Retrofitting District Heating Systems

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Retrofitting District Heating Systems

Creating Replicable Retrofit Models in Hackbridge

A report from BioRegional Funded by:

April 2012

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1 Executive Summary

Context

The UK is striving to achieve 34 % greenhouse gas emissions reductions by 2020 and 80 % by 20501. The UK’s domestic buildings contribute 23 % of the UK’s greenhouse gas emissions. Whilst new homes are being built to much higher environmental standards (Code for Sustainable Homes level 4 thermal standards become statutory in 2013), most of the UK’s existing building stock is very energy inefficient and so there is a lot of scope to reduce emissions from these buildings.

BioRegional are working in partnership with the London Borough of Sutton to make Hackbridge (the London suburb that is the home of BedZED) a pilot for how a zero carbon area could be achieved. A number of new developments are planned in Hackbridge. The developers of the largest of the development sites, Felnex Trading Estate, are investigating the potential for establishing a district heating network for their development. If this option is taken forward, it can be envisaged that this network could then be extended to the rest of the suburb. The London Borough of Sutton is keen to extend this network to cover not only the other development sites planned for Hackbridge, but also to existing buildings in the area.

Thus there is an urgent need to quantify the cost of supplying district energy to existing dwellings, looking at carbon dioxide savings per pound spent in comparison to more traditional retrofit measures (e.g. insulation) to achieve the zero carbon Hackbridge vision that is aspired to.

District heating is the supply of hot water from a central boiler plant or other heat source to buildings in a local area. Where possible, “waste heat” is used to power the network. This is heat that is produced as a bi‐

product of another process such as electricity generation and so is classed as “emission free”, since all emissions have already been attributed to the primary product.

It is also common for the central boiler plant to be a combined heat and power unit (CHP).

The second approach is the more traditional retrofit, whereby a building’s energy efficiency is increased by improving the building fabric (for example, cavity wall and loft insulation) and installing energy efficient or renewable sources of heat and electricity in the building itself.

Hackbridge lends itself to a district heating network because three potential sources of waste heat exist:

heat and electricity production using methane collected from the neighbouring landfill site; a pyrolysis plant to the north; and a proposed waste management facility to the east.

The costs and carbon savings from connecting the flats to an energy network supplied by waste heat were modelled. In addition, three other CHP units powered by biogas, natural gas and biomass were modelled.

These would be applicable to areas that do not have existing sources of waste heat available.

Key results

The study found that each of the district heating options achieves more carbon emission savings than the full traditional retrofit option (as much as 84 % in the biogas CHP unit scenario compared to 34 % with the retrofit approach), and at a lower cost. Unlike the district heating approach, however, traditional retrofit tackles other issues such as fuel poverty and thermal comfort. These were important considerations for the residents surveyed who, whilst in favour of both approaches, would prioritise the retrofit.

1 Climate Change Act 2008

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Furthermore, it was found that some retrofit measures provide far greater carbon savings per pound spent than others. For example, energy efficient light bulbs save carbon at a cost of 14 pence per kilogram whereas floor insulation saves carbon at a cost of £142 per kilogram. With this in mind, a model was created where a district heating network was combined with a “light” retrofit approach. The measures included in the “light retrofit” were those that would payback in a period of 25 years. Table 1 provides a comparison between the different options considered, showing costs, costs compared to carbon savings along with the advantages and disadvantages of each approach.

It should be noted that all approaches achieve considerably higher carbon emission savings when applied to flats with electric heating compared to those with gas heating. This is because using electricity is over three times more carbon polluting than gas to generate hot water.

Approach Cost per

flat (£)

Cost per kilogram of carbon saved

(£/kgCO2e)

Advantages & disadvantages

District heating

network 10,125 3

High carbon emission savings, no increase in thermal comfort, fuel bills remain the same,

cheapest option

Full retrofit 29,949 9 Lower carbon emission savings, expensive,

increase in thermal comfort, lower fuel bills District heating

network + "light"

retrofit

14,611 7 High carbon emission savings, increase in thermal comfort, lower fuel bills

Table 1: comparing costs, carbon emission savings and other impacts of three different scenarios As Table 1 shows, even a “light” retrofit approach adds significant expense to the district heating option, however the residents would benefit from lower energy bills and a more comfortable home.

