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Overcharged minisplit condenser leads to higher electricity bills

WildBunchFarm | Posted in Energy Efficiency and Durability on

I believe I have solved my problem of why my ductless minisplit system was performing so poorly. My condenser was overcharged with refrigerant by 3 lbs. I have attached a chart of my energy usage for the past few days. On the date of June 25th, the HVAC contractor came out and removed 3 lbs. of refrigerant from the system and thereafter, you can see that my energy usage dropped by 40-45%.

On the day the HVAC contractor came out, he hooked up an amp meter to the overcharged condenser and saw that it was pulling 24 amps with all of the 8 indoor units running full blast at 64 degrees. When he took out the 3 lbs of refrigerant the amps dropped to 12. Then when we set all of the indoor units to 75 degrees, the amps dropped further to 6 and then at one point it hit 4.5.

The contractor also mentioned something about the overcharged system hitting 500 psi or something and that it was really high.

Anyways, just thought I’d share this information with anyone who has an HVAC system that is performing poorly in terms of energy usage or if some of your units are short cycling. The only reason I stumbled upon this problem was because some of my indoor units were short cycling and on of the LG technicians suggested that my system might be overcharged with refrigerant. With excess refrigerant, it has to go somewhere and if it runs up into other units, it may cause the units to turn on when it senses the temperature difference in the line.

I’m still not 100% sure if this has solved my short cycling problem. I’ll have to wait until winter time to find out. But it sure has reduced my energy usage.

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Replies

  1. _matt_p | | #1

    Thanks, that sounds like really useful information to me.

  2. GBA Editor
    Martin Holladay | | #2

    Jimmy,
    First of all, congratulations on (apparently) finding the solution to your problem.

    Second, thanks for sharing your story on GBA.

    Here's my comment: For decades, energy efficiency experts have despaired at a significant problem: most residential air conditioners aren't properly commissioned. Excluding duct problems, which are a huge category of problems, the two biggest problems found by researchers are (1) failure to confirm that the system has the proper refrigerant charge, and (2) failure to confirm that the air handler provides the correct airflow rate over the indoor coil. (Fortunately, ductless minisplit systems don't need to worry about this second problem. But clearly, anyone with a ductless minisplit still needs to worry about the first problem.)

    Verifying that the system has the correct refrigerant charge is an essential part of installation and commissioning. If your installer failed to check the refrigerant charge, I'm tempted to say that your installer is an idiot. But the good news (I hope) is that your problem has been identified and solved.

  3. WildBunchFarm | | #3

    Thanks Matthias and Martin. Building an energy efficient house is certainly challenging with so many steps to get right along the way. A good HVAC contractor is a must even if you have to pay more money. I, of course, went with the lowest bid, but felt comfortable because I have the Green Building Advisor community for help! As always, this community is invaluable.

    Does anyone know how to calculate the COP of my HVAC system from kwh used and average temperature? I was trying to follow Dana's comments from this previous thread

    Here is what I came up with:

    - If heating/cooling balance temp is 60 degrees and my average temperature for the day in question is 81 degrees, then my CDD would be 21.

    - 1,000 kwh/month or 33.33 kwh/day is going towards non-HVAC related uses (hot water, plug loads, etc.) for a family of 5.

    - On the day with 81 degree average temp, we used 43.39 kwh. Subtract the 33.33 from 43.39 and we get 10.06 kwh being used by the HVAC system.

    - 10.06 kwh / 21 CDD = 0.48kwh/CDD. I'm assuming that is good because Dana said that an efficient HVAC system should be producing at most 1-1.2kwh/HDD, but my math might be wrong or the calculations for CDD vs HDD might be different.

    Anyways, thanks for any help you can give.

  4. Anon3 | | #4

    The Chinese units got better self protection built in, they would refuse to work and trigger a pressure error code. Then you would know immediately after installation.

    (You can get a mini split installed in China for usd$50, so they got some really heavy duty self protections built into the unit to make it idiot proof)

  5. GBA Editor
    Martin Holladay | | #5

    Anon3,
    I'm still waiting for you to tell us your name...

    You seem fascinated by the fact that you can get a ductless minisplit installed for $50 in China -- I think that this is the third time you posted that fact.

    I once got a sit-down restaurant meal in India for 25 cents. I once bought a new knapsack in the Soviet Union for 50 cents. But I fail to see the relevance of these facts.

  6. WildBunchFarm | | #6

    It's been a while since I posted, but my LG Multi F 8 zone split system was still giving me problems and I seemed to have solved a lot of my problems by purchasing the Premta000 wired thermostat. My problems included:

    - At night, my minisplits would only turn on when I set the remote control temp setting at 78 even when the indoor temperature was 68.
    - Minisplits heating at random times during the day when I didn't need it on because it was sunny out and the radiant heat was enough. (Note: if you are designing a new house, you have to take advantage of overhangs and windows on the south facing side. When it is in the 30s and 40s outside and sunny, during the day, I don't have to turn on any heat until a few hours after sunset.)

