2 wire WiFi upgrade, hydronic baseboard

northlakes

I’ve got a new mod-con boiler (IBC Vx 199) on a 3 zone (taco 570s) hydronic baseboard system. I want to install some WiFi thermostats to be able to remotely monitor and set max/min temps, as it’s a rental. I don’t need “smart learning” as I plan to advise renters to do very little adjustment of the temperature, works best when it’s constant. Just want to be able to control remotely. 

Existing thermostats are battery 2-wire, and I’m wondering if I could install something like the Tekmar 564. I don’t really need a Nest, have seen they do sometimes work on 2 wire, it just seems less reliable and I’d prefer not to worry about whether the transformer can handle 3 zone valves and 3 thermostats. 

Any advice on the 564 or any other solutions people like that don’t require new wire? A couple of these are a bit tricky to fish. Many thanks 

Jamie Hall

Considering that amount of power a wi-fi thermostat chews up, I'd be surprised if you could find a two wire one...

fentonc

What about putting the thermostat(s) near the boiler and just putting wireless remote temperature sensors in the units?

northlakes

fentonc said:

What about putting the thermostat(s) near the boiler and just putting wireless remote temperature sensors in the units?

Interesting, I didn’t realize that was an option? Units don’t have access to boiler. Do these remotes allow people to set temp?

northlakes

Jamie Hall said:

Considering that amount of power a wi-fi thermostat chews up, I'd be surprised if you could find a two wire one...

I think what I’m assuming is that the 564 kit allows you to insert a controller in between which powers the WiFi tstat using the same 2 wires. Maybe I misunderstand how it works. 

fentonc

@northlakes - No, they're just sensors. All of the control is either online or at the thermostat.

fentonc

Alternatively, have you checked the wiring to see if it's a 3-conductor thermostat wire, and only 2 are used? My thermostats (3 zone setup) had 3-conductor wire but the 3rd one was just unused, so it was pretty trivial to connect it to the 24VAC common.

Jamie Hall

northlakes said:

Jamie Hall said:

Considering that amount of power a wi-fi thermostat chews up, I'd be surprised if you could find a two wire one...

I think what I’m assuming is that the 564 kit allows you to insert a controller in between which powers the WiFi tstat using the same 2 wires. Maybe I misunderstand how it works. 

There is a limited number of situations where it may be possible to power a wi-fi or other powered thermostat with only two wires, but the situations are quite limited. To see why this is so, one needs to consider what the two existing wires actually do in terms of control -- and what power the thermostat needs to operate.

From the standpoint of control, the controller expects to see either an open circuit (off) or a closed circuit (on) between those two wires. That's all the controller expects, and all the controller can use. The thermostat in this situation draws no power -- it's just a switch.

Now from the standpoint of power, the conventional thermostat doesn't need any. The fancier ones do -- either batteries or, in most cases 24 VAC. In many controllers, when the thermostat is open -- not calling for heat -- there is a limited amount of power available on those two wires, and you can measure 24 VAC across them. Wehn the thermostat is closed -- on, calling for heat -- that available power disappears. There is no voltage between the wires. So. If the power demand is limited, a thermostat can be designed so that if it requires very little power, it can "steal" power from those two wires when the thermostat is not calling -- open -- and store that power for use to keep itself alive when the thermostat is closed.

So far so good?

oK. Several problems. First, if the thermostat draws too much power, the controller will see that as a closed circuit rather than an open one, as it should -- and interpret that as a call for heat and run the boiler or furnace. Not at all what is wanted. Controllers vary in how fussy they are about this. Second, the thermostat must be able to store enough power to keep it alive during a heat call, If the heat calls are relatively short, and the spaces between them are long enough, this can work. However, if the heat calls are longer, the thermostat will need a larger internal power supply (usually a small battery or a capacitor) and enough space in between calls to recharge that without tripping the boiler on as noted earlier.

