ductless mini split heating and cooling

[folivier]

As I understand it, mini split compressors are always running and the compressor speed (output) is variable from barely on to full capacity. This allows the mini split to continuously circulate the air rather than how a conventional unit comes on full capacity then shuts off. The temperature varies by a couple degrees each time this occurs. Additionally there is some efficiency boost by having a DC motor rather than an AC motor. The SEER values for some mini splits are rated much higher than conventional units.
Another feature is by having multiple zones that can be controlled differently. Not sure if this would apply to a large mini split that uses existing ductwork.
And they are very quiet inside and outside at the compressor. My son just installed one in a master suite addition and you can't tell it's running.

 

[skyking1]

I did two 120 volt units based on existing spare breakers and wire. I'd not hesitate to run a 230 volt, but the two 120V units do the whole home nicely.

 

[calmloki]

As I understand it, mini split compressors are always running and the compressor speed (output) is variable from barely on to full capacity. This allows the mini split to continuously circulate the air rather than how a conventional unit comes on full capacity then shuts off. The temperature varies by a couple degrees each time this occurs. Additionally there is some efficiency boost by having a DC motor rather than an AC motor. The SEER values for some mini splits are rated much higher than conventional units.
Another feature is by having multiple zones that can be controlled differently. Not sure if this would apply to a large mini split that uses existing ductwork.
And they are very quiet inside and outside at the compressor. My son just installed one in a master suite addition and you can't tell it's running.

We noticed a huge difference in electric bills after changing our pool pump - which ran full tilt boogie or not at all - for a variable speed pump. With pools you want a certain number of water exchanges through the filters each day and it is much less work for a pump to push water at a low speed and pressure for a longer period. Less work=less electricity and cost. A variable speed mini-split conditioning a targeted smaller area is heating or cooling less. Cheaper.

Location of ducting and loss to surrounding air doesn't seem magic. If the ducting is all inside a conditioned space - eh, who cares if it loses heat or cool. If it is flexi-duct up in the unconditioned attic it has about a 1/3 of the insulation the ceiling does and the temperature differential when flowing is much greater than from room temp to ambient. Loss/waste seems natural.

 

[folivier]

There are breakers that have 2 connections and the same size as a standard breaker. That allows you to add additional circuits, assuming you have the amperage capacity.

 

[OldShooter]

Can someone explain this? I keep hearing that mini-splits are more efficient (and not just to any supposed loss in the ducts, but that actual compressor efficiency). But I don't understand why this would be. They are air conditioners. ...

As I understand it the higher efficiency argument comes on the heating side, where the box is pumping the heat from outside into the house, not creating is by burning gas or electrical heating. I've been told that this is true down to about zero or -10F, at which point another heat source is needed. Electric baseboards for example.

As I understand it, mini split compressors are always running and the compressor speed (output) is variable from barely on to full capacity. ...

I don't think this is true in all cases. Our neighbor just added a maxi-mini-split on the side of his garage where we can see it from our bathroom sinks. The fan on that unit is either full on or full off. So I'm sure the unit is cycling.

 

[skyking1]

Our Pioneer units do cycle on and off, but it is slow ramp up on the compressor. Once it is going it can go faster and slower as needed. Inverters and DC motors are the bomb!

 

[Happyras]

I know lots of you have newer homes and was wondering if any of you have the ductless mini split systems for cooling and heating and what are your reviews on them. do you think they are better than the standard ducted system or less efficient and cost effective? thoughts?

Short answer, cost effective for isolated areas or for those who want to DYI, its much easier to install. Much more efficient for the money spent both with performance and duct losses. Cosmetically, if you can build new and conceal the line sets, great, but doing a retrofit the lines are exposed and should be covered.

Personally, if you want zone control, these are the way to go. Duct zone control gets pretty expensive to install control dampers and control wiring. you can be very efficient with zone control.

Well, I have installed a few full dual fuel HP/Gas furnace ducted systems, and my only issue has been calling a tech to do the vacuum draw down and silver solder the joints etc. However, now I have installed a few DIY type mini splits. My first was a MrCool 110v 12k for our barn apartment. Piece of cake to install, pre-charged line set, super easy and well made. Made in China is very typical for these, but the jury is out on life of the unit. I doubt the system is designed with all the protection features I look for in a condenser like a suction accumulator, but the controls seem very sophisticated.

I am in the middle of installing 2 systems 240v with 3 -12k indoor air units/system. Same brand, MrCool 36K. I looked up the data sheet on line, but it did not match the new design units I am installing at our DD. I was amazed that these have an HSPF of 11, and a SEER of 21.5, way more efficient than my central systems. They again, are a piece of cake to install with the pre-charged DYI line sets. Only issue I had was encountering the Aluminum wire in my DD Sylvania panel which was not installed with anti-oxidant grease. What a mess, they even paralleled 2 12 ga Romex wires to get a neutral, which is a big no bueno.

