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Electric consumption of ductless minisplit system during non-operational mode

mcpascaln | Posted in Energy Efficiency and Durability on

I am currently in market to install a ductless Mini Split system in my house. I live in Pennsylvania zip code of 15904. It will be a four-zone system to be placed into four different rooms at cost of $12k. A Nate-certified HVAC specialist will be responsible for this install.

Most likely, it’s going to be Mitsubishi brand. Here is the detail of the unit.

Mitsubishi Electric MXZ-4C36NA2-U1 Heat Pump 36,720 BTUs Cooling 15,436 BTUs Heating 19.2 SEER, 9.4 EER, 11 HSPF 12 Year Parts Warranty 12 Year Compressor Warranty Indoor Unit Selections Bedroom #1 Wall-Mounted MSZ-GL09NA-U1 8,028 BTUs Cooling 4,225 BTUs Heating Kitchen Wall-Mounted MSZ-GL12NA-U1 10,785 BTUs Cooling 5,519 BTUs Heating Bedroom #2 Wall-Mounted MSZ-GL06NA-U1 5,372 BTUs Cooling 2,845 BTUs Heating Bedroom #3 Wall-Mounted MSZ-GL06NA-U1 5,396 BTUs Cooling 2,845 BTUs Heating.

Total: $11,952 Estimated Payment: $498.00 Payment: /mo – Project Loan – 24 Months

My concern is the power consumption of this unit when its not needed during the cold long eight months of Oct-Nov-Dec-Jan-Feb-Mar-Apri-May.

I need only to cool my house only in summer four months of June-Jul-Aug-Sept. I am very concerned about monthly electric bills during non-system usage since it has to be continuously functioning throughout the year. This is regardless of whether you are using it or not.

Obviously, this is a concern. I feel, this amount of money paid toward electricity bill used during the 8-months of non-use is not anything closest to energy efficiently we all strive to achieve.

During winter, my house is heated efficiency at low affordable cost using a gas-powered boiler that heats the whole house through water-based Hot Water Radiator Fins. Please, advise me on what other alternative options I have.

Still though, I badly need a cooling system in summer because the hot weather is unbearable. If I had the option to turn off this system, it would be a money saving move. On other hand, if I were to install a window AC,I will have the opii to switch it off during the time its not needed. I am really confused and need advise from you pros.

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Replies

  1. Expert Member
    BILL WICHERS | | #1

    Why not use a mini split system that can also heat your house? I didn’t look up the one you have, but maybe it already can. If you’re planning to install the system anyway, and it can save you some money on heating, that extra savings can go towards paying off the unit. Keep your existing boiler as a backup heat source for really cold weather, or in case you have any problems with the mini split system. It’s always nice to have a backup!

    Bill

    1. mcpascaln | | #3

      Hi Bill,
      You asked, “Why not use a mini split system that can also heat your house? I didn’t look up the one you have, but maybe it already can”. Per what the contractor told me, by design, the Mitsubishi Ductless Mini Split system with more than two zones, function as cold and heat system.
      I really liked what you stated further that,” If you’re planning to install the system anyway, and it can save you some money on heating, that extra savings can go towards paying off the unit.”
      A big concern is that, natural gas is way cheaper than electricity. Currently, I pay about $60 monthly under budget billing plan with Penelec, a FirstEnergy company.
      The Nate-certified contractor even mentioned that if the system were to be installed, he will have to turn off the heat function because it would not be needed due to my house having natural gas.

      1. Expert Member
        BILL WICHERS | | #5

        Ok, time for a little bit of physics ‘splainin:

        Heat from resistance heat, like an electric space heater, tends to be expensive. All of the input electricity is CONVERTED into heat.

        A heat pump DOES NOT heat like a resistance heater! A heat pump works like an air conditioner in reverse: it uses the input electricity TO MOVE heat from outside to inside. Any temperature above absolute zero, -459*F, has some amount of thermal energy. With a typical air-source heat pump, you’re moving heat from outside to inside, even when it’s pretty cold out. It takes LESS electricity to MOVE existing heat than it does to MAKE heat from scratch.

        What this means is a heat pump tends to be cheaper to operate than electric resistant heat in nearly all conditions except for the very coldest weather. It’s usually cheaper to operate a heat pump than it is a natural gas-fired heat source too, although not as much cheaper as for electric resistance heat.

        Heat pumps often have so-called “auxiliary” electric resistance heat, but this is only used in very cold weather when the heat pump can’t operate efficiently. In your case, you already have a functioning gas-fired heating system, so you’d just use that as your heat when it was too cold outside for the heat pump to function instead of electric resistance “auxillary” heat. During all the transition months (fall/spring, and winter except at its coldest), you’re likely to come out ahead in terms of energy costs using heat pump to heat your house.

        Bill

  2. FluxCapacitor | | #2

    You absolutely can turn off the system when not in use.

    Who told you that the system has to be powered on at all times?

