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Thread: DC Fan Coil Unit energy efficiency

  1. #1 DC Fan Coil Unit energy efficiency 
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    http://en.wikipedia.org/wiki/Fan_coil_unit

    The above wikipedia page says this:

    "The reason that these DC Fan Coil Units are, despite their apparent relative complexity, becoming more popular is their improved energy efficiency levels compared to their AC motor driven counterparts of only a few years ago. A straight swap, AC to DC, will reduce electrical consumption by 50% but applying Demand and Occupancy dependant fan speed control can take the savings to as much as 80%."

    In my twisted logic I would have said that to have to include a transformer would introduce extra losses into the system - so I would have used a simple AC fan instead. Why does using a DC fan save energy?

    Thanks!


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  3. #2  
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    no ideas?

    my assumption is that a slower fan will allow a more efficient transfer of hot/cold......in car radiators for example you can have a coolant flowing too quickly through the radiator to allow the fins to dissipate the heat, so the heat builds up......

    in a similar scenario you don't want to push the air too quickly through the fins of a Fan Coil Unit as anything above the optimum air flow rate is wasted..........If I am not mistaken one cause of it is laminar flow which apparently forms an insulating layer...........

    would this assumption be correct?


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  4. #3  
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    The a-c motors they are comparing are probably the cheap-o shaded coil motors that don't develop much torque and run at low power factors. The reason the demand and occupancy dependent controls are more efficient is because they only run as fast as they need to.

    A slower running fan would not be more efficient at transferring heat. More flow means greater heat transfer. However, if you don't need the heat or the cooling, it's wasted energy.
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  5. #4  
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    Quote Originally Posted by Harold14370
    The a-c motors they are comparing are probably the cheap-o shaded coil motors that don't develop much torque and run at low power factors. The reason the demand and occupancy dependent controls are more efficient is because they only run as fast as they need to.

    A slower running fan would not be more efficient at transferring heat. More flow means greater heat transfer. However, if you don't need the heat or the cooling, it's wasted energy.
    Thanks harold - I appreciate that the demand and occupancy would work but am still unsure as to why changing for a DC fan over an AC one would make the system more efficient..........

    A 12V DC motor would have much less torque than an AC one even if it was of the shaded-pole type and need a transformer which would add losses and more parts to fail..............
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  6. #5  
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    Frankly speaking, we are manufacture for fan coil units(dekon-china), and since last year, we have got some inquiries from our buyers from USA and Taiwan, they request DC motor fan coil unit or EC motor fan coil units, which is much more energy efficiency and silent in function.<br>

    I really wish to learn this new product, and also i wish to share with all friends here our DC motor fan coil unit and EC moter fan coil unit, if they are really worthy of that high prices?<br>
    <br>
    I am a sales, i wish new technology comes to our products, but i also wish to have good prices which will lead a good sales, am i right?
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  7. #6  
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    Quote Originally Posted by fatman57 View Post
    Thanks harold - I appreciate that the demand and occupancy would work but am still unsure as to why changing for a DC fan over an AC one would make the system more efficient..........
    Because the process of AC to DC conversion, then drive with a DC voltage, is more efficient overall than a straight cheapo AC motor. That's why people use them.

    A 12V DC motor would have much less torque than an AC one
    It has as much torque as it is designed to have.

    even if it was of the shaded-pole type and need a transformer which would add losses and more parts to fail
    The primary failures in fans are mechanical - bearings and clogging primarily. Thus there is no real difference in reliability.
    dekon-china likes this.
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