[FullRangeMan]

I would like suggestions, tips and what to avoid on a Split 18K BTUs cool only.
Brands avaliable on market are:
Consul, Gree, LG, Samsung, Komeco, Electrolux, Fujitsu, Carrier, Springer.
Thanks

[macrojack]

I researched this to death last year and wound up buying a 24K BTU (2 ton) Mitsubishi 19 SEER. So far, so good.

What you choose should be governed by local circumstances, product reliability and availability and budget. I think it is wise to buy the highest SEER number you can get.

[Escott1377]

I would like suggestions, tips and what to avoid on a Split 18K BTUs cool only.
Brands avaliable on market are:
Consul, Gree, LG, Samsung, Komeco, Electrolux, Fujitsu, Carrier, Springer.
Thanks

Of the brands that you mention, I would recommend LG's ductless split model.

FYI - I was w/ Carrier for 15 years as a commercial sales engineer and now I am a regional manager for Mitsubishi Electric on their commercial product.  Just mentioning that so you do not think I am favoring any brand.

Good luck -

[JohnR]

I researched this to death last year and wound up buying a 24K BTU (2 ton) Mitsubishi 19 SEER. So far, so good.

What you choose should be governed by local circumstances, product reliability and availability and budget. I think it is wise to buy the highest SEER number you can get.

BTU and SEER are not terms that compute here, but we recently installed a reverse-cycle unit and one thing I noticed when comparing the specs was that higher-output units had lower specification in terms of efficiency. I concluded that the specs had to be a) at full output and b) were not linear. Otherwise it just didn't make any sense... I wasn't able to find efficiency vs output numbers. I am wondering, Tom, if you have any info on this?

[macrojack]

JohnR - I'm sure you know the meaning of the British Thermal Unit so I'm guessing a translation to tons may be what you are asking for. 12,000 BTUs equals one ton of capacity. SEER is an acronym for Seasonal Energy Adjustment Ratio.

https://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratiohttps://www.youtube.com/watch?v=bXU219b3Zdw

By "reverse cycle unit" I imagine you are referring to what we Yanks call a heat pump.

https://en.wikipedia.org/wiki/Heat_pump

I learned enough to make an informed choice about selection and installation options but I am not sufficiently schooled on the subject to move beyond advice into the realm of instruction. Those "For Dummies" books were surely initiated by someone who had me in mind.

There is a definite inverse relationship between capacity and efficiency. There is also a need for some precision in sizing a unit. Too large or too small are equally troublesome mistakes. I guess that is the most important thing to keep in mind. Numerous factors come into play including how many people are normally in the room. It sounded like Gustavo already has that determination in place.

[JohnR]

I'm not asking for instruction - my question is whether efficiency is linear with (delivered) output. If you have no idea, fine, no worries.

[JLM]

For residential applications occupant load (unless you frequently entertain indoors during cooling season) is a minor consideration (the average person generates 300 BTU of heat).  Bigger considerations for cooling would be refrigeration (which produces a net heat load), cooking (again relating primarily to entertainment), and tank type water heater.

In general the primary factors to account for are the design temperature and relative humidity for your area, house size, overall "R" (insulation) value of the house, thermal mass of the house (overall specific heat times the mass inside the thermal envelope), and overall air infiltration of the house (how much air leaks) are the factors to consider for heating or cooling needs.  Note that contractors are notorious for simply guessing on the needed unit sizes and typically guess high (labor cost is the same, more money for them, fewer compliants).

For a local (split system) unit layout of the house and proposed location of the unit can easily limit it's effectiveness.  "Under air conditioning" will only lower the relative humidity of the space, which does provide a degree of comfort relief but during peak outside temperatures will not lower the temperature in the house/space.

You'll probably pay more up front, but I'd look for a knowledgable contractor who has good reviews.  He'll carry good brands (that typically are the most efficient), can advise on proper sizing of the unit, and provide the best solution for your needs.

[JLM]

I'm not asking for instruction - my question is whether efficiency is linear with (delivered) output. If you have no idea, fine, no worries.

Typically John, all else being equal, efficiency should go up with machine size.  Perhaps the larger models were older (everything is getting more efficient it seems). 