    1. mcpascaln | | #4

      Hi FluxCapacitor,
      If you were to ask the Mitsubishi company if its recommended to turn off the ductless minisplit during the winter times of no need, they will say no that is because, its reliability will be negatively impacted.
      During winter, the system will need to be functioning to ward off ice and freezing status that can adversely impact its internal functioning. Unless it in-housed, the system’s reliability will be at stake. I get the impression, mini split ductless system are designed to be functioning 24hrs a day, 365 days a year.

      1. Jon_R | | #8

        > they will say no

        Do you have any proof of this, or is this conjecture?

        1. mcpascaln | | #10

          Hi Jon,
          I did read that elsewhere but cannot recall the source. However, today, I have fired a question to Mitsubishi Ductless Mini Splint unit through its facebook page. They tend to respond after a few days, Here is the question sent to them on October 13, 2019:-.

          "I understand that Mitsubishi's hyper-heating Inverter technology powering the ductless mini split system enables the heat pump to provide both cooling and heating during extreme cold climate condition. This means the unit runs all year non-stop consuming electric when its used or not. To save unnecessary electric bill charge for unneeded use, is it advisable or recommended to turn off the power to outdoor compressor unit during winter season when the heat is not needed?"

  3. walta100 | | #6

    I see no danger in turning off circuit breaker for the mini split system in the winter provided you turn on the breaker 48 hours before you operate the system. The danger is in cold weather, liquid refrigerant will migrate to the coldest part of the system. When the breaker is on the system runs a small heater in the compressor to vaporize any liquid before it could enter the compressor and damage the compressor.

    The other concern is that the indoor units and the associated condensation drain tube not fall below freezing as that could damage them. Your installer should be aware of your plan to not use the heating function and keep your drain in a warm space.

    My grandparents had a gas boiler and a heat pump they often used the heat pump when the outdoor temp was over 30° and they wanted a little heat without warming up 5 tons of concrete slab.

    Walta

    1. mcpascaln | | #7

      Hi Walter,

      You stated in part tht "...the danger is in cold weather, liquid refrigerant will migrate to the coldest part of the system. When the breaker is on the system runs a small heater in the compressor to vaporize any liquid before it could enter the compressor and damage the compressor"

      That is exactly what I had in mind when I indicated the system's reliability would be negatively impacted". Its certainly a concern since Mini Split ductless system are designed to last between 15 to 21 years under normal condition usage. Frequent yearly switch off during months of no need, risk damaging the critical compressor part.

      Its highly doubtful if Mitsubishi company would recommend this practice. I see that the long 8-months of no use would certainly consumer electricity, something that is a kin to wastage. It does not make sense to pay for something you really do not need or use. Yet keeping the system running continuously all year round is critical to maintaining its reliability.

  4. FluxCapacitor | | #9

    Have you been told this by more than one Mitsubishi rep? Ask where this is found In Mitsubishi’s installation or operation manuals.

    As Walter said ii believe it is not “critical” to keep the system powered all year.

    The out door compressor is not tremendously different from traditional central air systems that people cover up and shut down every winter.

    if you decide to keep the system energized (but not running) I think the kWh consumed throughout the winter would probably be unnoticeable on your electric bill anyway.

  5. mcpascaln | | #11

    Hi FluxCapacitor,

    Thank you for your insightful feedbacks. No, I have never been told 'by more than one Mitsubishi rep'. I have today sent a new question to Mitsubishi cooperation. I will share here their response. I do not see this recommendation to shut off the unit during winter posted anywhere in the Mitsubishi ductless mini split manual. I never knew that owners of the traditional central air systems tend to cover them up and shut down every winter.

  6. mcpascaln | | #12

    Here is a copy and paste from this site at https://ductless.ca/products/mitsubishi-m-series-mr-slim/. It states that “All Mitsubishi Electric ductless units have catechin plus air purifying and anti-allergy blue enzyme filters to eliminate bacteria, deodorize and kill viruses in the air. The filters also trap dust, pollens, mites and other particles which can cause allergic reactions”.
    Assuming I were to shut off the unit during the winter time of no need but keep it energized to prevent freezing, I really do not know if this kind of function continues throughout the year or when the system is only in operational use.

  7. walta100 | | #13

    I need to be very clear. If the unit has been deenergized it needs to be reenergized a full 48 hours before it is operated. Putting a note on the circuit breaker would be a good idea when you are turning it off.

    I am skeptical of this statement. “All Mitsubishi Electric ductless units have catechin plus air purifying and anti-allergy blue enzyme filters to eliminate bacteria, deodorize and kill viruses in the air. The filters also trap dust, pollens, mites and other particles which can cause allergic reactions”. If that said the blue coating reduced the surface tension and helped the coils shed water from their surface faster you could maybe claim some of those benefits.

    To my ear this sound like marketing BS In my opinion we humans have not invented a coating that can be applied once to a surface and will continually kill verses for years to come. I believe catechin is one of the latest cure all fads in Asia. I take all the sales literature with a grain of salt. Doubt you will find similar claims in the insulation or operating manuals.

    Deenergized the unit will not damage the coating in any way.

    Walta

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