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High Energy Consumption/Cost with Mitsubishi Ducted Minisplits

C L | Posted in Green Products and Materials on

The energy cost of the Mitsubishi Ducted Mini system is exponentially higher than projected.  The original contractor won’t address it; only provides email excuses.  A diamond Mitsu sub proposed emptying and recharging the system to confirm it is charged properly, which based on research is the correct way to check the charge, but is costly.

Would any of the following be appropriate next steps before investing in emptying & recharging the system?  If so, which order?

1. Revise t-stat hidden settings so exterior compressor (and I assume each unit) stops constantly running, and runs only when tstat calls for cooling (or heating).  I’m in a hot, humid climate.
2. Install an energy monitoring system to understand if the thing is running smoothly or has spikes/peaks (I’m sure there is a more technical way to express this) or do other troubleshooting.  It seems some of these systems might be more cost effective than emptying and recharging the system.
3. Other?

System has one outside compressors and three ducted minis.
Ducted dehumidifier in sealed crawl but turned off; manually turn it on if crawl humidity reaches 50%, so it only runs about 20 hours/month.
Mitsu t-stats do not have “dry” option; don’t know if that is the system or how it was programmed.
Temp set to cool if it gets 80 or above, and in winter to heat if it gets to 66 or above, in an effort to control the extraordinary costs.

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  1. RicRoll | | #1


    How did you end up proceeding? Having a similar issue with our ducted Mitsubushi system, installed last fall. If you hadn't yet done #2, how did you determine that it was over drawing? Just an electric bill analysis? If it's a problem with #1, then a refrigerant recharge will not solve it.

    I'm curious what guidance you found on changing the hidden settings? I might go thru the t-stat manual again (you know it's a sign when the t-stat manual is 4x as long as the hardware component manuals)

    Have you simply observed outdoor unit cycling while blowers are not in use?

  2. Dan Moore | | #2

    For a few hundred dollars, I decided to get the IotaWatt for electrical monitoring. Easy to install and use even for a non-electrician. I am sure there are other good ones out there as well but I can't speak for them. It has helped a lot to figure out what the system to doing, how it is cycling. I have diagnosed a couple problems myself just by watching the monitoring results and playing with the system, and I am no expert. Easily paid for itself and helped me give supporting evidence to make my case to mits and/or contractors. I have a mits multi with a ducted unit and two heads.

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