What Mini-Split has good "gone away" settings?

[CA_Tallguy]

Hey folks - I am in the market for a mini split but wondered if some of you who have them can tell me if your units allow for setting the unit to an automatic mode where if it comes on ONLY if it gets extremely hot or cold in the conditioned space.

For example, set so that cooling comes on if the inside temp goes over 85 and heat comes on only if it dips below 50.

Looking at user manuals it seems that most operate on just one set point temperature and the unit tries to maintain that. I suspect that most can be put in heat-only or cool-only mode to accomplish what I'm talking about with either high OR low temps but not both. Are there any that could be set to do both?

 

[Fueler]

I think you are trying to apply conventional thinking to a mini split.
They run continuous, yes but once the desired temp is hit they run in low gear so to speak. Not much amps, etc.
If you shut it way down then it takes more time and amps in high gear to get back to the set temp. I think you will lose whatever you think you will save.
At least that is the way I understand it.

FWIW anytime I tried trimming back a conventional system in hopes of saving a nickel I was rudely denied for the above same reason but in spades.

Another FWIW. On my split this summer I have learned to leave it in cool mode. The temps here have been weird this year with extreme ranges on a daily basis. If I leave it in auto mode and the building drops below my set point the heat comes on. Once the sun comes up it has to go all out to get the temp (cool) stabilized. In cool mode it just doesn't do anything if the building drops below the set temp and in the morning it's exactly where it needs to be.

Once the humidity days are behind us I will move it back to auto.

 

[CA_Tallguy]

Thanks for the reply, Dave, but it doesn't sound like you are fully getting what I'm after.

I'm really trying to avoid FULLY conditioning space that may be unoccupied for weeks or months at a time. Just want to take the edge off the heat and keep humidity in check during hot days.... and should I leave the building for a period going into fall and winter, have some protection against low temps and the few freezes we get around here.

So the unit would never be set to try to get to 70 degrees for these extended periods. I only want to dial back hot days to maybe 80 and cold days up to perhaps 50. So the goal is for the unit not to run at all between 50 and 80 degrees.

My folks do this in Palm Springs when they leave town to avoid baking all their household goods with a 100+ degree interior.

 

[CA_Tallguy]

One idea I am considering is to have 2 interior heads in each space.... say, one 9K BTU and then an 18k BTU. Both heads would be used when building occupied, but only the 9K BTU units would be left on when I go on vacation with about a 72 degree setpoint but they would be undersized so they would usually not be able to maintain that alone. That would hopefully be enough BTU's, however, to take the edge off the highs and lows.

This still does not seem ideal as those units would be operating during that middle 50 to 80 degree temp range and there could be days or weeks with mild temps and I would prefer that the units not run at all in my absence except should extreme temps arise.

 

[Fueler]

Needs a smart phone app doesn't it? That way you could check and adjust from afar. Maybe one of the pro guys knows of a external smart thermostat that can be used.

 

[CA_Tallguy]

Been doing a lot of research into the phone apps -- there are not many solutions out there.

LG has one that seems like a pretty inexpensive add on (except you need one module per interior unit). The reviews in the app store are terrible for it and give the impression that it doesn't even work for long periods of time.

Mitsubishi has Redlink available AND they supposedly just came out with a module to allow an interior unit to interface with Nest and any other system that interfaces with a "normal" thermostat. Redlink equipment can add up in cost... I believe you need 2 or 3 different bits for it to work via smartphone. With the other solution where it acts like a "normal" thermostat interface, I wonder if you lose some of the benefit of variable speed inverter energy efficiency. This module seems like it allows some external thermostat system to interface with it using 2 stages of heat and 2 stages of cool. Plain and simple, but maybe too simple! And again, you need one of these units (along with a thermostat to control it) for each interior head unit you have so the cost can add up.

So, sadly, it seems like the industry is behind the times when it comes to smartphone control. Plus, if there is a system that would allow me to just "set and forget" my "vacation" mode preferences (don't run between 50 and 80 degrees) then that would be more simple and preferable. And more cost effective.

 

[Fueler]

I don't remember which one but I am pretty sure at least one of the mfg can be hardwired to an external Tstat which means you can get a smart version.
Maybe they all can. Probably have to dig through the various install manuals if they don't say it outright.

 

[CA_Tallguy]

Looks like LG has a hard wired thermostat that has dual set points. This may be my most cost effective option. I am assuming that this is compatible with multiple zone units but need to do more research. About $125 per head unit for this. They also have wifi modules but for some reason they are apparently only compatible with a limited number of SINGLE zone units.

LG also has a few different modules including a "dry contact" board (need to verify that it will work with their residential products) that might enable use of a third party thermostat like Nest or Ecobee. Mitsubishi also has a module like this that was announced but doesn't seem available anywhere right now.

Mitsubishi also has "redlink" thermostats available with an internet gateway you can add. These units go for about $250 per head unit and the internet gateway is $100. I'd hope that the internet gateway can handle multiple units. Seems like the most robust solution but also crazy expensive. Maybe worth just biting the bullet and putting this on two heads for $600 to $700 total.

I get nervous with a lot of these internet enabled systems because I wonder how stable they are and how long they will be supported. It wouldn't surprise me if in 5 years the manufacturers no longer support older units. As such, the modules that allow use of third party thermostats seem like a good option so that they can be upgraded over time. Or, keeping it simple and just getting a unit that has dual set point control and/or wired thermostat available.

 

[Fueler]

Yup, next thing you know ISIS or the Prince will be hacking your AC which leads back to all your other accounts via the all things to all people Cloud.
Life sure ain't simple anymore.

 

[Dagny]

Before you buy one ask the people you are buying from to price a few parts for it . they work fine but are very expensive to repair.If it is at all possible to put something conventional in do it.

 

[rlitman]

I don't remember which one but I am pretty sure at least one of the mfg can be hardwired to an external Tstat which means you can get a smart version.
Maybe they all can. Probably have to dig through the various install manuals if they don't say it outright.

I think they all do, so you could always use a Nest as your external thermostat, but there is a big downside to this. You lose the multi-stage capability.
The external thermostat is "bang-bang", and basically defeats the variable speed compressor/fan that mini-splits use to get the best efficiency.

That being said, I KNOW I saw some mini-splits with occupancy sensors. Can't remember if they were Mitsubishi or Daikin...

 

[404]

The thing you want to adjust is called the dead band.

Be interesting if there is a secret menu where that could be set.

 

[rlitman]

The thing you want to adjust is called the dead band.

Be interesting if there is a secret menu where that could be set.

Most thermostats have adjustable hysteresis, but how does that effect the fact that they still cannot provide PID control?

 

[Milton Shaw]

I know most motel/hotel PAC's have a built in freeze sensor, that even when the system is turned off the freeze sensor will turn the unit on it heat mode when it reaches 40 or so indoor temp. You might check to see if these mini-splits have that already built in. The only was to defeat this sensor was to unplug the unit from the wall. They were included to keep motel rooms from freezing or their workers to have to go around and turn them all on when the temp gets low.

 

[404]

Most thermostats have adjustable hysteresis, but how does that effect the fact that they still cannot provide PID control?

Do not understand your question.