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Inverters or Non Inverters Sys 3 aircons???

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SittingBull
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Inverters or Non Inverters Sys 3 aircons???

Postby SittingBull » Sat, 01 Aug 2009 12:58 am

Hi guys, for my apartment, i have been receiving conflicting advices from sales reps as well as friends. Since i have 3 small bedrooms which i intend for installation of aircons, some sales reps have been telling me about how inverter ones are attributing towards savings of around 50percent of electricity bills. A few others on the contrary said that if it is for home usage and that the aircons are typically switched on for only short period of time, ie from late night to early morn of around 6-7hrs, or during usage of study rooms during the evenings for a couple of hours, inverters WOULD NOT be significant, as savings would amount to be almost negligible. As inverter aircons typically cost almost 50percent more, what are the advices of you guys, and which group of sales reps are telling the truth? Lastly, is it true that Mitsubishi ones are overwhelming superior to the rest of the brands? Many thanks.

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Bafana
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Postby Bafana » Sat, 01 Aug 2009 4:56 am

Both lots are telling you part of the truth (sortofish) ~ Sale Reps are Sales Reps lah. Do you have a separate outdoor unit for each indoor unit or you are combining some indoor units onto the same outdoor unit? When are you most likely to use your AC and for how long?

Inverter technology and Variable Refrigerant Volume (VRV) systems will save you money over a standard split but only if you use them enough and depending upon your indoor unit Vs outdoor unit arrangement. This is called your Payback Period. How much are they quoting for each system?
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Postby SittingBull » Sat, 01 Aug 2009 10:19 am

I dun quite get what you mean. I will be having 3 indoor units for the rooms.. There is the aircon compressor which will be on the aircon ledge. The way i look at it, since the ACs are only in the rooms, the master bedroom should have it switched on from 12-6am, the study room probably 9pm-1am at max, cos i am a fan person, and usage of the room is only limited to free evenings when i do some computer games and internet surfing. The 3rd room is a guest room, and i dun expect visitors every single week. Cost of an inverter is around 800 more than a non.

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Postby Bafana » Sun, 02 Aug 2009 6:43 am

Sounds like you will be running them a fair bit so payback may not be that bad on an 800 up front investment since Singapore electricity is expensive.

Understand you have three indoor units but how many outdoor (compressor) units will you have? One for each of the indoor units or one for all of them? Reason for asking this, is if you have one big Outdoor unit you will save more energy with inverter control than with three smaller ones since the inefficiencies of the smaller units will multiply.

In any case you could estimate your energy consumption at around 120 W/sq.m (conservative for Singapore and depends on how far down you want to cool too) for around 70% all divided by the units Coefficient Of Performance (COP) (ask the sales rep) (COP is another name for efficiency ~ COP 3.5 is conservative for split systems and can go way up for inverter/variable refrigerant systems) i.e for every 3.5 kW cooling you need you will need 1 kW electricity. Once you have this figure you can then times the whole lot by the run time of each unit and the electricity cost per unit kW.Hr to give you a rough idea on what your energy bill will be related to your air conditioning.

Do this for the standard system and the inverter system and you will work out how long it will take you to payback the extra over you spent on the inverter system compared to the standard. This will also give you an idea of how much money you will save buy using the inverter system.

My feel is you will probably find that the inverter will payback 6-7 yrs depending on the size of the spaces being cooled, construction, glazing/shading and your selected comfort level (temperature set point).
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Postby SittingBull » Mon, 03 Aug 2009 1:03 am

Well, it's just one compressor for all 3 units. On that, i guess inverter does extend the lifespan of it. However, for a 6hrs a night in the MBR, with the study occasionally, i am just worried that i am underutilising an invertor aircon sys 3. Just found out that the Mitsubishi one cost aroudn 2.8k with the non inverter around 800dols lesser.. Not much of a diff in the long run i guess.

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Postby Bafana » Mon, 03 Aug 2009 3:25 am

If your an owner occupier (buying for your own home) suggest you get the inverter as it will pay for itself overtime and be cheaper to run in the long time. If you are renting then buy the cheaper one (sorry landlords out there - that includes me, as I am one as well).

A single outdoor unit on three indoor units should have significant energy consumption savings using an inverter.
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