An Overview of Renewable Smart District Heating and Cooling

Applications with Thermal Storage in Europe

Fivos Galatoulas

1,2

, Marc Frere

, Christos S. Ioakimidis

1,2,*

ERA Chair (*Holder) 'Net-Zero Energy Efficiency on City Districts, NZED' Unit, Research Institute for Energy,

University of Mons, 56 Rue de l’Epargne, Mons, Belgium

Research Institute for Energy, Boulevard Dolez 31, Mons 7000, Belgium

Keywords: Case Study, District Heating and Cooling, Renewable Energy, Thermal Storage.

Abstract: A series of transformations in heat and cold distribution systems is undergoing with the introduction of 4

generation District Heating and Cooling (DHC) technologies. At the center of this process is the integration

of renewable technologies, such as solar heating, geothermal systems with large heat pumps and cooling from

natural water formations. In this context, smart DHC systems are designed and early prototype

implementations are demonstrated in sites across the world. The purpose of this paper is to trace the latest

advancements in existing DHC networks and to identify early smart city technologies incorporated. A

summary of basic components and characteristics is attempted with focus on thermal storage technologies

coupled with renewable heating and cooling.

1 INTRODUCTION

The process of supplying district end users, for

instance residential and commercial buildings, with

thermal energy in order to cover heating and cooling

demand, is in the scope of district heating and cooling

networks (DHC) involving efficient heat distribution

designs. Since their dawn, DHC network systems

exploited a variety of energy resources, namely,

geothermal, fossil fuel, waste and biomass

incarceration. In the context of development,

combinations of heat production methods and

resources employed in DHC, underwent a series of

transformations (Lund et al., 2014) with the latest,

driven by the impact of climate change and fossil fuel

shortage towards abundant solutions, pointing

specifically to renewable energy resources. Table 1

summarizes the main DHC technologies generations

along with distinguishing characteristics.

Historically, DHC technologies have been

adopted in parts of Europe, North America and Asia.

Only in Europe it accounts for 12% coverage of total

heat demand (Euroheat & Power, 2015), with leading

adopters Scandinavian, Central and Eastern European

countries, which since the second half of the 20

century invest in large scale heat distribution

infrastructure. Specifically, DHC infrastructure has

Table 1: Generations of district heating technologies and

primary resources.

Timespan Production Primary

Resource

Generation

1880-

1930

Steam

Boilers

Coal

Generation

1930-

1980

CHP and

Heat Boilers

Coal and

Oil

Generation

1980-

Today

Large-scale

CHP

Biomass,

waste and

fossil

fuels

Generation

2020-

2050

Heat

Recycling

Renewabl

e Sources

claimed a principal role in thermal energy supply for

urban areas in these countries. The setting in Western

Europe appears more moderate, where countries such

as Germany and Switzerland receive a stable

contribution from these systems.

District cooling covers space cooling needs in

residential and commercial instalments. In any case,

location induced constraints towards the applicability

of the technology can be surpassed, with working

examples demonstrated in cities spanning from

Sweden to United Arab Emirates.

This paper aims to provide an overview of

innovative realizations of Smart district heating and

cooling supply, with focus on projects combining

Galatoulas, F., Frere, M. and Ioakimidis, C.

An Overview of Renewable Smart District Heating and Cooling Applications with Thermal Storage in Europe.

DOI: 10.5220/0006785703110319

In Proceedings of the 7th International Conference on Smart Cities and Green ICT Systems (SMARTGREENS 2018), pages 311-319

ISBN: 978-989-758-292-9

311

distribution with thermal storage under a wide range

of conditions. The second section describes the

concept of smart DHC networks and related

regulatory framework in Europe. Section III

summarizes the available technologies according to

early smart DHC networks with thermal storage

deployed across Europe. A recently delivered case

study at Rotterdam concentrating elements of a smart

thermal grid, is presented in the fourth section.

Finally, technology limitations and future prospects

conclude the paper in section V.

