Will Nest Learning Termostat ever be truly compatible with a variable speed system?

[wpdi_wayne]

I had a Trane system installed in a whole-house reno, not knowing the Nest would not be able to be used (yes I would like to take advantage of all the speeds, not just one.

[CoolingWizard]

Basically, no standard programmable thermostat can handle or know how to control multiple speeds of a fan. What controls the multiple speeds of the fan is the control board inside the air handler. There are multiple choices on how to do that including electrically commuted motors (ECM) and three and four-speed motors. Basically during cooling the system can be set up to do maximum airflow for higher efficiency or a slower airflow in order to decrease humidity. For heating the blower typically starts at a lower speed to increase the heat gain distributed.  When it comes to ECM, they use a parameter table to either maintain a constant torque or maintain a constant volume of air flow. Those approaches are far more efficient than having a human have multiple fan speed control on the thermostat.

tell me why it is that you think you need to have control of the fan speed of your HVAC system?

Ken, The AC Cooling Wizard 

[wpdi_wayne]

Thanks for your reply. I don’t want control, per se, but love the Nest therm since I’ve had one in another house for 10 yrs. I have it set to eco mode, etc. when we’re away and like that it can sense when we’re gone. The Trane stat is supposed to have a geofence capability but I can never get it to work. Plus it’s UGLY. The rest of the house has modern looking switches, pop out outlets, and even linear diffusers - Also its touch screen is not good - requiring resetting often. The only saving grace is we put in foam attic insulation in FL and the thermostat is set at a constant and very comfortable 78 degrees, so self-learning schedules are not really needed. 

[Jake]

Hey there,

Thanks so much Ken for the helpful reply. 

I wanted to check in and see if you had any questions from here. Please let me know, as I would be happy to assist, and answer any you may have.

Best regards,
Jake

[wpdi_wayne]

My question was really - is anyone at Nest working on the learning thermostat going to someday make it able to control a variable speed air handler? I was not able to use one for the new Trane system that was installed in my whole-house reno. I had no idea it couldn’t be used. I love the one I have in another house. 

[CoolingWizard]

wpdi_wayne,

there is no real market for residential systems to have multiple fan speed controls in the hands of the homeowner. For example if you are running an air conditioner and decide on your own you want less airflow, then basically you’re causing the air conditioner system to work much harder to provide less cooling because it can’t deal with the Imbalance of heat load versus cooling capacity. The manufactures of these systems understand this and that’s why they went to the highly efficient ECM type motors. Then they can develop performance tables in the software to maintain a certain specific performance based on either constant velocity or constant torque. The resistance of the duct system or in the case of a owner who does not change the air filter, causes the ECM motor to work differently in order to maintain a specified flow of air over the cooling or heating Coil. Without the ability to have an owner be able to build a table in a thermostat, there’s no market value in having a thermostat to control multiple speeds of a fan when in fact there’s only one wire allocated to the fan control. The only conceivable way to do what you want if you have multiple span control only when you were on blower only and not running AC or heating. In other words you just want to circulate the air in the house and frankly, there’s no sense doing that on low versus high.  If all your goal is to circulate the air in your home you’d like the fan to run for as little as possible and turn the volume of the home air over more than once. I’m sure this is a lot more length of an answer than you were looking for but I hope it helps you understand why the manufactures have no incentive to design a thermostat that can support more than one fan speed without it being a proprietary control system that you find in condos and apartments.

Ken, The AC Cooling Wizard

[EdwardT]

Hi folks,

@CoolingWizard, thanks for the help as always.

@wpdi_wayne, I hope that CoolingWizard's response answered your question. Let us know if you have other questions and we'd be glad to assist you.

Thanks,

Edward

[EdwardT]

Hey wpdi_wayne,

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do.

Thanks,

Edward

[EdwardT]

Hi wpdi_wayne,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,

Edward