district heating for new builds

The applicability ofdistrict heatingfor new dwellings

CE299

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The applicability of district heating for new dwellings

Unless otherwise indicated, images are © BRE

Table of contentsIntroduction 3

1. UK district heating and building stock 4

2. The energy requirements for new dwellings in the future 62.1 Heating requirements 72.2 Heat and electricity requirements 11

3. The implications of low heat demand for district heating networks 133.1 District heating systems 133.2 The influence of heat density on the applicability of district heating 16

4. Low carbon and renewable supply technologies for district heating 194.1 Biomass only heating 194.2 Solar thermal 214.3 Renewable combined heat and power 224.4 Other technologies 244.5 Technology integration 24

5. Implementation of district heating 285.1 Energy services companies 285.2 Capacity for delivering district heating in the UK 29

6. Conclusions and recommendations for further work 30

Appendix A – Opportunities for cost reduction in the heat 31distribution pipe work: the Scandinavian research

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IntroductionThis report has been commissioned by the Energy Saving Trust to look at the role district heating couldplay in response to the demands of the Code for Sustainable Homes. It also examines how futurereductions in the heating requirements of new dwellings may affect the viability of district heating schemes.

• Section 1 looks at the UK implementation of district heating according to building stock.

• Section 2 examines the heat demand of new dwellings in the future.

• Section 3 reviews the implications of low heat demand on the viability of district heating networks.

• Section 4 provides a brief description of several low carbon and renewable district heating supply technologies and their role in achieving compliance with different levels of the Code for Sustainable Homes.

• Section 5 describes the role of energy services companies in the implementation of district heating schemes.


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1. UK district heating and building stockSpace heating and domestic hot water (DHW) needs within the UK domestic sector have traditionallybeen supplied by individual heating systems, either in the form of boilers using gas, oil or solid fuels – or through electric heating systems.

Community or district heating (DH) systems generate heat from one or more energy sources and deliverit to users via distribution pipes. DH schemes can normally be found in domestic or mixed usedevelopments. Domestic schemes vary in size from simple sheltered housing developments fed with a

communal boiler, through housing estateswhere several hundred homes are suppliedwith heat from a central energy source, all theway to city-wide heat distribution networksthat serve a wide range of customers. Figure 1shows a district heating scheme that connectsseveral apartment blocks in Aberdeen.

Figure 1: Seaton state district heating scheme, Aberdeen

1. Data is based on a survey of about 20,000 dwellings in England, Wales and Northern Ireland and covers the period 2003-04. The data

presented here has been adapted from the BRE report Desk study on heat metering prepared by Richard Hartless, Jonathan Williams and

Robert Burzynski. June 2007.

While district heating is widely extended and adopted in Scandinavian countries, the penetration of DHschemes within the UK is still very limited. Figures for 2004 show that only 2% of housing stock inEngland, Wales and Northern Ireland was connected to district heating systems1. Of this, 89% of thedwellings connected were flats and the remaining 11% were houses (see figure 2).

Figure 2: Proportion of individual and district heating systems (England, Wales and Northern Ireland)

2%

98%

Individual

Community

Proportion of individual and community heating systems

11%

89%

Flats

Houses

Proportion of flats and houses served by communityheating systems

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UK trends for new build housing stock indicate that more dwellings currently under construction may besuited to district heating than is the case with existing stock. For example, from 2002 to 2006, thenumber of detached houses decreased by almost 50% in favour of flats and maisonettes2. In 2006, flatsand maisonettes accounted for 40% of all new dwellings.

2. Adapted from Trade Sector Profile. Domestic Insulation 2007. www.eeph.org.uk Original Source: ONS / Department of Communities and

Local Government’s ‘Housing Statistics 2006’.

3. The Role of onsite energy generation in delivering zero carbon homes. A report from the Renewable Advisory Board. November 2007.

www.renewables-advisory-board.org.uk

A more detailed analysis of the new build housing stock3 shows that most new houses/dwellings are builtin small developments. For example, published figures indicate that 32% of new dwellings are indevelopments of less than ten homes: only 15% are built in developments of over 500 homes.

Both the type of housing and the size of the development will ultimately shape the range of technologiesto be implemented.

Figure 3: UK new housing built by type of dwelling

Flats and maisonettes

Terraced

Semi-detached

Detached

0%

20%

40%

60%

80%

100%

120%

2002 2003 2004 2005 2006

Summary

• Community or district heating (DH) systems generate heat from one or more energy sources and deliver it to users via distribution pipes.

• In 2004, 89% of all the dwellings connected to district heating schemes within England, Wales and Northern Ireland were flats.

• From 2002 to 2006, the number of newly built detached houses decreased by almost 50% in favour of flats and maisonettes.

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2. The energy requirements for newdwellings in the futureThe Code for Sustainable Homes (CSH)4 was published in England and Wales in December 2006. It isexpected to be progressively introduced through changes to the national building regulations, with an aimin England of achieving net zero carbon new build homes by 2016.

The Code for Sustainable Homes refers to six levels of energy efficiency, the final four of which demandprogressively higher levels of emissions reduction as follows:

• Code Level 3 (CSH3): 25% carbon reduction beyond 2006 Building Regulations requirements.• Code Level 4 (CSH4): 44% carbon reduction beyond 2006 Building Regulations requirements.• Code Level 5 (CSH5): 100% carbon reduction beyond 2006 Building Regulations requirements.• Code Level 6 (CSH6): net zero carbon homes (this level also includes energy use not covered by building

regulations, i.e. from cooking and appliances).

4. Code for Sustainable Homes. A step-change in sustainable home building practice. December 2006. www.planningportal.gov.uk

5. As given in the Code for Sustainable Homes. Technical Guide. October 2007.

6. www.passivhaus.org.uk

7. The heat losses parameter indicates the heat losses through the building fabric accounting for fabric (including thermal bridges), ventilation

and infiltration losses.

Code level 6 (zero carbon home) definition

• Heat loss parameter equal to 0.8 W/m2K.

• Net zero carbon dioxide (CO2) emissions including the energy consumed in the operation of space heating/cooling and hot water systems, ventilation, all internal lighting, cooking and electrical appliances.

• Achievement of Code level 5.

Source: Code for Sustainable Homes.

Technical Guide. October 2007.

Code level 6 further criteria

• Onsite renewable/low carbon is defined as: installations which are either on/in the dwelling or elsewhere on/off site where these directly supply the dwelling through a ‘private wire’ agreement.

• Green tariffs not allowed for.

• No connection to main gas*.