2 RENEWABLE DHC IN EUROPE

2.1 Smart District Heating and Cooling

DHC covers the generation and distribution of

thermal energy in districts. In the case of heating, the

design consists of a pipe network, filled with hot

water, and heat sources (centralized heat production

plant). Hot water circulates in the piping network

aided by pumps, from the heating plant to end-users

and backwards (Wiltshire, 2015). The heat hub relies

on heat exchangers placed at every end-user building,

in order to transfer heat from network to residential

node heating and hot water systems. Remaining water

from heat exchangers returns through the pipe

network and is pumped back to the heating plant,

where it is processed in a new heating cycle.

District cooling follows similar principles as

district heating. Indoor envelope temperatures can be

decreased with cold water, which is distributed in the

pipe network to end-user ventilation systems. Water

temperature ranges can start from approximately 6

at cooling site and return with approximately 16

Common methods developed for district cooling

supply comprise of free cooling (cold water from

lakes, seas or other waterways), absorption cooling

(uses a heat source to produce cold) and heat pumps

(produce heat and cold at the same time).

The vast majority of DHC networks operating

nowadays provide heat and cold generated from

centralized units (central plants) and are obliged to

comply with air pollution regulations, via the

enforcement of emission control methods, while,

efficiency and generation output volume differ

depending on the type of plant and energy resource

utilized (Wang et al., 2015). Undesirable fluctuations

in supply such as over-generation or under-generation

may result in energy waste or unsatisfied demand,

respectively. To this end, optimal management of the

generation units is required to ensure sufficient

energy distribution to end-users with maximized

efficiency, cost and minimum emissions.

Smart DHC introduces innovative solutions in the

domain of thermal energy management therefore

aiming to improve the performance of systems

(Mathiesen et al., 2015). Key technologies for this

transition are expected to be a) heat metering (smart

heat load meters, Gustafsson et al., 2016), b)

monitoring and automated control of heat exchangers,

triggering research in domains such as, Internet of

Things, thermal energy modelling and optimization

and power electronics and c) thermal storage with

complementary control systems (Wong et al., 2017,

Monti et al., 2016). Cogeneration and residual heat

usage, enable improved allocation of network energy

resources. From the end-user perspective, an upgrade

in radiator control through variable speed radiator

pumps is opted in order to facilitate network-

balancing issues without thermal discomfort side

effects. In a similar manner with smart power grids,

smart thermal grids can be designed, as heat load

consumers also contribute to heat production by

installing generation or storage components, where

besides participating solely in demand, they appear as

suppliers in a hybrid demand supply driven network

(van den Ende et al., 2015, Brand et al., 2014).

It is evident that major challenge for this

transition is to tackle efficiency drawbacks sourcing

from heat losses present in previous generation DHC

networks and low energy performance buildings. In

fact, when building refurbishment is considered as a

parameter in sizing of DHC systems, results indicate

additional economic and environmental benefits

(Pavičević et al., 2017). Increase in building energy

efficiency results in reduced heat demand, thus lower

performances are required for supply. At the same

time, heat losses in distribution pipes decrease in low

temperature district heating systems.

2.2 Legislative Framework

According to directive 2012/27 of the European

parliament, a common framework of actions has been

adopted regionally targeting efficient district heating

and cooling with high renewable energy shares for

2020’. The European directive defines efficient DHC

systems as those using at least 50 % renewable

energy, 50 % waste heat, 75 % cogenerated heat or

50 % of a combination of such energy and heat

(European Parliament, 2012). In Fig. 1 and Fig. 2,

current renewable heating shares and 2020

projections for European countries are illustrated

(REN21, 2017).

SMARTGREENS 2018 - 7th International Conference on Smart Cities and Green ICT Systems

312

Figure 1: European heating and cooling from renewable

sources shares in 2015.

Figure 2: European Heating and Cooling from renewable

sources projections for 2020.

It is important to mention that percentages

mapped in the figures refer to renewable sources

feeding all types of heating, not strictly DHC. It can

be observed that, Scandinavian, Baltic and Central

European countries have already achieved their 2020

targets, in contrast, Southern European countries,

UK, France and Germany maintain low renewable

penetration percentages for heating supply.

In national legislation level, Denmark and

Germany present the most comprehensive policies

related to DHC, providing details on federal support,

clean energy targets, connection obligations (appears

also in Poland) and end-user protection. In addition,

support policies may include low interest loans

(Japan), resource assessment subsidies (Switzerland),

tax incentives (US), and explicit targets (UAE,

Switzerland).