It makes theoretical sense to connect blocks of flats in Hackbridge to a district heating network because:

a) There are a large number of blocks of flats in one area;

b) There is already a planned district heating network proposed for the Felnex Trading Estate site which could be expanded to service the existing flats too; and

c) Sources of waste heat currently exist to power the network and there are more planned for the future.

However, it makes more environmental sense to reduce the energy demand of these buildings first with a light retrofit programme.

Whilst a district heating scheme would deliver high levels of emissions saving per pound spent, the initial capital investment required to set one up is large. Depending on the heat demand of the network, this may be sufficient to pay off the initial investment over a 25 year period. In the case of Hackbridge, the overall heat demand of the flats is not sufficient to generate enough profit over a 25 year period to match the initial investment, even if the waste heat could be bought for only 1p/kWh. In order to pay off the capital

investment within a 25 year period, an additional £150‐£300 per flat would be required per year.

Alternatively additional investment of between £4‐8,000 would be needed. If light retrofitting is done before the flats are connected to the district heating network there will be less heat revenue from the flats and therefore the additional investment needed would rise. The next steps will be to identify exactly how much the waste heat could be purchased for in order to undertake a full financial feasibility study for

connecting the flats.

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2 Introduction

The UK is striving to achieve 34 % greenhouse gas emissions reductions by 2020 and 80 % by 2050². The UK’s domestic buildings contribute 23 % to the UK’s greenhouse gas emissions. Whilst new homes are being built to much higher environmental standards (Code for Sustainable Homes level 4 thermal standards become statutory in 2013), most of the UK’s existing building stock is very energy inefficient.

There are two common approaches to reducing the carbon emissions³ from homes that can be done without country‐wide decarbonisation of the gas and electricity networks. The first is the traditional retrofit,

whereby the building fabric is improved (for example, increasing the levels of insulation), the energy generators within the home are made more energy efficient (for example, replacing an old gas boiler with a new one) and building integrated renewable energy technologies. The second approach is to generate low carbon energy locally and retrofit a district heating system into the home to deliver this low carbon heat as well as providing low carbon/renewable electricity to the national grid.

Planned Government initiatives such as the Green Deal and the Energy Company Obligation are paving the way for large scale roll‐out of retrofitting the UK’s existing building stock. However, current data suggests a rapid rise in the cost per tonne of carbon dioxide saved for dwellings after a £7,000 investment on traditional retrofitting measures, rising even faster after £11,000. Blocks of flats are some of the hardest building types to retrofit, due to their construction and multiple occupancy nature. They are therefore an obvious choice for connecting to district heating systems, as this can potentially provide a cost effective alternative to traditional full retrofit approaches, causing less disruption to residents. However, little research is available comparing the two approaches, which would allow owners of blocks of flats (particularly social housing providers) to make informed decisions about which approach is best for their building stock.

This report investigates which approach is the most economically viable and carbon efficient for blocks of flats in the suburb of Hackbridge, Sutton. Given the typical nature of these flats, the results of this study should apply to most other blocks of flats in the UK.

2 Climate Change Act 2008

3Throughout the document, the term “carbon emissions” refers to all greenhouse gas emissions.

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2.1 What is district heating?

District heating is where hot water is produced by a central boiler plant or other heat source and is piped into buildings to provide their space heating and domestic hot water for cooking and cleaning (see Figure 1).

Where possible, “waste heat” is used to power the network. This is heat that is produced as a bi‐product of another process such as electricity generation and so is classed as “emission free”, since all emissions have already been attributed to the primary product.

It is also common for the central boiler plant to be a combined heat and power unit (CHP). CHP involves the production of electricity and useful heat from a single plant, which is more efficient than generating electricity and heat separately. This is because during the generation of electricity from fossil fuels heat is also generated. With electricity from the national grid, this heat is mostly wasted as there are few heat users next to the power generation facility. Wasting the heat means that the efficiency of the conversion from fossil fuel to electricity is only around 40%. If that heat can be used, the efficiency increases to around 70%, as can be seen in Figure 2.

Figure 1: A typical district heating network. Source: Energy Saving Trust. (2004).

Community Heating – a guide.