* BN 26. Stamp Duty: Relief for new zero carbon homes. Budget

2007. HM Revenue and Customs

For Code levels up to and including 5 it seems like there will be no specific requirements in relation tohow to achieve the required CO2 reduction. This means that the same levels of CO2 reduction could beachieved from the use of energy efficiency and/or the use of renewable energy technologies, as long asthe fabric insulation and airtightness levels comply with the minimum regulatory requirements. However,according to its current definition5, a zero carbon home is required to achieve a heat loss parameter (HLP)of 0.8 W/m2K or less, which is equivalent to having a heat requirement of 15 kWh/m2 per year – similarto the PassivHaus standard6.

As part of the process of achieving zero carbon homes, the Department of Communities and LocalGovernment (CLG) has published a timescale that establishes targets for CO2 emission reductions relativeto 2006 Building Regulations. Table 1 shows the required CO2 emissions reduction, the timescale forimplementation and the required HLP 7 for different Code levels.

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Table 1: Carbon reduction and heat loss parameter required for different levels of the Code

CSH3 2010 25% Uncertain: HLP given by the Part ADL1 acceptable insulation and air permeability requirements.

CSH4 2013 44% Uncertain: HLP given by the Part ADL1 acceptable insulation and air permeability requirements.

CSH5 – 100% Uncertain: HLP given by the Part ADL1 acceptable insulation and air permeability requirements.

CSH6 2016 100% + appliances and cooking 0.8

Year CO2 reduction beyond 2006 HLP (W/m2K) Building Regulations minimum requirements

The following two sections look at the energy requirements for dwellings built to different levels of theCode. The first looks at the heating requirements while the second also accounts for electricity requirements.

A mid-floor flat (61m2) and a detached house (104m2) have been chosen for the analysis presented in thissection. This choice represents dwellings of high and low density; as we will see in section 3.2, housingdensity has a major impact on the viability of district heating schemes.

2.1 Heating requirementsThe heating requirements in a dwelling are dictated by both space heating and DHW requirements.

DHW requirements depend not only on the occupancy of a dwelling but also on the householder’spatterns of consumption. The CSH establishes minimum targets for water consumption under its differentlevels – this will consequently reduce the DHW requirements for the higher code levels. However, at thisstage it is not clear how these targets will affect the DHW requirements for building regulations energycalculations. SAP 2005 currently calculates the DHW needs assuming a standard occupancy profile – andthe DHW need is related to the floor area of the dwelling. The calculations here make the sameassumption and therefore the water consumption maximum allowances as defined in the CSH have beenomitted from the calculations.

The HLP indicates the level of heat loss through the envelope and considers fabric, thermal bridges andventilation losses – including infiltrations. The smaller the HLP, the smaller will be both the annual spaceheating demand and the magnitude of the heating design load.

The relative proportion of heat loss accounted for by these different elements is illustrated in figure 4 forboth a detached house and a flat.

The proportion of heat loss due to fabric losses and ventilation is very much dependent on the building shape.

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For the detached house examined in this section (a representative 2006 compliant dwelling), the fabricloss including thermal bridge loss is responsible for about 70% of the total heat loss, with the rest due toventilation and infiltration. For a representative 2006 mid-floor flat, fabric loss is reduced to about 60% oftotal heat loss.

To reduce heat loss further it will be necessary to address all of the factors which are fabric insulation,thermal bridges, ventilation and infiltration.

There will be a limit to the heat loss reduction achievable due to better insulation standards. And therewill be a point where ventilation losses will need to be reduced through construction techniques that usehigh levels of air tightness and mechanical heat recovery ventilation (MVHR) devices. So the additionalelectrical consumption of the MVHR system must to be taken into account. Different techniques can beused and they have been extensively examined in the development of the PassivHaus standards.

While CSH3 can be achieved through the demand-reduction measures, renewable generationtechnologies will be necessary to exceed the required CO2 reduction targets of CSH4.

To calculate the heat losses in this section, a progressive linear reduction between 2006 and the CSH68

space-heating requirements has been assumed. Values are shown in table 2 .

8. For a CSH6 dwelling, a space heating requirement of 15 kWh/m2 has been assumed.

Ventilation

Detached Flat

Thermal bridges Fabric

0%

20%

40%

60%

80%

100%

Figure 4: Heat losses for a 2006 Building Regulationcompliant dwelling

Heat losses for a 2006 compliant dwelling

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Figure 5 shows the estimated monthly combined space heating and DHW requirements for the flat anddetached house respectively at an average UK location.9 The effect of the heat loss reduction is to flattenthe curve through the different months of the year, indicating that the heating requirements areincreasingly dominated by DHW (rather than space heating).

Table 2: Indicative reduction in annual space heating for different code levels as a percentage of a 2006Building Regulations compliant dwelling

CSH3 2010 23% 21%

CSH4 2013 47% 43%

CSH5 – 52% 48%

CSH6 2016 64% plus 70% plus

Estimated space heating reduction below 2006Building Regulations

Code Revised Building Regulations Detached house Flat

Figure 5: Monthly variation of a dwelling’s heating requirements for different heat loss standards

2006 flat

kWh

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

CL4 flat

Flat (61m2)

DHW0

200

400

600

800

1000

1200

1400

1600

CL5 flat CL6 flat2006 detached

house

kWh

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

CL4 detached house

0

200

400

600

800

1000

1200

1400

1600

CL5 detached house

CL6 detached house

Detached house (104m2)

DHW

To estimate the weight of space heating and DHW requirements, figure 6 shows the overall dwellingheating requirements split between space heating and DHW for the different CSH standards. It shows howa CSH6 dwelling’s space heating would account for only around 30% of the total heating requirements.

The HLP values for different Code levels will depend on the minimum requirements for insulation and airtightness set in future revisions to building regulations, and the extent to which developments areencouraged to go beyond the minimum requirements by CSH credits for improved HLP.

Apart from in CSH6, minimum insulation and airtightness requirements for future building regulationshave not been set up. It is therefore difficult to estimate the HLP that will be required for different Codelevels. This task is even more complicated because compliance with the required CO2 reduction targetscan be achieved through different measures.

9. The average UK location is taken to be the East Pennines, as detailed in SAP.

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The important message to remember is that by 2016, the total heat load will be dominated by DHW.Space heating will account for less than a third of total heat load and may decline further.

Note: The overall hot water requirements of a dwelling would be increased by substituting electric heaters in dishwashers and washing machines with hot water circuits10 which could reduce distributionlosses from a district network and lead to lower carbon dioxide emissions. This may however, increase thecost of the appliances.

It is also important to consider the overall reduction in heating design load expected for typical dwellingsthat meet the higher Code levels. A comparison of these reductions is shown in figure 7.

