Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: KevinJ93 <kevin_es@whitedigs.com>
Newsgroups: sci.electronics.design
Subject: Re: A research team has managed to coordinate 100 domestic air
 conditioners to stabilise the power grid in real time, as if they were a
 flexible power plant.
Date: Sat, 14 Jun 2025 18:12:44 -0700
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On 6/14/25 5:02 PM, Don Y wrote:
> On 6/14/2025 4:09 PM, KevinJ93 wrote:
>> On 6/14/25 3:29 PM, Don Y wrote:
>>> On 6/14/2025 2:53 PM, Carlos E.R. wrote:
>>>> That's not what they are doing. They are changing the load in tiny 
>>>> parts of the cycle, 50 or 60 times per second. Changing the load 
>>>> waveform.
>>>
>>> No, they are deferring the start of the compressor and/or blower.
>>>
>>> As home thermostats are not precision devices -- AND ONLY MEASURE THE
>>> TEMPERATURE AT ONE LOCATION IN THE HOUSE'S VOLUME -- an occupant
>>> would likely never notice if the plant turned on at its "intended"
>>> setpoint or some delta above.
>>>
>>> The question is whether or not the control algorithm allows the
>>> local plant to be operated with greater *symmetric* hysteresis
>>> or if it just lets the cooling cycle be delayed without regard
>>> to the actual temperature.
>>>
>>> It's just silly to rely on antiquated control approaches when
>>> it's so easy to have smarts "at the edge".  E.g., how smart is
>>> it to allow the thermostat to call for cooling (or heat)
>>> one minute before the setpoint temperature is SCHEDULED
>>> (by the user's scheduling decisions!) to go up (or down) by
>>> an amount that likely exceeds the hysteresis in the system?
>>>
>>> E.g., house maintaining 68F for heat and at 1 minute prior to bedtime,
>>> the thermostat notices it is now 67.9F and calls for heat... when
>>> the setpoint will be lowered to 62 a minute later?  (and, the
>>> changing of the setpoint likely causing the heating cycle to be
>>> prematurely aborted:  "Oh, the house is now at 67.93 degrees
>>> and the setpoint is 62 so let's shutdown the plant instead of
>>> waiting for it to attain the OLD setpoint of 68F...")
>>>
>>> Imagine the stresses on the equipment by all this ineffective
>>> cycling (esp the compressor!)
>>>
>>> Ideally, you want to notice how the system behaves and tune
>>> your controls to maximize *it's* ability to satisfy the
>>> user's stated needs while reaping some rewards for the provider
>>> (and, ultimately, for the user by way of reduced capital
>>> investments)
>>
>> Many thermostats have had those features for at least the last decade.
>>
>> My ten year old Carrier thermostat addresses most of those items. It 
>> also has 
> 
> Then, how many minutes BEFORE as setpoint change will it ignore the
> scheduled change?  Does it look at the response of the interior to
> such changes and adapt so the "back off" varies with temperature,
> setpoint difference, outdoor temperature and wind speed?  Otherwise,
> you're just shifting the point at which it makes an unfortunate
> change in control.

I don't know how many minutes prediction it does but it is supposed to 
do similar to what you describe. There is very little user control, just 
to enable or disable the feature.

> [The thermostat that I designed for my parents, *40* years ago
> does those things.  But, still for a single measurement point
> in the house (e.g., my bedroom was always considerably warmer
> than the rest of the house; the kitchen always considerably
> cooler -- partly because of the house's orientation on the lot
> and partly because of the way the heating was plumbed).  But,
> the thermostat knew how to get the heat (no central air) *to*
> the desired temperature *at* the specified time -- instead of
> simply switching setpoints at those times]

That's what it's supposed to do. You set the times that you want it to 
be at the target temperature and it is supposed to learn and predict how 
much in advance to start heating/cooling. I have noticed that it starts 
operating at different times depending upon the weather/existing house 
temperature. I do have the room temperature logged by the home 
automation system and it seems to reach the target temperatures pretty 
much at the requested times.

>> an exterior outside temperature sensor and takes in weather 
>> predictions over the internet so that it ramps the temperature 
>> appropriately and maintains a comfortable temperature and humidity.
> 
> I do that here -- adding decision criteria as to when the swamp cooler
> can be called on to provide cooling (cognizant of a "comfort factor").
> If today's OUTDOOR temperature is likely to be more than ~30 degrees
> above the desired indoor temperature, then the cooler is ill-advised
> as refrigeration will be required once the indoor-outdoor differential
> reaches that point.  As I (currently) have to rely on manual action
> to vent the house adequately, you don't want to have to tell the
> homeowner to close all the windows so the ACbrrr can come online.
> 
>> The compressor protection is commonly built into the compressor 
>> control unit so that any command from the thermostat that compromises 
>> the compressor safety is ignored until safe.
> 
> The compressor won't usually turn ON until a suitable time has elapsed
> to ensure the compressor's pressure has leaked off to a safe starting
> point.  But, once commanded on, it will usually turn off as soon as
> told to turn off.  Has it done any meaningful work in that short
> time?  Or, just cycled out of blind devotion to the control signal?

There can be significant delay from manually altering the target point 
(for both enabling and disabling) but as the control input is not 
visible I don't know whether the thermostat or controller is doing that.

> This makes for some interesting design decisions.  E.g., if the
> user specifies a setpoint of 68F at 7AM and 72F at 7:30AM, it is
> possible that you might need to overshoot the 68F in order to
> be able to attain the 72F.  Likewise, specifying 68F at 7A
> and 65F at 7:30A... should it even bother trying to meet the
> earlier specification given that the user has effectively
> said he doesn't care about that temperature 30 minutes later?
> 
> Historically, the user is allowed to remain ignorant of the costs
> of his decisions.  Largely because the control systems don't
> have the knowledge -- nor ability -- to inform the user.
> 
> "If you raise your cooling temperature by 1 degree, I can save
> you $X today."