Introduction

To avoid pipe oversizing, Hysopt will aggregate and weigh the different heating applications in the network. On each pipe, the supply for

1. domestic hot water (DHW)

2. heating prioritised by DHW (e.g. when HIU’s are applied)

3. heating not prioritised by DHW (e.g. when electric heaters are applied)

are aggregated and weighted based on diversity factors.

Aggregation methods

Design flow rates for heating prioritised by DHW, heating not prioritised by DHW, and DHW in the common pipe sections are calculated separately.
To calculate the installation components (pipe sections, primary pump, storage tank, boiler, ...) it is however necessary to have one design flow rate and one thermal power. Therefor Hysopt has developed two methods to aggregate the flow rates and thermal power in the common pipes as explained below.

To select your aggregation method, go to the settings page.

In the tab “Domestic Hot Water Design Flows“, you can select one of the following two “primary flow rate aggregation methods”.

1. Maximum of central heating and diversified DHW flow

2. Weighted average of central heating and total DHW flow

Maximum of central heating and diversified DHW flow

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 because of the diversity we apply, 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. In this method, 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.

This method is always used to aggregate DHW and CH on the primary side of an HIU within one dwelling. Why? Either the HIU is in DHW mode, either the HIU is in CH mode.

Weighted average of central heating and total domestic hot water flow

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 HIU’s are in DHW smode, and all the others are in CH mode. 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 diversity 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). Below you can see an example which 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.

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 diversity (green solid line), as more apartments are added the difference increases. As explained above, because not all apartments uses DHW (simultaneity) the KIU’s that are left uses CH therefore the combined flow rate is calculated (black dots line).