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  1. #27
    Join Date
    Apr 2013
    Posts
    27
    Quote Originally Posted by LKJoel View Post
    I had kind of limited my mind to a variable speed compressor and VS motors when considering this scenario. And have seen before that %25 of full load does not equal %25 of full load amp draw
    It's an interesting discussion to be had though
    VRV systems are clearly very different in terms of input power usage.

    The daikin split concealed unit databooks suggest that the most efficient "seasonal units" have input power coefficients of 0.33-0.40, that is 30-40% of the nominal power rating is consumed at the lower cooling limit (around 40% of the max cooling load). The graphics they show are linear, that is input power rises linearly from the min cooling capacity though the the nominal used for EER to the maximum for a constant airflow and temperature.

    I assume that cycling begins below that.

  2. #28
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,014
    Quote Originally Posted by ACPM View Post
    First thanks for such a detailed reply.

    A water based system is not an option as this is an old building with ceramic walls and marble floors but more smaller air units is. The issue is will larger units consume more power to over produce cool air in comparison with smaller units which have a lower min cool air production output but reach 75% of the larger max output.

    The specification calls for zoning so only the rooms in use will have the ducts open in the evening. The "cold blast" concern is that even though the conduct will be sized accordingly (to max airflow with all outlets open) and the internal unit will reduce the airflow to a min, there is a case when all the cool air could be directed at just one room which actually needs only 50% of the larger machine minimum output.

    I'm edging towards slightly under powering the installation. We can forget the night time areas with impulsion and return motorised vents. Also, we can specify that with extreme external temperatures, one zone will have to be closed off so that the rest has enough cool air when the machine can only produce 70-80% of peak at or beyond the max outdoor temperature. In return for this, a smaller machine will consume around 140kWh less per year based on the new ESSER rating.
    Not trying to be a 'know-it-all'... however this is the reason a zoned system can have smaller equipment. MAX load only happens on the few most extreme days... and generally if the system is not operated with setbacks (day/nite temps), this is a small issue.

    IMO folks who do residential zoning know the things you described...
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