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CHP allows electricity to be generated near to heat users (as it is smaller scale than traditional power stations). This means that the carbon emissions per kWh of heat produced are lower than for a gas boiler because for the 1kWh of gas that is put in the system, not only is heat generated but also electricity.

Generating electricity using CHP to offset grid electricity results in carbon savings, regardless of the fuel used. The total carbon savings achieved by using heating from the network are therefore a sum of the emission‐free heat, plus the carbon emission savings from the more efficient generation of electricity compared to that produced for the grid.

It is possible to deliver the electricity directly to the buildings using a private wire system, but it is more common that this electricity is fed into the National Grid. This is because, in most situations, the community CHP unit would not be equipped to cope with peaks in electricity demand hence the buildings would need to remain connected to the National Grid to ensure a guaranteed electricity supply. Furthermore, setting up a private network incurs a high capital cost.

Excess hot water produced by the network is stored in large, insulated tanks. This means that, in cases where a CHP unit is used, it may be switched off during periods of low heat demand, for example, overnight.

The hot water tanks will be able to supply any heat demand during these times.

Since it is inefficient for a CHP unit to provide the peaks in the energy demand (for example, first thing in the morning when everyone wakes up and showers) an additional boiler would be required to meet these peaks.

District heating suits areas of high, constant heat demand hence densely populated, mixed use areas are preferable.

District heating is very common in Denmark and other European countries, where it serves the heat demand of whole cities. It is now becoming more common in new developments in the UK and, in some cases, has been fitted into existing buildings. For example, in Aberdeen, four multi‐storey blocks of flats built in the

Figure 2: Why combined heat and power is more efficient than conventional power generation. Source: DEFRA

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1970s which had electric storage heating have now been connected to a district heating network⁴. Similarly, five multi‐storey blocks have been converted from electric storage heating to district heating in Newcastle⁵. Like in the Aberdeen and Newcastle examples, district heating schemes are often managed by an Energy Services Company (ESCo). The ESCo will be responsible for the installation, financing, operation,

maintenance, regulation and billing of the network. For further information on ESCos please see Appendix 14.1.

2.2 Why Hackbridge?

Hackbridge is located in Sutton, a London borough which has pledged to become zero carbon‐enabled by 2025. Sutton Council and BioRegional would like Hackbridge to become the pilot that shows how this could be achieved.

Significant levels of regeneration are occurring within Hackbridge. A masterplan has been developed to create the UK's first ‘truly sustainable suburb'. Detailed plans include 1,100 new sustainable homes, more shops, leisure and community facilities, new jobs, sustainable transport including pedestrian/ cycle initiatives and improved networks and open spaces. The Council’s Core Strategy for planning was adopted in

December 2009. The strategy contains a commitment for all new buildings constructed in Hackbridge from 2011 onwards to be zero carbon.

The developers of the largest of the development sites in Hackbridge, Felnex Trading Estate, are

investigating the potential for establishing a district heating network for their development in order to meet the zero carbon requirement. To the east of Hackbridge is a landfill site from where methane is collected and burnt in a gas engine to generate electricity. Heat is a by‐product of this process and is currently not being used. One of the options being investigated by the developers of Felnex Trading Estate is building a heat pipe to deliver this heat to the Felnex Trading Estate. If this option is taken forward, it would then become possible to envisage extending this network to the rest of the suburb. The London Borough of Sutton is keen to extend this network to cover not only the other development sites planned for Hackbridge, but also to existing buildings in the area.

Thus there is an urgent need to quantify the cost of supplying district energy to existing dwellings, looking at carbon dioxide savings per pound spent in comparison to more traditional retrofit measures (e.g. solid wall insulation) to achieve the zero carbon Hackbridge vision that is aspired to.

This study only considers connecting blocks of flats to the network since these are seen to be some of the easiest buildings to connect to and costly to retrofit compared to the CO2 savings that can be achieved. One third of the existing building stock in Hackbridge is flats, making this an ideal place to look at how they could be connected to district heating. Many of these flats are owned by the London Borough of Sutton’s Arm’s Length Management Organisation, Sutton Housing Partnership, hence any changes to the flats would be easier to implement because the council owns the freehold for all the properties and can therefore require the flats to connect to the district heating network. Furthermore, the majority of the flats have electric storage heating therefore there is significant scope to reduce carbon emissions by retrofitting a district heating system.

