Strategic review of 4G Heat Networks in the UK
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Published in January 2018, the ADE’s ‘Heat Networks in the UK’ report highlights the contribution of heat networks to the UK’s energy and carbon reduction requirements and the opportunities to transform the way we heat our homes and buildings.
There is an increasing awareness of the signifi cant benefi ts for the UK from wider use of well-designed heat networks. SAV therefore actively supports development of sustainable buildings that focus on long life operation and performance, making optimum use of renewable energy sources - and which can be future proofed in line with 4th Generation (4G) heat network design philosophy.
SAV is committed to improving the indoor environment whilst using the minimum amount of energy.
Optimum indoor climate, minimum energy usage
Reference: 4th Generation District Heating (4GDH)Integrating smart thermal grids into future sustainable energy systems
http://dx.doi.org/10.1016/j.energy.2014.02.089
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Contents
Introduction .............................................................................4
Heat networks – a brief history .............................................4
Why we need 4G Heat Networks ...........................................5
Growth of renewable energy sources ...............................................5
Growing complexity of energy networks ..........................................5
Planning for energy storage .............................................................6
Low temperature operation .............................................................7
Building design ................................................................................8
Measure to manage.......................................................................10
Exploiting waste heat opportunities ...................................10
Making 4G Heat Networks a reality ....................................11
Does scale matter in heat networks? ..................................12
Block heating: West Bridge Mill .....................................................12
Multiple block heating evolving to district heating: Aberdeen Heat & Power ................................................................13
District heating: Fredericia, Denmark ..................................13
Summary ................................................................................14
References .............................................................................15
Strategic review of 4G Heat Networks in the UK
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IntroductionIt is now well accepted that heat networks are a key element in the UK’s commitment to reducing carbon
emissions. In September 2017 the Department for Business, Energy and Industrial Strategy (BEIS) stated:
“Heat networks form an important part of our plan
to reduce carbon and cut heating bills for customers
(domestic and commercial). They are one of the most
cost-effective ways of reducing carbon emissions from
heating, and their effi ciency and carbon-saving potential
increases as they grow and connect to each other.”
While 47% of the UK energy use goes to heating, the Committee on Climate Change has estimated that
around 18% of UK heat will need to come from heat networks by 2050 if the UK is to meet its carbon targets
cost effectively. Yet currently, BSRIA estimates that only around 2% of the UK’s heat demand is covered by
heat networks – compared to around 13% for mainland Europe.
The heat network consumer survey by BEIS (Dec 2017) suggests that heat network consumers, on average,
pay around £100 a year less for their heating and hot water, compared to non-network consumers, which
can be even larger with better design and operation of heat networks.
However, for heat networks to fulfi l their full potential during the low carbon transition it has become clear
that a sustainable approach is required to their design and operation. In particular, the new generation of
heat networks that integrate electricity, thermal and gas grids needs to be adopted to enable the wider
use of renewable energy.
Crucially, this 4th generation of heat networks (4G) needs to adopt an ‘open source’ approach to heat
sources, with the inherent fl exibility to exploit the best heat and power sources available – both now
and into the future.
Heat networks – a brief historyHeat networks (aka district heating systems) have been used for over 100 years around the world, gradually
improving in effi ciency through each generation.
The 1st generation of heat networks,
in the late 19th Century, distributed
heat in the form of steam. These were
superseded in Europe in the 1920s
by networks using water at around
100°C (2nd generation) and then in
the mid-20th Century by sub-100°C
networks (3rd generation).
Most of the heat networks operating in the UK today are of a 3rd generation design and, compared to
2G networks, feature a number of improvements. These include improved pipe insulation, wider use of
pre-fabrication and more effi cient energy production from a decentralised energy centre. They have also
introduced system metering as a fi rst attempt towards digitalisation.
“Heat networks form an important part of our plan
to reduce carbon and cut heating bills for customers
(domestic and commercial). They are one of the most
cost-effective ways of reducing carbon emissions from
heating, and their effi ciency and carbon-saving potential
increases as they grow and connect to each other.”
