Heat networks are front and center in numerous initiatives aiming at decarbonizing heat today.
As moving away from fossil fuels becomes a necessity, heat networks stand out for their potential to deliver cost-effective heat with low carbon output, achieving the much sought-after clean energy transition.
The clean energy transition has already been supported by key international organizations and public authorities, including the United Nations Environment Program. Through this institution’s report ‘District energy in cities’, the UN names a few noteworthy achievements of heat networks, including Milan’s savings of 2.5 tons of particulate matter, 70,000 tons of CO2, 50 tons of NOx and 25 tons of SO2 in 2011; and Oslo, which, at the time the report was published, had reduced the equivalent to 150,000 cars driving 15,000 km a year.
Energy used for heating accounts for around half of the EU's total gross final energy consumption, according to Eurostat. A figure that speaks of a pressing need to envision low-carbon, efficient heating systems that also deliver affordable heat to end users.
At this critical junction, heat networks present an unmatched potential that has already been tried and tested successfully in numerous initiatives around the world.
What is a heat network?
The most comprehensive definition of a heat network is that of a system that employs a single heat source to then distribute said heat in the form of hot water or steam through a network of pipes to various end users.
The reach of heat networks can vary, from various dwellings in a single building (more typically termed as communicable heating); to local clusters of buildings, entire districts or cities (district heating network).
Today, the most advanced heat networks include:
- 4th generation heat networks: centralized, operating at low temperatures and innovating by incorporating renewable energies as their source.
- 5th generation heat networks: focus on decentralization and modular design for escalation, able to operate at lower distribution temperatures (even lower than 4th generation), and which integrate heating and cooling possibilities thanks to heat pumps, as well as a wide range of renewable energy sources.
As such, even if all heat networks share the “single heat source” characteristic, specific implementations are heterogeneous and can be made to serve diverse needs.
All in all, heat networks provide economic and environmental benefits when there’s an accumulation of heating demand in an area.
Additionally, the capacity to incorporate a variety of heat generation methods (from combined heat and power (CHP) plants, to urban wastewater, and geothermal plants, among others) has put heat networks in the spotlight today.
Heat and cooling networks
While the term heat networks described above typically involves the transportation and generation of heat, the ‘single-source of thermal energy’ model can also be applied to cooling.
This is where cooling networks (or district cooling) come in: systems that distribute cooling energy in the form of chilled water from a single source to multiple endpoints. Air-cooled, water-cooled and sea-cooled models stand out today as the most efficient options for district cooling.
Additionally, heat pumps facilitate the generation of yet another efficiency: the development of systems that combine heating and cooling.
Structure of heat networks
As mentioned above, heat networks can assume various forms in order to adapt to each project’s needs. However, the following elements are typically present:
- Production plant: in charge of generating and supplying hot water or steam. The plant can incorporate a heat pump as a means of heat generation, as well as use various energy sources, including solar thermal or geothermal, among others.
- The Distribution Piping Network (DPN): working as a closed loop, the system is in charge of connecting production plants and end users, and conveys energy in the form of hot water.
- Energy Transfer Stations (ETS): in-building equipment that ensures heat is delivered to final users.
The role of heat pumps in heat networks
Within heat networks, the main role of heat pumps is to generate heat by extracting thermal energy from a natural heat source and amplifying it.
Heat pumps have been hailed for tapping into free, natural sources of energy and promoting the recycling of heat, so that energy that would otherwise be wasted is employed from sources such as industrial wastewater, groundwater, air or seawater, among others. The result is heat that minimizes carbon dioxide emissions and reduces energy costs.
Heat pumps bring in a number of benefits:
- They are highly efficient: they often produce several units of heat for each unit of electricity consumed (their average coefficient of performance or COP values typically ranges between 3 to 6). This also translates into heat that is cost-efficient.
- They allow for the electrification of heat: heat pumps use electricity to drive their refrigeration processes
- They promote the incorporation of renewable energy sources, including low-grade sources. They thus offer outstanding reductions in CO2 emissions, particularly in medium and low temperature networks
There are diverse approaches to integrating highly-efficient industrial heat pumps into heat networks. From retrofitting them as part of existing systems, to devising distributed heat pump models, where heat pumps are installed closer to the points of use.
Benefits of pairing heat networks and heat pumps
- It benefits from the increased efficiency of using a single centralized heat source.
- Can be designed to harness a wide-range of low-carbon energy sources, effectively activating the decarbonization of heat. Available heat sources are diverse and include heat from the air, bodies of water (lakes, rivers, seawater), recovered heat from industrial processes, cogeneration processes or renewable energy sources (geothermal, solar thermal, biomass…).
- Have the potential to generate circular models by employing energy sources that are locally-available and that would otherwise go to waste (such as wastewater or heat produced by data centers).
- Promote energy efficiency through the inclusion of industrial heat pumps, which also translates into lower operational costs
Challenges and solutions
High capital costs for heat pumps and electricity prices are frequently cited as obstacles to their widespread adoption in district heating, despite their potential for enhanced efficiency.
However, and as mentioned in the ‘Heat Pumps in District Heating’ report by the Department of Energy and Climate Change in the UK, they can offer supplementary benefits that sway the balance in their favor. For instance, the document cites the enhanced possibilities of networks that combine heat and cooling, an approach that provides a two-fold solution: heating and cooling loads are balanced; and decreased heat demand in warm seasons doesn’t lead to part-load operations, covering a typical source of inefficiencies.
Furthermore, additional advancements in smart control systems and thermal engineering are taking efficiency to new frontiers, challenging notions around the financial viability of heat networks. Such is the case of the incorporation of thermal energy storage (TES) technology, that provides peak load savings and outstanding increases in efficiency, thus promoting significant cost reductions.
All in all, the ability of heat networks incorporating heat pumps to enable an urban energy transition that is economically viable and sustainable, has been proven in a number of initiatives around the world. In this context, it’s not an overstatement to say successful projects largely depend on expert design that incorporates each project’s needs, limitations and potential.
At ARANER, we’re committed to designing district heating solutions that adapt to each project’s needs. By harnessing locally-available resources and having cost-efficiency and sustainability at their core, our district heating solutions put cutting-edge thermal technology to work.
Learn more by downloading our free guide about District Heating technologies, or get in touch with us and discover how we can help your project.
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