In addition to the waste heat from the landfill site in Hackbridge there are a number of other sources of waste heat in the vicinity, including:

4 Energy Saving Trust. (2003). Aberdeen City Council: a case study of community heating.

5 Homes and Communities Agency. (2011). District Heating Good Practice: Learning from the Low Carbon Infrastructure Fund.

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1. A pyrolysis plant. This plant heats waste to very high temperatures in the absence of oxygen. A gas is produced which can then be burned in an engine to generate electricity. Heat is a by‐product for which there is currently no demand. Hence this is a “waste heat” scenario similar to the landfill gas scenario; this heat could be used in the district heating network.

2. A proposed waste management facility may be built next to the landfill site to manage all the household waste from the London Boroughs of Sutton, Kingston, Croydon and Merton. This could be an energy from waste plant which would burn the waste in a CHP engine to produce electricity and heat which could be pumped around a district heating network.

3. A proposed anaerobic digestion plant which would also be built near the landfill site. This plant would produce biogas (methane) from food and garden waste. The biogas could be burned in a CHP unit to produce electricity and hot water which could feed the network.

It is possible that other sources of waste heat would be built nearby since Hackbridge is surrounded by industrial parks. It would also be possible to install a standalone gas or woodfuel (biomass) CHP unit to meet the heat demand. Table 2 shows how much waste heat is available as well as how much heat and electricity from the proposed energy from waste plant could be available. In addition, the amount of heat needed for the flats that could be generated from a biogas, natural gas or biomass CHP plant is shown along with the amount of electricity that would be generated.

Energy source Rated output Annual heat generation (kWh)

Electricity generated (kWh) Waste heat from landfill or

pyrolysis plant 4MWe 28,000,000 n/a

Biogas CHP 800kWth 4,824,777 4,824,777

Energy from waste 20MWe 156,000,000 175,200,000

Natural gas CHP 800kWth 4,824,777 4,824,777

Biomass CHP 800kWth 4,824,777 1,080,174

Table 2: Details of the different potential energy sources in Hackbridge

Finally, like the majority of places in the UK, Hackbridge’s telecommunications services need to be improved.

Currently, they are supplied by copper cables enabling broadband speeds of up to 10 MB per second to be achieved. The government has pledged that, by 2015, 90 % of the UK will have access to “superfast”

broadband speeds of up to 30 MB per second⁶. In order for this to be possible, the copper cables carrying the broadband from the network trunk to the buildings will need to be replaced with fibre optic cables.

Since the replacement of these cables will require digging up the roads and drilling into people’s homes, it would be sensible to combine this with the installation of the district heating network (if one was to be set up). Combining these activities could create an opportunity to reduce the costs associated with both.

6 Richmond, S. (12 May 2011) Superfast broadband 'for 90 per cent of Britain by 2015'. The Telegraph. [Online] Available from:

http://www.telegraph.co.uk/technology/broadband/8510062/Superfast‐broadband‐for‐90‐per‐cent‐of‐Britain‐by‐2015.html

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2.3 What does this report consider?

The purpose of this report is to assess whether the existing blocks of flats in Hackbridge could connect to the planned district heating, how much this would cost and what the carbon savings would be. This report has modelled a district heating network which provides space heating and domestic hot water for the blocks of flats in Hackbridge. The use of each of the potential energy sources described in Section 2.2 has been modelled and the carbon emission savings achieved by the network calculated. In addition, some other energy sources (biomass CHP and natural gas CHP) have been considered to cover all the potential scenarios that would be applicable to other areas. These savings have then been compared with those achieved by traditional retrofit measures such as loft insulation and cavity wall insulation in order to determine which approach is the most effective at reducing a flat’s carbon emissions per pound spent. The opportunity and extent to which the costs of the district heating network could be reduced by coupling the laying of the pipework with telecommunications data cables was also investigated.

Whilst calculating the potential carbon emission savings was the primary driver for this study, it was important to compare the impact of each approach on the residents: would either approach affect their thermal comfort or fuel bills and, if so, how? A household’s energy efficiency and the price of fuel are two components contributing to fuel poverty⁷. The government is trying to eliminate fuel poverty by 2016⁸. However, in 2009, four million households were still living in fuel poverty⁷. Any retrofitting scheme therefore also needs to be considered in terms of its impact on residents’ fuel bills and thermal comfort.

