Zoned Thermostats with Central Interface - What works well?

   / Zoned Thermostats with Central Interface - What works well? #11  
I made my own. I bought a PLC for 80 USD on Ebay and designed the logic. We have 5 heating zones and one AC all heated or cooled by geothermal heat pump. It switches from heating to cooling automatically, integrates HW heater to the geo etc. The bad thing about that is that if something happens to me it will be difficult to fix for somebody else. I did that because no system I liked was not available 10 years ago when we built our house. Total cost of PLC, cabinet, relays, contactor, temperature controllers, sensors etc was about 500 USD.
   / Zoned Thermostats with Central Interface - What works well?
  • Thread Starter
Our Honeywell controller allows us to choose 3-4 different behaviors for the electric strip heaters -- time based, temperature differential based, thermostat based, and a couple others that I can't remember.

One important reason to allow use of strip heaters with a geo system is to prevent the ground loop from chilling down too far in situations where the geo system requires very long run times to reach target temps in super cold weather. I believe it's in your interest to mix in a little strip heat in those situations (some people have backup propane/gas heat for those scenarios, which would be much more efficient than strip heaters).

Like everything, there is an optimum. All depends on the climate and many other factors, including how you set your thermostats. If you set the system to a much lower overnight temperature, the morning ramp up to a warmer temperature could result in long run times and cause efficiency to drop off as the ground loop cools.

We had our strip heaters turned off the first couple years due to a programming error. Got them activated middle of last winter and they've been available all of this winter. Have not really noticed if they are used a lot, and haven't yet seen any impact on the power bill. But I sure knew something was wrong last winter when we had a super cold snap and the geo loop temp dropped dramatically due to long run times.

Our system is oversized by a factor of almost 2. We have two 4 ton systems (8 tons total) sharing a single loop. I could get by with 3 tons total and electric strip on rare occasions or 4 tons without strip heat. Given that and how well we are insulated I've got my systems setup so they only run at a reduced 1st stage effectively making them 2-1/2 ton units instead of 4. Even into negative temps running 1st stage only my units cycle on and off and don't require continuous run times. We are at the end of our heating season and my current loop temp is at 39 degrees. No reason to add electric strips into the equation. The only time they would kick on would be when I was running setback temps when we are away which would be of no use to the loop or my electric bill.
   / Zoned Thermostats with Central Interface - What works well?
  • Thread Starter
They were not cheap but I finally found what I was after and really like them. Ended up with Sensi Wifi Thermostats. They have a sensi app that is ok but these things really come into their own when paired with the wink phone app. With wink you can control tstats individually or set up any number of grouped tstats to control as one unit. Add in their "robot" builds and you can do some pretty neat stuff.

Using wink I can now turn all tstats on or off with the push of 1 button. I can scroll through individual t-stats and adjust if needed. It really gets nice when building "robots" in the app.

Here's a couple of examples.

Fan Circulation Robot - When we run the fireplace it tends to get much warmer upstairs for obvious reason. I programmed a bot for heat detection. If the upstairs t-stat temperature rises above 73 degrees it turns turns the furnace fans in the whole house on to help circulate the air. When the temp drops below 70 degrees it automatically turns the fans back off.

Today it was sunny and 62 outside. Solar gain increased our master bedroom temp to 75 degrees. I shut the door to the master wing and left some windows cracked this evening. When the app detected the master bedroom tstat was at 68 degrees (our sleeping temp) it sent a notification to my phone. Walked in and shut the windows.

Here's some screenshots
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