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Old 05-04-20, 04:50 PM   #11
Mikesolar
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Quote:
Originally Posted by Mountaintop View Post
Mikesolar - I would be interested in seeing your setup on how you connected the Fujitsu to a storage tank. Are you using the lineset to steal heat from the system when in heat mode or did you put a heat exchanger on the discharge of the compressor? What water temperatures have you attained? What have you been using the water for?

Thanks,
Matt
For my test rig, I sized a flat plate heat exchanger to the output of the HP and I have a pump with a flow meter so I can get proper readings. I am using the indoor coils electronics but changing the thermisters to fool the control into thinking it is heating 21C air when in fact it is heating 40C water. I am then pumping the water to 2 old cast iron rads in my shop. It has been working perfectly for the last 2-3 months. Next step is to make a control that allows me to get rid of the indoor unit electronics. So far, BTW, the COP of the system has been around 3.5.

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Old 05-06-20, 10:06 PM   #12
Mountaintop
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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.
-Matt
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Old 05-07-20, 06:27 AM   #13
Mikesolar
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The thing I like about these units is that all the vital HP functions are in the outdoor unit and only the commands for the indoor temp measuring is on the indoor unit.

Currently, I just have the motor sitting on top of a 5gal water heater (in series with the rads) which functions as a table to hold the electronics and something to put sensors and valves on. The motor just tells me when the outdoor unit is on and its speed is a bit of an indicator of compressor speed (not very accurate).

I have not disconnected it because the lack of feedback from it would cause an error code.

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