With these impacts in mind, residents were then surveyed to find out their attitudes towards each of the approaches.

7 DECC. (2011). Annual report of fuel poverty statistics.

8 Warm Homes and Energy Conservation Act 200. [Online] Available from:

http://www.legislation.gov.uk/ukpga/2000/31/pdfs/ukpga_20000031_en.pdf

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3 Methodology

The following methodology was used in order to identify the most cost effective route to carbon reductions for blocks of flats:

3.1 Locating the district heating network and identifying the flats which could connect i) The proposed pipe‐work for the district heating network was located based on tender

documentation and information from the London Borough of Sutton.

ii) All blocks of flats within 1 km of the network were identified and the additional length of pipe‐

work that would need to be installed in order to connect the blocks to the network was calculated.

iii) The energy consumption (split into domestic hot water, heating and electricity demand) of each of the different flat types was already known through a survey conducted by Parity Projects⁹. This was converted into carbon emissions using the 2010 DEFRA greenhouse gas conversion factors¹⁰ (see Appendix 14.2). All scopes of carbon emissions (1 to 3: those associated with the direct combustion of the fuel, plus extraction, transport and processing of the fuel) were included in the calculations.

3.2 Calculating the cost of the connection to the district heating network

i) The cost of the additional pipe‐work required to connect the blocks of flats to the planned network was estimated. This comprises the main network ring and branches off to individual blocks of flats. A greater cost was incurred where the pipework would have to be laid under roads or pavements compared to where it could be laid under soft ground.

ii) The cost of connecting each flat to the network was calculated. For each flat, a cost was assigned to the installation of pipework within the flat, the heat interface unit (which allows the resident to control their heating and domestic hot water), and the installation and commissioning of the unit.

For flats with electric heating, an extra cost had to be assigned in order to remove the electric storage heaters and install the plumbing required for the district heating system.

iii) The cost of the energy generation equipment was calculated. This did not include the cost of building the energy centre or installation costs since it was assumed that these would be borne by the developer of the energy network for the new development planned in Hackbridge. Similarly, in more general cases, it is envisaged that existing buildings would be connecting to a pre‐existing network where these costs have already been borne.

iv) The three costs calculated in steps i) to iii) were summed together in order to calculate the total cost of the network. This cost was then divided by the number of flats that would be connected to the network to identify the connection cost per flat.

v) The potential contribution from broadband providers for providing fibre optic data cables with the heat network was investigated.

9Parity Projects. (2008) Energy Options Appraisal for Domestic Buildings in Hackbridge.

10 DEFRA/ DECC. (2010). 2010 Guidelines to Defra/ DECC’s GHG conversion factors for company reporting.

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3.3 Calculating the carbon emission savings achieved by the district heating network

i) The energy sources described in section 2.2 were modelled to supply the heat demand through a district heating network. In addition, a natural gas‐fired combined heat and power (CHP) unit and a biomass (woodfuel) CHP unit were modelled since these may be more common energy options for district heating networks elsewhere. Since it is inefficient for a combined heat and power unit to provide the peaks in the energy demand, an additional boiler would be required to meet these peaks. No peak‐load boiler was required for the waste heat and energy from waste scenarios since heat is produced in excess of the flats’ heat demand. The following generation scenarios were therefore considered:

a. Waste heat (from the landfill gas site or pyrolysis plant) b. Energy from waste CHP unit

c. Natural gas CHP unit + natural gas boiler d. Natural gas CHP unit + biogas boiler e. Biomass CHP unit + natural gas boiler f. Biomass CHP unit + biogas boiler g. Biogas CHP unit + natural gas boiler h. Biogas CHP unit + biogas boiler

ii) The carbon emission savings achieved by each of these energy generation scenarios were calculated.

3.4 Comparing cost and carbon emission savings of district heating with traditional retrofit i) The costs and carbon emission savings associated with individual retrofit measures had been

calculated previously for the “Formulating a zero carbon strategy for Hackbridge”¹¹ study.

Combinations of these measures were chosen in order to match the carbon emissions savings achieved by the various power generators considered for the district heating schemes. Behaviour change measures were not included as these are relevant for both traditional retrofit and district heating approaches.

ii) The carbon emissions savings and associated costs of the different district heating and retrofit options were compared to assess which option achieved the greatest carbon emission savings per pound spent.

