Tell us layout of your home, main living areas...I assume cost is not a factor and you are not interested in forced air system that would require ductwork...the minisplit could be zoned for each area to be served. I would start by getting a mini split dealer out to your home for an evaluation. You need to qualify his experience with zoning. Keep in mind these inside units for mini splits can be objectionable visually for some homeowners.

IMO

Thank you, Franco, for pointing out some of the problems. I assume the HVAC contractor would take care of these things. All of you, remember my original statement that this is primarily for AC and the heating function is supplemental. All rooms have in-floor radiant heat, with (mostly) separate zones. The main part of the house is 28' by 58'; half of it is an open L-shaped vaulted ceiling area which includes the living and dining area, and kitchen. The other half has a loft over it and this includes the master bedroom and master bath, plus some utility areas. The HVAC contractor (who hasn't seen the house yet) thinks I might need three inside units; I was thinking of putting one where the words "stove pipe" are and two back-to-back in the kitchen/MBR wall. The stove pipe doesn't exist, because we didn't want a fireplace/stove.

Franco,

First you said:

When the temperature outside drops too low, it inhibits a mini split system's ability to function effectively.

then you said:

...but dramatic temperature drops can drastically affect a mini split's ability to heat and cool during winter months.

and finally you said:

If you live in an area that experiences frigid winters, you will definitely want to consider a heat pump mini split system

The first two statements contradict the third statement. Do you see a problem with this?

Mtvhike, I am not clear exactly what you mean by “loft” and
“utility space”. To me, loft generally
means living space that is a partial floor level open to another space that
covers more than one typical floor in height.
Utility is utility living space or utility like mechanical utility?

Is that stairwell for the, basement, loft, or both?

Think carefully about whether you want to discount ducts
completely. I think that one challenge
that you will have is fitting equipment to your low load. I see in your floor plans the possibility of
sticking a mini split horizontal AHU in some space in a closet or high in a stair well and supplying way
more than one area with minimal mess.
They go down to less than 10 kBTU. If
you can place some soffits in in a not intrusive way, you might be able to
supply the whole place from one AHU. If
you do have a basement, it could be very easy. This is coming from a high wall
mini split chauvinist. What I don’t know
is if those types of AHU and the vertical ones (that go down to one ton or
below) can work with the low temp outdoor units.

Are you anywhere near Fly Creek? I had some dealings with Bennett Sandler at
Equity Energy a few years ago and was reminded of his presence there by another
contact that knows him a couple of months ago. (It seems like Fly Creek is
turning into a busy place.) Equity seems to be expanding their scope. He seemed like a smart guy and might be of
help with this or other projects. (They will probably try to sell you some evacuated tubes to reduce your dependence on electric heat.)

I perceive this home to be a very quiet place and the sound
that even a relatively quiet AHU makes might drive you nuts so I guess you are
going to want to check on noise levels carefully.

Ionized, thank you for your thoughtful reply. I don't know where Fly Creek is; I'm in Essex Co. (NY) which includes Lake Placid and the shore of Lake Champlain, across from Burlington, VT. Sorry about the terminology regarding the loft. Everything not in the living/dining area and kitchen has a ceiling and the loft is above the ceiling. The edge of the loft is a low wall so most of it is open to the non-lofted space; it is reached by the ladder shown in this photo. Utility areas are closets, hallway, etc. The stairwell is down to the full, finished basement, where AC is not needed. There is a conventional utility room there. By AHU do you mean Air Handling Unit (the inside unit?) I was thinking about mounting one above the cabinet shown in the photo, another on the opposite side of the same wall (in the MBr), and, perhaps, a third in the more open area of the living/dining area.

I'm actually in the northeastern Daks. The HVAC contractor uses Fujitsu mini-splits. They actually are a commercial refrigeration company, but are willing to consider my project. They are located in Peru, NY, just south of Plattsburgh.

I see. You will be fortunate if the commercial outfit can follow through if they are exposed to a wider variety of equipment. I guess that they will be installing, in contrast, residential equipment. The commercial stuff does some neat things, but it costly. It does variable refrigerant flow (VRF). That allows you to move heat from one place in the building to another. In a home, for example, if you have one room warm, another other cool, and you need a little dehumidifying, you could run one unit in cool or dehumidify mode and another in heat with the same compressor. The outdoor coil could be put out of the circuit.

I think that as a schoolboy I was in Peru at least once. I grew up, however, on the other side of Fly Creek from there in a deep river valley in Chenango County. I tell people that it would be the bottom of another finger lake if the South end was stoppered up like some of the valleys to the West. It is a nice geologic perspective from a couple of angles. As you drive down them, you get a good feel of how deep some of those lakes are. In addition, how easily that particular and other valleys could have been lakes as you look at the river beside you and the hilltops high above. I guess the same thing could be said to the North and East where the glaciers scraped out valleys, but they look less like fingers.

“I have resistance heated in floor radiant heat, which works great.”

To be clear, is that electrically heated wires in-floor or an electric resistance heated hydronic boiler?

I think I know what you mean but don’t want to assume.

SR

I know the answer. I would not respond, but the question raises another in me. Why, mvthike, did you go w electric boiler hydronic rather than straight from resistance heat in the floor?

That's what the general contractor recommended. I suggested the resistance heater in the floor, but he rejected that. Can you embed resistance heaters in the concrete basement floor?

I’m STILL not sure what you have installed!

If it’s an electric hydronic boiler (heated water or fluid) what’s the spacing between the pipes, what’s the pipe diameter and type, what temperature must the fluid be as per specs, how deep are the pipes imbedded in the concrete, how thick is the slab, how’s the slab insulated from the ground?

SR

It's an electric hydronic boiler. I don't have the information about the pipes in the concrete; the first photo is of the pipes emerging from the basement floor before it was poured. The second photo is of the first floor installation, before the flooring was installed. The third is the entire heating system.

Walter, what you wrote seems to indicate that lower operating temperature requires a sacrifice in efficiency and vice versa. Are you sure that is true?

Mike, in a word, yes. My impression is that concrete slabs are recommended for electric resistance radiant heat because you can heat up the slab when rates are favorable and use less electricity when it is more costly.

I would suggest looking at this system to see if it would meet your needs and budget. It would provide your hydronic heat with a heat pump at a substantial energy savings and deliver hydronic air-conditioning as well, the indoor AC units would look similar to that of mini-splits. Your existing hydronic boiler would only be used for supplement backup during extreme cold spells or in case of heat pump failure, such as compressor lockout. It can also heat your domestic hot water with a similar energy savings as well.

This would be a great alternative to full geothermal that is also possible but at greater cost.

Nordic Hydronic Heat Pump - Heating & AC

https://www.nordicghp.com/product/nordic-products/air-source-heat-pump/air-to-water/

http://www.nordicghp.com/wp-content/uploads/2017/09/001848SPC-02-ATW-45-HACW-Two-Stage-R410a-60Hz.pdf

IMPO

SR

Interesting alternative. If the heat emitter system was not already in place, the lifetime costs would be pretty high compared to forced air. Since the superbly expensive radiant floor hydronic is already there, it changes things some, but it is still a lot more expensive than an air:air heat pump,. How does the cooling capacity:heat gain ratio compare to the heating capacity:heat loss ration in that cold climate? Is overcapacity in either direction a problem? I guess a buffer tank could fix some of that evil if it is significant. This looks like a VRF system so it can make DHW at any time, cooling indoor space or heating it pumping heat to indoors, outdoors or to the hot water tank.