Central air VS ductless system

Discussion in 'HVAC Heating & Cooling' started by chaoster, May 23, 2008.

  1. chaoster

    chaoster New Member

    Aug 10, 2006
    I am thinking about a central air system in a 85 year old home. It has no ducts at all, It will be a complete new install. The central air will be cheaper. But I will lose some attic and closet space due to the blower and ducts. Which system would be better. The ductless system is a Mitsubishi (Mr.slim). The central air is a Carrier comfort series with a variable speed Blower. I also got an estimate for the performance model which also dehumidifies without the air being on. Is that function useful? It does cost a lot more. Any help/info will be greatly appreciated. TIA
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Have you looked into the high velocity, small diameter systems? The outlets are only a few inches in diameter and the velocity is high with a good difuser to distribute the air and prevent noise. The most outlets I've seen from a single ductless system is three. They can work well, but you do lose some wall space.

    As to dehumidification...you need to be able to move air across a cold surface to condense moisture. There are some techniques that run air through a chemical absorbtion bed, but you're still moving air through it. On those systems, once the chemical has absorbed as much moisture as it can, you have to then open a vent to the outside and heat it up to force it to release the captured moisture, so it isn't necessarily all the efficient, and you don't get any of the benefits of cooling.

    What some commercial units do is run both the heater and a/c simultaneously - the a/c to remove the moisture, and the heater to raiser the temperature, if the outlet temperature is too cold. That's rarely used in a residence.

    For moisture control...the best thing is a properly sized a/c unit (i.e., the worst thing is one that is too big). A variable speed fan can really help, too, as it extracts more moisture on each pass if the air goes over the coils slower. You feel much more comfortable with dry air, than colder, damper air.
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