Decision Regarding Mini-Split Zoning

[fireant911]

We are entering the heating/cooling stage of our garage and I need some guidance. There are three areas that we would like to heat/cool as part of this project - these areas are marked on the attached SketchUp drawing. The Garage Upstairs space has an area of 400 square feet (40' X 10'). The Connector (which will be our new laundry room) is 118 square feet (10'-3" X 11'-5"). The Sunroom is 476 square feet (44'-2" X 10'-9").

Our initial thoughts were to go with a conventional HVAC system but the Garage Attic space would not be able to be maintained very well without getting fancy with multiple thermostats. After some digging, it looked as if a multi-zone mini-split unit may be the optimal choice. Initially, I was considering a tri-zone, but given that the connector is just a laundry room it does not need its own zone and can be included as part of the Sunroom; therefore, a dual-zone may be our best bet (my hypothesis).

We received a quote from the HVAC person for $6,300 for a conventional HVAC unit and a $9,000 cost for a mini-split (no details were given regarding the size or number of zones)... but that is too expensive for our budget. In looking at the availability of multi-zone mini-splits, it appears that the labor portion is more than the cost of the units themselves! I do not want to get into a discussion about purchasing mini-splits on line because I have already read through too many of those arguments and seem to go on and on. I definitely will get more quotes but the consensus is, from what I have read thus far, the installation is often priced very expensively.

We live in Northeast Alabama. After looking at various sources, a 9,000 BTU (Garage Upstairs) ad 18,000 BTU (Connector and Sunroom) should work (taking in consideration our hot Alabama summers and the number of windows in the Sunroom). Since Inverters are present on practically all of the mini-splits, slightly over-sizing the Sunroof/Connector zone to 24,000 BTU's may serve us better (the Garage Attic is very well insulated and includes a radiant barrier so, I think, the 9,000 BTU is correct). Now my question is: are my assumptions regarding a dual-zone mini-split are correct?
Thanks,
Daryl G

 

[Highbeam]

Multi zone minisplits, that is multiple indoor heads on a single outdoor unit, are a bad idea. They are less efficient, cost more, and are harder to install than two single minisplits. You would be better served buying two minis. The smaller 9000-18000 btu units are plentiful with lots of great choices.

 

[theoldwizard1]

I'm no expert, but I would consider a separate unit for the Garage Upstairs. Because it is so long, it may require 2 interior discharge units to get reasonable heating/cooling across the length. If not, consider a ceiling unit with ductwork to both ends.

2 units may be more expensive to install, but will likely be less expensive to operate. You will save money on shorter line sets.

 

[BitChin1]

I would suggest individual mini-split units - much better efficiency and your install cost should be next to nothing (I know you will need to get several quotes to get there) - I installed 3 Mitsubishi 12k btu units and the install guys were only here for ~ 2hrs

You can have individual controll this way w/o complicated zoning and routing of lines.

 

[joe_padavano]

Multi zone minisplits, that is multiple indoor heads on a single outdoor unit, are a bad idea. They are less efficient, cost more, and are harder to install than two single minisplits. You would be better served buying two minis. The smaller 9000-18000 btu units are plentiful with lots of great choices.

Can you elaborate, please? I'm currently looking at LG Multi F and Multi V systems for an installation that would require five indoor units. I don't want five outdoor units. Also, the constraints of the project do not easily allow for ducting to reduce the number of indoor units.

I don't see installation costs as being any different, since I would have to run refrigerant lines to all five units either way. The LG distribution box actually reduces the amount of indoor line runs. I'd need five separate circuits for the five outside units vs. one for a Multi system. My estimate of parts cost is about the same either way. FYI, I'm using concealed ducted and all-in-one cassette indoor units, not the wall-mount style.

 

[Highbeam]

When you propose 5 !!!!! freaking indoor units then you've got bigger problems. Also, spec'ing out ducted and cassette units drives up the cost as well. Without better information I'd say you should consider a central, traditional, split unit.

Anything other than standard wall hung indoor units is getting exotic and the price skyrockets.

 

[Jackfre]

When you propose 5 !!!!! freaking indoor units then you've got bigger problems. Also, spec'ing out ducted and cassette units drives up the cost as well. Without better information I'd say you should consider a central, traditional, split unit.

