DOI: 10.1515/SBEEF-2016-0030
SMART THERMAL GRIDS – A REVIEW
CRISTINA STĂNIŞTEANUa, b
a
UTCB Technical University of Civil Engineering, 122-124 Lacul Tei Blvd, 020396 Bucharest, Romania
ASRO Romanian Association for Standardization, 21-25 Mendeleev Street, 010362 Bucharest, Romania
E-mail: cristina.stanisteanu@asro.ro
b
Abstract. In line with the Renewable Energy Directive
(2009/28/EC), EU member states have intensified their efforts
to increase the share of renewable energy in energy supply.
Renewable energy sources will be a challenge for the current
district heating concept, requiring system flexibility both in
terms of heat supply and heat consumption. Besides, they are
hard to accommodate in areas with high population density, as
it is the case with many towns and cities. The municipalities
will have to identify suitable locations, which in turn will lead
to distributed heat supply. The requirement of the 2010/31/EU
(EPBD) Directive that all new buildings will have to be nearzero energy buildings will result in buildings fitted with solar
collectors; some buildings will produce more energy than they
can use. To accommodate all these challenges, the scientists
have come up with the new concept of Thermal Smart Grids.
The renewable energy will then be shared with the whole
district heating grid, and the network will also be used for heat
storage when consumption is lower than production. Smart
thermal grids are expected to be an integrated part of the future
smart energy systems, integrated electricity, gas and thermal
grids.
Keywords: smart thermal grids, fourth generation district
heating
1. INTRODUCTION
Climate change and energy dependency require urgent
measures for the improvement of energy efficiency in all
areas. District heating and cooling systems are facing new
challenges, like energy saving measures implemented in
buildings and the requirements to use renewable energy
sources. Scientists are struggling to find new ways to make
district heating efficient and competitive at the same time.
2. THE SMART THERMAL GRID CONCEPT
Heat supply in European countries is at a turning point.
The present context – climate change, energy dependence
and depletion of fossil fuel reserves – forces European and
national authorities to take action. The Energy Efficiency
Directive (Directive 2012/27/EU) requires that all
member states seek solutions for the most efficient energy
use on the whole chain from energy producer to the end
user. The European Commission places energy efficiency
at the basis of the Europe 2020 strategy and emphasizes
the necessity of a new strategy in energy efficiency as an
essential part of ensuring the sustainability of energy
resources. In the current context, saving the energy
resources and reducing carbon dioxide emissions are
crucial. The Directive on the Energy Performance of
Buildings (Directive 2010/31/UE) imposes measures for
energy conservation in buildings and demands that all
new buildings in the public sector are “near zero energy
buildings” starting 2019 and that all other new buildings
are “near zero energy buildings” starting 2021.
The implementation of energy efficiency measures in
buildings results in reduced heat loads, which in result
leads to low performances of existing district heating
systems supplying these buildings. Scientists have found
that heat can be supplied to renovated buildings at lower
temperature levels, covering the lower heat load and
increasing the system efficiency at the same time, as heat
losses in distribution pipes are also much smaller in low
temperature district heating systems.
Demonstration projects, funded by the European
Commission and the Danish Energy Agency, have shown
that district heating systems running at low temperatures
are very efficient; so efficient, that they become viable
even in low linear heat density areas. So, a new concept
was born: low temperature district heating (LTDH).
Central heat systems operating at low temperatures have
opened the way for a multitude of old and new energy
sources. Low grade waste heat from various industrial
processes has now become appropriate for using in central
heating systems. The potential use of renewable energy
sources will increase: low temperature heat from
renewable sources can be integrated into the systems:
thermal solar panels, geothermal energy (possibly assisted
by heat pumps), and even heat produced from excess
electricity (i.e. from wind turbines). Biomass and biogas
are also options to be considered, especially in
cogeneration plants.
But the ‘near zero energy buildings’ requirement cannot
be achieved by high energy performance buildings alone.
