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Multiple Thermostat Control

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  • Multiple Thermostat Control

    I am adding radiant electric flooring for a whole house. Each radiant controller is good for a maximum of 15a, which at 220v, provides for up to 300 sq ft.
    They provide relays so that a single thermostat (and floor sensor) can control additional regions. An 1100 sq ft floor would require 3 additional relays.

    I'm thinking that a better alternative to the relays would be to have 4 separate thermostats. That way each floor section gets temperature cycled according to its own heat loss characteristics and floor sensor.

    With regard to setting of temperature setbacks and vacation modes, I'd like to not have to deal with 4 thermostats. Basement, 2nd floor, regular baseboard heating, and air conditioning actually could add 6 MORE thermostats!

    I've read the thermostat manuals and they all have a "remote control" inputs that can put the thermostat into setback mode.

    I have a "brute force" way of doing this but I'd like a wireless method.

    The brute force way to enable/disable 10 thermostats remotely is to have a small relay next to each thermostat. Power to this relay comes from a common, additionally and manually wired "setback relay" in the basement.
    This single setback relay be controlled by a single timer or even a touch thermostat (another!) functioning only as a timing device.

    The electrician's cost to centrally wire these 10 little relay boxes next to each thermostat is significant, even if they run on low 24v instead of 120.

    With all the remote control sophistication and technology available today, isn't there a wireless way to do this someway?

    I appreciate and look forward to discussing any and all suggestions.

    Last edited by MitchB; 06-30-2008, 08:40 AM.

  • #2
    Remotely accessible wireless thermostats

    Hi Mitch, you are absolutely right that it's indeed very possible to do all these control functions wirelessly and remotely. The question always comes down to how much you are willing to spend on the project

    From your comments it looks like it comes down to remotely controlling multiple wireless thermostats right? Or i'm i missing it?
    So this further breaks down to several problems:

    1) Wireless temperature sensors (thermostats) that communicate with a common receiver unit which in turn controls the HVAC unit. For Radiant since there's no HVAC unit receiver would actually activate different floor sections?
    2) Having the temperature sensor settings remotely controllable from a remote location? (or do you not care for remote control but rather control only from within the house?)
    3) Having the ability to simplify control of multiple sensors without having to cycle through each individually.

    Some comments:
    1) wireless temperature sensors: our most popular wireless thermostat system unfortunately requires user input to actuate. So whereas you can have multiple wireless thermostats "talking" to a single receiver, the receiver only responds to the temperature sensor that last issued a command. If each room will have it's own thermostat receiver pair then this is fine.

    2) The remotely accessible and remotely controllable temperature sensors we deal in are for telemetry or scada projects and usually for data logging or for integration with some other application software or PLC which controls a separate process. We never custom design solutions to control residential HVAC units since most commercial units don't have the right hooks for this, such home automation solutions already exist in packaged solutions and the ROI of such a custom solution is often not justifiable for home HVAC control. For example Honeywell communicating thermostats. Not sure if Radiant floor heaters would work but we can look into this.

    The trick to this is simple: If a sensor can be addressed/controlled from a computer then it can be remotely controlled. If it cannot the goal is to add an interface unit (signal conditioner) that makes it so. Many industrial sensors have this capability so we normally just have to find the right signal conditioner.

    3) This is a byproduct of the application software. If you can put all the sensors on a computer and control them on the computer then any arbitrarily complex control algorithms can be designed. We often use National Instruments Labview for such control applications. Again many standard fully packaged home temperature control systems will already have a control interface that will simplify or automate such features and provide "apply to all"-like features.

    So some options:

    i) Get 4 wireless thermostats that can be actuated by a relay adjacent to them. This saves on the cost of wiring multiple thermostats. The thermostats however need to be manually programmed for vacations etc. (what i'm assuming here is you still need some room sensor like floor sensor to decide when room is occupied to tell thermostat to kick in? Is this the case)

    ii) Do (i) above but have wireless thermostats also individually addressable from a local controller (computer). This way rather than walking to each thermostat you can just program them from your desk or in fact from anywhere in the world if you made that controller/computer available online.

    Have I made this unnecessarily complex? Please clarify what i'm missing (most likely missing something) and we can narrow down your solution space.


    • #3
      remotely controlling 10 existing thermostats

      Hi Thuor,
      Thanks very much for responding and the thinking time. I am familiar with Labview, but would like to go lower tech - i.e. no central computer.
      I'm mainly looking to solve, as you state it, problem 3.

      What I'd really like are say a dozen self-contained radio-controlled latching relay boxes. I don't even know if they are made. These could be battery operated and, like these wireless doorbell systems, use very little power except when changing state.

      The thermostats are special ones for radiant floor - they have both an air sensor and a floor sensor. I just want a single location to set them all to and from setback mode in unison. Perhaps running an additional low power set of wires from a central location to each thermostat location (to operate a 24v relay) is the simplest approach. The local relays would have their normally open contacts in series with the sensor wires. When energized the thermostat would control the floor normally. When de-energized, i.e. mid-day, the relays "open" the sensor wire circuit, turning off all floor heat.

      Maybe X-10 has something, though those are low tech and frequently not very well made or reliable.