Figure 6: Proportion of space heating and DHW requirements for different dwelling heat loss standards.Flat and detached house

DHW

2006 Flat CL4 Flat CL5 Flat CL6 Flat

Space heating

0%

20%

40%

60%

80%

100%

41%51%

35% 27%

73%65%59%

49%

Flat (61m2)

DHW

2006 Detached

CL4 Detached

CL5 Detached

CL6 Detached

Space heating

0%

20%

40%

60%

80%

100%

50%61%

43%32%

68%57%50%

39%


Space heating and DHW energy requirements as a percentage of total heating requirements

10. Persson, Tomas and Rönnelid, Mats. Increasing solar gains by using hot water to heat dishwashers and washing machines. Applied Thermal

Engineering, Volume 27, Issues 2-3, February 2007.

Figure 7: Indicative reduction in the design heating load for different Code levels

CL4 Flat CL5 Flat CL6 Flat

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

31%

21%

42%

CL4 Detachedhouse

CL5 Detached house

CL6 Detached house

0%

10%

20%

30%

40%

50%

35%

24%

47%

Heating design load reduction compared with 2006 Building Regulations

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2.2 Heat and electricity requirementsUnder current building regulations and up to CSH5 only, CO2 emissions from space heating, domestic hotwater, fans, pumps and lighting need to be considered. For CSH6, cooking and all appliances must beincluded.

Figure 8 summarises the estimated useful energy requirements under different Code levels, reflecting theneed to include cooking and all appliances for CSH6 requirements.

The importance of including the appliances in the energy balance is quite significant. Up to and includingCSH5, the useful energy requirements of the dwelling are dominated by the space heating and DHWrequirements. This is mainly because the energy used by the appliances and cooking are not included andmeans that heating dominates. However, for CSH6, the energy used by heating and electricity is equallybalanced, see figure 8.

It is also interesting to relate the annual heating to electricity requirements for different levels of the Code.This is shown in table 3 with and without considering the electricity used in the appliances and cooking. Note: values apply only to the dwellings examined in this report.


Figure 8: Contribution of heat and electricity energy requirements to the total energy requirements of adwelling under different Code levels (see figure 7 heating design load – peak demand)

Electricity

Flat (61m2)

Heat

0%

20%

40%

60%

80%

100%

86%88%

15%12% 14%

48%

52%

85%

2006 Flat CSH4 Flat CSH5 Flat CSH6 Flat

Electricity


Heat

0%

20%

40%

60%

80%

100%

87%90%

15%10% 13%

51%

49%

85%

2006 Detached

House

CSH4 Detached

House

CSH5 Detached

House

CSH6 Detached

House

Heating and electricity energy requirement

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Table 3: Annual heat to electricity requirements ratio

2006 Building Regulations 7.3 8.6 1.6 1.8

CSH4 6.1 6.8 1.3 1.4

CSH5 5.5 5.8 1.2 1.2

CSH6 4.9 4.9 1.1 1

Flat Detached house Flat Detached house

Excluding appliances Including appliancesand cooking and cooking

Summary

• By 2013 CSH4 will require 44% CO2 emissions savings above 2006 Building Regulations requirements. CSH5 will require 100% savings. Up to CSH5, CO2 emissions from space heating, domestic hot water, ventilation and lighting must be considered.

• By 2016 CSH6 all new homes in England will have to be built to net zero carbon standards - this accounts for all energy use within the dwelling, including cooking and appliances.

• Up to and including CSH5, the energy requirements and CO2 emissions of the dwelling (from the point of view of building regulations compliance) are governed by the space heating and DHW requirements. For CSH6 the CO2 emissions from electricity usage in the dwelling will be dominant.

• The HLP indicates the heat losses through the building fabric accounting for fabric (including thermal bridges), ventilation and infiltration losses.

• By 2016 the heat loss parameter in dwellings will be limited to 0.8W/m2K.

• Achieving a HLP of 0.8 W/m2K under CSH6 is equivalent to achieving heat loss standards similar to those permitted under the PassivHaus standard, i.e. space heat requirements of 15 kWh/m2y. Note: 15 kWh/m2 is an indicative figure.

• A smaller HLP will reduce both the annual space heating demand and the magnitude of the heating design load.

• A dwelling built to CSH6 will reduce space heating requirements by at least 60-70% compared with a 2006 compliant dwelling.

• By 2016 the total heat load will be dominated by DHW, while space heating demands will account for less than a third of total heat load and may decline further.

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3. The implications of low heatdemand for district heating networks3.1 District heating systemsDistrict Heating (DH) is where a number of buildings or dwellings are heated from a central source. Heat isdelivered to the end user through distribution pipes carrying hot water, as shown in figure 9 below.

Figure 9: Schematic of a district heating system

Distribution is normally via pre-insulated steel pipes, as shown in figure 10 below, courtesy of AberdeenCity Council.

The use of pre-insulated flexible plastic pipes is extensive in some Scandinavian countries such asDenmark, although they are normally used for smaller systems.

Figure 10: City-wide district heating pipe works

© Aberdeen City Council

Dwellings/offices/retail/schools...

Energy centreWoodchip/pellet boilerBiomass CHP

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Heat transfer between the distribution network and the building or dwelling’s internal heatingdistribution systems occurs via a hydraulic interface unit (HIU) installed in the building/dwelling. Amongother things, they normally include a heat exchanger(s) which substitutes the need for an individualboiler. The DH network usually guarantees instant access to DHW, therefore removing the need for hotwater cylinders or any type of individual boiler at a dwelling or building level. This frees extra space inthe dwelling, which is beneficial from a developer’s and resident’s point of view.

From the users point of view there is no operational difference compared with an individual heatinginstallation. Radiators equipped with thermostatic valves, programmers and room thermostats are thesame for both systems.

Once the heat network is installed, DH offers ‘fuelflexible’ energy provision. For example, fossil fuel-firedheat plants could be substituted in the future by new,renewable technologies such as fuel cells and biomasscombined heat and power (CHP). This means thatcarbon-intensive heating networks can be convertedrelatively simply to use low or zero carbon energysources.

Fuel flexibility increases the security of supply. Whenusing renewable fuel sources, heat-generating plant isnormally installed with backup boiler capacity such as agas or oil boiler. Multiple fuel types can therefore beeasily integrated within the same scheme.

In a DH scheme there is no need for a gas connection to the dwelling, provided occupants are happy to cookby electricity. This reduces the risk of fire and poisoningby carbon monoxide within the dwellings.

Figure 11: Detail of a domestic heat exchanger

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DH supply sources include both fossil fuel, e.g. gas fired combined heat and power, and renewableenergy sources (for example biomass).

