Kaksiputkinen

Kaksiputkinen, meaning “two-pipe,” describes a hydronic heating, ventilation and air conditioning (HVAC) distribution arrangement used in buildings. In this setup, a central plant provides water that is circulated through a two-pipe network to terminal units such as radiators, fan coils or convectors. The two pipes function as a supply and a return line, carrying water at either hot or cooled temperatures depending on the season and system settings.

Operation and structure: at each terminal unit, a control valve determines whether hot water or chilled water flows through the coil. In heating mode, the system circulates hot water from the boiler through the supply line and returns cooler water via the return line. In cooling mode, chilled water is circulated instead. The same two pipes serve all terminal units, which keeps piping relatively simple and cost-effective. However, because the system typically cannot simultaneously supply heated and cooled water to different zones, balancing comfort and energy use across a building can be challenging compared with multi-pipe configurations.

Advantages and limitations: the two-pipe arrangement is generally simpler and cheaper to install and maintain, making it common in older or smaller buildings. It is adequate where heating and cooling demands are similar or where simultaneous load diversity is limited. Limitations include reduced ability to meet concurrent heating and cooling needs in different zones, potential comfort drawbacks if controls and balancing are not well implemented, and lower part-load efficiency compared with more complex systems.

In practice, kaksiputkinen systems are often augmented with modern controls, zoning, and variable-speed pumping, or are gradually replaced by four-pipe or other multi-pipe solutions to improve flexibility and efficiency.