2.3 Potential Benefits

The widespread of renewable DHC systems is linked

with a number of potential benefits that can be

categorised into environmental, systemic, synergies

with urban environment and increased energy

security (IRENA, 2017).

In the first category, the following can be

recognized; a) achievement of clean energy targets,

higher renewable fractions are pursued, hence,

ensuring sustainability of the developed infrastruc-

tures, b) improvement of urban air quality, as carbon

dependent solutions lead to a series of negative exter-

nalities, especially in cities with dense populations

where air pollution evidently has diminished, c) rapid

and inexpensive green house gas emission reductions

and d) water consumption abatement, relevant to the

fact that natural water resources can be exploited for

example in cooling applications.

In the context of systemic benefits, at first, the

combination of technologies provides cross-sectoral

benefits, for instance, CHP can be coupled with

surplus from geothermal heat stating smart thermal

grids flexible, capable of handling variations present

in supply and demand, in short-, medium-, and long-

term; load profile is smoothened thereby relieving the

electricity grid. Moreover, utilization of local

resources in biomass or waste to heat systems creates

value in the financial chain and generates multi-scale

business schemes.

As urbanisation is rapidly progressing, integration

of renewable heat and cooling networks could free

construction space that would be necessary in

decentralized facilities (natural cooling). As a result,

visual impact is reduced and land-use can be

dedicated adaptively.

In countries recording major imports of fossil

fuels, local renewable sources ensure availability and

price securities. Similarly, using a mix of resources

secures the resilience of the energy system and can

achieve stable prices throughout operation.

3 TECHNOLOGIES

In this section main renewable technologies

integrated in DHC applications are described.

Depending on network size and complexity of the

network, the distribution system per se can function

as thermal storage or seasonal storage units may be

required (Lake et al., 2017). In Table 2, notable

renewable DHC applications across Europe are listed,

according to integrated technology (SDH, 2017,

An Overview of Renewable Smart District Heating and Cooling Applications with Thermal Storage in Europe

313

GeoDH, 2017, Perez-Mora et al., 2017, Bailer et al.,

2006, RES Chains, 2012, SIG, 2016)

3.1 Solar District Heating

Solar thermal systems transform solar radiation into

heat. Their efficiency is negatively influenced by low

irradiation and high temperature difference between

output hot water and outdoor ambient, leading to poor

efficiency during wintertime. Ensuring efficient use

in DHC requires them to be coupled to a seasonal heat

storage (to cope with the delay between efficient

production and heat demand) or to an absorption

chiller for cooling needs (alignment of efficient

production and needs). During wintertime, when low

temperature heat may be produced, they can be

connected to technologies that will upgrade the

temperature level (compression or sorption heat

pumps), (Hennaut et al., 2014).

Although, solar collectors have been used for

water heating in individual buildings, solar district

heating applications are recently rising as a

supplement for cogeneration (Joly et al., 2017). These

systems consist of large-scale flat plate solar

collectors deployed on landfill sites or on building

roofs paired with seasonal storage methods.

Specifically, large volume hot water storage tanks

store the heating medium during summer for use in

winter. Instead of tank thermal storage, underground

stores can be employed as either underground pit

thermal storage, gravel water underground storage or

last borehole storage. Exceptionally, aquifer thermal

storage is utilized, however, installation is more

complex and it is the least preferred method in solar

district heating systems. In borehole realizations,

secondary tanks can serve as a temporary node in the

network.

3.2 Geothermal District Heating

Geothermal district heating systems drain heat from

natural formations (geothermic wells) with high

underground temperatures and inject it to the

distribution network via injection pumps and heat

exchangers. A cool sink functions as a terminal for

the cooled fluid, thus completing the heating loop.

Surface features or shallow wells with temperatures

between 40°C and 150°C (Nielsen et al., 2016) are

suitable for hot water circulating in DHC systems,

whereas higher temperatures are ideal for electricity

generation. In shallow geothermal energy systems,

recovery of thermal energy (low or medium

temperature) is possible when paired with UTES

methods, such as borehole or aquifer storage.

