Hi John.  You might want to look at "precision air conditioning" systems (to use the vendors phraseology) designed for small computer rooms for some ideas ?

I suspect getting close to your temperature spec may be easier than your humidity spec ?  There may also be issues getting commercial units permitted / installed / inspected in a residential setting ?

As a side note I was impressed with the split unit my residential HVAC contractor installed during a recent Reno in my TV room.  The newer units seem to have finer temperature units than the older ones.  I don't believe my unit features any humidity control.

Hope this is of some interest.

Mark Spencer

Personally I'd be looking at a commercial ductless heat pump unit Mitsubishi MrSlim comes to mind in your case you would want a 'cartridge' type unit designed for ceiling mount the ones for data center use have humidity control as well.  Figure these units will hold +/- 2-3 deg F over long term

If you really want to go over the top get a used RF shield room.  Lots of used ones coming on market as stuff is going over 26Ghz.  Shipping will be the ugly bit as the doors are heavy

Content by Scott
Typos by Siri

On 10/26/2016 11:59 AM, John Ackermann N8UR wrote:

I built a "ham shack" room in my unheated barn.  8 by 12 feet,
interior lined with sheets of foil-backed foam insulation board,
then plywood over the insulation.  Walls, ceiling, and floor.  A
600 watt portable heater is more than enough to keep it
comfortable in the Michigan winter (-26F -32C in 2015)  This is
with no equipment turned on.  You problem will likely be getting
rid of heat.  A small, through-wall air conditioner might be a
cheap way of doing it.  Place the chiller outside the house.
The trick is to reduce the hunt differential.  Might be easy to
build your own thermostat circuit to control the compressor.
Another option might be a small window air conditioner dumping
into the basement.  That way you don't have to plumb the
refrigerant lines.

I don't know how humid it gets in Snellville, but the air
conditioner should take out the humidity.

At the end opposite the door, I have a bathroom-type exhaust fan
in the ceiling if it gets too unpleasant inside.  I have a
tunnel over the fan with acoustic foam inside to reduce fan noise.

When I installed the sheets of foil-backed insulation, I put
expanded aluminum mesh over the gaps.  It's a fairly-effective
Faraday cage too.  Sealing the door was a bit tricky, but when I
close it, signals decrease.  Useful when you have three
broadcast transmitters in the neighborhood.

Mike - AA8K

Rick, professional environmental chambers and their contents have a great
deal of thermal inertia. In addition, they have overbuilt refrigeration
systems, electric heaters, and de/humidifiers. You teach your lab rats to
enter the chambers as infrequently as possible, to close the doors as
quickly as possible, to assure that materials brought into the chamber are
as near as is practical to chamber temperature, avoid bringing open liquids
in, etc. A good chamber will easily hold +/- 1C and +/- 2% RH in free air,
even with powered equipment inside cycling on and off and occasional
entries. An air lock wouldn't help as much as you might think because the
human body is a much larger heat reservoir than the air that might be
exchanged while the door is open. Keep in mind, too, that most
chambers--certainly the ones that would interest John--are intended to
maintain stability fairly near external ambient conditions. High and low
temperature chambers are a whole different species of animal.

On Wednesday, October 26, 2016, Richard (Rick) Karlquist <
richard@karlquist.com> wrote:

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

On Wed, 26 Oct 2016 13:58:10 -0400
John Ackermann N8UR jra@febo.com wrote:

Probably the easiest is to get some glass/mineral wool insulation and
put it over all the walls, including ceiling and floor. I do not recommend
any foam or styropor based insulation as almost all of them are inflamable.
This should get you into the area of 10-100W/K thermal resistance for your
closet (assuming something like 4cm thick insulation gets about 40W/K).
Yous should put some vapor barrier on the inside of the insulation, as
otherwise you will get mold between the insulation and wall.

Assuming you have gear that generates 1-2kW of heat, that means you are
in the region of 100K to 10K above outside temperature. Now all you have
to do is getting the heat out. This can be easily done with an PWM fan
controller which you get for a couple of bucks on ebay/aliexpress.

In case you don't get enough heat inside, just add some heating element
that you run with constant power (eg a hair dryer run from a constant
current source).

I wouldn't go for A/C systems, as these need quite a bit of hysteresis
to work properly (2-3°C) and the switch on/switch off spikes will cause
all kind of headaches.

For added stability, fill the empty space in the closet with half-liter
PET water bottles and place a small fan blowing at them.

As for humidity control.. Guessing from where I think you live, you will have
a wide range of ambient humidity, which means you need to be able to both
control it up and down. The easiest solution there is to have an humidifier
constantly running (please use one that evaporates instead of sprays,
the latter is a good way to spread bacteria and mold everywhere. ultrasonic
devices are spraying) and use a controllable dehumidifier (they are available
for 100€) take the excess humidity out again.

As I mentioned, bacteria and mold are a problem with those. Either you
need to make sure that the water used in the humidifier is always fresh
and the water extracted from the dehumidifier gets discarded somewhere,
or you need to sterilize the water if you let it sit or, even worse,
circulate. Probably the easiest way to sterilize is UV light, but it
degrades all kind of materials, especially plastic.

All of this should be doable with 200-500€ and whithin a long weekend.

HTH

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

On 10/26/16 8:59 AM, John Ackermann N8UR wrote:

How tightly regulated?