3.5 Researching thermal comfort, fuel poverty and residents’ attitudes

i) The impact that each of the two options would have on the thermal comfort of the flats was considered.

11 BioRegional (2011) Formulating a zero carbon strategy for Hackbridge

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ii) An operator of an existing district heating scheme was interviewed about pricing; and the billing aspects of other district heating schemes were researched in order to establish the impact each option would have on residents’ fuel bills.

iii) A door‐to‐door survey was conducted with current residents of the flats owned by Sutton Housing Partnership to gather their opinions on the two different options.

3.6 Investigating the economic viability of a district heating scheme

i) The revenue and profit which could be made from a district heating scheme over a period of 25 years were estimated.

ii) This was compared with the capital cost of the network in order to establish the pay‐back period of the network in order to identify whether it would be economically viable to connect the flats to the network.

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4 Locating the district heating network and identifying the flats which could connect

Figure 3: Map of the district heating model

The proposed network piping is represented in Figure 3 by the thick blue and green lines. (The green line represents the most likely route that will be adopted for the network that might be provided by the developers of the Felnex Trading Estate, hence it has not been included in the costings.) The blue line represents pipe‐work running along the River Wandle which is a low cost route for the piping as no hard surfaces would need to be dug up. The energy centre would be situated in the Felnex Trading Estate, the heat from the landfill site would come to this energy centre where it could be topped up by back‐up boilers before being distributed to the buildings connected to the network.

Any additional power generation equipment would be situated here. A route has been mapped which serves as many blocks of flats as possible whilst avoiding as much hard surface as possible since digging up roads and other hard surfaces is more expensive than digging up soft ground.

The blocks of flats are highlighted in red and dark green. Dark green signifies those owned by the social housing provider, Sutton Housing Partnership. The thinner orange lines show where the pipework may branch off from the network trunk to transport the hot water to the individual blocks of flats.

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There are 65 blocks of flats in Hackbridge. Five of these have been excluded from the network since they are relatively isolated and their energy consumption is too small to justify the cost of laying the pipework out to them.

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The Sainsbury Family Charitable Trusts – The Climate Change Collaboration Retrofitting district heating systems

After assessing the energy consumption of each of the blocks of flats, three broad categories of flats were identified; these are the same categories as those used in the report, “Formulating a zero carbon strategy for Hackbridge”. Table 3 presents their key distinguishing features.

Category Number of

flats

Features of building fabric

Heating source

Age Annual heat demand per

flat (kWh/yr)

Associated CO2 emissions per flat (kgCO2e/

yr)

Annual electricity demand per flat (kWh/yr)

Associated CO2 emissions per flat (kgCO2e/

yr) Type E

186

Cavity wall insulation Loft insulation

Individual gas central

heating

1950s 11,341 2,305 7,560 4,665

Type F

602 Timber frame

Electric storage heaters

1990s

5,776 3,564 7,656 4,724

Type H

65

Cavity wall insulation Loft insulation

Individual gas central

heating

2000s 4,533 1,174 7,656 4,724

Table 3: Key features of the three flat types present in Hackbridge

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Flat type E represents 22 % of the flats in Hackbridge. All of the blocks of this type are owned by Sutton Housing Partnership (the Arms Length Management Organisation for the Council’s social housing stock).

However, some of the flats in the block are owned by leaseholders. These flats were built in the 1950s;

cavity wall and loft insulation have since been added. They have gas fired central heating. Because the owner of the freehold of these flats is the local council, it will be easier to implement the retrofitting of district heating in these flats.

Type F forms the majority of flats in Hackbridge (70 %). These were built in the 1990s. They have a timber frame which already has some insulation integrated into the wall. However, as there is no cavity in the wall it is not possible to increase the level of insulation without installing external insulation. This type of flat has electric storage heaters.

Type H represents the remaining 8 % of flats. These were built from 2001 onwards and have cavity wall and loft insulation. They have gas fired central heating.

None of the blocks of flats have a communal heating system, this study therefore allows for the cost of installing communal heating distribution infrastructure throughout each block of flats.