The new buildings can be fitted with new technologies to
produce energy from renewable sources (local renewable
energy sources). These buildings will be both heat
consumers and heat producers at the same time.
According to [1], in some periods more heat is produced
than it is consumed; it is recommended to transfer the
excess heat to the other buildings, reducing the share of
fossil fuels in the energy mix of the network. Energy
exchange between the buildings is advantageous in terms
of energy efficiency.
Renewable energy sources (solar thermal collectors,
geothermal energy) and heat pumps can be located in
available spaces and integrated in the district heating
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systems. This will lead to multiple distributed energy
sources of different temperature levels being present in
the network at the same time. Also, instead of having
energy sources on the one hand, and heat consumers, on
the other hand, some of the consumers will feed energy
into the network at the same time. Under these new
circumstances, the unidirectional network must turn to a
bidirectional network. To accommodate all these features
in one single network, future thermal grids will have to
undergo an important change; they must become
intelligent. So, the Smart Thermal Grids concept was
born, similar to the concept of ‘smart (electricity) grids’.
Both concepts focus on the efficient integration of
renewable energy sources, distributed energy generation
and involvement of consumers’ interactions [2].
According to [3], this approach allows any available
source of heat to be used. The main advantage of smart
thermal grids is their flexibility, their capability to
accommodate any changes that occur in supply and
demand of thermal needs in short-, medium-, and longterm [4]. The energy will be produced when available but,
at the same time, it will have to be available for use on
demand. This way, existing demand driven networks will
have to change and be driven by both demand and supply.
A smart thermal grid creates synergies between supply
and demand to generate the highest system efficiency [4].
According to [5], cascade usage of energy enables a
maximum exploitation of available energy resources. The
district heating systems must be designed in such a way
that heat is first supplied to consumers that need high
temperature (industry); low-temperature heat is then
transported to dwellings and other consumers with lowquality heat demand.
Smart thermal grids include some but not necessarily all
of the following:
- high energy performance buildings
- low temperature heating, high temperature cooling
- integration of local or distributed renewable energy
sources
- some heat consumers also become heat producers
- use of cogeneration and residual heat
- cascade usage to enable maximum exploitation of
available energy resources [5]
- shift from the demand driven network to a
combination of demand and supply driven network [6]
- flexible interactive networks
- heat storage
- integration of smart heat meters and more complex
control systems
- multiple temperature levels, including district cooling
- smart thermal grids, integrated in smart energy
systems (electrical-thermal-gas)
- national energy policy: the legal and institutional
framework to impose transition and to secure funding.
In 2014, SETIS (Strategic Energy Technologies
Information System) published a list of representative EU
and nationally funded projects in the field of smart
thermal grids that provides an overview of the current
research and development activities in this area.
The objectives of current research projects regarding
smart thermal grids include the estimation of potential for
RES integration in DHC systems at national, regional or
local levels, the development of solutions for this
integration into existing or new DHC systems, and
feasibility studies comparing diverse technologies and
their costs [2].
Although there are no large scale operational smart
thermal grids at this point, studies have been conducted
and demonstration projects have already been started.
Smart thermal grids pilot projects that are the basis of the
Key Innovation include the thermal network in Heerlen,
the Netherlands, the Sunstore4 demonstration in Marstal,
Denmark, the smart thermal grid at the TU Delft campus
in the Netherlands and the geothermal district heating
system in the Paris Basin [7].
Schmidt et al. (2012) consider that smart thermal grids
will play an important role in the future of urban energy
systems. Smart thermal networks need additional
metering and controlling capabilities to match supply and
demand profiles [8]. As heat generation from renewable
sources is variable and fluctuating, thermal energy must
be stored, in order to be available when it’s needed.
Depending on the size and complexity of the grid, the
network alone can be used for thermal storage or
additional storage units are required. Seasonal storage is
needed in some systems, so a new solution has been
developed for underground storage of thermal energy,
using two different technologies: borehole thermal energy
storage (BTES) and aquifer thermal energy storage
(ATES).
