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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Ambient temperature control
Date: Wed, 3 Jul 2024 06:43:40 -0700
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On 7/3/2024 6:05 AM, legg wrote:
> On Tue, 2 Jul 2024 08:26:24 -0700, Don Y <blockedofcourse@foo.invalid>
> wrote:
> 
>> On 7/2/2024 7:30 AM, legg wrote:
>>> What's the mtbf of a fan? a compressor? a pump?
>>> . . . . or a clamp and a block of aluminum?
>>
>> As long as it isn't significantly worse than the impact of NOT
>> having it, you don't care -- because some (relatively unskilled)
>> local contractor can fix those things.  You don't have to
>> hire a skilled member of staff to be on-hand to deal with the
>> "more sophisticated" technology's potential failures.
>>
>> I'd much rather have an HVAC guy come in and repair the AHU in
>> the datacenter -- even if it was an annual event -- than have
>> to risk servers crashing or having to be replaced (and the
>> data recovered).  The former is a "cheap", ubiquitous skillset;
>> the latter considerably costlier and critical.
> 
> You know what a brass tack is?

Exactly that!  You (as an owner of a piece of kit that you RELY on and
have invested considerable time/monies) don't care if it's theoretical
reliability is lowered; what you care about is how *effectively* reliable
that device will be.  How costly (time/money/inconvenience) is it to
KEEP it in service?

This is more than just reliability *or* availability.

If you had to replace a server because a cooling system outage allowed it
to experience 50C, you'd likely be significantly inconvenienced.

If, however, it can continue to operate at 50C -- but with some damage
that will eventually manifest in a reduced lifetime/reliability -- then
you can weather the short term "problem" and plan on taking action
to avoid the anticipated problem -- additional maintenance.

If it is the nature of your business to replace items regularly,
then it's likely that your replacement interval has already factor
into it these types of "disturbances".

If, OTOH, you don't expect to be replacing (expensive) kit, then
anything that compromises that assumption wants to be avoided.  How
often do you replace major appliances?  HVAC systems?  How inexpensive
(time/money/inconvenience) would the replacement need to be in order
for you to tolerate a shorter lifespan?

Or, how much MORE would you be willing to pay to avoid that
replacement?

[There are many devices that I would gladly "pay double" for the
ASSURANCE (not some legalistic "warranty" but the genuine
knowledge) that a device *won't* break in a given period of
time.  I.e., the equivalent of having a cold spare on hand -- but
without the space required to store it or the effort required
to put it into operation]

If your products have lifespans on the order of a decade or less,
(or, if they are inexpensive to buy/replace) then you likely never
consider these things.

[Our KWHr meter will be replaced this week.  Along with every
neighbor's.  This is the only way the expense of such an activity
can be reasonably managed -- sending out a linesman to replace ONE
meter would be extremely costly!  But, having a crew step-and-repeat
down the block is much more manageable.  What added feature would
motivate them to replace them a *second* time while they still
have serviceable life?]