Anything other than standard wall hung indoor units is getting exotic and the price skyrockets.

Highbeam, I agree with your first post and kinda sorta disagree with your second. As to the first, I have split the load at my home. I have a dual upstairs for the bedrooms. I have a much higher efficiency single unit downstairs. The downstairs unit is 25 seer and 12 hspf. The upstairs dual is 16.5 seer and I think around 8-9 hspf. I was going to get a triple but upon looking at cost(s), efficiency and use patterns, I went as described above and did it at the same equipment cost as the less efficient triple. With our new remodel I just installed a 15 in the new kitchen. I will pull the downstairs 12 and handle the entire 1000 sq ft with the 15. A note on that sizing. While it will get into the 100* range here, my house is shaded by an enormous 48" black walnut, a 125' Sequoia and a 125' pine so…

HB, as to your second post, there is no question that cost escalates on the more sophisticated systems, but that shouldn't be the only question in the value proposition, to me at least I know that the cost of the mini air handler is about 20% above the high wall units. I was up in N CA in summer of '12. I was speaking with a contractor about mini-split systems. He offered that he had done two almost identical homes in his area. One was a conventional hi-eff gas fired furnace/AC/duct. The other house he installed a Fujitsu Hybrid Flex Inverter system with 8 evaporators. That is a 48k outdoor unit that can handle from 36-64kbtu of indoor units. He said that installed cost of both systems was very close. I asked about operating costs and he said the mshp's were operating at about 45-50% of the cost of the conventional system. Simply higher equipment costs don't always tell the tale.

For the original poster, I think you have to look at your use pattern. How often is the garage and sunroom going to be occupied simultaneously. It may be best to separate them if you use one space or the other infrequently. Do you have the panel capacity to supply two electrical disconnects to handle two systems. Check the amperage rating of each system carefully before answering that. I have two units that are 15 amp breakers and one that is a 20 (the dual). the triple would be a 30 amp breaker. That will vary by manuf. You could handle the laundry with a Tjernlund Airshare and control it on a switched outlet.

We had a hot summer. I ran the mshp's daily. The upstairs would be run for a couple hours before going to bed and then I would turn it off and open the windows and run the interior evaporator on fan only. My July electrical bill was $90 and I had an electric water heater. With the re-model being almost done the elec water heater has been replaced with an lp tankless, so the next July bill should be around 45-50 bucks or less as I have also gone LED's for lighting.

As a disclaimer, I represented Fujistu in my business for 12 years. I no longer have any financial or professional connection with them or any mshp manuf. I will say that after 50 yrs in the business I will never again install a conventional furnace/heat pump/ductwork and that includes geothermal. The mshp's are just to good…imho…and experience.

 

[LS6 Tommy]

I've been installing individual & multi zone ductless splits in hard to condition spaces in my buildings for a while. Personally, I opted for two individual units for my house, but I have no major complaints about the multi zone units we've installed. I will say avoid the cassette units if you can. They tend to draw a lot of complaints about lack of even cooling/heating and low airflow, the run caps on the motors fail which requires removal of the control panel to replace the cap, they sometimes drip condensate from the discharge louvers and replacing the blower motor requires quite a bit of disassembly. I could go on, but I think you get my point about the cassette units...

Tommy

 

[joe_padavano]

When you propose 5 !!!!! freaking indoor units then you've got bigger problems. Also, spec'ing out ducted and cassette units drives up the cost as well. Without better information I'd say you should consider a central, traditional, split unit.

Anything other than standard wall hung indoor units is getting exotic and the price skyrockets.

Again, I'm NOT proposing five outdoor units, but a single unit driving five indoor units. This is why I'm asking why you are crapping on the concept of a multi split configuration, since there are many in service, so if you can elaborate on your prior comment, I'd appreciate it.

As for my particular project, it's a 300 year old saddlebag log house. There is no way to run a conventional central unit without large exposed ducts, and even then it would be very difficult to run them through the internal log and stone walls. Essentially, it's a pair of two-story log houses joined on a common log wall, with separate stone basements. The conditioned spaces do not communicate well side-to-side for return air flow, and the zones do not want to be up/down. This is why I'm using mini-splits, with essentially one indoor unit in each of the large rooms. I've spent a lot of time trying to configure a central unit (including things like the Unisco mini ducts) and it either doesn't work or is extremely unattractive.

I've also priced the indoor units and they are neither "exotic" nor overly expensive (~$500 - $800 per unit, depending on config and output). I've already done the Manual J calcs for sizing.

 

[Highbeam]

Again, I'm NOT proposing five outdoor units, but a single unit driving five indoor units.

Again joe, nobody ever said you were proposing 5 outdoor units.....

Your situation sounds particularly complicated and atypical. Certainly not a garage or a regular residence which is why you'll need to do your own research. Sounds like you already have.

 

[joe_padavano]

Again joe, nobody ever said you were proposing 5 outdoor units.....

I'm not here looking for an argument (which is starting to sound like a Monty Python skit ), but I was only responding to this:

When you propose 5 !!!!! freaking indoor units then you've got bigger problems.

And yes, my situation is particularly complicated, and I'll apologize to the O.P. because I didn't really want my question to hijack his thread, but I was interested in your original comment about the problems with multi-zone mini splits. If you have experience, I'd appreciate hearing about it, as I am trying to do as much research on this as possible. Thanks.

 

[fireant911]

Thanks for the interesting ad thought provoking responses! I spoke with our HVAC guy again earlier today (yes, he is very patient with us) and I suggested yet another scenario (a conventional system plus a mini-split for the Garage Attic). My wife is fanatical that the Garage Attic be fully climate controlled... maybe she is just trying to get me out of the house!!! This is proving to be a very difficult decision since so many options are available.

I am not aware that any issues exist with multi-zone mini-splits. In fact, I would be very surprised that this is true since so many are currently in use. I spoke, in length, to several people in the HVAC industry and none of them mentioned any problems with multi-zone mini-splits; in fact, it was much the opposite as the all parties were very happy with the mult-zone units. What are the problems that you are aware of?
Thanks,
Daryl G

 

[fireant911]

A quick update... I have been researching more and more after reviewing the responses. Certainly, the usage factor of the Sunroom will be much different than what the Garage Attic will actually see. Two individual mini-splits may actually prove to be the optimal solution. The technical data for individual units versus multi-zone may also further support this option. I will discuss this newest possibility with my wife to see what she thinks and then talk with our HVAC guy. If we go this route, I suspect that we will do installation in two phases (Sunroom now and the Garage Attic this Spring).

As for available power - our current panel is being fully utilized since we have gotten our garage wired; however, we have an unused 200 Amp service already connected to our home that we can put into service to supply power to the mini-splits.

Thanks for the input!
Daryl G

 

[Jackfre]

Daryl, there is absolutely nothing wrong with the operation of the multi-head unit. As stated, you just need to understand the efficiency/cost equation. The other advantage of the two systems is as you state you can stage the purchase/installation.

I would strongly recommend that you look at Air-tecs Mini-split wall mount systems. Get them off the ground and they will stay cleaner.

 

[Highbeam]

I am not aware that any issues exist with multi-zone mini-splits. In fact, I would be very surprised that this is true since so many are currently in use. I spoke, in length, to several people in the HVAC industry and none of them mentioned any problems with multi-zone mini-splits; in fact, it was much the opposite as the all parties were very happy with the mult-zone units. What are the problems that you are aware of?
Thanks,
Daryl G

The units work as advertised and are even not much more difficult to install. Look at the specs and the price. The multi zone minis are an inferior prodcut given current offerings. More cost, lower performance, and less redundancy.

 

[Beegs]

For what it's worth: I built a brand new home in NH. It is a cape style home that is not finished on the second floor. My basement is a full walkout and is finished. Two bedrooms in the basement and one bedroom on the first floor. 28'x32'

2x6 construction with 2" spray foam and fiberglass bats to make up the difference.

I heat my house only with my mini-split system. Daikin brand with four inside heads, one outdoor unit. I have a head in each bedroom and one in the living area. My last electric bill was $240.00 That covered everything....heat, lights, 60 gallon electric hot tank, one load of laundry per day and we are not real careful about leaving lights on etc...

NH has high electricity prices, so I am VERY happy. I do have a woodstove as backup in case of power outage. Hope this helps!