[JohnR]

Typically John, all else being equal, efficiency should go up with machine size.

Well, from the line of units that I looked at, that was not the case (the opposite in fact). That is why I asked.

To rephrase the question: suppose a 6kW unit has the same efficiency rating as a 3 kW unit. If I run the 6kW unit at half power, will it be as efficient as, less efficient than, or more efficient than the 3kW unit run at full power?

[macrojack]

I also found the opposite to be true, Jeff. The little 9000 BTU Mits unit was available at around 33 SEER whereas a 24,000 BTU unit like I needed could not offer more than 19 SEER. Going bigger dropped the number proportionately.

As for linearity, I would like an explanation of that as well. Maybe my installer knows. If so, I'll try to accurately convey his answer.

[SoCalWJS]

Well, from the line of units that I looked at, that was not the case (the opposite in fact). That is why I asked.

To rephrase the question: suppose a 6kW unit has the same efficiency rating as a 3 kW unit. If I run the 6kW unit at half power, will it be as efficient as, less efficient than, or more efficient than the 3kW unit run at full power?

This is NOT a definitive answer. I remember my wife (Civil Engineer who has worked in Inspection/Plans/Code Enforcement for most of her career) telling me that getting too large of a unit for your space is not good. You lose efficiency. From her statements, I believe you are correct - they are not linear. You want them to run at/near their max capacity for greatest efficiency.

[JLM]

I wonder if the smaller units are also newer (newer seemingly are always more efficient).  Are all the parts comparable?  I'm sure two half sized units would distribute cooling more efficiently than one larger one, so in effect be more efficient.

SoCalWJS,

Yes, the accepted wisdom is to size the unit to barely meet the needs: less air movement means less stratification of the air (colder on the bottom/warmer on the top); compressor cycles less often meaning less loss of compression of refrigerant. 

But you may not be fully comforted all the time:  design temperature is less than typical peak annual temperature, it's hard to know how well the house actually performs in terms of insulation and infiltration, and you may have a house full of guests that will generate more heat on hot days.  Plus distribution of air (from ductwork and especially split systems) is rarely perfect.

[macrojack]

This is NOT a definitive answer. I remember my wife (Civil Engineer who has worked in Inspection/Plans/Code Enforcement for most of her career) telling me that getting too large of a unit for your space is not good. You lose efficiency. From her statements, I believe you are correct - they are not linear. You want them to run at/near their max capacity for greatest efficiency.

I seem to recall that my Mitsubishi has an inverter which gives it continuously variable speed rather than just selectable (or automatic) stepped operating speeds. I do not know if this applies to the compressor or just the fan. The sales pitch indicated that the inverter was in place to maximize efficiency. If true, how would that square with the idea of "max capacity for greatest efficiency"?

It's beginning to feel like I have a lot of info that I don't fully understand. My unit operates automatically in terms of calibration but I have manual override on the remote that allows a setting called "POWERFUL".
It just occurred to me why we are talking about air conditioning - some of you are in summer. It's 19 degrees F. outside my house right now. Haven't used the AC in a while.

[thunderbrick]

This is NOT a definitive answer. I remember my wife (Civil Engineer who has worked in Inspection/Plans/Code Enforcement for most of her career) telling me that getting too large of a unit for your space is not good. You lose efficiency. From her statements, I believe you are correct - they are not linear. You want them to run at/near their max capacity for greatest efficiency.

+1!

[JohnR]

It just occurred to me why we are talking about air conditioning - some of you are in summer.

Yes, but reverse cycle aka split system works both ways right... That does raise another question about what the efficiency ratings really mean...?

[Atlplasma]

I would like suggestions, tips and what to avoid on a Split 18K BTUs cool only.
Brands avaliable on market are:
Consul, Gree, LG, Samsung, Komeco, Electrolux, Fujitsu, Carrier, Springer.
Thanks

FullRangeMan. Consider talking to an experienced split mini installer or, better yet, system designer. I really wanted to use Daikin units on my new house, but the hvac designer I looped into the process ran the numbers and found this approach was not practical (basically, too many spaces). We also looked at a ducted split mini configuration, but it was much less efficient than the standard system. In the end, I went with a conventional 18 SEER heat pump. It uses DC motors and keeps the house very comfortable at modest cost.