Integrated solutions (smart electrical-thermal-gas grids)
are now considered as viable solutions to ensure
maximum efficiency in future energy use.
3. RESEARCH PROJECTS, SMART THERMAL
GRIDS UNDER CONSTRUCTION OR IN
OPERATION
3.1 Dutch Smart Thermal Grid
A report released in 2016 by Studio Marco Vermeulen,
commissioned by CRA (Board of Government Advisors),
the Dutch Ministry of Infrastructure and the Environment
and PBL (Netherlands Environmental Assessment
Agency), proposes a new strategy for the sustainable heat
supply of various regions of the Netherlands. Currently,
the heat load of buildings and greenhouse farming in the
Netherlands is mostly covered by burning natural gas. In
order to become independent of the natural gas imports
and to mitigate climate change, several scenarios for
sustainable energy supply have been analysed. Two
options have been considered: local small-scale facilities
(such as heat pumps and solar water heaters) and heat
Scientific Bulletin of the Electrical Engineering Faculty – Year 17 No.1 (36)
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collective networks for heat production, storage, transfer
and distribution.
Currently, most buildings in South Holland are heated
with central gas-fired boilers. The cities of Rotterdam, the
Hague, Leiden and Dordrecht have district heating
networks based on either residual heat or cogeneration
systems running on natural gas (Figure 1). However, there
is a lot of unused residual heat from industry and power
plants, especially in the port area. The Green Deal signed
by the Dutch government and South Holland in 2011
provides that 14% of the heat demand will be covered by
waste heat and geothermal energy by 2020. In order to
meet this goal, the unexploited residual heat must be
transferred to the areas with high heat demand, such as the
cities of Hague, Delft and Rotterdam. Geothermal energy
will also be fed into the network. The “heat roundabout”
will provide heating for 350.000 buildings and 1000
hectares of greenhouse farming by 2020 (Figure 2). The
capital costs of the network are estimated at 4.5 billion
Euros, i.e. 520 million Euros for the main pipeline and 3.3
billion Euros for the distribution networks. As the project
is technically and economically feasible, the “heat
roundabout” is currently under construction. If
economically effective, further expansion of the network
is possible to supply heat to the remainder of the
consumers in South Holland.
In time, geothermal energy will replace the residual heat,
as it is more cost effective to reduce the distance between
heat supply and heat consumption. Studies have shown
great potential for geothermal energy in many regions of
Holland. Wells of different depths ensure different levels
of temperature for different consumers. The cogeneration
systems will be connected to the heating network, but they
will be running on biogas instead of natural gas (Figure
3). By 2035, all greenhouses in South Holland are
expected to be heated based on waste heat and geothermal
energy. In 2050, the network is expected to expand even
further and large areas will be connected to district heating
(Figure 4). The scientists are thinking of the Dutch Smart
Thermal Grid, a nation-wide heating network, where
parties will buy and sell heat in a competitive market
(Figure 5) [9].
Figure 1. Heat supply South Holland 2016 [9]
Figure 2. Heat roundabout South Holland 2020 [9]
Figure 3. Smart Thermal Grid South Holland 2035 [9]
Figure 4. Smart Thermal Grid South Holland 2050 [9]
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Heat storage will be implemented to ensure security of
supply and system efficiency, as heat could be produced
from renewable sources when heat demand is low (Figure
6). The future network will be open for all heat suppliers
and it will be used by energy producers to transport and
deliver heat to customers. An independent network
operator is needed to achieve this goal. A district cooling
system could also be developed as part of the grid.
The smart thermal grid will include advanced control
features to ensure both the security of supply and the
highest possible energy efficiency of the system.
Information and Communication Technologies will be
used for an optimum integration of energy sources, a high
efficiency operation of the system and communication
with the consumers [10].