    The Premta000 thermostat appears to have solved those aforementioned problems. It also allows you to set precise schedules for all seasons unlike the dinky remote controller that comes with the wall units. Only downside is the units cost around $269 and you also might need to rip out some drywall or find a way to snake the wire down the wall if you are installing the themostat after all the dry wall is up. It's best to keep the thermostat 10-30 feet away from the blower so that you can set the unit to only go by the wall thermostat temperature reading and not the thermistor in the actual wall unit which seems to not be accurate.

    In new construction or remodels, if you are using LG minisplits, the Premta000 is a must. It will solve a lot of problems. In the end, I would say if I could do it all over again, I would get Mitsubishi or Fujitsu minisplits as people don't seem to have as many problems with those. I see people complaining about the same problems with LG's across all these building and HVAC forums.

    And dare I say, I have some regrets not doing a conventional ducted system. It would've been cheaper and not given me so much headache.

  7. vap0rtranz | | #7

    >unlike the dinky remote controller ... It's best to keep the thermostat 10-30 feet away from the blower

    I do this with my dinky remote's "Follow Me" feature. My remotes have a thermometer, we set them in another room/hallway, and they send signals of the air temp back to head units over IR, so no wall teardown needed. Maybe not all manufacturers have thermometers built into the remotes? Mine is Bryant, aka re-badged Medea.

    >I have some regrets not doing a conventional ducted system. It would've been cheaper and not given me so much headache.

    You have lived with a conventional ducted system? that at least cooled with an air source heat pump? aka. almost all American home A/Cs.

    I lived with one such "typical" A/C system, an older 3 ton, that wouldn't cool 1,000 sq ft! on a single floor!! It had been overcharged. Found out after calling in an old-school, family owned HVAC guy. He chuckled when I stupidly asked "is that all? isn't doesn't need to be re-placed" His rhetorical and jaded response was:

    -- Why "pull & weigh" the refrigerant when one can just assume the system gradually leaks so by that assumption any issues must be solvable by adding MORE refrigerant? or tell you the system is old and needs replacing (like a good HVAC salesman)"

    Then he chuckled again, and removed the excess. My little home was finally cool again after he left.

    So to Martin's point, how does excess refrigerant have anything to do with unducted minisplits? The refrigerant details may be different, but both conventional and minisplits can be -- and evidently are often -- overcharged.

    Also, a new 3 ton air sourced heat pump cooling system would cost $4-6k where I live. That's assuming there's already ductwork and a furnance, and a single zone. I never got ductwork quoted here but hear that it's very labor intensive, and labor is big $$$. My 3 ton / 36 kBTU multi-split cost $9k to install, and it heats and cools. So I think the cost differences between conventional and unducted are becoming more of a wash.

  8. WildBunchFarm | | #8

    My LG remote control that comes with the unit does not control temperature. Yes, it senses the temperature in the room and displays it, but the thermistor in the actually wall unit senses the return air temperature and acts accordingly. This setup is not very accurate or reliable in my experience.

    Yes, I lived with a ducted heat pump before and it was fine for my climate in Virginia.

    For ductless minisplits, you have to really weigh in the refrigerant with precision.

    My house was a new construction. The ductless minisplit system cost me $3500 more.

  9. WildBunchFarm | | #9

    Actually, the minisplits cost about $1,000 over a SEER19 ducted system. It cost more for a SEER16 ducted system.

    Here were the estimates from back in 2016

    4 ton ductless system with 8 zones
    Total = $23,250

    Option 1

    Heil 15 seer single stage heatpump systems with ECM blower motors
    -1st floor 2.5 ton heatpump with 15kw aux heat
    Model# HSH530 & FXM4X30
    - 2nd floor 2 ton heatpump with 10kw aux heat
    Model# HSH524 & FXM4X24

    Total = $18,400

    Option 2

    Heil 16 seer two stage heatpump systems with variable speed blower motors
    - 1st floor 3 ton heatpump with 15kw aux heat
    Model# HCH636 & FVM4X36
    - 2nd floor 2 ton heatpump with 10kw aux heat
    Model# HCH624 & FVM4X24

    Total = $20,550

    Option 3

    Heil 19 seer two stage heatpump systems with variable speed blower motors
    - 1st floor 3 ton heatpump with 15kw aux heat
    Model# HCH936 & FVM4X36
    - 2nd floor 2 ton heatpump with 10kw aux heat
    Model# HCH924 & FVM4X24

    Total = $22,300

    ADD ONS

    Honeywell ERV Model# VNT5200 = $1900
    Honeywell Humidifier Model# HE300 = $450

  10. vap0rtranz | | #10

    Jimmy,

    That is a lot of money on those quotes, but it looks like many more zones / units that I have.

    Jp

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