do this is cheap.

Bob

On 10/27/16 7:37 AM, Bob Camp wrote:

This is an interesting point.. basically you'd turn your DOCXOs into a
TOCXO where the third oven is your time cave.. you make the set point
above the surroundings, so all you need to do to hold temperature is
to add heat - which is much, much more controllable in a gradual way
than removing heat.

The "two radiators and a pump" approach is appealing - you could set it
up so that the pump is variable speed. That said, there's a fair amount
of "custom fabrication" involved: you have to find some suitable
radiators, make the appropriate fittings and connections to your pump
and hoses, and arrange for fans to blow through them.  You might be able
to find something off the shelf - Grainger and McMaster are full of
interesting things - and things to cool hot water using air blowing
through the coils are probably a fairly off the shelf item.

And, would using a liquid thermal transfer path be any different than a
variable speed air vent between inside and outside?

What I'm looking for right now is a suitable controller that will run an
exhaust fan that fits in a 12x12" (approx) opening when the outside
temperature is "closer" to my target set point than the inside temp:

In Southern California, the outside air temp moves quite a bit during
the day and rapidly at the day/night transition, so when the garage is
hot, and outside is cooler, I'd like to exchange air.  Likewise, if the
garage is cold (cooled down overnight) and outside is warmer, I'd like
to exchange air to warm it up.

The standard "differential thermostat" seems to only do one of the
directions (turn on/off load when T1 -T2 > setpoint and T1 > setpoint),
and I suppose I could "wire or" two of these,  but it seems there should
be a 'More clever" off the shelf solution.

(and frankly, if someone made something that opened/closed my windows,
I'd love that too, for the same reason.. I can cold bias the house in
the morning, leave the AC off all day with the windows closed, and then
automatically open the windows in the afternoon/evening when the outside
temperature drops below the inside temperature setpoint)  In combination
with Time-of-Use electricity rates (something you should consider in
temperature regulation of your time cave - "store cold at night"), one
can cheaply pre-cool the house in "super off peak" time.

(Yes, I could program an Arduino to do this, but then I have to cobble
up a AC relay, a DC power supply, etc., etc....)

jimlux jimlux@earthlink.net wrote on Thu, 27 Oct 2016
at 07:51:37 -0700 in e46613e9-19c7-09dd-e006-83dce73419eb@earthlink.net:

http://www.mcmaster.com/#motorized-louvers/=14s2pox

--jhawk@mit.edu
John Hawkinson

In message 837330DB-2015-4AE5-8C9C-F444F569FC1B@n1k.org, Bob Camp writes:

Danger Will Robinson!

Under no circumstances should your dewpoint be above the temperature on
the other side of the door.

If you have 40C at 80% humidity your dew-point temperature is 35C, which means
that whenever you open the door your clock cave will fog up.

If you run your clock cave at 40C, humidity needs to be well below
30% to hold the dewpoint below room tempreatyre.  That is both hard,
expensive and prone to electrostatic discharges.

"fix that" is usually non-trivial, and from very to horribly expensive.

The cardinal rule is that you should only exchange air (basement/outside,
or cave/basement) when the air outside has lower ABSOLUTE humidity.

And I keep stressing that it is ABSOLUTE humidity, because people simply
don't pay it enough attention.

25C/40%RH air holds 9.2 g/m³ water ... as does 15C/72%RH air.

This is why a lot of people in costal climates who ventilate their
basement during summer "to dry out the basement" get the exact
opposite result:  The air outside is a lot wetter than on the inside.

One would think that somebody had designed fans to measure this,
but it is expensive: Cheap humidity sensors measure relative humidity
and you need to correct for both temperature and pressure to get
absolute humidity.

And therefore, at the risk of repeating myself again:

If you build your clock cave in the basement, it should be air-tight
and you should manage the humidity in it separately from the rest
of the basement.

PS: Here is a good webcalculator:

http://go.vaisala.com/humiditycalculator/5.0/

--
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 ba05e7bd-e12d-0106-bda8-3c24f7e3f993@earthlink.net, jimlux writes:

Antifreeze prevented that for me.

Right, it is not a viable method if you want to burn 100+W in your fridge.
I've made it work up to 50W with little trouble.

Absolutely.

But the problem in the basement setting is that the heat ends up
in your basement, which means the air can hold more moisture, which
you really do not want.

--
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 10/27/2016 11:06 AM, Poul-Henning Kamp wrote:

I learned this myself last summer.  We have a cottage on northern Lake
Michigan that is about 100 feet from the water.  There is a walk-out
basement that gets somewhat damp, though a dehumidifier usually keeps it
under control.  Last summer I opened the cottage later in the season
than usual, and the basement was very clammy.  So I decided to open the
slider doors and turn on a box fan to air things out...

When I came back downstairs a couple of hours later, standing water
had condensed on the cold floor tiles!  I had basically been
dehumidifying Lake Michigan.  Lesson learned (and I spent the rest of
the vacation trying to dry things out again).

Thanks for all the other comments in this thread.  I'm absorbing and
will try to summarize back to the group.

John

Mine were 8' x 10' x 7'. "Local pickup only"  ;)
The -20F chamber was 4' x 4' x 7'.
The -80F chamber was 2' x 2' x 5'.

How much space will you need, John? Chances are you could pick up a small
one on ebay and avoid all the jackleg schemes.

On Thursday, October 27, 2016, Poul-Henning Kamp phk@phk.freebsd.dk wrote:

--
If you gaze long into an abyss, your coffee will get cold.