Strategic review of 4G Heat Networks in the UK
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However, the design of 3G systems creates an issue for the increased uptake of renewable and low carbon
energy sources in the future as it ‘ties’ them to the heat sources they were originally planned to use. Typically,
this would be an energy centre powered by Combined Heat and Power engine backed by boilers.. While
there may be an opportunity to add lower carbon energy sources in the future, this would require extensive
upgrading of the energy centre and the buildings being served by the network.
Thus, a traditional 3G heat network is far from a sustainable solution. It is rather like an isolated island
community that is only concerned with its own issues with no consideration of wider global issues. As such,
3G design does not address the rapidly changing energy landscape and in particular, the growing use of
wind power in the UK.
Why we need 4G Heat NetworksIn developing new heat networks, it may be tempting to follow the path of least resistance and simply
roll out more schemes based on the 3G design criteria. However, this will fail to address the challenges
and opportunities that lie ahead, particularly in relation to the growing production of intermittent
renewable energy.
A key characteristic of 4G design is that it incorporates the wherewithal to manage the increasing complexity
of energy networks, and the intermittent availability of ‘green electricity’, effi ciently and cost-effectively.
Growth of renewable energy sources
Nearly a third (29.8%) of all UK electricity in the second quarter of 2017 came from renewable sources,
most of it from wind. Onshore wind generation increased by 50% in 2017, while offshore wind energy
rose by 22%.
This is just the beginning. The UK already has the largest offshore wind capacity in the world and this is
set to increase production rapidly thanks to a £320m investment pot made available by the UK government.
A number of offshore wind contracts have already been awarded to companies such as Ørsted (formerly
DONG Energy) and ENGIE.
In parallel, offshore wind costs have halved in recent years to under £58 per MW, making such investments
even more cost-effective.
A key difference between 3G and 4G
is that 4G Heat Networks are inclusive,
whilst 3G networks are exclusive.
Growing complexity of energy networks
As electricity consumption increases to power more and more ‘gadgets’ and electric vehicles, it is doubtful
the existing power grids will be able to meet demand.
Moreover, the growing production of renewable energy sources (many of which are intermittent) drives the
transition of the whole electricity sector to smart electricity grids with decentralised producers that will manage
both demand and surplus energy. This digitalisation, in addition to the necessity of the grid decarbonisation,
drives the different energy sectors (electricity, gas, heat) to team up to coordinate energy production with
consumption; this may benefi t from the new generation of heat networks that include stabilisation factors.
A key difference between 3G and 4G
is that 4G Heat Networks are
whilst 3G networks are
Strategic review of 4G Heat Networks in the UK
6
For example, when the wind isn’t blowing suffi ciently to meet power demand, another energy source needs
to come into play. Fast-acting gas fi red power stations are currently an important ‘stabilising’ factor as they are
able to ‘kick in’ at a moment’s notice - though, most of the time, much of the heat generated by this process
is not utilised like in CHP systems.
A better option is to make wider use of CHP in power
stations and more locally in buildings to provide the
required stabilisation whilst also producing heat that
can be used in the heat network. Using local CHP
very close to the building(s) being served will minimise
distribution losses.
The increased diversity of energy sources also
contributes to complexity, insofar as the traditional
heat sources of CHP and boilers will be joined by
technologies such as heat pumps, solar thermal
and/or PV, electric cells, waste heat etc.
Moreover, as buildings are designed to be more effi cient through better insulation and lean design, they
will have renewable energy sources built in, reducing the demand from the wider network. They may also
contribute any surplus heat or power back to the grid. So buildings will become more sustainable, being both
consumers and producers.
Planning for energy storage
As noted above, one of the main challenges posed by intermittent renewable energy sources - such as wind,
solar and tidal - is that times of highest generation may not coincide with times of maximum demand – for
example at night when winds may be highest but power consumption is low.
It is therefore essential to have a reliable and cost-effective way to store this energy until it is needed. Batteries
are often seen as the obvious way to store electrical power; however, this is far from economical. Studies have
shown that storing the energy as hot water is at least 100 times less costly than battery storage.