Extraction of geothermal heat has low spatial

requirements. Nevertheless, installation works are

challenging in urban settings. In some occasions,

geothermal cooling has been demonstrated in

conjunction with absorption chillers.

3.3 Heat Pumps

Compression and sorption heat pumps use low

temperature heat sources in order to transform them

into useable heat. Actual renewable contribution

depends on their seasonal performance factor and/or

on the way, the driving energy (electricity for

compression HP and high temperature heat for

sorption HP) is produced. Their seasonal performance

is positively affected if heat is delivered at low

temperature (low energy buildings equipped with low

temperature heat emission systems) and if the low

temperature heat source is at “high temperature”.

Preheating the low temperature heat source with solar

thermal panels is a way of boosting the seasonal

performance factor. High temperature heat source for

driving sorption heat pumps may be produced by

biomass boilers, CHP or from medium to high

enthalpy geothermal fluid.

3.4 Biomass District Heating

Biomass-fired heat-only boilers replace traditional

fossil fuel combustion in CHP plants and

simultaneously provide an efficient measure of

cutting greenhouse gas emissions.

A wide variety of biomass fuels exist, dominated

by wood fuels, mainly consisting of wood chips and

sawdust. Biomass comprises a relatively reachable

alternative, suitable for use within the present heating

infrastructure, although heating capacities of biofuels

are lower, raising the amount of required resources

(Lund et al., 2014).

3.5 Solar District Cooling

The operation principle of solar cooling systems

relies on passing the heat output of panels used in

solar thermal systems to an absorption chiller for

cooling. Absorption chillers are used in applications

driven from excess heat from industrial processes or

waste incineration plants. Usually, heat can be

collected in plants and later on distributed to smaller

units closer to end users (Perez-Mora et al., 2017).

Compared to solar heating systems, solar

irradiation trend follows and contributes to cooling

peak loads.

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3.6 Natural Water Cooling

Water in low temperatures, originating from district

water sources, such as rivers, the sea or lakes can be

utilized for cooling purposes. In general, the former

function as either the heat sink or a heat exchange for

generating chilled water. Cold water is drained from

the water source with an inlet pipe structure and, via

plate heat exchangers, chilled water is generated and

circulated to buildings at a higher temperature. There,

the cold water is either injected directly into the

district cooling system or coupled to a closed loop

network via heat exchangers (Wiltshire, 2015).

Table 2: Demonstration sites for renewable DHC

technologies in Europe.

Technology Site Capacity Ren Frac

Storage

SDH

Silkeborg,

80 000

MWh

4 Heat

Tanks

64,000 m

GDH

Paray-Vieille-

Poste, FR

12 MWth 30 Aquifer

Katri Vala,

Helsinki, FI

60 MWh 32

11,500 m

Cold

Water

tank

Biomass Växjö, SE 90 MW 60

25MW

Hot water

tank

SDC

ParcBit,

Mallorca, ES

3,000

43.2

2 Cold

Water

Tanks

100 m

NWC

GeniLac,

Geneva, CH

13,250M

30 Aquifer

4 CASE STUDY

Even though large-scale smart DHC networks have

not been completed at the moment (Lund et al., 2014),

a case study concentrating DHC technologies with

seasonal storage and attributes in the domain of smart

thermal grids has been selected in the context of this

paper. Mainly, detailed information was retrieved

from EU Smart Cities Information System

(http://www.smartcities-infosystem.eu).

As a demonstration site for the EU funded

CELSIUS project, Rotterdam participated on two

interventions: a) development of an energy system

supplying with under-floor heating and cooling in De

Rotterdam (Rotterdam Vertical City), a mixed-use

building with housing, commercial and recreational

functionalities, containing a total floor area of 160

000 m

; b) the creation of a heat hub aiming to

increase the efficiency of the waste heat distribution

in Warmtebedrijf, Rotterdam. Importantly, energy

system planning in Rotterdam follows an Energy

Approach Planning called REAP described in

(Lenhart et al., 2015).

4.1 Waste Heat Distribution System

Residual heat is produced by a waste incinerator

facility located in the Port of Rotterdam, thereby

distributed to Rotterdam. Furthermore, the plant has

a thermal exit capacity of 105 MW and the piping

network consists of a double pipeline system (total

length 26 km) connecting the plant with previous

district heating infrastructure. The developed heat

hub, started operation on the 4

quarter of 2013, was

installed near the waste heat transportation

infrastructure and the district heating system.

