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Old 03-20-17, 04:31 PM   #1
ChetT
Lurking Renovator
 
Join Date: Sep 2014
Location: CA
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Default adding Mini split to under floor radiant

Well this forum has been an interesting read. I hope you can help me with some informative comments regarding my project.
I have a small (1300 sq ft), two story farmhouse. Crawl space under the main house and a root basement under the kitchen. It has never had central heat or insulation. In the long ago past heating was done with wood stoves in the kitchen, middle room and living room. The 2 upstairs bedroom were heated using floor grates through the first floor ceiling. Today there is just one working wood stove in the kitchen.

The place was gutted last year. I’ve insulated the place and installed radiant tubing under the floors of both floors (I hate baseboard heat). For a variety of reasons electricity was the only choice for the heat source for the hot water. I love radiant heat but an electric boiler is not the most economical choice so I use the wood stove in the kitchen as much as possible.

I have a utility room above the kitchen that contains the water heater and the radiant system distribution components. I have installed a 1200 cfm fan in the utility room and it is setup to take air from the second floor, push it through the kitchen, through the downstairs rooms, up the front stairs, through the bedrooms and back to the utility room. The kitchen stove has plenty of heat output; I just needed to spread it around to the rest of the house.

So this is OK. When I’m burning wood t he stove does the bulk of the heating and the radiant keeps the floors warm. However if I’m not using the stove then the heat is all from the radiant which is 100% electric resistive. Fortunately the price of electricity is pretty good in the area but I’d sure like to reduce the cost.

I’m thinking of putting a single zone mini split in the utility room and use it as a heat source similar to the way I’m using the wood stove, i.e. circulate it around the house with the ventilation fan. That all seems pretty straight forward but here’s the part that I’d like to discuss.
The mini split has an outside unit that will connect to the inside head located in the utility room. I’d like to put a refrigerant to water heat exchanger in my radiant heating loop and use the hot output from the minisplit. I see the hot fluid coming out of the outside minisplit unit going into the HX in the radiant loop and then out of the HX and into the inside head unit for the minisplit and then back to the outside unit. I’d leave my existing electric boiler in place to act as backup or for supplemental on real cold nights.

Some questions I have…
What is the output temperature range from the minisplit?

Does it vary significantly at lower ambient temperature ?

What happens at the HX in the summer if I switch to cooling?

The inverter unit I am considering has a single control line that connects the head unit to the outside unit. The schematic indicates that there is one signal line between units. I assume that the head unit receives a signal from the remote and controls the outside unit based on the input. I assume that the signal line must control the compressor on/off and heat/cool. I might try to hijack that signal line and do my own control but I don’t know the protocol. If it’s just a matter of 4 different voltage levels then that would be pretty straight forward but if it’s some kind of pulse train it becomes more problematic. Any insight into this signal line would be appreciated.

I’d love to hear from this group on any critiques or advice or precautions. Thanks

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