Thus, 4G Heat Networks will be able to exploit surplus electrical power by converting it to heat energy for
storage. Ideally, this will be achieved using thermal stores utilising low energy technologies such as heat
pumps, though electric boilers would be another option.
In order to minimise distribution losses, such energy storage should be local to the building – either at the
site of the building itself or close to a nearby energy centre. This has serious implications for building design,
as provision must be made for considerably higher volumes of stored heat energy than would traditionally
be the case.
Strategic review of 4G Heat Networks in the UK
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In this respect the amount of thermal energy stored is determined by the physical volume of the stored hot
water and the differential (ΔT) between the temperature of the stored hot water (around 80°C) and the return
water temperatures of the system. Low return temperatures (ideally 20°C) will therefore help to maximise
the benefi ts of the energy store.
Electricity from renewable sources can also be converted to gas through
electrolysis (usually methane or hydrogen; sometimes called windgas if the
electrical power is from wind). The gas can then be stored or injected into
the gas grid utilising the current infrastructure.
Renewable electricity gas generation is growing in use and it reinforces the
need to create fl exible 4G Heat Networks that integrate electricity, power
and gas grids. It also reinforces the importance of keeping an open mind
with regards to the energy sources that may be available in the future -
and designing accordingly.
Low temperature operation
With each new generation of heat network, a key driving force has been the desire to improve effi ciency,
recognising that both heat supply and distribution are more effi cient at lower temperatures. Beyond this,
the use of lower temperatures opens the door to low carbon technologies that require lower
temperature operation.
In its Applications Manual AM12 ‘Combined Heat and Power
for Buildings’, the Chartered Institution of Building Services
Engineers (CIBSE) recommends operating temperatures for
radiator circuits to be 70°C fl ow and 40°C return for new
district heating systems/heat networks. The recommended
maximum return temperature from instantaneous domestic
hot water heat exchangers is 25°C.
4G Heat Networks will take the principle of low temperatures much further, using fl ow temperatures of
50°C with return temperatures perhaps as low as 20°C. In doing so, it will facilitate the inclusion of current
and future renewable and low carbon technologies that require lower operating temperatures.
Low return temperatures help to improve the effi ciency of other heat sources. For instance, the optimum fl ow
and return water temperatures for gas-fi red condensing boilers and condensing CHP are 55°C/30°C; for heat
pumps 40°C/35°C.
So, networks built today to operate at lower temperatures with these current technologies will still benefi t
from higher effi ciencies now and can be easily upgraded to use low temperature heat pumps and waste
heat sources in the future.
70 40
Strategic review of 4G Heat Networks in the UK
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Heatstorage
CHP coalCHP oil
Heatstorage
CHP wasteCHP coal
CHP oil
CoalWaste
Local District Heating District Heating District Heating District Heating
Dist
rict h
eatin
g gr
id
Dist
rict c
oolin
g gr
id
CHPbiomass
2-wayDistrictHeating
Centralisedheat pump
Futureenergysource
CoalWaste
BiomassCHP Biomass
Industry surplus
Gas, WasteOil, Coal
PV, WaveWind surplus
Electricity
Geothermal
Large scale solar
Coldstorage
Large scale solar
Industry surplus
CHP wasteincineration
Alsolow energybuildings
Energy
< 200 oC
> 100 oC
< 100 oC
50-60oC (70oC)
Temperature level
1G / 1880-1930 2G / 1930-1980 3G / 1980-2020 4G / 2020-2050
1G: STEAM 2G: IN SITU 3G: PREFABRICATED 4G: 4th GENERATIONSteam system, steam pipes in concrete ducts
Low energy demandsSmart energy (optimum interaction of energy sources, distribution and consumption) 2-way DH
Pre-insulated pipesIndustrialised compact substations (also with insulation)Metering and monitoring
Pressurised hot-water systemHeavy equipmentLarge ”build on site” stations
Development (District Heating generation) /Period of best available technology
Centraliseddistrict cooling plant
Seasonalheat storage
Steamstorage
Heatstorage
Biomassconversion
The lower temperatures also help to reduce the heat losses from distribution pipework.