The total annual heat demand of all the blocks of flats is 6,030,971 kWh/ year, which produces 2,623,555 kg of carbon dioxide emissions per year. The total electricity demand of the blocks of flats (excluding electricity required for heating) is 6,558,958 kWh/ year, which produces 4,047,336 kg of carbon dioxide emissions per year.

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5 Calculating the cost of the district heating network

In order to connect the blocks of flats to the network, the following infrastructure is required:

 Pipework from the front door of the block of flats to the planned district heating network.

 Internal pipework from the front door of the block of flats to the flat.

 A heat interface unit to deliver the heat to the flat’s central heating system and to allow the resident to control the heating and domestic hot water.

 If the flat doesn’t currently have a wet heating distribution system with radiators this would need to be installed.

 The energy generation unit to provide the additional energy generation capacity for the flats.

Costs for each of these infrastructure requirements have been estimated in the proceeding sections. All the assumptions used in estimating these costs can be found in the Appendix 14.3.

5.1 Pipework connecting the blocks of flats to the main district heating network

The total length of the pipework required to connect each of the blocks of flats to the planned district heating network has been measured and the cost calculated accordingly, as can be seen in Table 4. The cost of pipework per flat was calculated by dividing the total cost of the pipework by the total number of flats (853) that are to be connected to the network.

Type of ground that pipes will be laid in

Cost per m (£) Total length (m) Total cost (£) Cost of pipework per flat (£)

Soft 750 2,951 2,213,250

5,319

Hard 1,000 2,324 2,324,000

Table 4: Cost of pipework from planned district heating network to all the blocks of flats in Hackbridge The cost of laying the infrastructure may be lower than in a comparatively sized area, because the

geography of the suburb lends itself to soft dig (pipework can be laid along the river and in the soft ground which surrounds the potential heat sources and the suburb) this is cheaper than when roads need to be dug up.

5.2 Connection to each flat

Once the pipework reaches the block of flats, it then branches again to deliver the hot water to each flat. A heat exchanger would be required in each flat to transfer the heat from the network’s hot water to the cold water in the flat’s central heating distribution system.

In flats which currently have gas fired central heating, the heat exchanger would substitute the gas boiler and the hot water would be distributed around the flat through the existing pipework and radiators. In flats which currently have electric storage heaters, pipework would need to be plumbed in to allow the hot water to be distributed; this is called a wet heating system. This incurs an additional cost of around £2,550 per flat.

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The heat exchanger would be housed in a box alongside a heat meter (for billing) and the user controls; this whole unit is called the “heat interface unit” and is slightly smaller than a standard boiler (please see Figure 4). Further space is saved by the removal of any hot water storage tanks; since the network would provide a constant supply of hot water, a storage tank would no longer be required.

Figure 4: Picture of a heat interface unit4

It is technically feasible to connect any block of flats to the network. The cost of doing so varies depending on the complexity of plumbing required. For example, if pipework has to be drilled though multiple walls and floors rather than going up a central shaft then the costs would be much greater. A set cost of £2,200 per flat was used in the calculations¹². This figure is a conservative estimate, in the simplest of cases it may be around £1,800.

The costs associated with connecting the flats to a district heating network are summarised in Table 5.

Item Cost per flat (£)

Internal pipework from front door of block to flat’s

Heat Interface Unit (HIU) 2,200

Heat Interface Unit (HIU) 1,750

Conversion from electric to “wet” heating system

(where required) 2,550

Table 5: Costs associated with connecting each flat to a district heating network

12 Conversation with Vital Energi, on 12^th July 2011

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5.3 Energy generation

In addition to calculating the cost of the district heating network’s pipework and the cost of connecting the flats to the network, the cost of generating the heat for the network needs to be included in order to calculate the total cost of the network. The cost of harnessing each of the potential heat sources described in Section 2.2 was estimated.

Waste heat: Where waste heat could be extracted from the existing electricity generation process (the landfill gas site or the pyrolysis plant) and pumped around the network, a cost was assigned to the

equipment required to harness the heat. The current engines are designed to generate electricity only and so the heat which is produced is wasted. These engines would need to be converted to combined heat and power (CHP) generators which are designed so that both the electricity and the heat that they produce can be extracted.

Energy from waste: Where heat could be taken from the proposed energy from waste facility, no generation costs were assigned to the network since it is likely that the developer of the plant will be required to pay for the CHP unit as part of their planning permission.

