Residential Apartments - How to cater for HIU's/ Hot Water Cylinders when producing a CWS Hevacomp model

What is the preferred method for allowing a connection to these items of plant, we are experiencing issues when assigning the hot water loading units to the HIU / Cylinder within Hevacomp ie over sizing of pipework to the apartment and some of the distribution pipework.

The cylinder or HIU is set as a special outlet with the accumulative total of the hot water loading units.

Systems for the the apartments are been developed in line with BS EN806

Thanks in advance