I am about ready to buy controls for my new house build and have been thinking about the controls for the rooms.
The system is a Geothermal Heat Pump with Radiant Ceiling for the living space heating.
I am thinking that since I will be using the radiant manifolds that come with the actuator, that a thermostat per room that needs independent heat control, I would select one of the thermostats (Like the look of the Tstat7) and use the relay output to control the actuator on the manifold when heat is needed. Also, give feedback to the main control for humidity when in cooling mode for the fluid temperature control to avoid dewpoint condensing issues.
Is it possible to have this function with the Tstat7?
What configuration would be needed to have it function as a basic thermostat with the relay output to control up to 4-5 actuators (depends on how many loops are in the room). If the relays are good for up to 1A, then it appears I could wire several together to 1 relay output. (Could this exceed the 1A in some situations and require a separate SSR?)
Additionally, the thermostat would give feedback to the main controller so it could handle the Heat Pump control (which is essentially a separate control loop to keep the buffer tank at temperature) Would need some additional logic in the main control for either stage 1 or 2 operation and then also the backup combi boiler in case something happens to the heat pump or if there is snow melt calls so it can add additional heat.
Just trying to wrap my head around all the parts and the programming side of this control system. Any input would be appreciated.
The Tstat7 could do ‘two pipe’ heating and cooling as we call it, one valve does both heating or cooling depending on teh season. There are some examples for the Tstat8 on this forum which is the same as configuring of the Tstat7.
It can also perform the reporting back to a central controller as you describe, make sure to get the humidity option for the dew point calculations you mentioned there.
For multiple zones, you can consider the Tstat10, it is fully programmable and can manage 5 mechanical relays, two more if you were to use the analog outputs as binary outputs to energize a SSR. The mechanical relays do make a bit of noise so I’d mount that in a closet or near the manifold. They can also share information from the Tstat7’s over the RS485 network.
If you need a few more IO for the heat pump you can add another Tstat10, they can share information over the wifi and/or RS485 network if you wire that in.
So your bill of materials looks like two Tstat10’s, two solid state relays, plus a handful of temperature sensors for whatever number of zones and loops you want to keep track of. There’s several models which can be clipped onto pipes, strapped onto equipment, drilled into a wall and so on.
To manage the system you’ll want to have a Windows PC running our T3000. I know, you want an app for the phone and we’re working on it. There’s some posts on this forum about node-red which you could use to put something together in the meantime.
You mention that the mechanical relays make noise and to mount this in a closet. Isn’t the point of a thermostat to be in a room to control the temperature of that room it resides within?
How noisy is the relay? (I assume this is the same for all Tstats?) Sure would be nice to replace the Mechanical Relay with an miniature SSR…
Here is my usage as I see this for each room.
1 thermostat per room
Thermostat will turn on/off the zone valves for the loops on that thermostat on the manifolds (up to 5 loops on a room) If relay is too loud, then I guess my other option is a relay board that the T3 controls and more wire to the manifolds.
May add a wall temperature sensor for the associated closet so the temperature of the hall or closet is automatically maintained at a set temperature by the main controller (T3 series? Otherwise as you said, the T10 is programmable, so could put some logic into that and have it do the closet control) - I assume this sensor input must be monitored by the main controller for the T7/T8 thermostat and then do whatever logic is needed through the T3? - If so, then I assume that the main controller would be able to control the relay output state of the thermostat that has the control output for the hall or associated closet since this would not be your standard heat input to a furnace/ac unit? (Is this possible, or done better a different way?)
When using the thermostat in the bathroom, then I assume I can use the humidity sensor and report back to the main control to change the output for the ERV and ramp up air flow for the high humidity during showers?
Any other suggestions you may have are welcome. I am getting close to ready to purchase and need to work this out a bit more in my mind on how it will work for my wiring.
I have not really worked with RS485, but from what I can tell, just a pair of wires? Any gage in particular or an 18awg telephone wire twisted pair cable?