Tank thermal storage has been incorporated with

the use of a well-insulated buffering tank. The

capacity of the buffer is 185 MWh and the discharge

capacity is 30 MWth. Instead of placing the tank in

the surroundings of the waste incinerator facility, a

central area of the distribution network was selected,

aiming to increase buffering capacity efficiency, due

to the fact that heat is delivered in close proximity to

the end-user. Moreover, air quality is positively

affected by substituting gas-fired boilers in the

handling of peak load.

Optimal operation of the deployed infrastructure

assists in increasing the total heat supply without

investing in extra heat resources or upgrades in

network resources (buffers, pumping). To this end,

Smart technologies incorporated, include, buffering,

heat balancing, automated control and forecasting.

These elements offer more flexible control of the

energy system, mitigating possible malfunctions or

heating price volatility.

4.2 Renewable Energy System for De

Rotterdam

De Rotterdam is one of the tallest buildings in the

Netherlands (Zeiler, 2017). The major part of the heat

demand is supplied from a 16 km-long pipeline

connected to a waste-to-energy plant set on the island

of Rozenburg. A CHP plant, located at Capelseweg,

can serve as a reserve supply source in below zero

temperatures.

A small CHP (capacity of 250 kW), running on

biodiesel, was built-in the building, for renewable

generation of heat and power. However, due to high

An Overview of Renewable Smart District Heating and Cooling Applications with Thermal Storage in Europe

315

fuel cost and difficulties in transportation, it is not

preferred for frequent use.

High-temperature hot water supply is provisioned

for residential sections and for a hotel based in one of

the towers. According to Dutch water quality

regulations, hot water systems for residential use

must satisfy a minimum of 70 °C. Conversely, the

office towers can be supplied with water of lower

temperature. This difference in temperature demand

was essential for designing a system, which reduces

the temperature of the return line in the district

heating loop, eventually connecting the offices to the

return line (Fig. 3).

Figure 3: Layout of De Rotterdam’s energy system with

building typology.

Taking advantage of De Rotterdam’s location, on

the banks of river Maas, which maintains a low

temperature during the year, a natural water cooling

system was developed, as in the case of the

Maastoren, a skyscraper also located on the peninsula

(Molenaar, 2011). This centralized cooling facility

generates cold, pumping water through intake pipes

concluding in the river and passing it through three

water-cooled compression chillers (Fig.4).

River water filters are necessary for ensuring

water quality, supported by a compressed air system.

Piping is extended for the distribution loop and end-

users are provided through a metered connection,

meanwhile thermostats enable control of interior

temperature in rooms. Heat-reflective double-glazing

and windows to let fresh air inside reduce the cooling

demand.

Ambient temperatures are low throughout the

year; therefore, cooling demand is low in general. In

summer, where cooling demand rises, river

temperatures are between 15 and 25 °C, stating it

unsuitable for district cooling. Nevertheless, river

water is injected directly to the condensers (through

copper-nickel alloy pipes for anti-corrosion), where it

can be utilized for extracting heat from the ventilators

of the air conditioners, as lower condensation

temperatures, reduce air resistance in the condensers

and the amount of energy required for the cooling

compressor. Thermal storage is available via an

aquifer storage in the form of underground wells

under the sand layers of the soil.

Figure 4: Design and functionalities of the deployed Maas

river water cooling system in De Rotterdam.

The resulting system has a total cooling capacity

of 6 MW, leading to 50% savings of energy for

cooling. It functions in a modular way depending on

river water temperature illustrated in Fig, 5, where: a)

when the river water temperature is under 9

C: the

buildings are cooled with free cooling only; b)

between 9

C -15

C, a combination of free cooling

supplemented with compression chillers is used; c)

river temperatures over 15

C, only compression

chillers are used to cover the cooling demand of the

buildings.

Figure 5: Modes of operation according to river water

temperature.

