Nest thermostat for heat pump system and baseboard heat

[654Waites]

Good afternoon,

     I currently have two Nest E gen 1 learning thermostat connected to two separate simple two wire hot water baseboard zones off of a hot water boiler.  I am installing two ducted heat pump systems in each zone but would like to incorporate the fin tube as dual fuel at a certain OAT balance point. 

     I am a former controls electrician for over a decade so I have a good idea on the control logic and wiring but I am not 100% sure the gen 1 can handle this. Will I need to switch to a gen 3 stat?

    For additional reference, I will use a thermostat converter from the Nest to the heat pump AHU.  Although it will control a heat pump system the converter states that I need to treat the NEST thermostat as a conventional system when it comes to wiring.  I'm assuming since the gen 1 does not have a separate RC and RH I'm forced to buy the new one.

     Adding to this, I use remote sensors.  Will these still be compatible with the new NEST thermostat if needed?

Thanks

Jay

[AxelD]

Hi 654Waites,

Thanks for posting in the community! Sorry for the late response but no worries, help is here! Regarding your question about the installation of the Heat Pump systems, if both will need an additional R-WIRE to power them up. It will be needed to get the Nest Learning Thermostat because it counts with more wire spots. I'm happy to confirm that the Nest Learning Thermostat is compatible with temperature sensors. You can link them together without any problems.

Regards,

Axel. 

[654Waites]

Hi AxeID,

     I plan to install a Nest Learning thermostat on a Mitsubishi SVZ-KP18NA (air handler) and SV-KP18NA.TH (heat pump unit) using the PAC-US445CN-1 (thermostat interface).  I will also integrate my baseboard heat and drop my heat pump operation completely at pre-determined financial balance point (~25f). 

     Although I am using a heat pump system the PAC-US445CN-1 thermostat interface needs the Nest to be set up as a two stage conventional system in order to function properly and most efficiently.  Since the baseboard heat constitutes a 3rd stage of heat I need to know if the Nest can run as a dual fuel system conventionally as well.

     Ideally the thermostat would need to use balance point control and at ~25F only allow W3 to energize while restricting W1 and W2.

[AxelD]

Hi 654Waitesm

Thanks for replying! Please take a look at this article to Learn about multistage heating and cooling system.

Let me know how it goes. 

Regards,

Axel. 

[654Waites]

Hi Axel,

     The article you provided does not answer questions about my specific configuration.  I have the thermostat hooked up to a 2 stage heating and 2 stage cooling heat pump system; however, there is a 3rd stage of auxiliary baseboard heating.  Unfortunately, the HP system interface must be configured to receive a conventional thermostat interface although it is a heat pump system.  Because of this I'm unable to set the Nest thermostat up as a dual fuel system or else I wouldn't have an issue.

     Is there a way to disable heating stages 1 and 2 and just run stage 3 when temps are too low for the heat pump system in the scenario I provided above?  There are specific system details on my second reply above.

Thank you,

Jason 

[pereztzum]

Hi there!

Thank you for providing detailed information about your heating and cooling system. 
I understand the complexity of configuring a Nest thermostat with a 3-stage heating system and a heat pump. I apologize for the article shared that did not give you any answers, and I appreciate your effort. To provide the most accurate assistance, please answer the following question:

• Which type of fuel do you have?
• How is your thermostat set up (about wires)?
  • Can you provide me with a picture?

Please keep me posted; I will be more than happy to assist you.

Regards,
Brandon.

[654Waites]

Hi Brandon,

     I figured out how to use the dual fuel settings with the Mitsubishi pac44 thermostat interface.  I needed to install a double pole double throw relay in between both systems, wire the Nest as a two stage heat pump system with an auxiliary stage of heat and wire the interface board conventionally.  The o/b terminal will switch the relay between the stages of heating or cooling dependent on what is needed.

thank you