Re: [time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)
You would be amazed by the effectiveness of installing a small fan, mounted parallel to the wall, to create a slow whirlpool circulation in the room. Just a 10 w computer fan. If the air velocity is below 0.3 m/s it is hardly perceptible. That takes about 30 seconds to get around the room. The room becomes a well mixed volume of air. Heat sources distribute their burden of heat with only small local temperature rise. The room contains a 50 to 100kg mass of air and provides an averaging effect on perturbations. I have constructed 7 labs using this principle and have little difficulty keeping temperature swings below 1.0 degree C. The temperature control sensor must be very small (fast), exposed to the air flow, have zero hysteresis and be located on the wall that is opposite to the fan (and the AC unit). The temperature sensor directly controls the AC unit, with the overriding logic that although a 0.1C deviation from the set point can switch the compressor on immediately (not even a second of delay), when switched off the compressor can not be switched on again for about 2 minutes, the time needed for the gas pressure in the AC to subside. The natural cycle of about 2 - 3 minutes of on/off is attenuated by the integrated mass of the stirred air in the room. 1 Kw of heating or cooling is 1 kJ/s, air has an enthalpy of about 1kJ/Kg per degree C, so 100Kg of air heats/cools at 1/100 degrees per second. The room temperature gently cycles by a fraction of a degree as the AC cycles. If anything, the service life (10 years or more) of the AC unit is longer than conventional hysteresis sensor dominated chuggers. All of this occurs because you stirred the air in the room! cheers, Neville Michie > On 2 Nov 2017, at 6:32 AM, Poul-Henning Kamp wrote: > > > In message <20171101190841.366058d77e544d256b862...@kinali.ch>, Attila Kinali > w > rites: > >> 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. > > It is a matter of energy balance. > > Humans emit heat on the order of a hundred watts and the only way > to have that not affect the room temperture, is to "wash" it away > in airflow with much higher energy content, as is typically done > in clean-rooms. > > That still leaves you with the thermal radiation imbalance from the > higher temperature of the human skin, which is why "nano" laboratories > sometimes are kept at an uncomfortably warm temperatures. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)
In message <20171101190841.366058d77e544d256b862...@kinali.ch>, Attila Kinali w rites: >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. It is a matter of energy balance. Humans emit heat on the order of a hundred watts and the only way to have that not affect the room temperture, is to "wash" it away in airflow with much higher energy content, as is typically done in clean-rooms. That still leaves you with the thermal radiation imbalance from the higher temperature of the human skin, which is why "nano" laboratories sometimes are kept at an uncomfortably warm temperatures. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)
I remember visiting the metrology lab in HP Palo Alto (Glen Whatshisname) when I worked for them in the early 70s. There was a set of toggle switches on the wall; for every person inside, one switch was turned on. I don't know how well it worked but apparently, well enough for 1970s-vintage metrology. Jeremy On Wed, Nov 1, 2017 at 11:08 AM Attila Kinali wrote: > On Wed, 1 Nov 2017 15:37:38 +0100 > Magnus Danielson 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 > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Sent from my iPad 4. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)
On Wed, 1 Nov 2017 15:37:38 +0100 Magnus Danielson 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
