One Mini-Split or Two?

[Supervstech]

Any insight into some saying that when just one zone is on, all zones cycle the coolant and this it uses much more energy than if it was a single unit with the one zone on?

Most have solenoid valves isolating the refrigerant to the inactive systems.

 

[Madcodger]

Any insight into some saying that when just one zone is on, all zones cycle the coolant and this it uses much more energy than if it was a single unit with the one zone on?

I can tell you this... We have a Daikin with two indoor "head" units in a studio apartment with a very open floor plan, 1,176 SF. One unit is in the living room area on one end of the building, the other (smaller) head unit is in the bedroom. It does a great job heating and cooling the building, here in Maine, where it gets pretty cold. We usually leave the bedroom head unit off unless it's hot out and we're using AC, as we like the bedroom cooler than the rest of the house. So, in the winter when we're in heat mode, the bedroom unit, when off, often makes a sort of thermal expansion noise "clicking" sound unless we turn it on, which immediately makes the noise stop. The only explanation I have is that the refrigerant is circulating up to and around that head unit. It's pretty darn aggravating, frankly, as it often results in us turning on that unit when we don't wish to do so. We're building a new house that will utilize mini-splits. They won't be Daikin, and each will be a single head unit.

 

[DrZ123]

I can tell you this... We have a Daikin with two indoor "head" units in a studio apartment with a very open floor plan, 1,176 SF. One unit is in the living room area on one end of the building, the other (smaller) head unit is in the bedroom. It does a great job heating and cooling the building, here in Maine, where it gets pretty cold. We usually leave the bedroom head unit off unless it's hot out and we're using AC, as we like the bedroom cooler than the rest of the house. So, in the winter when we're in heat mode, the bedroom unit, when off, often makes a sort of thermal expansion noise "clicking" sound unless we turn it on, which immediately makes the noise stop. The only explanation I have is that the refrigerant is circulating up to and around that head unit. It's pretty darn aggravating, frankly, as it often results in us turning on that unit when we don't wish to do so. We're building a new house that will utilize mini-splits. They won't be Daikin, and each will be a single head unit.

Good to know! I am considering the MrCool or EG4 DIY units as my home is on an inaccessible island so I see advantages of 1. Not having to hire a likely expensive HVAC tech to do the job and 2. Having intimate knowledge of the system as I'd be installing it

Sounds like single head is the way to go although I don't live the idea of 3-5 outdoor units!

 

[Quattrohead]

I'm sure you could get creative with some metal work and stack two together or maybe find a place up on the roof out of the way.

 

[Madcodger]

Sounds like single head is the way to go although I don't live the idea of 3-5 outdoor units!

I feel your pain. But I'm gonna do it anyway. The clicking noise is soooo aggravating (and multi-heads are less efficient, too).

 

[n2aws]

Besides that you only have one condenser for the multi split units, are there other downsides?

I have seen mixed reviews on if the multis use more energy if only one zone is on, vs a single zone unit?

I likely will need 4 zones and to have 4 outside units is a lot...

If I were in your shoes and needed 4 heads, I'd consider doing 2, 2head units. You have less to install outside (appearance and labor), but also you get the redundancy of.. if an outside unit fails, you have the other to fall back on.

I'd probably try to have it laid out so that 1 head from each outdoor unit, cooled a space that could be isolated. That way, if there was a failure, you could still keep (for example) a bedroom cool, just by closing it's door. Or an office cool, just by closing it's door.

Lets say I'm doing 2 heads in a "common" area (living room/kitchen/dining area). and then 1 head in each of 2 bedrooms, what I'd likely do is:

Unit A, 1 head in living room, 1 in bedroom A
Unit B, 1 head in living room, 1 in bedroom B.

Now, no matter which outdoor unit fails, I could sleep in comfort in either bedroom A or B. Additionally, since this is a solar forum.. Assuming you have batteries, you can potentially connect one of these units up to be powered as a critical load when the power is out, and still sleep in comfort.

Anyway, this may not entirely fit your use-case, but it's what I would consider doing.

 

[Frank in Thailand]

We live off grid and have 5 x 8500btu Daikin units, they can only cool
Price in Thailand $400

SEER of 23. Something, not bad at all
Also de reason to get smaller units as the bigger ones where hardly scratching the 20 rating (4-5 years ago)

Two in the living room, bedrooms, hobby room.

Insulation of a house will determine how much BTU you need.

