Hi Alan,
Your analysis applies to the particular unit you analyzed.
In the limit of perfect insulation, the conclusion will not be true.
The water cannot get cold when the heaters are turned off. Thus zero
energy required to restore the temperature.
Clearly, the insulation of the "well insulated" water heater examined
was not perfect.
The relevant question becomes: How close to perfect insulation is the
OCXO under discussion. It probably isn't even close. The case
temperature gets hot rather quickly. So your conclusion may apply.
73 de Brian/K3KO
P.S. This topic brings to mind an analysis of piping insulation on a
cylindrical pipe done way back in college. Up to a point, adding more
insulation helps. Beyond that point, adding insulation hurts. The
surface area increase overwhelms the added insulation benefit.
On 10/15/2014 00:29, G4GNX wrote:
Some years back, I was asked to do a study on the current consumption of
a particular style of beverage vending machine. The device had a water
tank which was well insulated and the water was heated by a 3KW heater,
to just below boiling point. The client wanted to know whether there
would be a saving in consumed energy, if the heater was switched off
overnight. Careful study re4vealed that it actually cost more to heat
the water from cold than leave the heater connected permanently,
controlled by its thermostat.
There have been numerous papers published to this effect regarding well
insulated domestic heating systems and although there is sometimes a
benefit in reducing the overall temperature when the building is
unoccupied, heating from cold as opposed to leaving the heating running
under thermostatic control, costs more, even over a short period.
The oven used by a stable crystal oscillator is a thermostatically
controlled heating device. Nuff sed! :-)
73,
Alan. G4GNX
-----Original Message----- From: Edward R Cole
Sent: Tuesday, October 14, 2014 10:47 PM
To: Elecraft@mailman.qth.net
Subject: Re: [Elecraft] K3EXREF Query
David,
10w is 7.3 kwH/month. I would doubt that is a large expense, even in
GB. Locally, its about 8 cents/kwH but in the bush it might be as
high as a couple dollars since diesel fuel for the generators costs
are huge (local diesel is $4.10). I know it would require conversion
to liters and all that to come up with equivalent costs, but most
households run hundreds of kwh/mo. Leave your TV plugged in but
turned off and it still consumes about 50w. I have plug strip to
remove ac from all my home TV systems when not in use. I leave power
to the satellite receiver as it keeps the LNB powered and stable
(Otherwise it takes 5-10 minutes to acquire signal and download data
at startup).
Simple solution is to leave the reference oscillator running
continually. The K3 TCXO-3 will still drift on power up but this is
compensated by EXREF every 4-seconds so frequency stability is held
to better than 0.1 ppm. I measured +/- 2 Hz at 28-MHz on my K3. But
if you watch the REF*CAL frequency you will note it incrementing from
49.380.000 to something like 49.380.080 in several minutes and then
settle down near that value (indicating start-up drift has stopped).
By not running your reference full time you will have to wait 15 to
30 minutes for it to fully warm up. I also have a rubidium but run
it only for precise frequency calibration of the OCXO couple times
per year. My mw counter internal TCXO is always in agreement with
the Rb so I do not bother for routine frequency checks. The rb is
only +/- 5 E-11 so not as good as GPS but good enough for my use.
73, Ed - KL7UW
-------------
From: David G4DMP <da...@g4dmp.fsnet.co.uk>
To: Mike Harris <mike.har...@horizon.co.fk>
Cc: elecraft@mailman.qth.net
Subject: Re: [Elecraft] K3EXREF Query
Message-ID: <ulj9aoep0tpuf...@g4dmp.fsnet.co.uk>
Content-Type: text/plain;charset=us-ascii
About 10W for the MV89A double oven CXO, when run from a linear 12V
power supply. NOT trivial at today's prices for electricity in Great
Britain.
73 de David G4DMP
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