Now wi-fi thermostats -- the poster child being the Nest, but others are somewhat similar -- were designed for forced hot air applications, those being in the majority. Those are characterised by short cycles with usually more or less equal spaces between cycles -- the ideal conditions to recharge the thermostat. Therefore they work well enough, though sometimes with a resistor kludge, in such applications on two wires. However3, hot water heat -- never mind steam -- uses much longer cycles, and the little internal power supply in the thermostat runs out of power -- and the thermostat goes dead. And you can't fix it with two wires, because you simply can't supply enough power through those two wires in the short off cycle to recharge the power supply, even if the power supply were big enough.

So. Three wires. One constant 24 volts. One constant return. and one switched wire, usually but not always a switched return.

EdTheHeaterMan

It appears from the instruction manual for the Tekmar 564 that the 2 wire set up is just what you are looking for. The controller will be places in the boiler room where the 2 conductor thermostat wires are connected to the zone controls. The Tekmar 564 HVAC interface module is in the boiler room and the Tekmar 564 display module is in the room or apartment where the old thermostat was located. it is designed to connect to the interface module with only 2 conductors. those 2 conductors are the only wires needed for the display. All the power using WiFi components are close to the boiler room where there is room to run additional 24V power transformers as needed.

Jamie Hall

Interesting. I wonder what the communication protocol between the display module and the interface module is to allow for both power and data? I don't suppose Tekmar would say... ?

EdTheHeaterMan

You will need to purchase one Tekmar 564 for each thermostat you want to control.
You may also want to purchase a Taco Zone valve control relay in order to make the connections and eliminate some of the problems that the Taco 570 valve actuators may cause. Those 570 actuators use a lot of power and the best solution is to use the ZVC 403 to power the valves and connect each Tekmar HVAC Interface to it the Thermostat side from each zone on the Taco ZVC 403.

EdTheHeaterMan

Jamie Hall said:

Interesting. I wonder what the communication protocol between the display module and the interface module is to allow for both power and data? I don't suppose Tekmar would say... ?

I'm sure there is power thru the 2 wires to light up the display and make everything work on some lower voltage. At the same time a communication signal is interpreting the inputs from the user and from the temp. and humid sensors in the display module.

It’s like the ignition modules that send 6000+ volts to spark the ignition and also accept the flame rectification signal in the same ignition wire. How does that not blow up the delicate flame sensors circuit in those controls?

It’s Magic Jamie

northlakes

Thanks so much for all these responses.

Sounds like if you need a dedicated Tekmar controller for each thermostat and then also a separate zone controller that’s not quite what I was expecting… maybe I need to take one more look at how difficult new wires would be to pull, then make the call from there. 

HVACNUT

GGross

The 564 comes as a package with the interface box.

northlakes

HVACNUT said:

Ok, this is what I was expecting was possible, a powered wireless bridge of sorts. Will research! Thank you. 

HVACNUT

northlakes said:

HVACNUT said:

Ok, this is what I was expecting was possible, a powered wireless bridge of sorts. Will research! Thank you. 

You can do tons with that. The tenants don't even need to see thermostats. You can install wireless sensors in the living space and mount the thermostats in the mechanical room. If theyre in the living space you can lock in minimum and maximum temperatures.
You can even set the background color to match the drapes.

northlakes

Thank you for all the advice here. After reading about problems people had with various “common-maker” wiring solutions, wireless sensors, expensive RedLink systems, ended up feeling like running more wire made the most practical sense. Added two new cables where I *could* fish (oof but got it done) and added a 24v external transformer for the tricky thermostat that would have required too much demo. Installed a Taco 4 zone control and 3 ecobee lites. All seems to be working well, fingers crossed. 

*For those interested, I had planned to use my old transformer to power the stats and let the zone control run the valves, as I’d read the ZVC likely couldn’t run both. After a call with Taco they said 40VA on this model was enough to run 3 and 3. (Now running 3 ZVs and 2 thermostats on ZVC transformer)