Closed heating systems are defined as hot water systems in which temperatures of 110 °C or more are achieved and the pressurised water is used as a heat transfer medium.

Hot water systems are used in district heating plants for cities or for the transfer of heat in industrial plants.

The water in a hot water boiler must not evaporate. The safety flow temperature of the hot water boiler must thus be lower than the saturated water pressure associated with the safety temperature.

Hot water boilers are suitable for district and local heating networks, as well as for industrial processes.

In systems that require temperatures exceeding 100 °C, the hot water boilers no longer fall within the scope of EN12828 for heating systems but instead within EN12953 for fire-tube boilers. To ensure that the water does not evaporate when it exceeds 100 °C and remains liquid, a certain system pressure is required. The system pressure increases with the flow temperature and is not only dependent on the steam pressure, but also on the control accuracy of the safety valves and fittings such as the temperature limiter, pressure limiter and safety valve. The system pressure is thus well above the evaporation point.

Schmid product range:

  • Low pressure hot water boiler 550 – 6500 kW, flow temperatures 100 – 108°C, safety pressure 6 bar 
  • High pressure hot water boiler 700 – 6500 kW, flow temperatures 120 – 160°C, safety pressure 15 bar 

All Schmid hot water boilers are designed as forced circulation boilers with external pressure holding systems according to EN12953-6 A 4.

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