Mini-Split AC: How Much Additional Electricity Use ?

[albert436]

Maybe I will start a new thread for the question I have on this topic.

My mom's house is ~2800 square feet, and is located in San Diego East County. (It gets hot!) It has open beam cathedral ceilings. The roof has thick composition tiles with a layer of that insulation board that looks like styrofoam sandwiched between two layers of tin foil, basically.

If I put a mini-ductless split inverter system in her house (4 bedroom, 3 bath, 2 largish living rooms, dining room), how much additional electric usage can I expect to have per month/year ? (I mean using the A/C liberally.)

I anticipate going with a mid-range efficiency system, like in the 16 - 18 range just due to cost considerations. This is off the top of my head since the last time I looked at the systems online.

Can anyone give me an idea on this?

Thanks!

[mungosocal]

Any particular reason you're looking at mini split versus a conventional system?

[albert436]

In order to be able to cool individual rooms for one thing.

[mungosocal]

Get some quotes on the mini split system vs central. I had thought I wanted mini split as well, and instead went with a new central unit with all new ducting and in a new attic location for about 12k. A bit smaller house.

Personally I think it would be nuts to go heavy on the AC and add a solar power system sized to sustain it without first having done something to improve the insulation of the house. That said, I would guess you are looking at an extra 600-900 kwhrs monthly for up to six months of the years. Depends on how liberal the AC use would be, and just how leaky the house is. And the issue about only cooling certain rooms adds a ton of variability to the equation.

[albert436]

Thanks MSC, great minds think alike, as the saying goes. A couple of years ago I had all her "regular size" windows replaced with dual paned. She's got a couple of pretty largeish picture windows that would be prohibitively expensive to replace so we left those alone, but she's got some shades she can roll down outside of them, which helps some.

A year+ ago a reputable local company came out to look it over and said the original ducts were actually undersized and would need to replaced in any case to do any sort of retrofit A/C job.

Funny this just jogged my memory about how when I am driving my mom somewhere, I always want the AC turned up and she always wants it turned down, lol, well she's 90 and her metabolism is likely running a bit slower than mine.

Just getting that ballpark is very helpful and I do appreciate your input. Certainly haven't ruled out going to a central AC/heat pump system but looking at all the options, including "self-install" of a few individual room ductless units to start with. We had to run new electric out to the pool and in the process took power around the back of the house where we will need it and also put in a subpanel back there.

Yeah, it's complicated ! Trying to kill three birds with one stone as it were.



Thanks again for your response though, very helpful as a place to start !

[Bill SEPA]

Solar PV then AC/heat pump mini split

I did this and learned a few things.

First I got the PV and wiped out my electric bill - YAY!!

Then I realized that I could convert my winter time heating (Fuel Oil Boiler) to electric using a mini split primarily for the shoulder seasons and to take some of the heating load during the peak winter (Jan/Feb).

Well here is how it worked out......
My electric use was HUGE and almost doubled what I had previously wiped out with the PV. BUT I was still saving money over the price of #2 fuel oil. So now I am looking to add more PV to cover the wintertime use of the mini split heat pump.

The benefit of the mini split for me is zoning. I only heat and cool the rooms that I am using rather then central air/heat.

Hope this helps.

[Naptown]

I did this and learned a few things.

First I got the PV and wiped out my electric bill - YAY!!

Then I realized that I could convert my winter time heating (Fuel Oil Boiler) to electric using a mini split primarily for the shoulder seasons and to take some of the heating load during the peak winter (Jan/Feb).

Well here is how it worked out......
My electric use was HUGE and almost doubled what I had previously wiped out with the PV. BUT I was still saving money over the price of #2 fuel oil. So now I am looking to add more PV to cover the wintertime use of the mini split heat pump.

The benefit of the mini split for me is zoning. I only heat and cool the rooms that I am using rather then central air/heat.

Hope this helps.

Zoning is great in that instance. But to get the greatest gain from it would need to insulate between the zones.
Not easy to do in an existing house.
When I built a house for my parents 40 years ago they elected to install electric baseboard heat.
We did insulate interior walls around rooms that may not be used. (Spare bedrooms)

[albert436]

Thank you gentlemen, that is very helpful.

I think we are in a somewhat milder climate than both of you, at least in the winter time.

I would anticipate most of the added expense being in the summer for air conditioning use.

Bill does your system also provide AC, or do you even need it where you live ?

[Bill SEPA]

Thank you gentlemen, that is very helpful.

I think we are in a somewhat milder climate than both of you, at least in the winter time.

I would anticipate most of the added expense being in the summer for air conditioning use.

Bill does your system also provide AC, or do you even need it where you live ?

Yes it provides zoned ac and heat
Today is 90 degrees and humid. The mini split is keeping the house nice and cool.

[albert436]

Thanks Bill.