About Pipe Network Calculation Potable Water
Explains the concept of pipe network calculation in potable water.
Detection of Network Geometry and Components
Before calculation, the pipe network is detected with all its details. This is done automatically after clicking Calculate. Only those components are detected whose system types are entered in the Settings dialog.
To analyze the geometry of the pipe network, the section parts are determined first. Section parts in the pipe network will be delimited by T-pieces or by components where pipe dimensions change (e.g. transitions).
The program then searches for the starting component of the pipe network. This could be a drilling and tapping clamp for cold water, a potable water heater for hot water and circulation or a partial network start, respectively.
On this basis, the flow paths of the pipe network are determined. Flow paths always lead from an initial component to a discharge valve, a partial network end or a termination (exhauster). The number of flow paths in a regular potable water pipe network is thus always equal to the number of installed end components.
Before calculating the pipe network, you can set some parameters in the Configurations dialog, e.g. the maximum static pressure, limits for velocities in different types of pipes and the maximum volume for hot water pipes without circulation.
You can also set the dimensions of placed components groups to exclude them from nominal diameter adjustment. This is useful, for example, if you use certain sections with associated sanitary objects multiple times in your model and do not want the varying pressure losses that result from the different positions in the pipe network to cause dimensioning of the components. To do this, combine the corresponding sections and sanitary objects into a model group and activate in the Configuration Apply dimension of a Revit group. A modification of the nominal diameters of components of the determined model group is then only possible via the respective parameter in the properties of the component in the model.
In the beginning of the pipe network calculation, the program determines the peak flow rates from the calculation flow rate in the pipe network. They depend on the selected building type and/or the assigned usage unit. You can set the building type globally for all sections in the Settings dialog or assign it individually to each section.
If you have assigned different building types within the same pipe network, the program selects the most unfavorable building type for section parts connected to different building types.
Considering the calculated total flow rate, which consists of peak- and continuous flow rate, the section parts are dimensioned in such a way so that prescribed maximum velocities are not exceeded. These are either defined in the Settings or defined individually for each section part.
Determining peak flow rate with DIN 1988-300 allows for three scenarios:
- Section parts within usage units
Are calculated according to usage unit-volume flow rate. In a section part with a connected usage unit, the two largest volume flow rates from discharge valves are used for the calculation (two users maximum). During this process, certain consumers (e.g. second washbasin, bidet, shower in combination with bathtub) are not considered for the peak flow rate based on the assumption that these are not operated simultaneously with another consumer within the same usage unit.
- Section part outside of usage units
The NE-volume flow rate is compared with that from the building curve. The smaller one will be used. If two usage units flow together, both volume flow rates are summed, compared to the building curve and the smaller of the two used for dimensioning.
- Section parts outside of usage units, for cases when consumer not assigned to a usage unit flow together.
Only the peak flow rate from the building curve is used.
Pressure losses for appliances (meter, valves, etc.) and fittings resulting from this dimensioning determine the pressure loss to be used by pipe friction in each flow path. The section parts that need to be considered for R-value calculation are dimensioned using the available pipe friction pressure gradient to achieve minimum flow pressure for all flow paths. The minimum flow pressure may also be slightly below the minimum flow pressure at individual discharge valves if this has been defined as permissible in the Settings. With this dimensioning, the velocities in the network and hence the pressure losses due to zeta value and possibly pressure losses for appliances change dynamically. These changes are tracked by the program to facilitate a differentiated calculation at all times. Maximum velocities for each section part are also constantly monitored.
Furthermore, to relieve surplus pressure at discharge valves, the network needs to be hydraulically balanced. Section parts belonging to more than one flow path are dimensioned such that they use up as much of the available pressure loss as possible. In consequence, some section part may be dimensioned smaller than those following after it. You can prevent this by activating the checkbox Always dimension decreasingly in the Settings dialog.
If you partitioned your network into several partial networks, the networks farthest away will be calculated first. The resulting data will be forwarded to connected partial network ends.
Circulating pipes are automatically recognized by the program via their system class and are dimensioned along with the entire network during calculation. You can switch between viewing the Potable water- or Circulation system in the calculation dialog, under System.
Within the same network, several circulation systems are possible:
- For pressure zoning in large buildings.
- For calculating several buildings (with each having its own potable water heater) connected to the same potable water system.
In the calculation dialog, you can switch the calculation of the circulation system to Simulation mode. Nominal pipe sizes, pump- and valve settings for the selected circulation system are fixed during simulation mode. The resulting mass flow rates and temperatures are then analyzed on the basis of these data.
A simulation is required for cases of large differences between the pressure recovery of the pump and the pressure loss of a flow path, since this leads to greater deviations between target and actual mass flow rates, resulting in different temperatures in the network. Existing systems can also be analyzed using the simulation mode.
If the hygienic minimum temperature of 70 °C is undercut during the simulation in Thermal disinfection mode, the program tries to increase the pump speed as a first step. If that measure fails or if the pump is from a neutral dataset, the temperature of the storage tank is increased from 75 °C to a maximum of 85 °C.