“A District Heating Heat Interface Unit (HIU) is a device used in district heating systems to interface between the centralized heat source and individual heating systems in residential or commercial buildings. District heating systems distribute heat generated from a central location (such as a power plant or a combined heat and power facility) through a network of pipes to multiple buildings, providing a more efficient and environmentally friendly way to heat homes and buildings compared to individual heating systems.

The HIU serves as a connection point between the central district heating network and the internal heating system of a building. Its primary function is to control the heat exchange process, allowing residents or occupants to access the heat and hot water they need while maintaining efficiency and flexibility.

Components of a District Heating Heat Interface Unit (HIU):

Flow and Return Connections: The HIU is connected to the district heating network via flow and return pipes, which carry the hot water to and from the central heat source. These connections are where the heat exchange takes place.

Plate Heat Exchanger: The plate heat exchanger is a critical component that transfers heat from the district heating network to the building’s internal heating system. It consists of a series of plates with small channels in between. Hot water from the district heating network flows on one side of the plates, while colder water from the building’s heating system flows on the other side. Heat is transferred through the plates without the two water streams mixing.

Pumps: Pumps are used to circulate the hot water within the HIU, ensuring efficient heat transfer between the district heating network and the building’s internal heating system. There are typically separate pumps for the district heating side and the building side.

Temperature Sensors: Temperature sensors are placed at various points in the HIU to monitor the temperature of the incoming and outgoing water streams. This information is used to control the operation of the HIU and maintain optimal heat exchange conditions.

Flow Control Valve: This valve regulates the flow of hot water from the district heating network into the plate heat exchanger. It helps to control the amount of heat transferred and maintain a consistent temperature in the building’s internal heating system.

Safety Devices: HIUs often include safety features such as pressure relief valves and temperature limiting devices to prevent overheating or excessive pressure buildup.

How a District Heating HIU Works:

Hot Water Inlet: Hot water from the district heating network enters the HIU through the flow connection.

Plate Heat Exchanger: The hot water flows through the plate heat exchanger on one side of the plates, transferring its heat to the colder water on the other side of the plates without direct mixing.

Pumps: Pumps circulate the water on both sides of the plate heat exchanger, ensuring efficient heat transfer.

Temperature Control: Temperature sensors measure the incoming and outgoing water temperatures. The control system adjusts the flow control valve and pump speed to maintain a desired temperature on the building side.

Building’s Internal Heating System: The heated water from the HIU is then distributed to the building’s internal heating system, which can include radiators, underfloor heating, or other heating devices.

Return Connection: Cooled water from the building’s internal heating system returns to the HIU through the return connection.

Plate Heat Exchanger (Again): The plate heat exchanger on the return side can recover any remaining heat from the building’s return water, increasing overall system efficiency.

Cooled Water Discharge: Cooled water from the building’s return side is discharged back into the district heating network.

By efficiently transferring heat between the district heating network and individual buildings, HIUs help optimize energy usage, reduce waste, and provide consistent heating and hot water services to residents and occupants.”