I've been looking into this to make a chamber of that general size that
is around 10-15C and 50% RH  (for incubating sausage duplicating an
Italian cave<grin>)...

Most kitchen stuff (refrigerators, etc.) tend to have fairly big
fluctuations of temperature as the compressor cycles, although if you
put a lot of mass in the controlled space that certainly slows it down.

There are also a variety of things like cold storage (for florists, for
example) - they tend to be assembled out of simple building blocks:
insulated wall panels, a cooler unit, a door.

Lab incubators or commercial baking is another source (imagine raising
bread consistently)

However, all these kinds of applications can easily tolerate a 5C swing
in temperature since the thing being controlled is fairly massive and
its internal temperature will vary less.

The challenge with a "small" space is that when the cooling unit comes
on, you're blasting in cold air, and it's not "well mixed".

Hi John,

such a project is quite practical.
I spent a working lifetime in textile physics research.
Air conditioned rooms were in great demand and access was limited.
So I did what I could with what I could get.
In spite of what conventional wisdom (or lack of wisdom ) says you
can get good performance from a reverse cycle window air conditioner unit.
For humidity control, you should be able to make do with unilateral control downwards,
set the room to a humidity that is lower than the lowest ambient humidity. You may even compromise
by setting humidity at say 40% and tolerate the rare occasion that it drops below. It may be worth it
so avoid the mess of bilateral control.
Now, so far you have the recipe for a system that produces great swings in temperature and humidity,
not what you want.
The important step is the controller and a small fan or two that gently swirls the air around the room,
at a velocity about 0.5m/s, which is only just on the threshold of perception. The swirling of the air
means that within a time frame of 30 seconds the air is mixed into one thermal mass.
The control has several requirements.
The temperature must have a very rapid response time one or two seconds. A very small glass
encapsulated thermistor in the general air flow are used. Thin film humidity sensors can be fast
enough for humidity control.
The controller is directed at motor control.
The motors are switched with substantial zero voltage switching solid state relays, - no QRM.
The rules are for both motors, the motor can be switched
on within a second of the control temperature being reached, but only if a “decompression time” has elapsed.
No noisy switching is possible because any on signal starts the decompression timer.
This would be about 2 minutes for a window unit. This is necessary to avoid harm to the compressor through
over frequent cycling, and it does not have to start under load.
This may seem catastrophic for control, but the
result is benign.
The fan in the window unit and dehumidifier are left running, probably on “low”.
Changeover from heating to cooling on the reverse cycle unit occurs automatically when a 6 minute timer
detects no motor operation. This may seem a bit slow, but it happens at a time when heating or
cooling are hardly needed.
How it works: Your 2 * 3 * 3 metre room contains 18 Kg of air, effectively in a single mass.
When the window unit cuts in the temperature rises of falls at a constant rate of about 2 degrees per minute. When the
set point is crossed this ramp will stop within a few seconds. The temperature then slowly falls or rises
until after 2 minutes IF it is on the wrong side of the set point the motor starts up again.
Typically the motor runs 15 seconds and stays off for 200.
My rooms had an average temperature that did not shift more than a tenth of a C. They only used the minimum power
needed, when required, peak variation was about 0.5C. Remember you have to keep the air volume mixed.
The thermometer was mounted in the general air stream about half way around the loop from the AC unit around the room.
One of my rooms had 30% windows and double brick walls but not other insulation.
The window units did not have shortened lives because of the “frequent cycling” because they were started under the right conditions.
I did publish this 30 or 40 years ago in an Australian electronics magazine.

cheers,
Neville Michie

On 10/26/16 9:34 AM, David J Taylor wrote:

You can buy the smallest "window" airconditioner and "plumb" it to your
chamber (I used dryer vent hose, cardboard, and lots of duct tape)

Attached is a plot temperature and RH of an insulated box about 1.2
meter wide, 2 meters tall and 60 cm deep, filled with 100 or so 750 ml
bottles of liquid.

The temperature is fairly stable, but the RH varies wildly - basically,
when the AC unit kicks on, it sucks all the water out of the air in the
box, and then, when it turns off, the (damp) walls of the box rapidly
rehumidify the air.

On 10/26/16 10:58 AM, John Ackermann N8UR wrote:

Heating is easy (proportional control of a resistive heater)

1C is going to be very tough unless you have some way to variably mix
cold dry air from your cooler with room air.  Air conditioners don't
like being short cycled.
The challenge is that "cold" is usually available in a bang/bang way, so
you need something to low pass filter it.

If you had a large source of cold water, you could use a proportional
control valve and some sort of radiator with a fan.

Or, have a massive thermal sink between your "controlled space" and
"where the ac unit is".. If you imagine a meter thick slab of, say, Gold
(good conductivity, very high density), it would act as a very effective
low pass filter between the cycling of your AC unit and your controlled
space.

I started my control system by putting a 5 gallon bucket of water in a
refrigerator, and then using a variable speed pump into a radiator in
the chamber.  This worked quite well, but you run into all the problems
with a liquid loop system: stuff grows in the water, water corrodes
stuff, it leaks, etc.

If your instruments/clocks were insensitive to variations in line voltage
you could vary your rooms line voltage with a variable auto transformer
(end up being a heater with tons of surface area). Or pack enough OCXOs in
there so they end up thermally servoing the room.

On Wednesday, 26 October 2016, jimlux jimlux@earthlink.net wrote: