Mini-Split AC - Sizing, Installing, Pros and Cons

[Twigg]

Okay, this is about our house and not specifically about the bus sitting in the yard.

However, bus talk gave me the idea, and I am hoping the following discussion will help those looking to use a mini-split either at home or on the road.

We have an elderly ranch-style home above a crawl space. The house is quite a bit bigger than the county thinks it is, but here I'm concerned only about the 1700 or so square feet that comprises a fully open living-room, dining room and kitchen on one side, and three bedrooms on the other.

We also have a fully enclosed hallway big enough to be another room and leading to a workshop that is 32' by 32'. Above that is a 900 sq ft room that is partly finished. On one end of the house is a sunroom that is around 25' by 15' and the tornado shelter is under the floor.

The current AC is a very old Ruud Package unit blowing (sometimes) cold air from 3 1/2 ton of AC and heating with a 100k btu furnace. I have been nursing the thing along for 10 years and it was already past its sell-by date when I started. Replacement cost would be around $6000. The vents are in decent shape.

We were thinking of a HELOC to replace it and do a few other things, but I'm having second thoughts about simply replacing like with like. The advantage of a straight replacement would be lower costs and better cooling, because the new one would work properly. Yet it remains a single-zone system and changing that would cost a fortune in labour and parts.

So I got to thinking about mini-splits for the entire part of the house currently cooled by the present system.

My thought was to use one, dual-zone unit for the living room and kitchen/dining room. Size would be around 12000 + 9000 for the kitchen and living room respectively.

The bedrooms would be covered by a second, three-zone unit with 9000 btu for each bedroom.

Advantages are that running costs could be lowered while vastly increasing the flexibility of the system. For example, each bedroom could have its own temperature control, and timing, as could the living room and kitchen/diner although I'm sure we would end up trying to balance those at roughly the same.

Basic cost for the two systems I've priced at around $4000 and presumably there would be extra for the bits required for installation. For example, I haven't found out whether or not the kits include line-sets, and they are not cheap unless you make your own (which I am prepared to do).

So .... thoughts?

[cadillackid]

im a big fan of minisplits for A/C and for light heat loads.. I have 3 of them in my house albeit they are modified as i didnt want the "ugly" wall units in every room so I tore them apart and managed them into a ducted system.. (now they make em that way if you want to use standard registers)..

the multi-zone systems work well and can be oversized a bit since they vary their speed based on the cool / heat required. when buying a multi-zone size the indoor units accordingly with the outdoor.. some of them are sold as 3 zone with 3 12000 BTU indoor units only to find out the main unit maxes out at 30,000..

one of the advantages you also get is the ability to heat.. and its really good heat too.. esp down to about 45 degrees or so (depending on the price of gas vs electric in your area).. they will blow warm air down to close to 0 but at a cost compared to a 90%+ gas furnace..

most of them come without linesets.. and you'll need one for each indoor unit.. you can make them.. but you need R410A capable soft refrigeration tubing.. DONT use regular copper pipe!. you will need a GOOD! flaring tool if you want to make your own. R410A operates at High pressures..at times 400 PSI+.

even with factory made linesets, the flares have been a source of leaks over the years in these units.. you'll need to insulate both pipes on the linesets.. the expansion device is in the outdoor unit so both pipes need insulated from the elements.
generally dont use more than 50 feet of line for any one run.

you'll need 4 wire SO cable to go from the outdoor unit to each indoor unit... the units MAY come with this but dont count on it..
Black - hot
White - Neutral
Red - COmms (yes comms is high voltage.. 30+ volts)
Green - Ground

you'll need pads or a wall bracket for each outdoor unit to sit on.

you'll need an electric circuit and outdoor shut off with weather-proof conduit from the box to each outdoor unit.. (one of them you'll be able to re-use from the old unit).

you'll need some plastic flexible drain hose.. I run it through the wall and down the side of the house with the wires and freon lines...

You'll likely want to hide the linesets inside of line-hide as they go up the side of the house. I like diversitech speedi-channel brand.

the units usually come with the through-the-wall sleeve. but check to be sure.

I have bought a lot of stuff over the years from www.acwholesalers.com out of miami.. they seem like pretty good people.. they hasve a lot of the little extra bits like pads, linesets, insulation, etc if you decide to go that route.