Figure 5. Dutch Smart Thermal Grid 2050 [9]
3.2 The Hague’s Heat Initiative
The Hague’s Heat Initiative, founded by the Hague
municipality, brings together all stakeholders to ensure
affordable heating for customers within a competitive DH
market in the city of Hague. The initiative is a result of the
market failure of the existing district heating system in the
city, as customers have started to look for alternative
solutions for heating.
The project starts with a number of small heating grids
(heat islands), which will be later combined into a smart
thermal grid. Eventually, the system will be connected to
the regional “heat roundabout” which is a part of the
future “Dutch Smart Thermal Grid”.
Studies have been conducted and the result is that the new
heating grid is the best solution for about 100,000
households. As nobody can be forced to become a
customer of the new system, incentives have been created
to stimulate the consumers to connect to district heating.
Energy saving measures will be implemented at no cost in
all houses connecting to the system. Additionally, there
will be no costs associated to the connection to the system.
There is also a possibility for the customers to become
heat producers, and deliver energy in the network when
they produce more energy than they can use.
The heat load of renovated buildings will be diminished,
so the heat will be supplied to the consumers at lower
temperatures than in traditional district heating systems.
This will result in much lower heat losses and higher
efficiency of the system.
The new system is intended to be sustainable and
contribute to the reduction of CO2 emissions, so the heat
generation will be based on geothermal energy and
biomass. Residual heat from industry is also considered in
the initial stage of the project, but will be abandoned in
the future stages, as it is not sustainable. More renewable
sources are considered for further stages, including heat
produced from excess electricity (i.e. from wind turbines).
Figure 6. Average monthly heat demand and production. In
one year the demand equals the production but discrepancy
is found in time of production and consumption [10]
3.3 Low-exergy transmission pipes for storing and
distributing heat at different temperature levels
(LowExTra)
The LowExTra project, funded by the German Federal
Ministry for Economic Affairs and Energy, analyzes
medium and long-term solutions for space heating in
buildings. As a result of the EPBD (the Energy
Performance of Buildings Directive) requirement to build
„near-zero energy buildings”, the project introduces the
new LowEx heating network concept, as a flexible system
allowing buildings to be heat consumers and heat
producers at the same time. The new district heating
network can absorb or deliver thermal energy, depending
on the circumstances; it can supply energy to the
consumers according to their needs and at the same it is
able to integrate the heat the customers feed into the
network: solar, geothermal, waste heat or heat recovered
from various processes [11]. The heat delivered by
various heat sources, including renewables, has different
temperature levels, and the temperature required for
heating different spaces and for domestic hot water
preparation is also different, so the LowEx networks will
have multiple temperature levels on several lines, instead
of mixing the heat into one single distribution grid (Figure
7). The network is also capable of storing thermal energy
when heat supply exceeds heat consumption. The LowEx
Scientific Bulletin of the Electrical Engineering Faculty – Year 17 No.1 (36)
grids work as energy storage tools similar to vertically
stratified storage tanks, with inputs and outputs at
different temperatures. As a result, the LowEx grids will
be able to supply thermal energy at different temperature
levels, according to the customer’s needs (15°C, 30ºC,
45ºC, 60ºC, etc.) [12]. In order to meet all these
requirements, LowEx smart grids require complex control
and process management systems. The LowExTra project
partners are: the Technical University of Berlin, The
Hermann Reitschel Institute and the Institute for
Ecological Economy Research (IÖW) The project
proposes an integrated research approach: the technical
and economical feasibility of the smart multi-line grid will
be assessed, while the interest of the stakeholders (heat
producers and/or consumers, system operators) and the
political framework required for implementation will also
be analyzed.
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Figure 8. Minewater 2.0 project with a typical process
situation [13]
3.5 Smart Thermal Grids in Zurich, Switzerland
Three smart thermal grids are under construction in
Zurich, Switzerland: the Hönggerberg Campus network
(Swiss Federal Institute of Technology), the Friesenberg
network and the Richti Areal network.