8500 BTU on 32m2 room was enough to cool at +42c down to 26c..
For our good insulated house.

Yours...
Don't know.

As many have stated, multiple smaller units are cheaper to buy, easy to install, and have higher efficiency per unit.
Besides this, you don't need to turn them all on

Installation is simple.
You don't need expensive HVAC installer.

Will made a great video about it.

And it really is that simple.

Tips:
- use nylog or loctite blue
- absolutely vacuum pump and vacuum test. (If you didn't make a good tight connection with the flares, the vacuum test will show)
- let the vacuum pump run at least 15 minutes, close the valves, stop the pump and wait 30 minutes to see if the vacuum drops.

- when all is OK, the line staying vacuum, open the large tube first.

If you would do the small tube first, you drain the compressor from refrigerant oil.
Not a really huge problem, it won't break, but it's better to have all parts lubricated

Vacuum pump, $100 bucks, money well spend.

If you hang the outdoor unit on a wall...
It will make vibration noises.
Depending on your house, that can be a lot (!!)

When on a concrete slab, use some rubber dampening feet.

As long as you don't need to extend tubes, brazing and such..

Absolutely easy.

If you do need to extend..
Study a lot on YT.
CO2 and silver solder. Regular solder isn't strong enough for R32
And without CO2 you get gunk in the lines that will kill your system in a few years. (Or months)

I was surprised "is this all there is to it?"

That easy

 

[Aridom82]

Today is a very hot day here, so i am measuring what my system is doing, take this as an example.
Two Mitsubishi Kirigamine Style 9000 btu each are keeping 16° C degrees difference temperature using 940 watts in total, 2000sqft appartment good insulation.

 

[Supervstech]

I can tell you this... We have a Daikin with two indoor "head" units in a studio apartment with a very open floor plan, 1,176 SF. One unit is in the living room area on one end of the building, the other (smaller) head unit is in the bedroom. It does a great job heating and cooling the building, here in Maine, where it gets pretty cold. We usually leave the bedroom head unit off unless it's hot out and we're using AC, as we like the bedroom cooler than the rest of the house. So, in the winter when we're in heat mode, the bedroom unit, when off, often makes a sort of thermal expansion noise "clicking" sound unless we turn it on, which immediately makes the noise stop. The only explanation I have is that the refrigerant is circulating up to and around that head unit. It's pretty darn aggravating, frankly, as it often results in us turning on that unit when we don't wish to do so. We're building a new house that will utilize mini-splits. They won't be Daikin, and each will be a single head unit.

Odd.
Most daiken units that I install have isolated circuits with solenoids.

 

[Madcodger]

Odd.
Most daiken units that I install have isolated circuits with solenoids.

Well, I wish you had installed ours! It's really aggravating. If a solenoid were stuck open, would that cause it to behave as described ?

 

[sunsurfer]

Its nice to have redundancy for when one fails. Thats why they call them mini-splits and not whole house splits.

 

[adobopr]

I'm getting here a bit later and haven't read everything before, but I do know a bit about ACs.

First of all, you absolutely want an inverted based AC. They will save you a significant amount of energy and provide a most consistent cooling experience. I read that you said that 240V ones are more expensive than 120V ones, but where I live it's the exact opposite. At least here in PR, you can get a 12k BTU 20 SEER inverter AC for $600 and that includes installation.

I don't know anything about this new SEER2 rating, but SEER (1?) is pretty straightforward.

You can easily calculate how much energy the compressor consumes with the SEER rating by dividing the BTUs of the unit by the SEER rating, so a 12k BTU unit at 20 SEERs is 600W for the compressor at full blast. The rest of the unit does consume power too, so it will probably be around 650W-700W at full blast. When the unit starts what I call inverting (I know it's not accurate but whatever) you will see a reduction in power consumption. In my house when my 12k 20 SEER ACs start inverting, they can get down all the way to 300W consumption.

In my experience, the higher the BTU rating the lower the SEER rating, so it's usually more efficient electricity wise to get multiple units. You also get some redundancy.

In terms of oversizing from 9k to 12k, I would go ahead and get the 12k. They tend to be more common and with an inverter, it will just throttle down quicker. You should not see significant differences and it will cool down the room faster.

Hopefully this was useful.

 

[Samsonite801]

Besides that you only have one condenser for the multi split units, are there other downsides?

I have seen mixed reviews on if the multis use more energy if only one zone is on, vs a single zone unit?

I likely will need 4 zones and to have 4 outside units is a lot...