I intended to install these two on existing feeds from two prior hot tubs, now I need to run new wire which is a real pain. I hate aluminum wire, I have seen too many melt downs. Even poorly installed copper will arc and start fires, but with Aluminum it is just a matter of when.

 

[ERD50]

As I understand it, mini split compressors are always running and the compressor speed (output) is variable from barely on to full capacity. This allows the mini split to continuously circulate the air rather than how a conventional unit comes on full capacity then shuts off. The temperature varies by a couple degrees each time this occurs. Additionally there is some efficiency boost by having a DC motor rather than an AC motor. The SEER values for some mini splits are rated much higher than conventional units.
Another feature is by having multiple zones that can be controlled differently. Not sure if this would apply to a large mini split that uses existing ductwork.
And they are very quiet inside and outside at the compressor. My son just installed one in a master suite addition and you can't tell it's running.

Thanks, but that begs the question - why don't central units incorporate these features (outside of the zoning feature)? I had our HVAC replaced a few years ago at the previous house, went 2 stage, variable speed fan (the compressor was just two speed) and high efficiency - the outside compressor was HUGE, like a fridge but maybe shoulder high? It was really, really quiet. I could barely hear it right outside the window of that room next to it. If I stood five feet away, the neighbor's unit, ~ 25 feet away, was louder.

... Location of ducting and loss to surrounding air doesn't seem magic. If the ducting is all inside a conditioned space - eh, who cares if it loses heat or cool. ...

Yes, I think too much is made of this "losing to the ducts". If your ducts are well designed, there should not be any real issue there. Personally, I think building codes should outlaw ducts in the attic (or for areas where it is common to put the HVAC in the attic, have high level requirements for the insulation/leakage) and on outside walls.

-ERD50

 

[euro]

. Personally, I think building codes should outlaw ducts in the attic (or for areas where it is common to put the HVAC in the attic, have high level requirements for the insulation/leakage) and on outside walls.

-ERD50

I think you are overreaching a little bit on this as far as generalizing. For one thing, ducts can (and often ARE) be very well insulated, so heat/cool loss even in unconditioned attics or crawlspaces are minimal. Second, while you may be right that in Northern Illinois an attic HVAC system is more questionable, here in the mid-Atlantic/South, the climate is milder and attic ducting/airhandlers are EXTREMELY common (and quite efficient). If your house sits on a concrete slab, and you are not allowed to use attic or outside walls to route air ducts, then you are left with very, very few options....

 

[OldShooter]

... Personally, I think building codes should outlaw ducts in the attic (or for areas where it is common to put the HVAC in the attic, have high level requirements for the insulation/leakage) and on outside walls. ...[ERD50

Yup. And they should specify house paint colors, design of shingles, number and type of windows, ... Nothing should be beyond being controlled according to the taste of the code writers; cost-effectiveness and personal preference be damned..

 

[NW-Bound]

I am an empty nester with a two-story house, with 5 rooms upstairs unoccupied (1 room was my electronics hobby room, and the other 4 are guest rooms and storage).

I installed two Pioneer mini-splits for the ground floor: one for the living space and the other for the master bedroom. They have been working great, and the central HVAC is now unused, unless when I turn it on briefly to "exercise" it. Of course the room upstairs get abandoned to the heat or cold of the season.

Mini-splits with variable-speed fans and compressors are great energy savers. And they keep each respective area well ventilated for an even temperature. Yes, they are quiet, compared to my central HVAC.

The main reason for installing the mini-splits was to be able to power them with inverters running off solar+battery power. The large central AC would require a huge inverter weighing 200 lbs which can handle a surge load up to 36 kW. The cost was not the problem, but what turned me off was its idle consumption. With no load, this big inverter burns 180 W. That's 4.3 kWh/day, an awful waste.

As it turns out, the power from the solar+battery gets stretched further with the efficient mini-splits, and unless it gets very hot at 120F high, I have enough power to last overnight until daylight again.

I have been thinking about installing more mini-splits for upstairs, and perhaps removing the central AC, but I don't know if I want to work that hard.

 

[JP.mpls]

They are a reasonable option if you want to add heat or A/C and you don't already have ducts in the house or room. If you already have ducts, stick to a conventional system. Also, my experience is that these mini-splits, even the ones rated to -15 degrees F work better as air conditioners than they do as heaters when it gets extremely cold.