CHP is the generation of electricity and the use of the heat that is generated in the process as a by-product. This allows system efficiencies that exceed conventional electricity-generating technologies.

CHP systems can use a range of electricity generating techniques, however reciprocating internalcombustion engines are the only technology in common use in district heating schemes in the UK.

As a rule of thumb and in order to achieve attractive economical returns, CHP plants need to run for atleast 4,000-5,000 hours per annum, which is equivalent to running the plant about 13-14 hours everyday of the year. In order to meet the threshold criteria for good quality CHP, it is necessary for themajority of the heat generated to be used. This is easily achievable in mixed-use developments wherethe load diversity smoothes the heat profile and allows the plant to maximise the number of hours thatusable heat is produced. For a domestic-only scheme where heat requirements normally occur for a fewhours early in the day and in the evening (see figure 12) thermal storage is normally required to matchthe heat output of the CHP with the heat demand profile.

The use of highly responsive top-up sources such as gas boilers is normally required in DH schemes tocope with variations in demand, ensuring that enough heat is produced at any time to supply both peakspace heating and DHW requirements. Sufficient plant capacity and a suitable distribution network sizeand controls are fundamental to ensuring this.

100 units of fuel

45 units of heat

30 units of electricity

Figure 12: Typical dailyaverage heat profile in arepresentative mid-heatingseason day for different Code levels

2006 flat

dw

ellin

g t

her

mal

load

0:00

1:00

2:00

3:00

4:00

5:00

6:00

8:00

9:00

10:0

0

11:0

0

12:0

0

13:0

0

14:0

0

15:0

0

16:0

0

17:0

0

18:0

0

19:0

0

20:0

0

21:0

0

22:0

0

23:0

0

7:00

CL4 flat CL5 flat CL6 flat

25 units waste heat

Combined heatand power plant

Indicative CHP energy balance

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3.2 The influence of heat density on the applicability of district heating Successful implementation of a DH scheme relates primarily to a site’s building density and morespecifically, to its heat density11. This is due to the high capital and installation costs of the heatdistribution network. The greater the distance between dwellings, the longer the pipe run and thegreater the costs, even though the heat sold remains fixed. Figure 13 shows two hypothetical DHschemes supplying the same amount of heat for a high and a low density development. The distributionnetwork required to supply the block of flats is considerably smaller, even allowing for risers andhorizontal heat distribution within the flats.

11. Heat density refers to the amount of heat required per m2 of land or per pipe length.

12. http://www.energysavingtrust.org.uk/housing

Figure 13: Housing density influence on the distribution network required for a certain amount of heat demand

Detached housesTotal heat demand HPipe length L1

FlatsTotal heat demand HPipe length L2 (L2<L1)

Historically it has been assumed that densities above 50 dwellings per hectare, e.g. a development offlats, justify implementation of a district heating scheme based on economic parameters. However, therequirement for zero carbon homes involves a step change in carbon savings. So district heating schemesmay need to be applied at lower densities (e.g. for houses) than has traditionally been the case, eventhough there will be higher costs involved and heat demands will be lower due to improved HLPs.

Figure 14 shows the cost breakdown of a DH installation according to the District Heating Indicatorspublished by the Community Energy programme in May 2004. The diagrams use amalgamated costsobtained for DH schemes that use different technologies (either heating-only or CHP) and have differenthousing densities. Although the higher cost range could be representative of low-density schemes, oneneeds to treat the information with care as under the Community Energy programme12 there were only afew low-density schemes. Nevertheless, in the case of low-density schemes, the heat network is oftenthe single largest element of the scheme’s cost.

The feasibility of low-density DH schemes will more than likely depend on the ability to deliver costreductions in the DH distribution network.

LOWDENSITY

HIGHDENSITY

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The Swedish sparse district-heating research programme has been looking at ways to increase thecompetitiveness of community heating in low heat-density areas13. In contrast to the UK’s motive forimplementing DH in low-density developments (to achieve zero carbon homes), the Swedish researchresponds to the need to expand existing DH schemes to include low-density areas. Its conclusionstherefore need to be seen in perspective. Nevertheless the Swedish experience and those of otherScandinavian countries needs to be taken into account if the UK is to successfully implement DH in lowdensity areas.

Ultimately, the benefits of DH schemes will depend on the ability of centralised heat production tooutweigh the disadvantages relating to heat distribution. While this has been already successfully achievedin high density developments, more work is required to examine the viability of implementation of DH inlow heat density areas.

Figure 14 shows the variation of the district heating network cost with the dwelling density.

Figure 14: Cost breakdown of district energy schemes. Source: Community Energy Indicators. May 2004.The Energy Saving Trust

5%

2%

Energy centre40%

20%

38%

Heatnetwork

Electrical connection

Heat network

Internals

Consumer connection

Low cost scenario

3%

2%

43%

32%

23%

Heatnetwork

Energy centre

Electrical connection

Heat network

Internals

Consumer connection

High cost scenario

13. Nilsson S.F. et al., Sparse district heating in Sweden, Appl Energ (2007), doi : 10.1016/ j.apenergy.207.07.011.

Figure 15: District heating system capital cost variation with housing density (dwellings/hectare)

cost per dwelling

ho

usi

ng

den

sity

15%12% 14%

48%

DG capital installation costs – influence of housing density

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Lower heat losses mean that the building heat design load will be smaller. This could offer opportunitiesto reduce the pipe diameter and that will reduce the capital investment required for the distributionnetwork and, potentially, the installation costs. Smaller pipe diameters may allow for smaller trenchesand therefore smaller excavation and refilling costs.

Some Scandinavian countries are also examining the possibility of installing heat storage in dwellings toreduce pipe diameters further, particularly in low-density developments.

Section 2 of the report has shown how heat loss reductions mean that heating requirements in dwellingswill be increasingly driven by the DHW requirements. For a given dwelling density, this means that theheat density will be smaller and that the life cycle costs of the heat delivered per dwelling will increase.This phenomenon will be more significant in those areas where the housing density is already lower e.g.groups of detached houses.

In addition, lower heat densities mean that higher distribution losses are likely to occur. This issue needsto be considered before deciding the suitability of DH in low-density areas.

Appendix A of this report summarises the current research in some Scandinavian countries to identifyopportunities for reducing the cost of heat distribution networks.

Summary

For district heating schemes:

• Viability decreases with lower dwelling and heat densities.

• The heat network is often the highest capital cost element, particularly in low-density developments.

• The capital cost of the heat network per dwelling increases as dwelling density drops.

The lower heat demands of new dwellings in the future will mean:

• Heat demand density will be lower and cost effectiveness worse for any given dwelling density.

• Smaller diameter pipes can be adopted, although cost per dwelling increases.

