[time-nuts] Temp/Humidity control systems?

jimlux jimlux at earthlink.net
Wed Oct 26 16:19:58 EDT 2016

On 10/26/16 10:58 AM, John Ackermann N8UR wrote:
> On 10/26/2016 1:00 PM, Richard (Rick) Karlquist wrote:
>> On 10/26/2016 8:59 AM, John Ackermann N8UR wrote:
>>> I may have the opportunity to build a small "clock room" and am
>>> considering whether I could make it an environmentally controlled space.
>>>  I'd like to learn about the options for doing this.
>>> The space would probably be 6x8 feet or so, in a basement with one
>>> outside wall.
>> I'm lost with the basic concept here.  Help me understand this.
> This room would be a large closet in my basement where two racks of
> various OCXO, Rb, Cs live. There wouldn't be a lot of in-and-out
> traffic. I'm not looking for 0.01 degree regulation -- <1 degree C and a
> few percent humidity throughout the year seems a reasonable goal.

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 

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.

> What I envisioned was a very small heat pump or other heating/air-con
> unit coupled with some sort of proportional control. I just don't know
> where to start looking for that, or what other issues to be thinking about.
> (I know the way time-nuts think, and I recall the great ideas posted
> here in the past about using an old refrigerator, or burying standards
> in a deep hole -- but this would be wrapped into a bigger construction
> project that I'm going to be managing from a distance, so I need to keep
> it fairly straight-forward.)
> Thanks, all!
> John
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