Introduction

In collective housing (apartment buildings, dormitories, service flats, etc...) projects the heat distribution for central heating (CH) 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.

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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 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). The DHW flow rate increases non-linearly, as a consequence, the DHW flow rate at the upper apartments will be determining the flow rate,  as the number of apartments increases the CH flow rate takes over. The maximum of both will be used for component calculation (pipe sections, primary pump, storage tank, boiler, ...). The design flow rates, thermal power and temperature regimes (CH and DHW) are shown on the labels below. 

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In the second method the weighted average of central heating and total domestic hot water flow is taken into account. In contrast to the first method this method takes 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 some cases a flow rate which is too low. Hysopt uses the simultaneous 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_dot_CH,DHW). In the calculation below the above example (see chapter Simultaneous flows for DHW) is used to explain how the combined volume flow rate is calculated. On the basis of the known supply temperature, flow rate and thermal power, the return temperature is calculated.

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