In order to achieve zero carbon homes, district heating schemes may need to be applied at lower densities than traditionally has been the case, even though there will be higher costs involved compared to individual heating systems.

Heat distribution losses in low density housing areas will be higher.

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4. Low carbon and renewable supplytechnologies for district heating DH networks can be supplied by a variety of low and renewable carbon heat sources, primarily:

• Biomass boilers.• Solar thermal collector fields.• Biomass CHP.• Other sources such geothermal, waste heat and waste to energy heat recovery.

4.1 Biomass only heatingA suitable definition of biomass for the purposes of this report is any fuel, whether solid, liquid or gas,derived from a renewable organic source14.

Both woody and non-woody biomass sources exist. Woody biomass includes short rotation coppice, forestresidues, untreated wood waste and crop residues such as straw. Non-woody biomass refers to vegetableoil crops, animal residues and industrial waste.

Woody biomass can be either burnt directly as a raw product or processed into other forms such as pelletsor woodchips. Pellets and woodchip boilers are the two most common technologies for DH biomass schemes.

Wood pellets can be obtained by refining sawmill products and from different wood processingoperations such as furniture manufacturing. Wood pellets for use in building heating applications arecylindrical and have a diameter of 6 to 12mm and length of 10 to 30mm. They have less moisture contentthan woodchips and thus have more energy content for the same volume. They are, however, moreexpensive to produce and may require longer delivery distances.

The main sources for woodchip within the UK are forestry and woodlands (e.g. whole trees, loggingresidues, thinning and tree maintenance), wood processing (e.g. sawmill co-products like slab wood andjoinery residues) and recycled untreated timber from pallets and construction industry.

Woodchips can also be obtained from dedicated energy crops which are specifically grown for fuel purposes.

14. Community heating using new and renewable sources. The Energy Saving Trust.

Figure 16: Woodchips

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Woodchip boilers have higher capital costs than pellet boilers, although the fuel is cheaper and thereforethey are normally more cost-effective for large installations such as DH. Both pellets and woodchips canbe used by such boilers operating automatically.

A rich methane gas normally referred to as biogas can be obtained via the gasification of biomass15.Biogas can be used in conventional gas boilers for DH heating applications but it could also potentiallybe distributed to individual households via the conventional gas pipe network.

Vegetable oil crops can be harvested and converted into biofuel. Biodiesel is a variant that can also bemade from the processing of waste oil. However, these fuels are often diverted for use in helping tomeet the requirements of the Renewable Transport Fuel Obligation.

Both biogas and biodiesel heating systems are not yet a common practice in the UK. And the carbonintensity of biodiesel is uncertain, so the extent of carbon savings remains unclear.

Possible contribution of biomass heating boilers Biomass boilers usually operate along with some type of top-up boiler to provide winter peak demands.This approach allows the number of hours the boiler operates to be kept close to its optimal capacity,increasing the seasonal boiler efficiency. It also offers the most cost effective approach. Wood-fired boilersrespond relatively slowly to changes in heat demand, so are not suitable to cope with peak demands.

Depending on the technology used, biomass boilers for DH residential schemes can be sized to meetbetween 50-70% of the peak heat demand and can supply around 70-80% of the total heatrequirement. Higher levels of biomass penetration will require a greater amount of thermal storage tosmooth the heat demand. Using biomass boilers in district heating should therefore enable CSH4 to beachieved. In order to achieve higher Code level requirements, some sort of renewable electricitygeneration would be required. This could be done, for example, with photovoltaics or wind turbinesconnected to the wider power distribution network, or biomass CHP.

It should be noted that under buildingregulations, biomass is not classified asa zero carbon fuel. To account for theenergy used in processing andtransportation, the fuel is assumed tohave a carbon content of 25gCO2/kWh,roughly equivalent to an eighth of thecarbon content of natural gas. Thisfactor is allowed for in the analysispresented above.

Note: The current version of SAP,SAP2005, allows users to define dwellingssupplied with biomass DH schemesusing pellets, woodchips or biogas.

15. See section 4.3 on renewable CHP.

Figure 17: Typical proportion of the annual heatingrequirements supplied by heat only wood fired boilers

Top-up

Hea

t re

qu

irem

ents

Biomass

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0%

20%

40%

60%

80%

100%

Typical proportion of annual heat requirementssupplied by biomass boilers

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4.2 Solar thermalAlthough solar thermal DH development in the UK is negligible, it is an emerging technology in Nordiccountries, especially in Denmark. There are currently 12 district heating schemes in Denmark served inpart by solar thermal collector arrays. Given the comparable solar resource with other northern Europeanlocations, solar district heating in the UK should be technically possible (although in most parts of thecountry its solar resource is slightly less than Denmark).

Applications of solar thermal energy in DH schemes can range from large schemes serving largedevelopments to smaller schemes serving a block or group of dwellings (see figures below).

While small domestic solar thermal installations in the UK usually provide only DHW, solar thermal DH alsosupplies part of the space heating requirement.

Larger solar DH schemes consist of ground-mounted collector fields whilst smaller applications could installthe collectors integrated with the building roof (see figure 19). The use of ground-mounted collectors hasthe disadvantage and expense of significant land requirements. This could be overcome in built-up areaswith roof-mounted installations which are more suited to installation on low-rise blocks of flats.

Figure 20: Solar DH plant, 20,000 m2.Marstal, Denmark. Source: ARCON /ESTIF

Figure 18: Large Solar thermal DH for PassivHouses.Source: Ritter Solar / ESTIF

Figure 19: Collector field for DH, Eibiswald,Austria. Source: S.O.L.I.D. / ESTIF

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Earlier solar DH installations used the solar heat to increase the temperature of the return cold pipe of theDH system. This approach does not require thermal storage but needs a supplementary back-up heating source.

Other schemes combine diurnal thermal storage with a few days capacity. This approach has been used insome Danish schemes supplying most of the DHW base load requirements. A back-up/top-up source is required.

Modern applications of solar DH use seasonal thermal storage allowing the storage of heat from summerto winter. This approach can increase the annual solar share (the percentage of total heating requirementssupplied by solar). Seasonal thermal storage is still in development, and although there are schemes thathave implemented this approach, it is not yet recommended for commercial applications.

In general, solar DH schemes will generally supply a small proportion of the heating requirements. However,if used in very low heat-loss dwellings, solar thermal could contribute a greater proportion of the heatingrequirements. As an example, roof-integrated solar collectors combined with an on-site 200m3 thermalstorage tank have been installed in a block of eight apartments in the town of Burgdorf in Switzerland16.

