Fundamentals

Steam and hot water play a central role in energy and heat supply. They differ significantly in their area of application, physical properties and technical requirements. These differences must be taken into account in the planning and operation of steam and hot water boiler systems in order to achieve an economical and efficient system.

For both media, the principle applies that higher pressure in the system raises the boiling point. Pressures of up to 30 bar are used in Bosch boiler systems. During steam generation, the aim is to achieve a phase change from a liquid to a gaseous state. This gives steam a high specific heat capacity (enthalpy) and enables it to transfer large amounts of energy. In contrast, when using hot water, it is crucial that the boiling point is not exceeded and that the medium remains in a liquid state.

These different physical properties also result in differences in manufacturing and distribution. The generation of steam requires more complex system technology, e.g. with regard to water treatment and condensate management. In hot water systems, on the other hand, the focus is on hydraulic integration into the overall system. Unlike steam, pumps are required to transport hot water through the network.

Steam boilers are regulated by the pressure in the system; if the consumer draws more steam, the pressure in the boiler drops, whereupon the boiler’s combustion system kicks in and generates more steam to maintain the set operating pressure. For hot water boilers, the control is based on the temperature in the boiler. If the heat transfer in the hydraulic system increases, the return temperature to the boiler decreases. The combustion system then reacts to maintain a constant temperature in the boiler and therefore a constant flow temperature.

This results in various areas of application for hot water and steam. While steam is increasingly used in industrial processes that require high and rapidly available energy (e.g. food or chemical engineering) or as superheated steam to drive steam turbines, hot water is used in building technology, local and district heating supply, and also in industry. Each project must be examined individually to determine which of the two types of boiler is more economical and efficient for the specific application, or whether a combination of both types would be more appropriate.

Hot water boilers are subject to the same legal regulations as steam boilers. The high pressures result in safety requirements, such as the safety chain for shutdown in the event of a malfunction, which must not be bypassed under any circumstances. Simplified installation conditions only apply to boiler systems below 110 °C and < 0.5 bar. The environmental and emission protection requirements (e.g. sound) differ regionally and locally, but are the same for both application areas with conventional combustion systems or alternative fuels.

All Bosch boiler systems for steam and hot water can be equipped ex works for future-proof technologies, e.g. hydrogen utilisation. Hybrid systems with additional electrical heating are also possible. However, purely electrically powered hot water and steam boilers, which Bosch has already successfully established on the market, play a particularly important role in the energy transition.