Re: zoned or not zoned?? thermostatic control of multiple spaces

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

To answer your last question first:

One could/can use simple inexpensive, traditional Honeywell thermostats that
have a bimetallic spring as the temperature sensor and a mercury (ugh :-( tilt
switch as the switching mechanism. But these have a manual COOL-OFF-HEAT
setting in part because you can only set the dial to one temperature, not two.
If there are inexpensive thermostats available that let you set two
temperatures (I dunno), that is, separate COOL ON and HEAT ON settings, they
might be adapted to your use. Okay so far?

Assuming that you have a thermostat arrangement (whether one or two physical
units)  that complete two circuits with a Single-Pole, Single-Throw (SPST)
switches when the temperature is TOO COLD or TOO HOT (that is, "call for" heat
or cool), you use this information to override the signal from your
conventionally installed 4th/7th thermostat which is the Tstat that controls
the boiler most of the time.

Assuming for the moment that your boiler control consists in a 24VAC circuit
that needs to be completed with a SPST switch, and you have a conventional
thermostat with effectively a SPST switch like the Honeywell I describe in the
first paragraph above,

TstatTerm1 -- NC_TooHot_1 -+- NC_TooHot_2 -+- NC_TooHot_3 -+--- Boiler
                           |               |               |
                                                    NO_TooCold_1
                                                           |
                                                    NO_TooCold_2
                                                           |
                                                    NO_TooCold_3
                                                           |
TstatTerm2 ----------------+---------------+---------------+--- Boiler

where NC_TooHot_x are the Normally Closed (NC) contacts of a relay and
      NO_TooCold_x are the Normally Open (NO) contacts of a relay.

So any closure of any NC_TooHot switch will turn off (override) the boiler
unless any of the NO_TooCold-x switches are closed. One can modify the
override logic by (eg) moving the location of the NO_TooCold_x switches to the
locations shown with the + .

Note that the circuit diagram above shows the control signal to the boiler,
not the signal from each SPST switch in each thermostat to each relay coil,
Right?

The relays themselves are powered by whatever voltage the relay coils that you
choose should happen to need (12vdc, 24VAC etc). One wrinkle is that the
anticipator circuit in the conventional thermostats described are designed for
24VAC so you might avoid complications by using 24VAC throughout -- but maybe
not, Depends on the thermostat chosen.

HTH ... Marc
Marc_F_Hult
www.ECOntrol.org


On 6 Dec 2006 20:14:47 -0800, "Lighthouse" <gruntledlark@xxxxxxxxx> wrote in
message  <1165464887.275804.321050@xxxxxxxxxxxxxxxxxxxxxxxxxxx>:

>Marc, this sounds pretty close to what i want to do. not the Aprilaire
>thing (way outta my budget), but the other. hope you don't mind helping
>me out w/ a few of the details. ok, conventional therms, cat5, serial
>wiring, parallel wiring. i'm down w/ all that. i'm not sure about the
>24V xformer and the relays. i'm assuming that both of those get
>installed in the boiler room along w/ my 7th therm. what kind of
>relays?  is the 24v xformr the kind used in doorbell circuits? how do
>those fit into the wiring scheme? is it possible for you to sketch this
>out for me?
>
>what would be the difference w/ using an AUTO therm instead? as for
>discouraging tampering w/ the settings i could possibly camo the therms
>inside the casing of a smoke alarm unit.
>
>thanks for the ideas!
>
>Marc_F_Hult wrote:
>>
>> I would do this with three (or four) communicating Aprilaire 8870
>> thermostats and Homeseer software running 24x7 on a low power dedicated PC.
>>
>> But here's a solution that doesn't use a PC, is extremely reliable,
>> presumably inexpensive compared to your energy bill, could be installed
>> and(or) serviced by any competent HVAC serviceman, does not look out of the
>> ordinary to the occupants, could be incorporated as part of a future zoned
>> system, and requires no custom programming, PICs, soldering etc:
>>
>> 1) Install two inexpensive, conventional thermostats in each apartment in
>> no-tamper (fat chance! ;-) enclosures. Thermostat wire is OK but I suggest
>> using CAT-5.
>>
>> 2) You'll need 24VAC transformers and relays as well as the thermostats.
>> You might also find a low-cost  thermostat with an AUTO setting (not manual
>> Cool-Off-Heat as is conventional) that could replace each pair of
>> thermostats.
>>
>> 3) In each apartment, set one thermostat to COOL with the maximum tolerable
>> high temperature (say 76 F), and one to HEAT at the maximum tolerable low
>> temperature (say 66 F).
>>
>> 4) Install a seventh (!) thermostat in a centrally located ('average')
>> location that you can access.
>>
>> 5) Use each of the COOL outputs to energize a relay the controlled contacts
>> of which are wired in parallel fashion with the other two. This creates a
>> logical OR to force a TOO COLD OVERRIDE.
>>
>> 6) Use each of the three HEAT outputs to energize a relay the controlled
>> contacts of which are wired in parallel fashion with the other two. This
>> creates a logical OR to force a TOO HOT OVERRIDE.
>>
>> 7) Control the boiler with centrally located thermostat's output in series
>> with the TOO HOT OVERRIDE (TOO HOT opens circuit) and in parallel with the
>> TOO COLD OVERRIDE (TOO COLD completes circuit).
>>
>> This creates a system in which the building w/should not exceed any of the
>> six independently set table TOO COLD OVERRIDE and TOO HOT ORERRIDE limits
>> and between those limits is controlled conventionally by the centrally
>> located thermostat.
>>
>> As implied earlier, the fly in the ointment is the concept of a
>> "tamper-proof" thermostat enclosure.
>>
>> ... Marc
>> Marc_F_Hult
>> www.ECOntrol.org