Possible contribution of solar thermal district heatingSolar assisted DH could be used together with biomass boilers. In summer, the biomass boiler could beshut down, allowing for the solar field along with a smaller fossil fuel backup source to supply the heating requirements.

Further research is recommended in order to establish the potential for solar thermal systems to servedistrict heating in the UK. Close to our major towns and cities, land values are very high. However, ifspatial constraints could be overcome and adequate thermal storage is allowed for, solar thermal in DHcould contribute to reducing the carbon emissions at sites with an adequate solar resource. If theexperience in Denmark was replicated, solar DH schemes could enable CSH4 to be achieved.

Note: SAP2005 does not allow the user to define solar thermal aided district heating. This barrier needs tobe addressed, if the technology is to be adopted.

4.3 Renewable combined heat and powerNew and emerging technologies also allow for the use of bioenergy systems in CHP. CHP can then bereferred to as biomass CHP and it can constitute a renewable solution if the biomass is sustainablysourced. There are different fuels that can be used for biomass CHP.

A rich methane gas currently known as biogas can be obtained though the gasification of wood fromshort-rotation coppice or forestry residues. The biogas can be directly used in internal reciprocatingengines, although significant cleaning and treatment of the gas is required beforehand.

Currently the use of wood gasification to obtain biogas is best applied to schemes of the order of at least1MW electrical capacity. Under current building regulations, this would involve a development of at least1,000 homes. Published figures17 indicate that only 9% of new build stock occurs in developments over1,000 homes. So the technology needs to be developed further to be viable in smaller developments.However, the issues associated with smaller CHP installations are not just technical, there are alsoorganisational and managerial issues associated with operating smaller schemes.

16. www.swissinfo.ch/eng/science_technology/detail/Sun_shines_on_one_of_a_kind_apartment_block.html?siteSect=511&sid=8159403&rss=

true&ty=st

17. The Role of onsite energy generation in delivering zero carbon homes. A report from the Renewable Advisory Board. November 2007.

www.renewables-advisory-board.org.uk

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Biomass CHP systems can use also solid wood. A boiler burning wood is used to generate steam thatdrives a steam turbine to produce electricity. The low-pressure exhaust steam is then available for heating.This is only used for very large industrial applications.

There is one manufacturer18 within the UK that offers a variant of this technology, but it is still in its earlystages. It claims that it can use wood chips, coppiced willow and miscanthus to drive a closed-loopturbine. The plant under development generates about 200kW of electrical capacity, which would allowits implementation in smaller developments.

Biodiesel CHP uses diesel-based reciprocating engines running on fuel that can be obtained fromvegetable oil and from the processing of waste oil for instance.

Because of the higher viscosity of liquid fuels like biodiesel, liquid engine systems tend to wear quickerand hence have higher maintenance requirements and shorter lifetime expectancy. As a result, CHPsuppliers in the UK have tended to concentrate on gas-fired CHP systems.

Possible contribution of biomass combined heat and powerIt should be noted that SAP2005 includes a cap that limits the contribution of CHP in achieving carbonreductions in new dwellings. The original purpose of the cap was to curb the carbon savings achieved byover-reliance on those natural gas-fired CHP systems that have high electrical efficiencies. It appears thatthe same cap may result in the carbon savings from biomass CHP being severely underestimated, as theelectricity from biomass CHP is assumed to have the same carbon content as the grid (and the full carbonsavings are not allowed to be carried through on the heating side).

This issue has been brought to the attention of those responsible for SAP and, it is understood and will bereviewed as part of the wider review of SAP following the launch of the Code for Sustainable Homes. It isessential that this issue is resolved, otherwise one of the main routes to helping to achieve Code levels 5and 6 will be unnecessarily restricted.

18. www.talbotts.co.uk/bgen.htm

Figure 21: Energy centre for a biomass gasification plant. Wick

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4.4 Other technologiesOther technologies can be used to supply heat to district heating schemes.

The use of geothermal energy has been exploited successfully at one location in the UK. This is the casein the Southampton city wide geothermal district heating scheme19. Hot water at 74°C is pumped upfrom 1.7km beneath the city. At the surface, heat exchangers are used to supply heat to the wider cityDH scheme.

Waste heat from industrial processes can also be used to supply heat to DH distribution, from a nearbydistillery for instance. In addition, burning municipal solid waste offers opportunities for heat recoveryand this is used in Sheffield, Nottingham and Lerwick.

Ground source heat pumps (GSHP) can also be used to supply district heating networks. However, inmost situations, this would involve the installation of two separate distribution networks: one for thespace heating and another one for the DHW. This would severely increase the cost of an already capital-intensive technology.

4.5 Technology integrationTraditionally, radiator heating systems in the UK have operated at a supply water temperature of 82°Cand at a return temperature of 71°C. Existing DH schemes therefore ideally need to be able to operateto this temperature regime. New schemes can however be designed for different operating temperatures.

Underfloor heating systems, for example, typically operate 50°C with a return temperature of 43°C. Thisfavours the use of technologies such as solar thermal and condensing boilers.

Lower temperatures can enable DH systems to make direct use of low-temperature heat sources. Heatpump performance is best at lower supply temperatures. In DH schemes they need to be integrated inlow temperature heating networks and ideally combined with underfloor heating systems. Providing the65°C required for DHW is still a problem for this technology.

Gas-fired CHP and other renewable technologies can initially be integrated to offer a low-carbon sourceof heating. There are, however, compatibility issues which need to be taken into account. These areshown in table 4.

19. Urban district heating and cooling: the Southampton district energy scheme. IEA DHC. http://www.iea-

dhc.org/download/KN1640%20Southampton%20v2.pdf

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Table 4: The compatibility of renewable heat technologies supplying standard operating temperatures20 inDH schemes

20. 90°C supply flow temperature and 71°C return.

Biomass No issue. Boilers are capable of providing Biomass fuel supply.(wood) boilers heat at the required temperature.

Biogas boilers No issue. Biogas can be obtained from different biomass processes. The gasification of wood is one of them but this technology is not yet proven in long- term operation in the UK.

Biofuel boilers No issue. Unlike other fuels, the carbon intensity of biofuels is uncertain and hence the carbon savings are unclear.

Solar thermal Not achieved in any UK scheme. Some Danish schemes operate with very low temperature DH and have integrated solar thermal.

Ground source Only with poor performance. Although heat pumps GSHPs might be physically capable of

raising the return temperature of the DH above 65°C, the drop in the coefficient of performance (CoP) at such temperatures means there will not be a significant carbon benefit over gas fired boilers. Very low temperature heating presents fewer obstacles.

Technology Physical ability to raise the return Other issuestemperature of the DH

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Summary

• Pellets and woodchip boilers are the two most common technologies for DH biomass schemes.

