The Importance of Air-Cooled Heat Exchangers in a Decarbonized Future
As the world shifts towards a more sustainable future, the role of air-cooled heat exchangers has become increasingly critical in decarbonizing the heating and cooling sectors. These versatile heat transfer devices can unlock the potential of renewable and waste heat sources, enabling the integration of air-based thermal energy systems into modern district energy networks and thermal distribution infrastructure.
Addressing the Heating and Cooling Challenge in Urban Areas
The building sector, responsible for nearly 50% of final energy consumption and over 25% of greenhouse gas emissions in Europe, has lagged behind in the green transformation (Mathiesen et al., 2019). Urban areas, home to 75% of the EU’s population and expected to rise to 85% by 2050, are particularly crucial in tackling this challenge (United Nations, 2018). The combination of high energy demands, dense populations, and the urban heat island effect creates a pressing need for innovative heating and cooling solutions.
Geothermal Energy: A Versatile Renewable Resource
One promising solution lies in the integration of geothermal energy into district heating and cooling (DHC) networks. Geothermal energy, a natural and renewable resource, can be harnessed at various depth levels and temperature ranges to provide sustainable heating, cooling, and even electricity generation. The Earth’s ability to store and produce heat, with temperatures exceeding 1000°C at 99% of its volume, presents a vast, untapped potential (Hoornweg et al., 2011).
Transforming District Energy Systems with Air-Cooled Heat Exchangers
Air-cooled heat exchangers play a vital role in enabling the integration of geothermal energy into modern DHC networks. These heat transfer devices can efficiently utilize low-to-moderate temperature geothermal resources, typically ranging from less than 10°C to over 90°C, for both heating and cooling applications (Lund & Toth, 2020). By seamlessly integrating these air-based heat transfer systems, DHC networks can evolve from centralized, fossil-fueled systems to decentralized, multi-source, and climate-neutral solutions.
Harnessing the Versatility of Air-Cooled Heat Exchangers
Air-cooled heat exchangers offer a versatile and adaptable approach to extracting and distributing thermal energy from a variety of sources, including geothermal, solar, and waste heat, within urban district energy networks.
Maximizing Efficiency through Temperature Optimization
One of the key advantages of air-cooled heat exchangers is their ability to operate efficiently across a wide range of temperature levels. By aligning the temperature requirements of the heat demand (e.g., space heating, domestic hot water) with the available heat sources, these heat transfer devices can optimize the exergetic performance of the overall system (Kavvadias et al., 2019). This “exergetic prioritization” principle ensures that low-grade heat sources, such as ambient geothermal energy, are utilized for space conditioning, while higher-grade heat is reserved for industrial processes or domestic hot water.
Integrating Geothermal Energy into Modern DHC Networks
Air-cooled heat exchangers enable the seamless integration of geothermal energy into modern, fifth-generation district heating and cooling (DHC) networks. These advanced network typologies use on-site available geothermal resources at different temperature levels to provide base-load heating and cooling, complemented by flexible, high-enthalpy sources for peak demand (Della Vedova et al., 2015; Manente et al., 2019).
| Geothermal Heat Source | Temperature Range | Potential Applications |
|---|---|---|
| Shallow Geothermal | Less than 30°C | Space heating and cooling, heat pumps |
| Low-Enthalpy Geothermal | 30°C to 90°C | Direct heating, district heating, industrial processes |
| Moderate-Enthalpy Geothermal | Above 90°C | Electricity generation, high-temperature industrial processes |
By utilizing air-cooled heat exchangers, these modern DHC networks can leverage geothermal energy as a base-load supply, while incorporating other renewable and waste heat sources to create a truly sustainable and resilient thermal energy distribution system.
Enabling Seasonal Thermal Energy Storage
In addition to their role in heat transfer, air-cooled heat exchangers can also support the integration of seasonal thermal energy storage solutions, such as underground thermal energy storage (UTES) systems. These storage technologies, which can utilize both solid subsurface and groundwater-filled pore spaces, enable the efficient seasonal shifting of thermal energy, further enhancing the overall sustainability and flexibility of the district energy network (Manente et al., 2019).
Addressing Urban Cooling Challenges with Air-Cooled Heat Exchangers
As climate change and urban densification drive up cooling demands in cities, air-cooled heat exchangers offer a sustainable solution to mitigate the urban heat island effect.
Transitioning from Conventional Cooling Systems
The traditional vapor compression cycle (VCC) cooling systems, while highly reliable, are characterized by high electrical energy demands and the rejection of excess heat, which can further exacerbate the urban heat island effect. Air-cooled heat exchangers provide an alternative approach, utilizing geothermal energy for efficient and environmentally-friendly cooling (Manente et al., 2019).
Direct Geothermal Cooling and Reversible Heat Pumps
By tapping into shallow geothermal resources, air-cooled heat exchangers can facilitate direct geothermal cooling, where the cold stored in groundwater or subsurface is transferred to buildings, requiring significantly less electricity compared to VCC systems. Furthermore, reversible heat pumps leveraging air-cooled heat exchangers can provide both heating and cooling, seamlessly transitioning between these functions based on seasonal demands (Della Vedova et al., 2015).
Integrating Geothermal Cooling into Urban District Energy Networks
The integration of air-cooled heat exchangers and geothermal cooling into modern DHC networks enables the creation of district heating and cooling (DHC) systems. These networks can provide both heating and cooling services to urban consumers, empowering them to become “prosumers” who can both consume and produce thermal energy, further enhancing the overall efficiency and sustainability of the system (Kavvadias et al., 2019).
Roadmap for Widespread Adoption of Air-Cooled Heat Exchangers
To unlock the full potential of air-cooled heat exchangers in urban district energy networks and thermal distribution systems, a comprehensive roadmap is necessary, guided by bold visions and collaborative efforts.
Ambitious 2030 and 2050 Goals
The EU-funded COST Action Geothermal-DHC has set ambitious goals for the integration of geothermal energy and district heating and cooling networks in Europe. By 2030, the aim is to increase the share of DH networks in the heating and cooling sector from 12% to 30%, while also raising the share of geothermal energy within DH networks from less than 3% to over 10%. By 2050, these targets are set to reach 50% in both cases (Geothermal-DHC, 2021).
Enabling the Geothermal Decade
The European Geothermal Energy Council (EGEC) has proclaimed the next decade, from 2020 to 2030, as the “geothermal decade,” emphasizing the critical role of this renewable resource in the green transformation of the energy sector. To achieve this vision, various stakeholders, including policymakers, industry leaders, and research institutions, must collaborate to drive the widespread adoption of air-cooled heat exchangers and other geothermal technologies within modern district energy networks (Geothermal-DHC, 2021).
Fostering Technological Advancements and Innovative Applications
Ongoing research and development efforts, such as those undertaken within the Geothermal-DHC COST Action, are crucial for advancing the design, efficiency, and integration of air-cooled heat exchangers into urban district energy systems. Innovations in materials, control systems, and hybridization with other renewable technologies will further enhance the performance and versatility of these heat transfer devices, unlocking new applications and enabling a seamless transition towards a decarbonized future (NREL, 2024).
Conclusion: Embracing the Air-Cooled Heat Exchanger Revolution
As the world strives to achieve ambitious sustainability goals, the role of air-cooled heat exchangers in transforming urban district energy networks and thermal distribution systems has become increasingly paramount. By seamlessly integrating geothermal energy, these versatile heat transfer devices can unlock a new era of efficient, renewable, and resilient heating and cooling solutions, paving the way for a greener and more livable urban future.
