[SATLUG] Re: Any Technical/Automation-Hacking/Override info on the CPS Energy Saver Thermostat?

pcdls.ronin pcdls.ronin at gmail.com
Mon May 17 03:06:05 CDT 2010

I'm well aware of it's intended operation and use.  Historically, things
like this (coming from a central authority) always start out voluntary,
then, they find out some way of coming at you sideways.  I believe we
can all cooperate to achieve great things but it must remain voluntary
and decentralized.  Linux is a perfect example of this.

In reference to the OP's question, if you have a 24 Volt Thermostat, a
24VAC thermostat can be overridden if you have access to the control
signals of the split-system AC.  Signal identifiers may differ with make
and model of your split-system but their general control functions are
typically the same.  These signals are what the thermostat uses to
actuate the relays that control your air handler and condenser
assemblies.  If you cannot override the electronics of this thermostat
directly, you could access the control signals and gang a second
thermostat that you control along with the thermostat that you wanted to
hack, this would require some application of relay logic to facilitate
and will look kludge-y as hell.  I wouldn't recommend this unless you
have intimate knowledge of how your split-system AC works.  Plus,
touching 24VAC can still hurt quite a bit.

The typical split-system AC, mine in this case, consists of a
air-handler/evaporator coil assembly on the inside of the home and a
condenser assembly on the outside of the home.  Normal cycling occurs
when a temperature threshold is reached on the thermostat (a bi-metal
relay variety or a digitally monitored and  controlled variety), and a
signal to the exterior assembly's control board triggers the condenser
to cycle on by closing 120VAC relay to the compressor.  If the air
handler's blower is not permanently configured in the 'on' position,
then this signal will also trigger the blower to turn on as well via a
timer relay that introduces some turn-on and turn-off delay to the power
cycling of the air handler's blower assembly.  As the condenser's
compressor operates, refrigerant is compressed from the low-pressure
line of the system to the high-pressure line of the system.  In the high
pressure line, condenser coils cool the compressed refrigerant
liquid/gas.  The high pressure line connects up to the evaporator coil
via a thermostatic expansion valve (think of it as a fancy atomizer
nozzle but with extra mechanical controls) that will atomize the
'cooled' high pressure refrigerant liquid/gas to an even cooler low
pressure gas (work and heat in thermodynamic processes).  The liquid to
gas conversion causes the evaporator coils to cool down significantly,
allowing the air passing through the evaporator coils to cool and
thereby cool down the home as the air handler's blower distributes the
air to the vents.

I've always wanted to incorporate a secured, web-enabled control board
that could monitor the entire AC system: high line and low line
pressures, coil temperatures, refrigerant flow, thermostatic expansion
valve displacement, blower speeds, relay actuations.  Now that would be


Henry Pugsley wrote:
> I think you're missing the point .. it's not about who is deciding how
> hot or cold your house is.  From what I've read about this, CPS will
> cycle your A/C during peak load times to smooth the load cycles.  I've
> seen this happen both in Florida and Texas: the first hot day of
> summer causes brownouts and blackouts because everyone sets their
> thermostat for 72 degrees and they all kick on at the same time.
> Great, now you have no A/C at all and it's 100F outside.
> The deal doesn't sound all that bad:
> 1) You get a free programmable thermostat (this alone saves you money)
> 2) The cycling only happens during peak times (3pm-7pm) of peak months.
> 3) Cycling doesn't happen more often, it just happens at better times.
> 4) You can remove yourself from the project temporarily or permanently.
> What I get from #3 is they want to setup a sequence across the grid so
> that as one house cycles on, another one cycles off .. to keep all the
> houses from cycling on at the same time and causing brownouts.  You
> control the temperature, they control when the A/C runs to maintain
> that temperature.
> The bigger issue here is that the power grid is overloaded and it's
> getting worse as people put more power hungry electronics in their
> homes (honestly, who needs 6 computers, 3 gaming systems, and 2 plasma
> TVs? ;)).  I suppose the alternative to centralized power cycling
> would be to increase electric rates to the point that no one can
> afford to run their A/C.  Or maybe do tiered billing like the cell
> phone companies and charge 2x more for power during peak times than
> off-peak times.
> I guess from the security perspective, the only big risk is that
> someone could access the system and force everyone's A/C to cycle on
> at the same time, thus causing a brownout or blackout.  Of course that
> can happen now, it's just not as likely.  It's a voluntary program of
> course, but in the end it could help avoid situations like I described
> above.
> -Henry
> On Sat, May 15, 2010 at 5:02 PM, pcdls.ronin <pcdls.ronin at gmail.com> wrote:
>> In general, centralizing technologies are a bad idea as it creates an
>> opportunity for controlling bodies to eventually "legislate" away the
>> individual's ability to decide for oneself.  Besides, what "genius"
>> decided that CPS needs to control our thermostats?  Isn't it *our*
>> responsibility to decide for ourselves how hot or cold our homes are?
>> Or, how well insulated and energy efficient our homes are?  All economic
>> behavior on our parts is dependent upon our personal resources.  We,
>> typically, don't let anyone else control our economic behavior.  If, and
>> when, we do allow it, it's usually under coercion and force.
>> This is a bad idea that I suspect will be fraught with security issues.
>> And, there *will* be security issues once you put the power to control
>> your AC in the hands of centralized bureaucrats.  Remember, we're
>> dealing with people who attempted to commit fraud over the nuclear power
>> debacle (in collusion with many political actors, it takes more than
>> "two employees" to try to pull that off).
>> Now, if they were to provide the technology (linux-enabled with entirely
>> open-source applications that utilize a highly encrypted link over ssh
>> 2.0) that the user, alone, controls.  Then, I'd probably have no problem.
>> pcdls
>> Tweeks wrote:
>>> Follow up thread I found on this the topic of security and hacker implications
>>> of centrally controlled mass AC controls:
>>>       http://www.schneier.com/blog/archives/2008/01/hacking_thermos.html
>>> Tweeks
>>> On Saturday 15 May 2010 11:26:53 am Tweeks wrote:
>>>> Hey..
>>>> I saw a couple of old threads on the CPS offered free digital thermostat.
>>>> It looks like it is remote controllable by CPS via two way pager control
>>>> w/web integration (on their side).. Not a huge fan of this.. would have
>>>> preferred a home broadband connection that I could control.. but whatever.
>>>> Does anyone have any info on how controllable these things are?  It's
>>>> designed to allow CPS to help regulate peak load distribution so that they
>>>> can do some sort of time division smoothing of everyone's AC loads.
>>>> Interesting idea.. but I would like to maintain override control if need
>>>> be. Any protocol or wired-hack info also of interest, integration with any
>>>> linux home automation systems (like Zoneminder, MisterHouse, etc).  I think
>>>> it's this model:
>>>> TH8000
>>>> http://www.yourhome.honeywell.com/Home/Products/Thermostats/7-Day-Programma
>>>> ble/VisionPRO+8000.htm
>>>> NEway.. lemme know if anyone has really dug into one of these before.
>>>> Tweeks
>> --
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