In heating systems, different consumers may have varying requirements for temperature, pressure, heat transfer fluid quality, and circulation conditions. For example, a boiler room may operate with a high-temperature circuit, while a building’s heating system requires different parameters. Connecting such sections directly can complicate regulation and create additional operational risks.
One way to address this issue is to install a heat exchanger. It transfers thermal energy between two circuits without directly mixing their heat transfer fluids. This allows each circuit to operate under its own hydraulic and temperature conditions.
What Does Heating Circuit Separation Mean?
A heating circuit is a closed part of a system in which a heat transfer fluid circulates between a heat source and consumers. Depending on its purpose, a system may include several circuits: a boiler circuit, a heating circuit, a domestic hot water circuit, or a process circuit.
Circuit separation means that the heat transfer fluid from one circuit does not flow directly into the other. Instead, thermal energy is transferred through a heat exchange surface.
For example, water with specific pressure and temperature parameters may circulate in the boiler circuit, while the building’s heating circuit may use a heat transfer fluid with different operating settings. The heat exchanger transfers heat between them while keeping the two fluid flows physically separated.
How Does a Heat Exchanger Separate Circuits?
Most systems of this type use surface heat exchangers, particularly plate or shell-and-tube models. Their design provides two separate channels or spaces for the heat transfer fluids to flow through.
The hot heat transfer fluid enters one side of the heat exchanger, while the cooler fluid enters the other. A heat transfer surface separates them and allows energy to pass through. The liquids themselves do not mix.
The operating principle can be summarized as follows:
- The boiler circuit transfers heat through the heat exchanger surface.
- The heat transfer fluid in the secondary circuit is heated.
- The heated fluid circulates to radiators, underfloor heating systems, or other consumers.
- The cooled fluid returns to the heat exchanger for reheating.
Thus, a heat exchanger not only transfers heat but also provides hydraulic separation between two parts of the system.
Why Separate Heating Circuits?
Circuit separation is necessary when different parts of a system operate under different conditions or when a direct connection creates technical limitations.
Different Temperature Conditions
A boiler may operate at a heat transfer fluid temperature that does not match the requirements of the end system. For example, radiator heating, underfloor heating, and process heating may require different temperature conditions.
A heat exchanger allows the required amount of heat to be transferred to the secondary circuit, where the temperature can be regulated independently. This simplifies the operation of systems with different types of consumers.
Different Operating Pressures
The boiler and heating circuits may have different operating pressure requirements. This is particularly relevant for large buildings, industrial facilities, and systems where the heat source and consumers are located at different elevations or connected by extensive piping networks.
A heat exchanger allows the hydraulic conditions of the circuits to be separated. Each circuit can have its own circulation pump, expansion vessel, safety equipment, and other components selected according to its operating parameters.
Protecting the Boiler and Equipment
Separating the circuits can help reduce the impact of the heating network’s heat transfer fluid on boiler equipment. For example, the secondary circuit may accumulate contaminants, corrosion products, or other impurities that should preferably be prevented from entering the boiler.
However, a heat exchanger does not eliminate the need for water treatment, filtration, or heat transfer fluid quality control. It only physically separates the fluids, while the effectiveness of equipment protection depends on the system being properly designed.
Easier Maintenance and Modernization
Separate circuits are easier to regulate, maintain, and modernize. For example, replacing or modifying the secondary heating system can be carried out without extensive intervention in the boiler circuit.
This is particularly important for industrial facilities, where different consumers may operate according to different schedules, and shutting down the entire system to service a single unit may be undesirable.
Where Is Heat Exchanger-Based Circuit Separation Used?
This arrangement is used in both building and industrial heating systems.
In boiler rooms, heat exchangers can transfer heat from the boiler circuit to a building’s heating system, a heating substation, or a domestic hot water circuit.
In multi-story buildings and large administrative facilities, circuit separation helps ensure the independent operation of different parts of the system, including systems with different hydraulic parameters.
In industry, heat exchange equipment is used to separate circuits serving process equipment, cooling systems, production-area heating, or hot water preparation. In such applications, not only temperature and pressure but also the compatibility of materials with the working fluids are important.
Which Heat Exchanger Is Used to Separate Heating Circuits?
The choice of equipment depends on the system’s capacity, temperature, pressure, heat transfer fluid flow rate, fluid composition, and maintenance requirements.
Plate Heat Exchangers
Plate heat exchangers are widely used in heating and district heating systems due to their compact size, high heat transfer efficiency, and flexible heat exchange surface area selection.
Gasketed plate heat exchangers are convenient where regular cleaning is required or access to the heat transfer surfaces is necessary. Brazed models may be used in compact systems where small dimensions and the absence of detachable connections are important.
Shell-and-Tube Heat Exchangers
Shell-and-tube heat exchangers are used in industrial systems that require substantial thermal capacity, high operating parameters, or specific mechanical strength requirements.
They can be used for separating heating circuits, process heating, cooling, and other applications. The specific design is determined by the operating conditions and the characteristics of the working fluids.
What Should Be Considered When Designing the System?
Installing a heat exchanger alone does not guarantee that the system will operate correctly. The equipment must match the design parameters of both circuits.
The selection process takes into account the thermal load, supply and return temperatures, heat transfer fluid flow rates, operating and design pressures, hydraulic resistance, fluid properties, and allowable pressure losses.
It is also important to provide circulation pumps, isolation and control valves, filters, temperature and pressure monitoring devices, and, where necessary, automatic control systems.
For industrial equipment, additional factors include construction materials, corrosion resistance, cleanability, maintainability, and compliance with safety requirements.
Conclusion
A heat exchanger makes it possible to separate heating circuits without losing the thermal connection between them. One circuit transfers energy to the other through a heat exchange surface, while the heat transfer fluids remain isolated.
This solution helps establish independent temperature and hydraulic conditions, increase system flexibility, simplify maintenance, and adapt heat supply to the needs of different consumers. For boiler rooms and industrial facilities, the correct selection of heat exchange equipment is an important part of ensuring reliable and efficient system operation.