The biggest drawback I saw when I installed a Mr Cool 4-head (34k outdoor unit) setup for my brother-in-law's house, was that his upstairs gets really hot, and his downstairs is generally naturally cooler a lot, so when this is occurring, Mr Cool set to 'auto' mode, the 2-heads (each 9k) upstairs are commanding cooling, while the downstairs 2-heads (each 12k) are commanding heat, so since the multi-system cannot do heat and cooling at same time, the auto mode has to gang fire (round-robin), run heat for 50%, then switch to cooling for 50% of the time, and then it doesn't always keep up (it is an older house built in the 30's or something).

My first thought is, if I ever did a multi-system in the future, I would've done one 2-head multi for upstairs, and one 2-head multi for downstairs, but every floor (with such drastically different micro-climates) should have their own outdoor unit.

But beyond that, I like the idea of not having a single point of failure (better redundancy) to have one-to-one, indoor-to-outdoor, or floor-to-floor at least.

 

[Madcodger]

Just a quick observation to add about portable units, discussed earlier in this thread. We have a small 10x20' building with 2x6 walls, mineral wool insulation to about R21. R38 in the ceiling, R20 in floor. We use it as an exercise studio. Because it doesn't get terribly hot here in Maine, we purchased an 8K BTU Black & Decker single-hose portable unit for it. What a waste of money. Took up a huge amount of floor space, ridiculously loud, and struggled to keep the building at 74, our desired temp. We had an older 6K window AC we weren't using, so I stuck it in a window of the building and removed the portable. It's been fantastic. Cools the room easily, and is a bit quieter than the portable, although nowhere near as quiet as a mini-split. That building has propane heat, but we may install a mini-split in there next spring. But a portable? Oh, no, no, no. Never again if there's another option.

 

[DrZ123]

The biggest drawback I saw when I installed a Mr Cool 4-head (34k outdoor unit) setup for my brother-in-law's house, was that his upstairs gets really hot, and his downstairs is generally naturally cooler a lot, so when this is occurring, Mr Cool set to 'auto' mode, the 2-heads (each 9k) upstairs are commanding cooling, while the downstairs 2-heads (each 12k) are commanding heat, so since the multi-system cannot do heat and cooling at same time, the auto mode has to gang fire (round-robin), run heat for 50%, then switch to cooling for 50% of the time, and then it doesn't always keep up (it is an older house built in the 30's or something).

My first thought is, if I ever did a multi-system in the future, I would've done one 2-head multi for upstairs, and one 2-head multi for downstairs, but every floor (with such drastically different micro-climates) should have their own outdoor unit.

But beyond that, I like the idea of not having a single point of failure (better redundancy) to have one-to-one, indoor-to-outdoor, or floor-to-floor at least.

That makes sense. For my purposes, this is a summer cottage so it will be 95% for AC, I can't really ever see needing heat at the same time as cooling.

 

[740GLE]

Another work around is leaving the head units in all Cool or Heat with fans in auto. The hot room will get cooled and the cool rooms will just throttle down to nothing.

If it’s from May thru September, they’ll all be on cool, I have no issues if one is cooler than another, I won’t need hear anywhere. In the spring/fall months I’ll just run heat on the first floor only let it rise up stairs.

 

[robby]

Get multiple Condensers and eliminate future headaches. Eventually the Condenser will fail and it typically happens when you’re having an extremely hot day or month.
Those are the times when everyone is out of stock and your HPVC guy is overloaded and has stopped answering his phone.

 

[forbin]

Not to derail but I'm very curious about this. Are you totally off grid? How has the freeze drier worked in this situation? How big of a draw is it? Thx

We're totally off grid, but we haven't tried freeze drying anything yet.

 

[forbin]

What I was going to say before my wife grabbed my phone and posted in a childish manor (because I spend too much time, here)

Was that our mitus triple head unit only opens a valve if the room unit is on, and the compressor only runs enough to maintain adequate pressure for the load. When the room unit is just trickling in the cold air, if you’re quite enough you can hear it cycle ever so small amounts to maintain temp.

Your wife is a hoot. Hang onto that lady.

 

[forbin]

Today is a very hot day here, so i am measuring what my system is doing, take this as an example.
Two Mitsubishi Kirigamine Style 9000 btu each are keeping 16° C degrees difference temperature using 940 watts in total, 2000sqft appartment good insulation.
View attachment 164121
View attachment 164122

I love that power consumption!