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Downsizing is done by changing the temperature regime of the end-units, however, before you can start lowering the temperature you need to know to what supply temperature you can lower down. The easiest way to do is is to lower down the supply temperature setpoint of the boiler through a sensitivity analysis.
At a certain point, the boilers will not be able to provide enough heat and the 'building load space heating” will drop down. At this temperature, the drop in building load means an inability to provide the necessary heat. In the example below the fourth simulation significantly drops down. The temperature for the third simulation is therefore chosen as supply temperature.
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Th The temperature regime change needs to be executed by using the ‘Change regime and power’ function in Hysopt (shortcut: Ctrl+Shift+R), which can be found in the ‘Operations’ menu (
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IMPORTANT NOTE: the physics behind the change regime and power function are very specific to radiators only. Therefore, you can not use this calculation for air handling units and domestic hot water. |
Before clicking this function, make sure all end-units that need to be downsized are selected. Then, the pop-up window below appears, where three parameters are required: the target supply temperature, the target return temperature and the target room temperature. After clicking the ‘Apply’ button, the downsized end-unit heat capacities are calculated by Hysopt and the downsized temperature regimes are applied. Finally, it is important to redo the ‘Compute design flows’ step to recalculate all powers, temperatures and volume flows. Once the temperature regime of the end-units is lowered, also make sure to lower the heating curves and/or temperature setpoints in the system.
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