• Biomass (wood-fired) boilers are not suited to cope with peak demands.

• Biomass district heating boilers can help to achieve up to CSH4.

• The applications of solar thermal energy in district heating schemes can range from large district heating schemes serving large developments to smaller schemes serving a block or group of dwellings.

• Larger solar DH schemes consist of ground-mounted collector field, whilst smaller applications could make use of collectors integrated in the building’s roofs.

• While smaller solar thermal installations aim to only provide DHW, the use of solar thermal DH also allows part of the space heating requirement to be supplied.

• If used in very low heat loss dwellings, solar thermal could contribute to a greater proportion of the heating requirements.

• The use of solar thermal technology in DH requires further research in the UK.

• Current and short-term applications of biomass CHP are likely to be limited to developments of at least 1,000 homes.

• The current version of SAP does not adequately account for the full carbon benefits of biomass CHP.

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Table 5: Applicability of renewable energy sources for district heating schemes in the UK

2013 2016(Code level 4) (Code level 6, zero carbon homes)

Gas fired CHP • Potential to achieve CSH4.• Proven technology.

Biomass heating • Subject to fuel supply issues. • Proven technology.

Solar thermal • Highly dependent on technology development.

• High solar fraction required to achieve CSH4.

Biomass CHP • Potential to achieve CSH6.• Technology development is likely to

be achieved in the UK within the medium term.

• Likely to be applicable only in major developments.

• Subject to fuel supply issues.• Likely to incur heat dumping for only

domestic developments.

Fuel cells • Highly dependent on technology development.

• Hydrogen obtained from renewable sources will be required.

Waste heat from • Proven technology.industrial processes • Already used in DH schemes.or municipal waste • CO2 savings dependent on the waste

heat source.

Geothermal • Applicability limited to the availability of suitable underground water temperatures.

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5. Implementation of district heating 5.1 Energy services companiesAn Energy Services Company (ESCO) is an entity that is set up to provide an energy service, includingenergy efficiency, energy savings and/or sustainable provision of energy. ESCOs can follow differentbusiness models21.

• Fully driven by the public sector with no private-sector involvement.• Public-sector driven with private sector involvement in design and build.• Public-sector driven and operated by the private sector.• Private-sector driven with or without public sector encouragement.

CLG statistics22 show that for the year 2005, around 82% of dwelling stock was in the private sector. Ifnew build stock follows the same trends this means that the involvement of ESCOs in purely privatedevelopments will be increasingly be a model to follow for the implementation of DH schemes. This isalready occurring in London where planning policy requires all new major developments to either connectto existing DH schemes or to set up new DH networks.

In a hypothetical model, the ESCO could be used to design, build and operate the system. The developercould contribute to all or part of the capital investment.

The capital contribution of the ESCO will depend on the business model implemented. The ESCO willrecover the contribution to the capital cost by selling heat and electricity if CHP schemes are used.

The application of DH in low heat density developments, as has been seen in the previous section, willunavoidably incur higher capital costs per unit of heat sold. This can be reflected as either (or both):

• An increase in the capital costs of the scheme.• Increase in the costs of the heat delivered (where part of the capital cost is included in the heat charge).

From a developer’s point of view, connection costs could be compensated in part by avoiding the capitalcosts of individual boilers and gas connection. In addition DH frees up space thanks to the removal of the boiler.

DH offers an alternative way of achieving CSH6 dwellings and therefore it is important to bear in mindthat its costs will need to be compared against alternative solutions.

From a resident’s point of view, DH avoids the need for boiler maintenance and replacement, minimisesthe risk of fires and/or carbon monoxide poisoning, offers instant access to DHW at high pressure suitablefor showers and increases the living space.

The ESCO would be in charge of billing the dwelling occupant. While in social housing flat rates aresometimes offered, heat meters will be required in private homes and the occupant will be charged forthe amount of heat used.

On a wider scale, an ESCO can be a Multi Utility Service Company (MUSCO). A MUSCO could be formedto deliver heat, electricity, water and communications. It is expected that there could be cost benefitsarising as the heat mains can be installed in service ducts at the same time as other services, such ascommunications are provided.

21. Making ESCOs work. Guidance and advice in setting up and delivering an ESCO. February 2007.

22. Department of Communities and Local Government’s ‘Housing Statistics 2006’.

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5.2 Capacity for delivering district heating in the UKThe UK DH industry is small compared to Scandinavia. Only a few consultancies have experience ofanalysing and designing district heating schemes. This includes a couple of very small firms that have beenoperating in the field for over 30 years.

Due to a push for DH within the planning system, a larger number of consultancies are starting to analysedistrict heating, but they do this from a very low experience base and risk repeating some of the mistakesof the past.

There is also only a small number of ESCOs with experience of installing and successfully operating districtheating in the UK. And a small number of companies have experience in particular areas, e.g. pipeinstallation and heat metering.

Overall, the UK industry is small in capacity and may struggle to cope with a large expansion in the use of DH.

It may be help to seek involvement from companies based in European neighbour countries wherepenetration of DH is high. These companies have state-of-the-art knowledge of all aspects of thetechnology, are accustomed to working in other countries, and know the best way to develop emergingschemes.

The UK has been a member of the IEA District Heating & Cooling programme. The programme carries outresearch on a range of associated issues including network optimisation, integration of CHP, better pipeinstallation techniques and district cooling. Renewed participation in this programme could be exploredas a good option for assisting overall effective scheme design and operation.

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6. Conclusions and recommendationsfor further workA combination of demand reduction and district heating with heat-only biomass would meet the buildingregulations requirements of 2013, i.e. CSH4.

In order to achieve zero carbon dwellings, renewable CHP technologies are likely to be required,particularly for high density development. However SAP needs to be modified to fully recognise thecarbon savings of the technology.

Heat requirements of new dwellings in the future will be reduced due to constraints set by the HLP.Heating requirements in dwellings will therefore be increasingly driven by DHW requirements. For a givendwelling density this means that the heat density will be smaller and that the life cycle costs of the heatdelivered per dwelling will increase. This phenomenon will be more significant in those areas where thehousing density is already lower e.g. groups of detached houses.

The role of DH in providing low and zero carbon homes will depend on the ability to deliver costreductions in the district heating distribution network, which in turn is linked to dwelling density.

Heat distribution losses for DH applications in low-density areas can be significant. This issue needs to beaddressed before considering DH schemes for such applications and should be object of further research.

More research will be required if DH is to play a significant role in the government’s zero carbon homesobjective. Work should focus on gaining experience in implementing solar thermal and renewable CHP –and it should also look at how to reduce the costs of the heat distribution network. Much can be learnedfrom the Scandinavian DH experience.