Freedom,
I just had a quote for installing one. The guy claimed they have a newer generation of the mini split that works way better as a heater.

I have an older version in my cabin that isn't very good at heating the place up. It works great as a ductless AC unit though.

My house has a boiler. I can't stand the looks of these things. I'm interested in the ceiling mount Mitsubishi units, but can't find anyone to install one.

Take care. JP

 

[wmc1000]

I had a 2 Ton mini split installed last year in my post frame workshop - 1800 SQ. Ft. with 12 ft ceilings.
Had no problem heating even with temps as low as 5 below zero and heating set at a toasty 72 degrees during the day and 62 at night. Unit will provide heat as low as -15 degrees.
Electric bill during the coldest month was less than $100 more than before.

 

[NW-Bound]

Location of ducting and loss to surrounding air doesn't seem magic. If the ducting is all inside a conditioned space - eh, who cares if it loses heat or cool. If it is flexi-duct up in the unconditioned attic it has about a 1/3 of the insulation the ceiling does and the temperature differential when flowing is much greater than from room temp to ambient. Loss/waste seems natural.

I think you are overreaching a little bit on this as far as generalizing. For one thing, ducts can (and often ARE) be very well insulated, so heat/cool loss even in unconditioned attics or crawlspaces are minimal. Second, while you may be right that in Northern Illinois an attic HVAC system is more questionable, here in the mid-Atlantic/South, the climate is milder and attic ducting/airhandlers are EXTREMELY common (and quite efficient). If your house sits on a concrete slab, and you are not allowed to use attic or outside walls to route air ducts, then you are left with very, very few options....

My central HVAC uses ducts in the attic. While it rarely drops to below freezing, and when it does it's only 1 or 2 nights each year, we get to 120F in the summer nearly each year. And when it's 120F in open air, in the attic it would be 150F easily, even with gable ventilation.

I once made an experiment in the summer. With the AC off but the fan on, I measure the temperature at the intake ceiling mounted filter, then the outlet temperature at the register furthest in the house. This was done when the ambient outdoor was about 110-115F, as I recall.

I was shocked to see a big difference. The temperature rise was more than 5 deg F. Is that the norm? I don't know.

I will wait till it gets hotter in a month or two, then repeat the measurements and keep better records this time.

 

[ERD50]

My central HVAC uses ducts in the attic. While it rarely drops to below freezing, and when it does it's only 1 or 2 nights each year, we get to 120F in the summer nearly each year. And when it's 120F in open air, in the attic it would be 150F easily, even with gable ventilation.

I once made an experiment in the summer. With the AC off but the fan on, I measure the temperature at the intake ceiling mounted filter, then the outlet temperature at the register furthest in the house. This was done when the ambient outdoor was about 110-115F, as I recall.

I was shocked to see a big difference. The temperature rise was more than 5 deg F. Is that the norm? I don't know.

I will wait till it gets hotter in a month or two, then repeat the measurements and keep better records this time.

That's gotta be a big hit on your AC (though I guess you are mainly using the mini-splits?).

If we assume the AC air is ~ 60F out of a vent not going through a hot attic, and you're trying to maintain, 77F(?) in the house, that's a 17F delta. So a 5F gain through the attic is 5/17ths, ~ 30%. That's a lot of lost delta, and extra AC run time.

I'd really want to get those ducts massively insulated.

-ERD50

 

[ERD50]

I think you are overreaching a little bit on this as far as generalizing. For one thing, ducts can (and often ARE) be very well insulated, so heat/cool loss even in unconditioned attics or crawlspaces are minimal. Second, while you may be right that in Northern Illinois an attic HVAC system is more questionable, here in the mid-Atlantic/South, the climate is milder and attic ducting/airhandlers are EXTREMELY common (and quite efficient). If your house sits on a concrete slab, and you are not allowed to use attic or outside walls to route air ducts, then you are left with very, very few options....

I thought I allowed for that when I said " (or for areas where it is common to put the HVAC in the attic, have high level requirements for the insulation/leakage) ". It's [-]never[/-] (almost got me!), rarely "one size fits all".

Yup. And they should specify house paint colors, design of shingles, number and type of windows, ... Nothing should be beyond being controlled according to the taste of the code writers; cost-effectiveness and personal preference be damned..

I hear ya, but things like this aren't so transparent to buyers. I'm really not a fan of regulation, but there is a place for it, and I think building standards are one.

If everyone had a good knowledge of best practices in structural, HVAC, electrical, roofing materials, plumbing etc, and could inspect all this on their own (nothing hidden under a foundation or behind a wall), maybe we could do away with building codes all together.

