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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.design
Subject: Re: Ambient temperature control
Date: Tue, 02 Jul 2024 10:33:50 -0400
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On Mon, 1 Jul 2024 06:41:26 -0700, Don Y <blockedofcourse@foo.invalid>
wrote:

>On 7/1/2024 4:24 AM, Martin Brown wrote:
>> On 01/07/2024 02:14, Don Y wrote:
>>> Assuming you can keep a device in its "normal operating (temperature)
>>> range", how advantageous is it (think MTBF) to drive that ambient
>>> down?  And, is there a sweet spot (as there is a cost to lowering the
>>> temperature)?
>> 
>> There can be for some high performance low level OPamps. Deliberately running 
>> them as cold as is allowed helps take the LF noise floor down and by more than 
>> you would predict from Johnson noise. ISTR there was a patent for doing this 
>> back in the 1980's. Prior to that they tended to heat the front end to obtain 
>> temperature stability and low drift.
>> 
>> https://ppubs.uspto.gov/dirsearch-public/print/downloadPdf/4883957
>> 
>> Made possible with the advent of decent solid state TECs.
>
>We don't design products (industrial/consumer) that are "finicky" -- as
>it leads to higher TCOs.  You don't want to need to control the environment
>*or* have "skilled tradesmen" on staff to maintain/assure correct
>performance.
>
>The most common example (that I can think of) where temperature is
>controlled FBO the electronics would be datacenters.  But, from the
>research I've done, there, they simply set a desired temperature for
>the cold aisle and largely ignore the resulting hot aisle temperature
>(except to ensure it doesn't climb out-of-bounds).  I.e., they
>don't close the loop on the hot aisle to control the cold aisle's
>setpoint (cascaded control).
>
>And, they don't get the cold aisle "as cold as possible" so they
>acknowledge there are diminishing returns in doing so -- likely
>cheaper to just pan on a (potentially) shorter upgrade cycle
>than to waste electricity trying to eek out a bit more life.
>
>Interestingly, I can't find anything other than "lore" to
>explain why a *particular* cold aisle temperature is chosen.
>Amusing to see how much folks DON'T know about the science
>they apply!
>
>When I designed my disk sanitizer, I did a fair bit of research
>regarding temperature effects on drives -- because we process a
>shitload (thousands) of *used* drives, annually and you don't want to
>reuse a drive that has an increased chance of failure (based on
>its previous environment, SMART data or observations while exercising
>it).  The old "10 degree C" saw proved to be totally inappropriate,
>*there*.
>
>OTOH, I suspect it *is* worth noting for power supplies (as I
>see most failures being toasted power supplies in otherwise
>"healthy" products).  I suspect power *cycling* is a culprit, there
>as I've seen failed solder joints where it looked like repeated
>thermal expansion had led to the failure.
>
>>> Also, is there any advantage to minimizing the hysteresis between
>>> the ACTUAL operating temperature extremes in such a control strategy
>>> (given that lower hysteresis usually comes at an increased cost)?
>> 
>> Depends how temperature sensitive the thing is that you are protecting. The 
>> example I recall they were aiming for medium term stable 6 sig fig measurements 
>> with the lowest possible noise.
>
>I've needed to control temperature in applications where it was
>key to the *process* being controlled.  E.g., monitoring exhaust
>air temperature to determine the "state" of the bed and a cascade
>loop on the inlet air handler to drive that to a desired state.
>
>But, there, you have lots of money for the equipment and can buy
>good/precise/fast control with things like face-and-bypass as
>the primary controlled variable (so the control loop for the
>heater/chiller can be cruder and more energy efficient).
>
>"In the small", refrigeration is the only practical means of
>lowering ambient temperatures.  And, that adds to operating costs.
>If you can tolerate a wider deadband then the cooling cost
>can be lower (e.g., cool to X degrees and let it *soak*, there,
>before letting it warm to Y degrees instead of foolishly
>trying to maintain the environment at some Z>X and <Y).
>As you likely have LESS ability to precisely size the HVAC
>to fit such a small load, deadband becomes a key consequence
>of that selection process.
>
>[Gotta wonder why data centers in northern latitudes don't
>exploit outside air more agressively during the winter
>months!]
>
What are the HVAC costs in data processing and server facilities?

That's just to maintain ambient <40C.

RL