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Appendix A – Opportunities for costreduction in the heat distribution pipework: the Scandinavian research

This appendix summarises some of the research undertaken in Sweden regarding the implementation ofdistrict heating in low heat density developments. Main references used are:

• IEA – DHC Annex VIII. District heating distribution in areas with low heat demand density.

• Nilsson S.F. et al., Sparse district heating in Sweden, Appl Energ (2007), doi :10.1016/j.apenergy.207.07.011.

• Person, Tommy (2005). District heating for residential areas with single family housing – with special emphasis on domestic hot water comfort. June, 2005. Doctoral thesis. Lung Institute of Technology. Lund university, Sweden.

• Local district heating system using flexible plastic pipes. March 1996. CADDET brochure number R 247.

For other IEA DHC reports, dealing with better pipe installation techniques and materials, see www.iea-dhc.org.

Heat distribution network costs can be broken down as follows:

• Capital costs of the distribution system.• Distribution losses due to the heat losses in the distribution network.• Distribution cost due to pumping losses.• System maintenance costs.

A.1 Capital costs influence in the heat delivered costsThe capital expenditure per unit of heat delivered by a district heating network is dependent on the costsassociated with the installation of the distribution system, the pipe diameter and the line heat density –amount of heat delivered per pipe length (figure A.1).

Figure A.1: Heat delivered costs due to capital investment

line heat density (heat delivered per pipe length)

cost

15%12% 14%

48%

costs of the distribution network and pipe diameter

cost

15%12% 14%

48%

Heating delivered costs due to capital costs

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In order to reduce the heat production costs due to the initial capital investment one could:

• Reduce costs due to the installation of the distribution network.• Use a smaller pipe diameter.• Increase the heat density.

A.2 Opportunities to reduce installation costs of the distribution network

Design stage decisions Opportunities to reduce the capital costs of installation of the distribution network need to be firstidentified at the design stage. Some of the issues to be considered are:

• The use of twin pipes have been shown to reduce heat distribution losses compared with single pipes. They can also be installed in narrower trenches although may require more complicated welding works.

• The use of plastic pipes23 in contrast to steel pipes can reduce the pipe work capital cost. Flexible pipes can facilitate alternative pipe layouts and reduce the number of pipe bends. The possibility of using plastic pipes will ultimately be related to the operating temperatures and pressures of the distribution heating system.

• Backfilling works can be reduced if the pipes are laid down in open areas such parks and gardens. The storage of the excavated materials on-site and its use for backfilling will also reduce the installation costs.

• The contractual arrangements for the installation of the pipes will also influence the end installation costs.

Pipework diameter The impact of reducing pipe diameter on the costs of the distribution network is reflected in figure A.2.According to the Swedish experience, pipe material is responsible for about 25% of the total networkcosts. The rest is taken up by labour works for the trenching, laying pipes and refilling works.

It is common practise to oversize the distribution network pipe diameter to provide the network with theability to cope with future increases in the heat demand.

The reduction in the heating requirement of new dwellings in the future means that the design heatingload will be significantly reduced. This can offer opportunities for material cost reductions.

On the one hand, smaller pipes reduce the heat losses in the system, which will be especially important inlow heat density application. On the other hand it will increase the system pumping requirements andassociated costs.

Optimum pipe sizing should carefully account for all the issues mentioned above.


23. Extended practice in Denmark.

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Heat density Historically, densities above 50 dwellings per hectare, e.g. a development of flats, have been used todetermine when a district heating scheme should be implemented, based on economic parameters.However, the requirement for zero carbon homes require a step change in carbon savings. So districtheating schemes may need to be applied at lower densities, e.g. houses, than traditionally has been the case, even though there will be higher costs involved and heat demands will be lower due toimproved HLPs.

Where market requirements or design criteria signify lower density developments, it will be fundamentalto maximise the amount of heat delivered for a given length of pipe. With this in mind it will be crucialthat the connection rate to the DH scheme within the development is maximised.

A.3 Running cost influence in the heat delivered cost

Distribution heat losses costsThe cost of heat losses due to distribution will depend on:

• Heat density – heat losses, among other factors, are proportional to the length of the distribution pipe. Therefore, low-density developments will incur higher heat losses as the pipe length for a certain amount of heat delivered is longer than in higher-density applications.

• Pipe diameter – see A.2

• Pipe insulation – the benefits delivered by better insulated pipes will depend on the relation between their ability to reduce heat losses and the increased capital cost of the insulating material.

• Low cost heat-generating technologies will reduce the costs associated to the distribution heat losses.

Figure A.2: Distribution heating pipe work costs (Swedish experience)

Labour works fortrenching and refilling

25%

75%

Pipe materials

Costs of distribution pipe work for CH schemes

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Pumping and maintenance costsThe cost related to the pumping of the water in a DH network will depend on the pipe diameter and thelength of the pipe work. In a typical Swedish scheme the energy required for pumping represents about 1% of the total energy delivered.

Cost due to the system maintenance represents about 1% of the total investment in the distribution pipesand about 10-15% of the total distribution cost. These figures, however, depend on the specific scheme.

Figure A.3: Line heat density, heat generation cost, pipe diameter pipe insulation influence in the cost ofthe heat delivered by a district heating scheme

line heat density (heat delivered per pipe length)

cost

of

the

hea

t d

eliv

ered

du

e to

dis

trib

uti

on

loss

es

15%12% 14%

48%

cost

of

the

hea

t d

eliv

ered

du

e to

dis

trib

uti

on

loss

es

heat generation cost (pipe diameter) (insulation value)

15%12% 14%

48%

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Energy Saving Trust, 21 Dartmouth Street, London SW1H 9BP Tel 0845 120 7799 Fax 0845 120 7789 [email protected] www.energysavingtrust.org.uk/housing

CE299 © Energy Saving Trust September 2008. E&OEThis publication (including any drawings forming part of it) is intended for general guidance only and not as a substitute for the application of professional expertise. Any figures used are indicative

only. The Energy Saving Trust gives no guarantee as to reduction of carbon emissions, energy savings or otherwise. Anyone using this publication (including any drawings forming part of it) mustmake their own assessment of the suitability of its content (whether for their own purposes or those of any client or customer), and the Energy Saving Trust cannot accept responsibility for any loss,

damage or other liability resulting from such use.

So far as the Energy Saving Trust is aware, the information presented in this publication was correct and current at the time of the last revision. To ensure you have the most up to date version,please visit our website: www.energysavingtrust.org.uk/housing The contents of this publication may be superseded by statutory requirements or technical advances which arise after the date of

publication. It is your responsibility to check latest developments.

CE299

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