Originally Posted by
ACPM
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.