I don't think requiring very good insulation on ducts that must be run through attics in areas of other than mild climates is over reach, and probably not that expensive either.

-ERD50

 

[explanade]

Are these the systems you see in Europe, mounted high on the wall with a remote control?

Never seen them in the US though.

 

[NW-Bound]

Are these the systems you see in Europe, mounted high on the wall with a remote control?

Never seen them in the US though.

Yes.

They are popular in Europe and Asia, as they are easy to add on to existing homes.

Mini-splits are just catching on in the US, because we have a tradition of having HVAC which is a luxury elsewhere in the world.

It can be like the progress from landline telephones to wireless phones. Newer technology is cheaper, and often better.

 

[explanade]

Yeah I can see that the heating isn't as efficient because the hot air stays closer to the ceiling.

Some of them can have a rotating mode where the vents are moving up and down but you can't have the vents stay pointing downwards.

Some central air installations have trouble pushing up a lot of cold air upstairs.

That's where it might be nice to have one of these systems for the upstairs rooms.

 

[NW-Bound]

Mine automatically point the louvers downward more in heating than in cooling mode.

I use an infrared thermometer to compare the temperature at the crest of my vaulted ceiling (14 ft) to the temperature at ground level. The temperature differential is a lot less in the winter (2-3F) than in the summer (5F).

 

[explanade]

Hmm, I think cooling a high ceiling place is more difficult.

So you installed yours toward the top of the vaulted ceiling instead of say 8 or 9 feet high?

 

[NW-Bound]

Mine are mounted at about 10 ft high, on an interior wall. Due to the layout of the house, the drain lines need a long run over the adjacent garage attic to get to the outside. I want a good slope for drainage.


PS. The thermostat measures the temperature at the indoor air handler which is high-mounted. Cold air sinks. Therefore, I found that if I set the temperature at 79F, I get 76F at ground level. The top of the ceiling may be at 80-81F.

 

[folivier]

Living here in south Louisiana AC's are still being installed with the evaporator and ductwork in the uninsulated attic. The ductwork is made from 1/2" rigid insulating board (if that thick). And yes it gets hot here. So much that it's difficult to find anyone willing to work in your attic in the heat of the summer. When the AC starts up there is a brief shot of hot air before the cooled air comes out of the ducts.
But that's the way it has always been done. I hate when I hear that. The resistance to mini splits from the AC contractors is incredible. They hate them because of the ease of installation and they work so well. They can't overcharge customers like they can for a central AC installation.
My DS just had one installed in a master suite addition. I told him that we could install it ourselves easily. (I've done some AC work in the recent past and feel confident that I could do it) He had his AC contractor install it. It only took him 4 times to get it right. He made so many simple mistakes that the last time I was there watching him. When I saw the fitting that he had to cut out and solder in a new one I was amazed. It was twisted and leaking because he didn't backup the fitting he was tightening onto.
Years ago there was an AC guy in New Orleans that was advocating for building an insulated air conditioned box around the evaporator in the attic. He claimed the unit would last longer because of less thermal changes and would work less since it wasn't fighting against the extreme heat. The local AC contractors hated him and basically put him out of business. And they're still installing the evaps. in the attic!
Resistance (to change) is futile!

 

[freedomatlast]

Mine are mounted at about 10 ft high, on an interior wall. Due to the layout of the house, the drain lines need a long run over the adjacent garage attic to get to the outside. I want a good slope for drainage.


PS. The thermostat measures the temperature at the indoor air handler which is high-mounted. Cold air sinks. Therefore, I found that if I set the temperature at 79F, I get 76F at ground level. The top of the ceiling may be at 80-81F.

Fujitsu offers a remote thermostat/temp sensor that can be wired in for this type of situation.

 

[JoeWras]

I like them, especially for retrofit solutions, but they are not perfect.

My biggest complaint is lack of filter surface and options to catch dust and other things. This can be "fixed" with an auxiliary filter unit if it is a concern -- you know, one of those units you stick on a table or in a corner.

I have some experience maintaining minisplits and discovered some irritating issues. In certain conditions, they could get moist inside and catch dirt on the condensing moisture. This would eventually cause a disgusting black layer build up on some smooth internal surfaces. After a period of low use (spring/fall), the next time the fan kicked high, chunks of crap would fly out.

It is difficult to take apart and clean these areas. What I've read is that you can fix this issue by forcing the fan to run a bit higher or longer, which stops the internal condensation issue. Oh, and this is really only a problem in very humid areas like Southeast USA.

I think installers are learning how to deal with them. Like so many smart devices, there are a slew of configurations that must be done for a good install. Most of these are hidden to the end user. The defaults are not always appropriate for every application. Good installers know what to do.