The Friesenberg (Familienheim-Genossenschaft) network
(Figure 9) will supply 2.300 apartments and houses (5.700
inhabitants) with 35.000 MWh for heating and 80.000
MWh for cooling. A part of the heat load is covered by
waste heat from Swisscom Data Centre. Some of the
buildings have solar thermal collectors and there are three
heat pumps also feeding into the system [14].
Figure 7. In LowEx heating networks, consumers can be
producers at the same time and feed in heat from different
sources, including renewables. Consumers therefore
become prosumers. [11]
3.4 Minewater 2.0 project in Heerlen the Netherlands
A pilot district heating system has been in operation in
Heerlen, the Netherlands, since 2008. It uses the mine
water in the abandoned Oranje Nassau coal mines to
supply a low-temperature district heating system. Now the
system is being upgraded to a full-scale network, based on
a totally new concept. New renewable energy sources will
be added to the system, such as cogeneration based on
biomass, solar thermal panels, as well as waste heat from
industry and data centres. The mine water reservoirs will
be used for thermal storage, rather than as an energy
source. The hydraulic and thermal capacities of the
reservoir and wells will be maximized; the network will
be extended and the main pipelines will be resized.
Sophisticated control systems will be implemented to
ensure both thermal comfort and the maximum efficiency
of the system. The energy exchange (both heat and cold)
will take place between the buildings in the same network
and also, by means of the mine water, between networks
located in different areas (Figure 8).
The system is fully automatic and has 3 control levels:
building level (based on temperature), cluster level (based
on flow rate) and wells level (based on pressure) [13].
Figure 9. Layout of ‘Friesenberg’ FamilienheimGenossenschaft (FGZ) network in Zürich [15]
The grid is fitted with 280 (225 m deep) boreholes and
152 (250 m deep) boreholes for seasonal thermal storage
(Figure 10 and Figure 11).
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Figure 10. ‘Friesenberg’ Familienheim-Genossenschaft
(FGZ) network in Zürich [15]
Figure 11. Seasonal Balancing of Heating/Cooling Demand
[14]
The heating network was designed to work at low
temperature. A complex system will be implemented for
monitoring, control and dispatching. A part of the network
is in operation since November 2014 (Figure 12 and
Figure 13) and had an important impact on CO2 emissions
associated with heating the buildings (from 9.500 t/a in
2011 to 7.500 t/a in 2015). The CO2 emissions will
continue to decrease, dropping to less than 1000 t/a in
2050) (Figure 14). The fossil fuel share in the energy mix
for heating and cooling the buildings has dropped from
100% (2011) to 80% in 2015 and will continue to drop to
14% in 2050 (Figure 15) [15].
Figure 13. Operating figures – Load of Boreholes Field for
‘Friesenberg’ Familienheim-Genossenschaft (FGZ)
network in Zürich [14]
Figure 14. Greenhouse Gas Emissions for ‘Friesenberg’
Familienheim-Genossenschaft (FGZ) network in Zürich
[14]
Figure 15. Energy mix for ‘Friesenberg’ FamilienheimGenossenschaft (FGZ) network in Zürich [14]
The Richti Areal network will supply 5.700 MWh for
heating and 6.000 MWh for cooling to buildings having
an energy reference surface of 145.000 m2. A part of the
network is in operation since January 2014 [14].
The future Hönggerberg network will supply the campus
buildings (10.000 students) with 27.000 MWh for heating
and 16.000 MWh for cooling [15].
4. CONCLUSIONS
Figure 12. Operating figures – Waste heat demand and
delivery for ‘Friesenberg’ Familienheim-Genossenschaft
(FGZ) network in Zürich [14]
The transition to the fourth generation of district heating
systems and the implementation of smart thermal grids is
inevitable. Urban networks (power grids, gas grids,
thermal grids, waste water grid) will interact in the future
to ensure reliable energy supply and maximum energy
efficiency [2]. This is the only way we can achieve high
living standards, security of heat supply, climate change
Scientific Bulletin of the Electrical Engineering Faculty – Year 17 No.1 (36)
mitigation [8] and sustainability of energy resources at the
same time.
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