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Sami Karjalainen, HVAC engineer at Oulun Energia Heating Services, recommends that the heating room be inspected from time to time.

The heating substation - the heart of a district-heated house


Heating substations used by properties heated with district heat have several names. It is most commonly called a heat exchanger. However, its official term is heating substation.

The reason people use different names for the same device may be due to district heating’s history. In the early days of district heating, at the end of the 1950s, district heating didn’t have its own equipment, but used the equipment used by the processing industry. These devices were called heat exchangers. Especially people from older generations still say heat exchanger when talking about heating substations. Although you can hear younger people say it sometimes too.

At some point, someone realised that actually, heat wasn’t being exchanged, but rather distributed. The heat is distributed from district heated water through the surface of the heat exchanger into heating and hot domestic water.

Heat exchanger is still a very common term for the entire heating substation even though it is actually only one component of the heating substation. As its name suggests, a heating substation is a station that distributes heat, and includes not only heat exchangers, but also pumps, valves, an expansion tank, and an automatic control system. In heating substations, there are usually at least two heat exchangers: one for heating and one for hot domestic water. A heating substation may also contain separate exchangers for ventilation or for more than one different heating circuit.

Left, the heat exchanger; right, the heating substation of the detached house.

The heart of a district-heated house

There is a good reason the heating substation can be called the heart of a district-heated house. In Oulu, the Toppila power plants and, since autumn 2020, the Laanila biopower plant provide the heart its first beats. In power plants, district heating water is heated to 65 to 115 degrees Celsius, after which it is distributed to properties’ heating substations via the district heating network. In the properties’ heating substations, the district heating water circulates through heat exchangers, giving off heat to be used for heating the property and for hot domestic water. The heating substation is the more efficient the cooler the district heating water is when it returns back to the district heating network.

District heating is easy to use and the heating substation equipment requires barely any maintenance. The heating substation’s automatic control system ensures that each room is warm and that there is sufficient hot domestic water. However, the heating substation and its automatic control system alone do not guarantee even room temperatures; for that, the heating network also need to be balanced. However, this work should be left to the experts.

The heating substation does not require a lot of space. Typically, the heating substation of a detached house has a width of about 60 cm, a height of about one metre, and a depth of about 40 cm. In addition, the piping and their insulation take up some space. There is no need for separate accumulators.

Heating substations are operational for a long time

Heating substations are also long-lasting. The physical life of a heating substation is approximately 20 to 25 years. When the heating substation reaches this age, it is worth considering replacing the heating substation in its entirety. However, it may be necessary to replace individual components along the way, such as pumps and control valves.

It is recommended to carry out a thorough health inspection for the district heating equipment when it is 10 to 15 years old. The health inspection determines the current condition of the equipment and its possible repair needs. The health inspection tests that the equipment works as designed in order to ensure that the heating substation continues to operate in an energy-efficient manner throughout its physical life, before a new and livelier device takes its place.


Heating substation instructional videos | Oulun Energia

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PLEASE NOTE!  ARA, the Housing Finance and Development Centre of Finland, is granting subsidies in 2022–2023 for the transition to cold district heating in residential buildings. Read more below!

Sami Karjalainen, HVAC engineer at Oulun Energia Heating Services, recommends that the heating room be inspected from time to time.

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