Large Heat Pumps in District Heating Systems: How they work

Large Heat Pumps in District Heating Systems: How They Enable Efficient and Low-Carbon Heating

District Heating (DH) may be a century-old concept, but its role in today’s energy transition has never been more relevant. As cities and utilities pursue cost-effective decarbonization, district heating networks must become more efficient, intelligent and flexible.

Modern DH customers demand three things: reliability, affordability, and easy control and optimization. At the same time, utilities are under pressure to drastically reduce CO₂ emissions while maintaining security of supply.

To meet these challenges, large-scale heat pumps have emerged as one of the most effective technologies for transforming traditional district heating into a low-carbon, future-proof energy system.

Why Are Large Heat Pumps Important for Modern District Heating?

District heating systems are increasingly shifting away from fossil-fuel-based boilers toward electrified and renewable heat generation technologies. Organizations such as Euroheat & Power and the International Energy Agency (IEA) consistently identify large heat pumps as a cornerstone technology for decarbonizing district heating networks.

Large heat pumps allow DH systems to:

• Recover and upgrade low-grade heat

• Reduce primary energy consumption

• Lower operating costs

• Integrate renewable electricity

• Stabilize energy prices

• Reduce CO₂ emissions

At ARANER, large-scale heat pumps are a key element of integrated district heating solutions designed to meet long-term sustainability targets.

What Are Large Heat Pumps?

A heat pump is a system that uses external energy—typically electricity—to transfer heat from a low-temperature source to a higher-temperature sink.

A heat pump is considered large-scale when its capacity exceeds 1,000 kW (1 MW). Depending on technology and compressor type, large heat pumps can reach capacities of 20–30 MW and deliver outlet temperatures of 90–100°C, making them suitable even for high-temperature district heating networks.

Why Large Heat Pumps Are Highly Efficient

Large heat pumps achieve very high efficiency—expressed as Coefficient of Performance (COP)—especially when the temperature difference between the heat source and the heat sink is low.

They use a refrigerant cycle to:

• Absorb heat in the evaporator

• Upgrade it through compression

• Release useful heat in the condenser

How Do Large Heat Pumps Work?

Large heat pumps operate mainly using two thermodynamic cycles:

Vapor Compression Heat Pumps

This is the most common technology in district heating applications.

The vapor compression cycle includes:

• Evaporator

• Compressor

• Expansion valve

• Condenser

It is widely adopted due to its:

• High efficiency

• Operational flexibility

• Broad capacity range

• Maturity and reliability

Absorption Heat Pumps

Absorption heat pumps are driven by thermal energy instead of electricity and use working pairs such as:

• Water / ammonia

• Lithium bromide / water

While effective in specific applications, vapor compression heat pumps remain more common in DH systems due to higher performance and easier integration.

Why Are Large Heat Pumps a Perfect Fit for District Heating?

Large-scale heat pumps are particularly well suited to district heating because they can upgrade locally available low-grade heat sources into valuable thermal energy.

Typical Heat Sources

• Waste heat from industry or data centers

• Sewage water

• Groundwater

• Rivers, lakes or seawater

• Excess heat from cooling systems

By using electricity—ideally from renewable sources—large heat pumps significantly reduce fossil fuel dependency.

Combined Heating and Cooling Benefits

When heating and cooling demands exist simultaneously, large heat pumps can:

• Recover waste heat from cooling processes

• Supply district heating

• Dramatically increase system-wide COP

This makes them ideal for district heating and cooling networks, industrial zones and urban developments.

Large Heat Pumps and the Future of Smart Cities

Future cities face a structural challenge: heat demand and heat supply are often spatially and temporally mismatched. This leads to energy waste unless systems are integrated intelligently.

Large heat pumps play a critical role in:

• Smart city energy systems

• Sector coupling (power–heat–cooling)

• Integration with thermal energy storage

• Flexible demand response

When combined with heat storage, large heat pumps enable advanced energy management strategies that align perfectly with smart city concepts promoted across Europe.

Importantly, they can be:

• Integrated into existing DH networks

• Installed as add-ons

• Designed as stand-alone systems

How to Choose the Best Large Heat Pump for a District Heating System

Selecting the right large heat pump requires a detailed engineering assessment.

1. Availability of Heat Sources

The heat source must be:

• Abundant

• Reliable

• Close to the DH network

Common sources include sewage water, groundwater and surface water.

2. System Design and Operating Strategy

Large heat pumps should be designed for:

• Baseload operation

• High efficiency at part load

• Long annual operating hours

Peak loads are typically covered by:

• Electric boilers

• Biomass boilers

• Gas or oil-fired boilers (as backup)

3. Refrigerant Selection

Common refrigerants include:

• HFCs (e.g. R134a)

• HFOs (e.g. R1234ze)

• Natural refrigerants such as ammonia (R717)

Low or zero Global Warming Potential (GWP) is a key requirement.
ARANER designs systems that comply with local regulations while maximizing performance.

4. Compressor Technology and System Layout

• Screw compressors (often for ammonia)

• Centrifugal compressors (large capacities)

• Two-stage designs for improved performance and reliability

Large Heat Pumps vs Boilers in District Heating

Compared to conventional boiler systems, large heat pumps offer:

• Much lower CO₂ emissions

• Higher overall efficiency

• Reduced reliance on primary energy

• Better integration with renewables

With supply temperatures up to 90–100°C, large heat pumps can support even traditional DH networks. The transition toward 5th Generation District Heating, with supply temperatures around 60°C, will further increase their efficiency and attractiveness.

Conclusion

Large-scale heat pumps are a cornerstone technology for the decarbonization of district heating systems. By leveraging waste heat and renewable electricity, they deliver high efficiency, flexibility and long-term sustainability.

As district heating networks evolve toward lower temperatures and smarter operation, large heat pumps—engineered and integrated by experts like ARANER—will play a central role in building resilient, low-carbon urban energy systems.