Dual fuel control for Mitsubishi heat pumps

dr_c

Last fall I had Mitsubishi heat pumps installed for air conditioning and efficient heat - an MVZ-AA7, MSZ-GL and two MFZ-KJs - complementing an existing 3-zone modern Bosch greenstar hydronic baseboard propane boiler system. In the winter, I primarily use the heat pumps for heating, but when the temperatures get below 10F, I would like to automatically switch from the heat pumps to the boiler.

What are thoughts on the easiest way to accomplish this? Using Kumo Cloud would seem to work (with a Kumo station to override calls for heat above a given temp) - but then I'm still keeping separate thermostats for both systems. Not very slick looking but could work.

One of my Mitsubishi units already has the MRCH1/MIFH1 RedLINK remote control system – If I upgraded all the Mitsubishi controls to RedLINK controls, could I use something like a Honeywell HZ432 panel to manage the system?

Thanks for your experience.

Best,

Dr.C.

HVACNUT

You might need to call Mitsubishi on that one.
A zone board might work if the Mitsubishi controllers are hardwired 24v AC.
If so, the ductless system and the boiler zones will need isolation relays because the thermostat inputs on the zone board only accept one 24v power source.
W1 for the ductless, W2 for the boiler. Each thermostat must be 2 stage heat. The zone board also needs a dedicated 24v, 40va transformer.
If the thermostats are being programmed to energize stage 2 at set temperature rather than a differential, I'd add antifreeze to the heating system.

hvacfreak2

The number for the conventional interface is PAC-US444CN-1. You could use a dual -fuel tstat to change-over from Mitsubishi to zone - valve on each ( I've heard good things about Ecobee products for small remote management ).

dr_c

Thanks for the comments. Actually, I almost (technically did) put one of those PAC-US444CN-1’s on order - before I realized a major problem; That interface allows for the use of a conventional thermostat control, not heat pump control - and when a Honeywell, Nest or Ecobee thermostat is set up for conventional operation, the capability of calling for dual fuel backup heat is not available. I’m guessing I could use a DPDT relay to convert O/E & Y1, Y2 into Y1, Y2, W1 & W2, but that is only a guess... frustrating.