Introduction
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Hysopt incorporates an extension of the DIN 1988-300 (2012) standard into the Hysopt software. We have extended the calculation to cope with simultaneous central heating and domestic hot water usage, and with combination of power needed in mixed systems.
In the example below, there is a shower- and a kitchen tap. When the flow rates are summed the total flow rate is 0.22 l/s, When using the simultaneous factor this becomes 0,17 l/s. For one satellite unit the difference between total and simultaneous flow rate is quite small, in case of a building with several units the simultaneous flow rate can go to 10% of the total flow rate which have a big impact on the pipe selection.
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In the text above the design flow rates from CH and DHW in the common pipe sections are calculated separately, therefor it has to be taken into account that some of the satellite units use DHW simultaneous and others will use CH. Simply taking the maximum of CH and DHW flow rate would result in a flow rate which is too low. Hysopt uses the simulateous factor f = DHW,S / DHW,T and then compensate for the central heating volume flow rate and thermal power on units not in DHW mode, by computing the combined volume flow (V_dotCH,DHW). In the calculation below the above example is used to explain how the combined volume flow rate is calculated.
In the graph below, the design flow rate of DHW and CH is shown as a function of the number of apartments. The CH flow rate, logically increases linearly as the number of apartments increases (blue solid line). In the case of DHW the total flow rate DHW (green dots line) is much higher than the DHW flow rate with simultaneity (green solid line), as more apartments are added the difference increases. As explained above because not all apartments uses DHW (simultaneity) the satellite units that are left uses CH therefore the combined flow rate is calculated (black dots line).
