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Robaroni 10-14-17 07:59 AM

Mini split for heating only
I have 10.6Kw of PV and I want to add a mini for my great room (26' x 26'). I figure my PV will cover the mini during the day plus sending power out to the grid. At night I'll use the grid to run my mini. I live in a cold climate and don't need cooling so a heating only unit is fine.

Any recommendations for the best mini for this application?


jeff5may 10-15-17 08:24 AM

The manufacturers in general design different unit for different regions or climates. If you are searching for a model that has a distinct energy advantage in the winter season, you have your work cut out for you. Regardless of the sales brochures' claims, the air-source units all suffer when the mercury drops. The older cap tube metered systems had a more or less linear COP and BTU output that corresponded directly with outdoor temperature. With the newer EEV metered systems, this is not so much the case any more.

The newer systems are much smarter in their operation, and they switch operating modes when it gets cold outside. How they do what they do really depends on how the manufacturer programs the control board. As always, the more expensive units in the lineup are programmed to behave more aggressively and/or have increased functionality versus the more economical units. Some of these units have the same guts in them, and the control board program is the only real difference in the design of the model. Naturally, the more robust unit will have a remote control with more buttons on it, and a more stylish indoor unit to look at.

There is an increasing trend among manufacturers designing units that perform much better than the old-style units in very cold outdoor temperatures. These units pretty much all have variable speed compressors in them, and operate on two basic platforms. The super turbo models sacrifice overall energy savings to provide rated BTU output when it is frigid out. They do this by spinning the compressor as fast as it can to boost head pressure. The more advanced models have a dual-stage compressor in them, with some sort of intercooler between stages. They switch compression ratio when it gets cold out, allowing the compressor to change its operating parameters to fit real-world conditions. The electronic expansion valves in the rigs take care of the refrigerant metering side of the circuit in both types of model, extracting as much heat as possible from the outdoor air.

A good few of our fellow ecorenovators have expressed their satisfaction with Gree units. The cold climate, sub-zero operating, variable speed unit they offer is the Crown series. The Terra series is also a variable speed inverter, but it doesn't dig so deep into the negative temperature zone. Gree makes other lines, but they are geared more for air conditioning mode, and may actually stop heating completely when the temperature drops, due to automatic low ambient cutout.

Naturally, if you have the means to install a water or ground source unit, the efficiency is not going to suffer when it gets cold outdoors.

ecomodded 10-15-17 11:00 AM

Thats the type of unit I need although Price matters to me so I will likely get a ebay Senville model when its time.I say I need it as Im not worried about cooling. If the Gree was not much more or the weather especially brutal I think it would be worth the extra money for the cold model.

It would help you size the unit right instead of buying over size for a few cold months.

Robaroni 10-16-17 09:43 AM

Thanks for the help.
Several factors are taking place here. First I'm trying to reduce heating oil as much as possible. The other thing is my grid intertie power. I have been notified by my electric coop that ~ 2020 when my contract runs out they will switch me from the ~10 cents a kWh to what they pay for power to ~3.5 cents. At this point I want to utilize as much of the energy I make as I can, if that means turning on oil filled radiators than so be it. As of now my EV charges for free and I'm about 7 to 8 hundred dollars ahead on my electric bill but I have no intention of selling power back at 3.5 cents a kWh even if I have to open my house to an EV charging station!

pinballlooking 10-16-17 12:58 PM

Take a look at this Gree Crown
It seems like it would meet some of your requirements. Heat down to -22
And these units are not as costly as a couple of the bigger names
Crown | Gree Comfort

I have three of the Terra systems and have been happy with them but they donít heat below 5 dredges F

The Gree Crown would be better for you and that is what I would buy today if I needed one.

Here is a DIY install of one.

Robaroni 10-16-17 05:45 PM

Rich did a really nice job. I plumbed my house and wired it but I may be over my head installing a large unit like his. I don't have some of the gauges and tools he used.

pinballlooking 10-16-17 06:20 PM

What size do you need?

You can do it.

They come fully charged. You just need to pressure test them and vacuum them down.
Here is how I did mine. I had never done any of this before
My tools.

Another Rich installs. Very useful.

Robaroni 10-16-17 07:38 PM

My room is 26 x 26 but here's the thing, I already have radiant in the floor so this will just run the house most days when the temps are above, say, 30F. I don't mind if the oil kicks in once and awhile when it gets super cold. I'm thinking 9 to 12k.

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