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316

Finally, the cooling system is installed in a

spacious room, offering potential extension with

more water-cooled chillers when demand rises, as

further construction work is opted on the Maas

peninsula. This will ensure that the systems built into

The Rotterdam, such as the Maas water system, can

be deployed as efficiently as possible while also

saving space in the new buildings. Sustainability of

the project may be enforced with the integration of

solar panels, urban wind turbines, aquifer thermal

energy storage (already widely available in the

district heating system and used in the Maastoren

energy system), extraction of thermal energy from the

sewage water and more.

5 CONCLUSIONS

This paper presented an overview of options in

implementing smart district heating and cooling

systems in Europe with integrated thermal storage

components. In this stage of DHC system design,

main objective is to deliver efficient networks,

utilizing renewable resources and technologies.

Renewable energy-based heat production

technologies offer a wide variety of coupling aiming

at maximizing the system efficiency. These coupling

may lead to complex system architectures appealing

for smart management based on energy efficiency

(mainly maximizing the renewable contribution), cost

effectiveness and comfort.

Adding heat storage capacities offers degrees of

freedom in managing such systems. Heat storage

technologies may be envisaged for the following

reasons: (i) technical operation (e.g. Biomass boiler)

often need a heat storage to prevent from too many

on-off when the heat demand is low compared to the

installed thermal power, (ii) rising the solar

contribution to heat demand, (iii) forcing the heat

production of a unit when it offers good performances

(e.g. compression air to water heat pump have better

performances when outside air temperature is high),

(iv) storing heat for dealing with variable electricity

tariff and or maximizing green electricity use (when

heat the production technology uses electricity

(compression HP) or uses it (CHP)

Up to now storage technologies that were used in

heating city districts are mainly based on the sensible

heat storage principle (storage process results from a

temperature lift of the storage material) whereas

latent heat storage systems (storage process results

from phase change of the storage material) and

sorption heat storage systems (storage process results

from a physical or chemical sorption of a vapour in a

solid or a liquid) are still at the demonstration or R&D

levels.

However, current technologies demonstrate

limitations in applicability and aiming in satisfying

100% of heating demand from renewable energy

systems remains a major challenge.

Concerning solar district heating, drawbacks

include, space limitations in urban environments, and

even with large storage tanks, compensating seasonal

demand requires the use of cogeneration to serve the

baseload. Moreover, solar irradiation is inversely

correlated with heating demand peaks. Hence, the

efficient performance of the system is heavily

dependent on location. In Scandinavian countries

where the heating season has a longer duration, it is

possible to divert solar generated heat directly to end

users. More energy will be fed into the system if the

temperature difference between the collector input

and output is maximised. In established systems, the

high return temperatures create a barrier to the

integration of solar heat

In the case of geothermal district heating,

similarly with solar heating, greater amount of heat

can be extracted due to lower water temperature in the

network return line. Thus, produced heat is fittest for

baseload satisfaction. A significant cost for design is

the assessment of geothermal resources, which

requires highly specialized personnel. Access to land,

mineral and water rights accompanying geothermal

projects involves complex administrative procedures.

Biomass adoption supports the conversion of coal

power plants to biomass fuel combustion, depending

on technologies, fuel availability and cost. This

presents the advantage of utilizing existing

infrastructure and procedures, as well as efficiently

allocating space in dense urban environments.

The case study of Rotterdam exhibits how existing

DHC infrastructure can benefit from the introduction

of renewable technologies and thermal storage. Early

attempts to integrate smart techno-logies in the energy

system for balancing heating loads and optimising

buffers, pumping and new nodes will ensure

sustainability with high efficiency. Possible revenues

from the operation of the more efficient and energy

system can be returned to tenants and property owners.

For new buildings connected to the district cooling

system, an upgraded Energy Performance label is

issued, whereas existing buildings lack an economic

drive for replacing their existing compression chillers,

as it is not cost efficient. This is a promising example,

as more smart thermal grid realizations in Europe are

expected in the coming years with countries adapting

their regulatory frameworks in order to support the

operation of such schemes.

An Overview of Renewable Smart District Heating and Cooling Applications with Thermal Storage in Europe

317

ACKNOWLEDGEMENTS

This research was funded by the EC under the FP7

RE-SIZED 621408 (Research Excellence for

Solutions and Implementation of Net-Zero Energy

City Districts) project.

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