Tests in Denmark with residential heat networks have shown that fl ow/return water
temperatures of 55°C/35°C reduce heat losses from distribution pipework by around
75%, compared to traditional higher temperature systems (e.g. 80°C/55°C).
The holy grail for 4G Heat Networks is to reduce these, fl ow and return temperatures
even further, to 50°C fl ow/20°C return.
Building design
It is essential to consider that buildings designed now will be part of the building stock for more than 60 years,
contributing to the UK’s carbon emissions throughout this time. The 2050 targets that have already been put
in place should therefore be infl uencing the design of buildings being constructed today.
At the heart of the 4G heat network philosophy is the need to start with a building design that has the
inherent fl exibility to evolve with time and leverage new opportunities for energy and carbon savings as
they become available.
Consequently, 4G heat network design needs to recognise that once buildings and distribution systems have
been constructed it is diffi cult to change them. The inherent fl exibility of such systems is at the energy centre,
which can be upgraded relatively easily and cheaply at any time.
50 20
Strategic review of 4G Heat Networks in the UK
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Thus, the starting point is the building(s) served by the network, which need to be as energy effi cient as
possible using high thermal insulation standards, heat recovery systems and intelligent controls, while
design for new build buildings should maximise opportunities for natural daylight. Where appropriate,
buildings should also incorporate local heat and power generation technologies in combination with wind,
solar thermal, photovoltaic, air or ground source heat pumps, electric boilers and thermal store. Such local
generation and utilisation of different energy sources, helps to optimise the fl exibility and the heat network
operation, reducing both costs and carbon emissions.
Crucially, buildings that are constructed today and
connected to energy plant using fossil fuels should
be designed in such a way that they can easily
switch to using energy from renewable and waste
heat sources if the energy centre is upgraded
in the future.
To facilitate this, the heat emitters used in buildings should be designed
to operate at lower temperatures than is traditionally the case, to
exploit the benefi ts of low temperature operation already discussed. If
underfl oor heating is used, this will already be designed for low temperature operation. However, if the heat
emitters are to be radiators, these will need to have a larger surface area to ensure suffi cient heat transfer
from the lower temperature water passing through them.
This use of ‘low temperature’ radiators has other benefi ts for applications such as schools and care homes,
where high temperature radiator surfaces pose a safety risk. Rather than encasing the radiators, as is currently
the case to prevent direct access to the radiator, low temperature radiators will be inherently safer.
In parallel with these aspects of the building’s design, provision needs to be made in the design for signifi cantly
higher volumes of thermal storage, as discussed above.
If the building and the distribution system are designed with 4G Heat
Networks in mind, the heat sources become a side issue.
Typical Heat Network Design
EnergyCentre
Dynamicand Flexible
Fixed Long Term Capital Expenditure
Multiple Heat Sources
Distribution PipeworkThermal Store
HeatMeter
HIURadiators / Underfloor
ConsumerZone
Heat NetworkDistribution System
Consumer Threshold
Strategic review of 4G Heat Networks in the UK
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Measure to manage
To be truly ‘smart’ 4G Heat Networks need to incorporate intelligent metering that goes beyond billing to
provide real-time data on energy consumption in individual apartments/spaces and across the entire network.
Frequent data enables energy monitoring of performance of buildings, helps to
identify opportunities for improvement and allows visualisation of consumption for
each consumer. Smart metering therefore helps to optimise outputs from the energy
centre and across the distribution network, as well as helping consumers to instigate
behavioural changes to reduce their energy consumption.
Exploiting waste heat opportunitiesCurrent and future heat networks will play a vital role in meeting the UK’s carbon reduction targets, as laid
down in the Climate Change Act 2008. Through the Heat Networks Investment Project, £320m of capital
funding is available to support heat network projects due to be deployed in the next few years.
The problem here is that the HNIP only included large schemes, not small-scale block networks. There were
also diffi culties in accessing the available funds.