-Christopher

[Twigg]

Thank you Christopher, that helps.

I had been looking at the website you recommend.

I'll watch out for the under-sized units and avoid them.

The copper pipe for R410a seems easy to get, if a little pricy. From what I am reading the required wall thickness appears to be the same for both R22 and R410a up to 1/2" diameter. I think the maximum size I would need is 3/8"

Buying a good, eccentric flare-tool isn't too difficult and I had read about problems with flares, even on factory produced sets. So much so that some installers cut them off and make new flares.

I assume the condensor units come pre-charged for specific total length of lineset ... how much variation is permissible?

Vacuum pumps are cheap too. I don't need a fancy pro version, just one good enough to pull a vacuum a few times.

The construction of this house would make it fairly easy to pull the lines up the inside of the exterior wall for a neat install at the front of the house, at the back it doesn't matter.

I believe you can also get indoor units that would mount in the attic and blow down through the ceiling to avoid big boxes on the walls.

[cadillackid]

you can get cassette units which are big squares in the ceiling, or you can get ducted inits that can be attic or cawl space mounted and then you can have regular registers like you do with your central system. when I did mine those ducted units werent really available yet, so like i do with a lot of things I built my own.. (over 9 years ago and they are still going strong).

the install book usually tells you how much refrigerant the condensor holds and for how many indoor units.. the 9000 and 12000 BTU units I think mostly use 1/4 for the liquid line and 3/8 for the suction line, however some do use a 1/2 suction. the unit specs will tell you what you need.

MOST typically they are charged for 15 feet of lineset, 410A is tricky, a minisplit will run slightly over-charged more than it will run slightly under-charged.. (opposite of a normal A/C).. the outdoor units contain an accumulator which holds excess liquid refrigerant when the unit is in the cooling cycle.. low refrigerasnt will manifest itself noticeable at first in heating cycle when it cant condense the refrigerant to liquid in the indoor unit..

you'll want a Good vacuum pump, you need to pull it WAY down to clear the moisture for best performance..

of course since i used to be in the HVAC industry, I always recommend, vac down and charge with 150 PSI of nitrogen and test for leaks.. when I installed mine I caught two slight flare leaks that were solved before I lost a drop of refrigerant.. in 2010 I had a copper line inside one of my outdoor units crack.. there is some tight bendy copper inside and one was likely factory defective.. I made a new loop, stay-bright 8'd it in (no way I was ever going to be able to leave a torch in there long enough to braze).. never looked back.. (my custom software caught the failure while I still had 43 degree air at the vents)...

you'll want to get the port size adapter... darn chinese had to use a different gauge port size on these things.

you'll do great with this project, you are good at building stuff.. if I was closer id come out and help you get it all started up, i love doing A/C stuff..

I sometimes miss the HVAC industry though I definitely dont miss pulling off the covers of a busted A/C to uncover a Nest full of mad yellow-jackets.. on a roof-top.. nowhere to run..
-Christopher

[JDOnTheGo]

A big thank you to Christopher!

My biggest complaint and reason for discounting mini-splits has been those "ugly" wall units. I had not seen the concealed duct option. This now becomes interesting again!

Just when I think I have made a decision.....

[Rivetboy]

Originally Posted by cadillackid

you can get cassette units which are big squares in the ceiling, or you can get ducted inits that can be attic or cawl space mounted and then you can have regular registers like you do with your central system. when I did mine those ducted units werent really available yet, so like i do with a lot of things I built my own.. (over 9 years ago and they are still going strong).

the install book usually tells you how much refrigerant the condensor holds and for how many indoor units.. the 9000 and 12000 BTU units I think mostly use 1/4 for the liquid line and 3/8 for the suction line, however some do use a 1/2 suction. the unit specs will tell you what you need.

