Overestimation of the required pressure in the cold water source in the installation with flat stations

Product	InstalSystem 5
Type of article	TIP&TRICK
Source for translation	2023-06-02

Problem description

During calculations of the installation with flat stations the following diagnostic message may appear:

• The V_s value calculated for the water supply installation connected to the flat station is higher than the value entered in the V̇_{HW Appartment} field. Calculations further take into account the entered value.
  
  

  1. Overestimation of the required pressure in the cold water source.
  
  

Solution

This hint relates to the determining the required pressure at the source of the water supply system. The key parameter in such calculations for installations with flat stations is Hot water outflow (Vs). The program offers two ways to take this value into account by specifying in the General data window Manner of defining: Hot water outflow:

• User specified - value of Hot water outflow declared manually;
• Acc. to calc. of the module: Water supply systems - value of Hot water outflow calculated by the Tap water systems module.
  
  

  2. Manner of defining: Hot water outflow.
  
  For more information, see: Designing installations with flat stations

The message appears when User specified method is chosen. The value V̇_{HW Appartment} set in the General data window or in data table of Flat station affects the pressure losses in the primary heating circuit supplying the flat stations and the heating output of heat exchanger.
For the calculation of pressure losses in the tap water circuit the value V_s computed accordingly Tap water systems module is taken, regardless of which method of calculation is chosen.
The value V_s is typically higher than the value V̇_{HW Appartment}. This is the reason of overestimation of the required pressure in the cold water source.
The following steps can be taken to reduce the required pressure in the cold water source:

• Adjustment of Normative outflow (HW)(Q_n HW) for single points of use;
• Exclusion of Q_n HW value for the selected point by specifying Not considered in the Demand type field;
  
  

  3. Normative outflow (HW), Demand type.
  
  
• Choosing for calculations the water supply standard DIN 1988-300.