[Escott1377]

Alright I'll chime in w/ a little more information.  Typically for a residential application, contractors will size for 300 sq ft / Ton or 12,000 btu's of cooling.

If you oversize your unit, you have terrible humidity swings since temperature and humidity are not linear.  So, as your cooling unit satisfies your temperature on your wall stat, the compressor will turn off and your room will become very humid.  This goes on and on w/ wear and tear on your compressor as well.

The new models of ductless products - Mitsubishi, Samsung, LG, etc. use an inverter driven compressor which matches refrigerant flow to the amount of cooling in the space required.  They also use a variable speed condenser fan.  Rather a 2 speed compressor, an inverter is essentially infinite when matching the load.  The inverter design also allows the unit to operate w/ better characteristics of a standard heat pump since it can extract more heat down to lower temps.

In regards to commercial products, you cannot make a blanket statement regarding efficiency vs. capacity.  There are products that instead of using forced air used chilled water to distribute cooling thru the building.  W/in that same vein, some of these machines are air cooled and some water cooled.  Water is better at heat transfer than air so water cooled units are typically more efficient (but require a cooling tower) to take the heat away for the building.

The product that I work with now is a commercialized version of the mini split.  We are actually able to simultaneously heat and cool at the same time by recapturing the heat of dissipation and recirculating to zones calling for heating while other zones are calling for cooling.  Often times, heat from the compressor is also used to supplement when ambient temps are required.  Reverse that around for phase exchange to get to the sub cooled liquid for cooling and you have a topic that my wife has no interest in.

[macrojack]

As JLM indicated there are a plethora of considerations when opting for air conditioning. My house is only one level, faces west and has baseboard hot water heat - no existing ducting. Previously, we had an evaporative cooler which I hated for a long list of reasons. For years I explored the pursuit of AC but never made the move because of perceived cost and/or difficulty. After the solar panels were installed in Nov, 2014, I became very conscious and sensitive to how we used electricity and how much we used. Much to my surprise, I discovered that the Mini-split ductless system could run at the same consumption level as my swamper or lower. In practice this proved to be true.

After the AC was installed, I set about sealing our house envelope and insulating as much as we could practically accomplish.

As I begin writing this I realize that the many small or large considerations we applied would mean little to most others. For instance, we have a very arid climate allowing for a smaller load than most of you face. We have strategically located flora surrounding the dwelling. We keep weird hours. Our bedroom is on the north side of the house. Et Cetera.

It all comes back to the advice I've read several times in this thread - hire a pro. That's what I did.

[FullRangeMan]

Thanks boys for your prompt advices.
I want the machine just for summer.
Requirements are reliability and low price,
I dont want pay maintenance bill and legal warranty are just 1 year.
So hi efficiency and low noise are secondary.

Here installers in general are not reliable as source of information.
I have see no Mitsubishi brand here.
There is other 2 minor brands: Mideia and Elgyn.

I unaware what is split ductless, here all split are installed w/2 copper tubes connecting the internal/external units, more power cord and output water hose.

So far I have see Samsung Max Plus 18000 BTU Frio AS18UWBUXXAZ are the cheapest unit at R$1.653,00 just over $415USD
https://www.econtinental.com.br/ar-split-samsung-max-plus-18000-btus-frio

[Escott1377]

I don't know anything about Elgyn, Midea is Chinese and from a Mitsubsihi perspective, we generally consider them less quality.

Ductless is what you describe.  Typically an evaporator (indoor unit) is mounted to the wall with your 2 copper tubes running to the external unit - these are called your liquid and suction lines.

All of these products have very low sound since they are using a much small fan to deliver the air.  You will probably have to put your hand on the unit to verify it is running.

Also, when in operation, the compressor typically never shuts off.  It will vary its speed to match the cooling requirements of your space.

I am not sure where you are located, but try Mitsubishipro.com to locate a dealer and mylinkdrive.com for more information on the units.  M series is the Mitsubishi rsesidential product line.

Again, I know these sites as an employee, but LG, Samsung, and Carrier all make nice products as well.