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Old 05-06-20, 09:06 PM   #12
Lurking Renovator
Join Date: Aug 2018
Location: Upstate NY
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Very nice idea! I install and service mainly Mitsubishi and Fujitsu mini splits for my own business and work as a HVAC tech at a local college. I plan to interface a unit with my radiant heat system at my home. We currently have a propane boiler which has been pretty much shut down since April 2009 when I installed two Mitsubishi FD12 units and upgraded the outdoor units with the FE12 controllers so base heaters could be installed to control ice buildup. One indoor unit is located in the basement and another one on the main floor. Being rated at 12,000 btu cooling, we can typically get over 19,000 btus of heat from the indoor units when it is 0F outside and run the temperature set point up so it runs at maximum capacity.

Our basement radiant floor tubing is in a well insulated concrete floor so low water temperatures would be perfect for that application. Since the indoor unit control boards monitor fan motor operation, what did you use to convince the control board there was an operating fan motor? I know depending on the model, some control boards look for a pulsed signal which is representative of fan motor RPMs. Sounds like you are in the process of identifying the communication protocol signals between the indoor and outdoor unit. I do like the idea of using a controller to take the place of the indoor unit control board, that would allow for better tailoring and control of the system. From my experience the RLSH Fujitsu models have slightly better performance at lower ambient temperatures than the Mitsubishi FE and FH H2i series, but both units are excellent.

Have you noticed any different characteristics when the unit goes into defrost? I bet the outdoor coil melts off fast with that warm water circulating through the flat plate heat exchanger, and since you are using high mass cast iron radiators, I bet you never knew the defrost took place since you were probably radiating heat the entire time.
Please keep us up to date on your control system project.
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