Whatever the source of the investment, if such investment is to yield maximum returns and enable a
cost-effective transition from fossil fuels to local renewable and secondary heat sources, such projects
need to incorporate the characteristics of 4G Heat Networks.
Achieving this in practice will require the collaboration of all stakeholders from building owners/operators
and architects through to planners, builders, engineers and maintenance contractors.
It also necessitates a change from the ‘bigger is better’ mindset to take advantage of the potential for many
relatively small block heating schemes. Such schemes are more commercially viable than extensive city-wide
schemes and ideally placed to take advantage of local renewable and heat sources.
A key tenet of the 4G approach is the ability to make use of whatever
energy sources are available locally – the more distant the energy source,
the higher the distribution losses and the lower the overall effi ciency
of the system.
Strategic review of 4G Heat Networks in the UK
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Inevitably such local energy sources will vary considerably from one area to another, the following
are just some examples:
• Electrical power from wind, solar, tidal sources.
• Waste heat from factories, waste incinerators and large
computer facilities (server farms).
• Heat from biomass sources.
• Heat from solar thermal.
• Heat from geothermal and groundwater sources
• Heat and power from CHP plant.
• Heat from heat pumps driven by renewable electricity.
• Traditional fossil fuel heat sources.
Making 4G Heat Networks a realityAs already discussed, heat networks tend to be either large district heating schemes or small block heating
schemes, and both have potential benefi ts.
The greatest potential for larger district heating schemes is where there is a low-cost heat source relatively
close to the buildings that will be connected to the heat network. Obvious examples include a power station
producing waste heat that can be captured and used in the heat network - or surplus heat from industrial
processes and/or waste incineration.
For such schemes to be viable it is essential they have a source of low cost heat, because of the cost and
disruption of constructing the distribution infrastructure.
Where such low cost heat sources are not available locally it will generally be more practical to consider smaller
schemes – often known as block heating or communal heating. These are very straightforward and require
only the installation of heating and hot water pipes in the building, creation of an energy centre (typically
on the same site) and provision of heat interface units in each space being heated.
Consequently, block heating schemes are commercially viable and easy to implement, compared to large
district heating schemes. As many cities in the UK seek to use brown fi eld sites for small housing developments
(20-25 dwellings) there is considerable scope for the creation of small, smart 4G Heat Networks.
District Heating Block Heating
Strategic review of 4G Heat Networks in the UK
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Does scale matter in heat networks?
Block heating: West Bridge Mill
West Bridge Mill in Kirkcaldy is an
example of the potential for small
block heating scheme. This is a multi-
residential development which involved
refurbishment of a former B-listed
rope mill. It comprises 16 separate
fl ats housing vulnerable young people.
Electrical power and hot water for
space heating and domestic services
are generated by CHP, with heating
and domestic hot water in each
apartment being managed through
heat interface units (HIUs).
The CHP meets over 70% of the site’s electrical demand and any surplus heat generated is stored at 80-85°C.
This thermal storage reduces the use of back-up gas boilers.
Data from the daily operation of the CHP system can be read on site and is also transmitted via the internet
to a monitoring station. As well as reducing annual CO2 emissions by around 100,000 kg, this block heating
scheme is providing residents with signifi cantly cheaper space heating, hot water and electricity than if they
were using mains gas and electricity.
72%77%
67%
29%41%
53%
65%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
180,000
2011 2012 2013 2014 2015 2016 2017
Building Power Consumption CHP Heat Production [kWh]
CHP Electricity Production [kWh] % Contribution on electricity
West Bridge MillBuilding electricity consumption & CHP contribution
Strategic review of 4G Heat Networks in the UK
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Multiple block heating evolving to district heating: Aberdeen Heat & Power
As new block heating schemes are
developed in the same locality, they
may be joined to form larger district
heating networks. This is illustrated by
the Aberdeen Heat & Power district
heating scheme.
In the fi rst phase of this project,
electric heating in around 2,350
apartments in 33 multi-storey blocks,
and 15 public buildings, has been
replaced with a heat network based
on block heating schemes and
served by CHP.
