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DC Inverters for Air Conditioners

written by: Om Thoke • edited by: Lamar Stonecypher • updated: 8/31/2011

Using the latest advancements in inverter technology, air conditioners are quieter to run and more economical to operate than conventional AC units. Let’s learn what this inverter technology is all about and the operating principle of these newer air conditioners.

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    An air conditioner described as using "inverter technology" or "inverter equipped" has the ability to continously control its thermal transfer rate by modifying the compressor's speed in response to the demand for cooling. So, the basic operating principle of an inverter is pretty straightforward as it is comparable to the technology used in cars, where you need to press the accelerator harder to go faster. The same rule applies here, too!

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    What Does It Do?

    The fixed speed compressor in a standard air conditioner runs at 100% capacity when it is started, but an inverter unit starts at a low level and then progressively enhances its capacity, depending on the requirement to heat up the room or cool it down. Fixed speed compressors start or stop automatically in order to sustain the desired temperature, but an inverter unit regulates regulates the capacity of the compressor instead.

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    How Does It Work?

    SEER 21 DC Inverter Air Conditioner - image credits: made-in-china.com DC inverter air conditioners make use of a variable frequency drive to regulate the motor's speed, thereby controlling the speed of compressor too.

    This variable frequency drive includes a rectifier that converts the incoming Alternating Current (AC) to Direct Current (DC). It then utilizes Pulse Width Modulation (PWM) of the DC in the inverter to generate AC of desired frequency. The alternating current is used to drive an induction motor or a brushless motor.

    Since the frequency of the alternating current and the speed of induction motor are directly proportional to each other, the compressors in an inverter window air conditioner unit operate at various speeds.

    The current ambient air temperature is then sampled by using a microcontroller and then the compressor's speed is adjusted appropriately.

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    The Size Factor

    Air Conditioner DC Inverter Wall Mounted Split Type - image credits: manufacturer.com Size also plays a vital factor here; oversized units are likely to produce a higher kVA and kW output in comparison to properly sized units.

    According to latest studies (Proctor Engineering, 2003), a 3-ton air conditioner for home usage, with the current technology that will have a diversified local peak of .4 to .5 kW less than existing SEER 1 0 units, can be easily built.

    Secondly, the SEER rating is not a very precise predictor of peak kVA or kW. As a matter of fact, several techinques deployed by the AC manufacturers that aren't very efficient in increasing the SEER include:

    • Variable speed compressor
    • Evaporator fan time delay
    • Scroll compressor
    • Two speed compressor

    At the moment, most of the variable speed units have higher current harmonic distortion and lower power factor range.

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    Advantages of Using Air Conditioner with Inverter Power

    Using inverter technology for air conditioners has several advantages:

    • The efficiency of air conditioners is enhanced since the start/stop cycles are eliminated. Hence, quicker cooling or heating can be attained.
    • The life of the components is also extended for the same reason.
    • Sharp fluctuations in the load that the air conditioner puts on the power supply are also eliminated.
    • Inverter air conditioners are cheaper to operate and are less prone to breakdowns.
    • The outdoor unit is normally quieter than that of conventional air conditioners.
    • They are more stable in operation and work without any fluctuations.

    Additionally, installing wall mount AC units gives you several advantages; you can read more about them, and how to install a through-wall or wall-mounted air conditioner here.

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    Downsides

    This advancement in technology is, however, not free from drawbacks.

    • Conversion energy losses are as high as 4 - 6% for each of the conversion steps; this loss is the result of energy conversion from AC to DC and then back to AC.
    • The complexity of the circuit becomes more complicated, adding to the production cost.
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    Buying Advice

    An inverter window air conditioner would make a great choice for those who live in places with hot climatic conditions wherein these cooling systems need to be used all the time. Here are a few buying tips for picking up the best unit to meet your requirements.

    • The first thing that you have to consider is the size of the room. Smaller units are sufficient for smaller rooms, while larger units are required if the room is pretty big; this is a great energy saving tip!
    • It is recommended to choose a dual-purpose unit with cooling as well as a dehumidifying feature; this can come handy since you’ll not need to use a separate heater in cold climates.
    • The brand is also one of the most important aspects to be taken into consideration; Fujitsu, Whirlpool and Daikin are our recommendations.
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    Other Applications

    The principle behind operation of inverter technology has been applied to a number of common household appliances that we use on daily basis, ranging from washing machines, down to microwave ovens. With the ability to achieve up to 30% higher operating efficiency than conventional AC units, operate more quietly, and probably be more reliable, inverter air conditioners are a great pick.

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