The temperature difference is the difference between the flow and return temperatures in a heating or cooling system. This difference fundamentally determines the efficiency, energy consumption and operation of the system. The temperature difference is usually given in degrees Celsius (°C), and the optimal value depends on the type and purpose of the system.
Temperature gradient in heating systems
Heating process: On the supply side, water heated by a boiler or other heat generating device flows. The water transfers heat to radiators, underfloor heating or fan-coil units, which transfer the heat to the air in the rooms. On the return side, the cooled water returns to the boiler to be heated again.
Example of temperature steps in heating systems:
- Traditional radiator heating: 75/65 °C (flow/return)
- Underfloor heating: 40/30 °C
- Low temperature systems: 55/45 °C
Efficiency and temperature gradient: With a higher temperature gradient, less water is needed to achieve the same heating output, resulting in less pumping energy and lower energy consumption. In the case of condensing boilers, the lower return temperature enhances the condensation process, increasing efficiency.
Temperature gradient in cooling systems
Cooling process: Water cooled by the cooling device flows on the flow side.
This cold water extracts heat from the rooms, for example through fan-coil units or chilled ceilings. On the return side, the heated water returns to the chiller to be cooled again.
Example of temperature steps in cooling systems:
- Conventional fan-coil systems: 7/12 °C (flow/return)
- Systems requiring a higher temperature difference: 6/16 °C
Efficiency and temperature step: A larger temperature step allows for a reduction in refrigerant flow, which requires less pumping energy and improves the energy efficiency of the system.
The importance of temperature control
Optimal operation: An incorrectly selected temperature setting reduces system efficiency, increases energy consumption, and can even shorten the lifespan of devices.
Hydraulic balance: The appropriate temperature gradient ensures that each branch of the system receives the required amount of heat evenly.
Design considerations: The temperature step must be determined based on the properties of the heat generating and heat dissipating elements when designing the system.
Practical applications
For condensing boilers: Low return temperatures maximize boiler efficiency by promoting the condensation of water vapor in the flue gas.
In heat pump systems: A low temperature stage increases the efficiency ( COP ) of the heat pump, especially when using underfloor heating or low temperature radiators.
In district heating systems: The large temperature step reduces the network pumping energy, improving the economy of the system.
Advantages and disadvantages
| Advantages | Disadvantages |
|---|---|
| Improves system energy efficiency | If the temperature gradient is too large, the rooms will heat up more slowly. |
| Reduces pumping energy | If the temperature setting is too low, the water volume requirement increases. |
| Supports the efficiency of modern low-temperature systems | Incorrect sizing can cause hydraulic problems. |
Summary
The temperature step is a key parameter in the design and operation of heating and cooling systems. The optimal temperature step ensures system efficiency, reduces energy consumption and increases the system's lifespan. During design and control, the characteristics of the heat source, heat sinks and the entire system must be taken into account to achieve the best possible performance.