Following these initial block heating phases Aberdeen Heat & Power has continued to develop its heat
network to create a wider district heating scheme, adding a further four blocks of fl ats and another
fi ve public buildings.
The result is that typical fuel costs to tenants have been reduced by
as much as 50%!
District heating: Fredericia, Denmark
In time, smaller district heating
schemes can be combined to create
larger schemes that continue to deliver
the key benefi ts of 4G Heat Networks.
The Fredericia district heating
scheme in Denmark, for example, is
a consumer-owned district heating
company suppling heat and hot water
to connected properties. Around 99%
of the heat load for the connected
properties is met by a combination of
waste heat, CHP and the surplus heat
from a local oil-refi nery.
This is one of eight local district heating companies that are connected to the regional heat transmission
system TVIS, which serves 83.000 homes. The fact that all district heating (DH) companies in the area are
interconnected through one system, enables effi cient use of the surplus heat which would otherwise have
gone to waste.
Strategic review of 4G Heat Networks in the UK
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SummaryDuring their long history, heat networks have evolved to meet a range of demands, which include energy
effi ciency, costs, space, environmental impact and health & safety.
Whilst 3G heat networks are able to address some of these requirements in a limited way, they lack the
key ingredients for a fl exible, responsive and sustainable system that continues to evolve. In short, in terms
of heat network evolution, they are a ‘dead end’.
With an overarching need to reduce carbon emissions, it is essential to plan and manage a transition to
4G Heat Networks within smart energy systems that combine and co-ordinate production and consumption
among heating, electricity, gas and transport systems.
Such sustainable systems will focus on the wider use of low grade renewable and waste heat sources to a
greater extent than ever before, with the ability to manage intermittent energy sources, so every aspect of
the system design needs to address this.
More effi cient buildings with low energy requirements, and onsite energy generation and thermal storage, and
heating systems designed for low temperature operation will be served by highly insulated distribution systems
with low heat losses, from an energy centre that is able to utilise a range of constant and intermittent local
energy sources.
As such, 4G Heat Networks will also underpin the creation of smart, sustainable energy systems based on
low temperature heat networks interacting with low energy buildings to deliver a range of key objectives
that include:
• Cheaper energy
• Lower carbon energy
• Reduced energy imports
This will also lead to variable solutions according to specifi c regional demands, as well as a new approach
to the roles of the energy market, public knowledge and market regulations.
Gas
Electricity
Heat
Network Fusion 4G
Strategic review of 4G Heat Networks in the UK
15
References• 4th Generation District Heating (4GDH) Research Centre, http://www.4dh.eu/
• Paper: 4th Generation District Heating (4GDH): Integrating smart thermal grids into future sustainable energy systems
• The ADE, Market report: Heat Networks in the UK, Published 31 January 2018
• The ADE, Shared Warmth | A heat network market that benefi ts customers, investors, and the environment,
Published 31 January 2018
• BEIS, Heat Networks Consumer Survey: consumer experiences on heat networks and other heating systems,
Published 7 December 2017
• BEIS, Heat Networks Investment Project (HNIP), Published 7 April 2017
• Climate Change Act 2008
• Committee on Climate Change, https://www.theccc.org.uk/
• Department of Development and Planning, Aalborg University, Denmark, http://www.en.plan.aau.dk/
• Department of Civil Engineering, Technical University of Denmark, http://www.byg.dtu.dk/english
• Danfoss District Energy, Denmark, http://districtenergy.danfoss.com/#/map
• Kamstrup District Heating, Denmark, https://www.kamstrup.com/en-uk/business-areas/heat-metering/district-heating
• Jan Eric Thorsen, Oddgeir Gudmundsson and Marek Brand, Danfoss District Heating Application Centre, DK-6430
Nordborg, Denmark, Distribution of district heating:1st-4th generation
• CIBSE AM12 2013
• CIBSE Heat Networks CoP for the UK 2012
• SAV Systems ‘Delta T’ Design Guide 2014
• SAV CPD: SAV-Danfoss FlatStations - 4G Lean Heat Network Design
This document is based on the best knowledge available at the time of publication.
For further information please contact:
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