 

[fireant911]

We are still investigating the mini-split scenario. It is exceedingly difficult to even size a unit because all of the available calculators all yield VERY different answers. I think that slight oversizing may be okay given that these units are all inverter driven so the units can adjust their speeds according to the actual room needs.

I have another question regarding our Sunroom (476 square feet / 44'-2" X 10'-9"). Because this room is long, my wife posed the question of rather than get a single 24K BTU unit for that room could we instead install two 12K BTU units in that room. I am curious if this configuration is advantageous (it looks like we will be using a multi-zone unit anyway) and are there any advantages/disadvantages to this layout?

Beegs, I have tried to use your story as leverage but my wife is proving to be a difficult sell at this point!

 

[JakeKohl]

I've got two large rooms that are heated and cooled with mini-splits (LG Art-Cool). My 2nd floor office is 24x36 and I have a moderately sized 1/2 bath in one corner. My garage is the same size but has an adjoined workshop (now a tool room) that is roughly 12x19.

When I installed the mini-splits, I considered the multi-zone units but, at the time, the price for two individual units and one dual zone unit were almost the same. Because I don't intend to heat and cool the garage full time, I thought that the properly sized single zone units would be more efficient.

I was also concerned that I get enough heating and cooling into the 1/2 bath upstairs. The reality is that if the door is left closed on that bath overnight, the room does not get conditioned but if the bath door is left open (even slightly), the temperatures in that room are completely stable and managed by the HVAC. In the garage, even the adjoined shop temperature gets evened out with the garage very quickly if I leave the door open between the two.

In short, I've been impressed by how well the units move air. Both of mine have "chaos swing" that moves the louvers left right and up / down and they distribute conditioned air around the spaces very well. I would figure that one of the minisplit units would handle the entire sun room. As a backup plan, you may want to incorporate a couple of ceiling fans to help mix the air just in case.

 

[fireant911]

Jack,
Thanks... and especially thanks for the narrative about how well your units work. My wife has been asking about how well these units move the air around corners and in long spaces. I have already shared your story with her and will try to contact our HVAC guy with our final (hopefully) scenario. Yes, ceiling fans are already part of the equation.

Earlier today, I made a full scale mock-up of the wall unit so that the wife could see the 'footprint' that the standard wall mount heat pump will occupy. She has signed off on this so I must react before she changes her mind!!!

 

[theoldwizard1]

I have another question regarding our Sunroom (476 square feet / 44'-2" X 10'-9"). Because this room is long, my wife posed the question of rather than get a single 24K BTU unit for that room could we instead install two 12K BTU units in that room. I am curious if this configuration is advantageous (it looks like we will be using a multi-zone unit anyway) and are there any advantages/disadvantages to this layout?

With a room that size and with that much glass, you a definitely going to need 2 air handling units as well as ceiling fans to get even heating/cooling.

Someone more knowledgeable than I will have to tell you if one compressor with 2 air handlers (and longer refrigerant lines) or 2 systems (with hopefully shorter lines) is better. Of course another issue is "hiding" the outside unit. Make sure it has adequate air flow.

 

[Jackfre]

I will always vote for two smaller avaps over a single large unit. I think it balances the air flow better. As well, you will frequently find that the space can be handled by one of those smaller units. Also, in checking the specs on my Fujitsu literature the 24 is 18 seer. The 12's are 25. Redundancy is also good in the event that one unit fails.

Until I had the kitchen and bath addition done this year I took care of the whole downstairs, kitchen, LR, Den with the single 12. Variable speed helps tremendously in this. Basic physics. Heat wants to go to cold and air flow even at a low rate will stir the air for continuous circulation.

 

[fireant911]

Jackfre,
That is a very interesting observation regarding the SEER ratings of the 24K units versus that on the 12K's. Yes, logically, I too thought that two units in that Sunroom would be better for airflow and actual conditioning of the air contained within but I never included the additional SEER efficiencies with the smaller units into the equation. This is certainly becoming a complex decision making process! The more research I do, the more questions I have. There is absolutely no consistency between the recommendations of the HVAC folks I have spoken with. So now the more ideal layout may be for a four-zone system (two 12K units in the Sunroom and a separate zone for the Connector and the Garage Attic).