MOST typically they are charged for 15 feet of lineset, 410A is tricky, a minisplit will run slightly over-charged more than it will run slightly under-charged.. (opposite of a normal A/C).. the outdoor units contain an accumulator which holds excess liquid refrigerant when the unit is in the cooling cycle.. low refrigerasnt will manifest itself noticeable at first in heating cycle when it cant condense the refrigerant to liquid in the indoor unit..

you'll want a Good vacuum pump, you need to pull it WAY down to clear the moisture for best performance..

of course since i used to be in the HVAC industry, I always recommend, vac down and charge with 150 PSI of nitrogen and test for leaks.. when I installed mine I caught two slight flare leaks that were solved before I lost a drop of refrigerant.. in 2010 I had a copper line inside one of my outdoor units crack.. there is some tight bendy copper inside and one was likely factory defective.. I made a new loop, stay-bright 8'd it in (no way I was ever going to be able to leave a torch in there long enough to braze).. never looked back.. (my custom software caught the failure while I still had 43 degree air at the vents)...

you'll want to get the port size adapter... darn chinese had to use a different gauge port size on these things.

you'll do great with this project, you are good at building stuff.. if I was closer id come out and help you get it all started up, i love doing A/C stuff..

I sometimes miss the HVAC industry though I definitely dont miss pulling off the covers of a busted A/C to uncover a Nest full of mad yellow-jackets.. on a roof-top.. nowhere to run..
-Christopher

Thank you Christopher for sharing all of that info. Do not know if that is the trail that will be chosen but knowledge is power and the truest power is sharing knowledge, which you do so often.
As for meat bees, that is the California version, when I was still working on roofs I carried two cans of bug dead!
My run for the jungle story was bucking up a downed tree into rounds then throwing the rounds in the truck. One of those rounds was full of really mad meat bees. Got a few bites and jumped in to a stock pond and lived .
Funny story now but pure terror when it happened!

[cadillackid]

Originally Posted by JDOnTheGo

A big thank you to Christopher!



My biggest complaint and reason for discounting mini-splits has been those "ugly" wall units. I had not seen the concealed duct option. This now becomes interesting again!



Just when I think I have made a decision.....

When I first heard of mini splits I got excited till I saw those ugly wall units.. except LG had one that looked like artwork.. no joke it was called art cool... so I tore apart the units and made my own ducted cool boxes.. learned that the temp sensors were designed for 7 feet off the floor. Hacked the software and built a board to control the units by computer and fake the room sensors..
the result are minisplits that look like the rest of my house.. nice normal vents


One variable speed air handler for all zones and modulated dampers let me keep the CFM correct..


iPad on the wall for master control.


My roommate is old school so each Zone has a regular style thermostat.







And lots n lots of code to make it all work ... it also modulates the gas furnace when it’s too cold for heat pumps.. the result is one set of registers , 3 zones, high efficiency and ultimate comfort..

Aren’t you glad they make this stuff to buy now rather than build .
Christopher

[Twigg]

Originally Posted by cadillackid

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[cadillackid]

Originally Posted by Twigg

The thumbnail won't open.

tapatalk slammed the whole post so I deleted it temporarily and fixed it on a real computer...

[cadillackid]

Originally Posted by Rivetboy

Thank you Christopher for sharing all of that info. Do not know if that is the trail that will be chosen but knowledge is power and the truest power is sharing knowledge, which you do so often.
As for meat bees, that is the California version, when I was still working on roofs I carried two cans of bug dead!
My run for the jungle story was bucking up a downed tree into rounds then throwing the rounds in the truck. One of those rounds was full of really mad meat bees. Got a few bites and jumped in to a stock pond and lived .
Funny story now but pure terror when it happened!

meat bees!! yeah they are the same here... and you better bet there were cans of Bug-Dead-NOW in my tool bag after that!!

dont tell the EPA but i can say for sure that Dupont FREON-22 also does a decent jpb of warding them off!
-Christopher

[Twigg]

That's way beyond anything I had in mind, but it's very nice to see it all implemented like that.

[cadillackid]

Originally Posted by Twigg

That's way beyond anything I had in mind, but it's very nice to see it all implemented like that.

yeah I know, I tend to get a bit carried away when I build stuff...

Daikin was the purveyor of Ducted multi-zone split systems with VRV-III, Daikin was only commercial and sold through elite dealers for the longest time.. then goodman and Daikin Merged and now you can buy Daikin equipment off the shelf..

the advantage to Daikin minisplits is mainly integration into automation systems... they offer Wi-Fi thermostats with real wall buttons for those that dont want to use a wireless remote, or want the ability to adjust the system remotely or with a timer, etc..
-Christopher