[time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)

Attila Kinali attila at kinali.ch
Wed Nov 1 14:08:41 EDT 2017

On Wed, 1 Nov 2017 15:37:38 +0100
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

>  Silly people 
> want a relative comfortable temperature and well, building A/C is 
> typically bang/bang regulated so you get what you paid for.

My short stint in the HVAC business taught me, that it's surprisingly
difficult to stabilize room temperature to better than 2-5°C.
It starts at such simple things as measuring the temperature.
The position of the sensor and its distance to the wall make a huge
difference. Just 1cm further away from the wall, or 10cm up or down and
you get 2-3°C difference. An A/C system usually controls the temperature
of the air inlet, which is the simplest thing to do, but actually you want
to control the (heat) power flow into the room. And this is something that
has not been possible with standard equipment until recently.

The best we can do today is to have a well insulated room (no windows
with whith unknown power flows) and measure the temperature at a few
strategically choosen points. Then control the heat influx and
outflux using an approriate control loop. This will still result
in deviations of 1-2°C when somone walks in.

			Attila Kinali

It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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