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Wiring a De-humidistat Control with an Emerson Sensei WIFI Thermostatt

Wiring a De-humidistat Control with an Emerson Sensei WIFI Thermostatt

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Old 08-22-17, 05:11 PM
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Wiring a De-humidistat Control with an Emerson Sensei WIFI Thermostatt

I have a home in hot humid Florida. As is typical in Florida, our AC was controlled by a traditional thermostat but also has a separate "de-humidistat" control wired "in series" with the thermostat. By de-humidisat, I mean a control that allows you to set the desired humidity. By having it wired in series (vs parallel), both the thermostat set point and the de-humidistat set point must be exceeded for the AC to be turned on. When you are at home, the de-humidistat is set to "ON" and the AC is full under control of the thermostat. When away from the home, the de-humidistat is set to 50 or 55% and the AC to 80 degrees. This allows the AC to only run when the humidity goes above 50 or 55% to avoid mold. My question is this: Recently I installed an Emerson Sensei "smart thermostat" in order to be able monitor both temperature and humidity on my iphone while away from the home. I followed the instructions from Emerson as to how to wire the Sensi based on the wires connected to the original thermostat which did NOT have a connection to the 24v power wire from the AC unit. The thermostat functioned fine with the de-humidistat set to ON (eg. only the thermostat controls the AC.) The wifi also worked fine and I was able to see temp and humidity on my iphone as well as change the set temperature remotely. However, I then found out with further research that the wifi was operating only on the Sensei's 2 AA batteries. Given that I am gone several weeks at a time, the batteries would go dead. However, you can attach the 24v power line from the AC blower unit to the Sesei and have the wifi powered by that such that the batteries are only for back-up. The 24v wire was in the wire bundle so I connected to the AC blower unit and to the Sesei per the instructions. Again, the thermostat including the wifi connection worked fine with the de-humidistat set to ON. However, upon leaving the home, I entered my usual "away settings" of 80 for the thermostat and 55% for the de-humidistat. What I failed to realize until after I was gone is that both the AC AND the WIFI connection work only when the temperature AND the humidity are above the set points. Therefore, I am not able to see the temperature and humidity on my iphone remotely (and change the temperature setting if I wanted to) when the AC unit is actually running (ie both the temp and humidity set points have been exceeded. Kind of defeats the whole reason for have the wifi thermostat. I contacted Emerson and asked if the Sesei could be wired to function with a de-humidistat in series and I was told NO. Not sure they really understood what I was asking. I suspect there is a way to do it but I am not sure how. Has anyone out there done this successfully and can tell me how? Many Thanks
 
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Old 08-23-17, 07:30 AM
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Your AWAY issue seems like a contradiction. When the Tstat is calling for cool AND the dehumidistat is calling for cool (or manually set to "ON") your series control loop should be closed and the Tstat should be visible and the wifi should work. I suspect something awry in how you've supplied external power to it. Where did the old Tstat get power?
I'm not familiar enough with the unit (I have one) or your custom setup to know what's needed to make it work correctly.

Isn't there a digital wifi Tstat that's made to control both temp and humidity? I feel the Sensei is a fine unit for basic temp control, but is pretty "dumb" in that it only displays humidity (alternating with time display, and too small to see without glasses), and setting fan speed is a hidden feature with no display or direct access.
 
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Old 08-23-17, 07:32 PM
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Thanks for your quick response. What I would like to be able to do and I thought the Sensei would allow me to do was 1. Use my iphone or computer to monitor temperature and humidity in my home when I'm away form it for extended periods
2. Use my iphone or computer to change the temperature set point remotely.
In fact, when the de-humidistat is set to ON, I can successfully do 1 and 2 above and it works great.
The problem comes when I want to actually use the de-humidifier to keep humidity below a certain level. If the dehumidistat is set to anything other than "ON", for example 50%, the AC will only come on if both the humidity set point has been exceeded and the temperature set point has been exceeded. This is good and exactly what I want to happen so that I minimize AC run cost but still avoid high humidity in the house. What isn't good is that in this "away" mode, I can only see the temperature and humidity (and change temp set point) on my iphone in those periods when the AC is running (eg the circuit is complete because both the temp and humidity are above set points. The WIFI is only powered on when the temp and humidity setpoints are exceeded. When the set points are not exceeded and the AC is not running, then the WIFI is not running. (Not sure why the battery in the themostat is not kicking in as the back-up in these situations.
I wired it according to the instructions provided in the Sensei iphone app which they provide based on how the wires were connected to the thermostat that the Sensei is replacing. However, their instructions do not take into consideration that a dehumidistat is wired in "serial" between one of the wires from the AC control board and the thermostat. (I'm not there right now and I don't remember which of the wires. I do believe that there must be a way to have the WIFI in the thermostat powered from the 24 volt line from the AC control board, use a dehumidistat control as I describe above in "away mode" and still have the wifi connection working in periods when the AC is not actually running because the temp or humidity are below the set points. I just don't know how to do it.
 
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Old 08-23-17, 09:30 PM
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Welcome to the forums.

It's like reading a short story.

The WIFI is only powered on when the temp and humidity setpoints are exceeded. When the set points are not exceeded and the AC is not running, then the WIFI is not running. (Not sure why the battery in the themostat is not kicking in as the back-up in these situations.
I have not found a wifi thermostat that does not use a C wire to be extremely reliable regardless of the manufacturers claims. Simply put..... if you're going to use a wifi stat.... get the C wire to it. You may be able to use on of those create a C modules.
 
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Old 08-24-17, 08:16 AM
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It sounds like you are breaking the R or C circuit with your humidistat.
It should only break the Y circuit.
 
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