Introduction
In collective housing (apartment buildings, dormitories, service flats, etc...) projects the heat distribution for space central heating (SHCH) and domestic hot water (DHW) can be implemented using satellite units. The satellite unit system exists of a central boiler room with a boiler and pump, heat distribution happens via a shared circulation pipe. The central heating and domestic hot water needs of each individual apartment is managed by a satellite unit.
...
When carrying over these norms to the space central heating system (satellite boilers or heat exchangers), the propagation of simulateous power also becomes important! This effect is amplified by the fact that space central heating often operates at lower power but higher flow rates / smaller temperature delta and domestic hot water heat exchangers operate at higher power but lower flow rates.
Hysopt incorporates an extension of the DIN 1988-300 (2012) standard into the Hysopt software. We have extended the calculation to cope with simultaneous space 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.
...
On the basis of the DHW design flow rate at the level of the heat exchanger and the performance of the heat exchanger (UA-value - W/K, from the technical specifications of the manufacturer), the primary DHW flow rate is calculated which is necessary for the transfer of the required thermal power. In this example, the primary flow rate 0.86 m³/h and the secondary flow rate 0.6 m³/h. The primary and secondary flow rate of space for central heating remains unchanged. The example below shows that there is a big difference between thermal power and flow rate according to SH CH and DHW, also the UA- value of the heat exchanger has a influence on the primary return temperature and flow rate of DHW.
...
Now the design flow rates and thermal power (SH CH and DHW) are known on the primary side of the satellite unit. In order to determine the design flow rate and thermal power into the common pipe sections, the SH CH flow rates are summed (0.33 m³/h + 0.33 m³/h = 0.66 m³/h). The DHW simultaneity flow rate is calculated as explained in the box below: the simultaneity flow rate per unit is converted to liters/sec (1), then to a total flow rate in liters/second (2) using the inverse simultaneity formula, the total flow rates of the different satellite units are summed and calculated back to a simultaneity flow rate. According to the standard the calculation needs to be done in liters/second.
...
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.
