Overview

Often as part of a Cold Water System (CWS) there will be a supply to a related Hot Water System (HWS). Thus there is a requirement to take the demand of the HWS into account.

Method

As BS EN 806 is based around the highest single loading unit in a system, care should be taken when choosing the most appropriate approach for your designs.

One option would be to create a Netsys HWS project to calculate the demand of your HWS alone.

Then, when modelling your CWS, to take the HWS into account you could take the resulting design flow calculated from the HWS project and enter this into your CWS project as a Special outlet with Continuous Flow, in litres per second.

Please note that this will simply add the additional flow rate into your system, so care should be taken to ensure this approach meets your design requirements. 

The above principles also apply should you wish to represent a series of outlets (e.g. a whole floor / zone) in one single outlet. To comply with the guidance of BSEN 806 it would be advisable instead to model the complete system, with all individual outlets.

You should not attempt to specify this cumulative demand as a single, large Loading Unit

Doing so is not in accordance with BS EN 806 (detailed here) for two reasons:

• This would further diversify the flow of the CWS. The diversity would have already been taken into account in your HWS project when entering the Loading Units for each HW outlet.
  
  
• The calculation method for BS EN 806 requires the value for the highest single Loading Unit - 15 Loading Units is the highest value it expects to find at any single outlet. This can be seen as highlighted on the graph below. (It would be very unlikely to find values exceeding this at a single outlet, however should this be the case then the option to instead enter a continuous flow figure is available).