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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Now the design flow rates and thermal power (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 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.
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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. On the basis of the known supply temperature, flow rate and thermal power, the return temperature is calculated.
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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). 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).
Parameterization of the satellite unit
The satellite unit must first be "parameterized" according to the manufacturers specifications, by clicking on the pencil a pop up will appear where the user can fill in the manufacturers parameters. The UA-value is calculated according the parameters.
Furthermore the design flow rate of DHW is determined as the maximum flow rate from the Eco-design draw-off pattern (S, M, L, XL - XXL) that can be set by the pull-down menu (see usage pattern). For simulations the draw-off pattern between the apartments can be shifted in time so not all apartments use DHW at the same time. The requested design temperatures can be filled in the upper fields.
