According to DVGW worksheet W551, a minimum of 60°C temperature must be reached in the hot water storage tank. Due to the circulation, the water must be returned to the storage tank at a minimum of 55°C. This task is carried out by a circulation pump. This ensures the required supply temperature is maintained and pathogens are killed. In order to realise the even distribution of water temperature, a controlled flow through all the pipes of the drinking water installation is necessary. As different plant components have different pressure losses, the differential pressures of the individual hot water pipes must be determined and adjusted by "adjustable resistors" in the pipe network. This hygiene calibration usually takes place by means of pre-settable control fittings. Where there is too much water, the water flow is slowed by the pre-setting.
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