Biogas CHP: In the scenario where biogas produced by an anaerobic digestion plant would be used to generate the power, the cost of a CHP unit was assigned to the network as this would be generated by the owners of the network.

Biomass and natural gas CHP: In the biomass and natural gas CHP scenarios, the cost of each of these units was assigned to the network.

In each scenario, except for the waste heat and energy from waste plant scenarios, the cost of the peak load boiler was included. The waste heat and energy from waste plant scenarios did not require a peak‐load boiler since the heat produced is well in excess of the flats’ heat demand.

Boiler type Capacity (kWth) Baseload and Peak Total Cost (£) Cost per flat (£)

Gas CHP & gas back‐up 800 & 200 765,172 897

Biomass CHP & gas back‐up 800 & 200 1,012,000 1,186

Biogas CHP & gas back‐up 800 & 200 765,172 897

Gas CHP & biogas back‐up 800 & 200 765,172 897

Biomass CHP & biogas back‐up 800 & 200 1,012,000 1,186 Cost of connecting flat types E & H (gas heating) to the district heating network = £3,950/flat

Cost of connecting flat type F (electric) to the district heating network = £6,500/flat

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Boiler type Capacity (kWth) Baseload and Peak Total Cost (£) Cost per flat (£)

Biogas CHP & biogas back‐up 800 & 200 765,172 897

Waste heat from landfill gas 19,500,000 753,172 883

Energy from waste 156,000,000 0 0

Table 6: Costs of the different energy generation plant possible for Hackbridge

The costs in Table 6 show the total cost of each of the energy generation options, but do not include auxiliary costs such as costs of the energy centre and installation costs. This is because, in the case of

Hackbridge, the proposed district heating network would be an extension of the one proposed for the Felnex Trading Estate, hence these costs would already be covered by the developer of that site. Similarly, in more general cases, it is envisaged that flats would be connecting to a pre‐existing network where these costs have already been borne. If an energy centre were required it is likely to cost in the region of £450/m2. An energy centre to accommodate equipment for up to 1,000 buildings would be in the region of 20m by 15m.

This would have a total cost of around £135,000.

It can be seen that the biomass CHP unit is the most expensive option. This is because of the more complex nature of the generator required. The energy from waste scenario is the cheapest as the cost would be borne by the energy from waste plant owner. The remaining options cost similar amounts.

5.4 Coupling a district heating network with the installation of fibre optic cables

The possibility of combining the installation of the district heating network with fibre optic cables in order to reduce the costs of the network was investigated. Before starting this study BioRegional assumed that government funding would be available to support the switch from copper to fibre optic cables. Therefore this funding could be used to cover some of the digging costs. In August 2011 it was announced that £530 million would be provided for this purpose. However, Hackbridge will not be eligible to receive any of this because it is situated in London where no funding has been allocated. It is thought by the Government that private investment will cover all costs there¹³.

Whilst no funding from the government can be obtained, the coupling of fibre optic cables with a district heating network installation could present other opportunities to reduce costs. Telecommunications service providers would be keen to combine the work¹⁴ and could offer around £150 per property connected to the developer who is laying the district heating pipework down if they include fibre optic cabling¹⁵. Whilst this won’t contribute to the costs of the district heating network significantly, it would mean that, at the very least, the installation of a district heating network would allow Hackbridge residents to enjoy a better quality of broadband services than they currently receive. Furthermore, a fibre optic cable communications

13 BBC. (16 August 2011) Rural broadband funding ready for England and Scotland. [Online] Available from:

file:///Y:/ACTIVE/00073%20‐%20Zero%20Carbon%20Hackbridge/Working%20documents/Project%202%20‐

%20SCT_Retrofitting%20district%20heating%20systems/Reference%20docs/fibre%20optic%20cable/BBC%20News%20‐

%20Rural%20broadband%20funding%20ready%20for%20England%20and%20Scotland.htm

14 Conversation with Peter O’Connell, Hackbridge Programme Director, on 27^th January 2011.

15 Conversation with the Inexus Group, on 22^nd September 2011.

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infrastructure would make metering and billing of all services cheaper and easier, since the services can be measured directly without need to manually read the meters.

5.5 Total cost of the different district heating networks

Summing the piping, equipment and energy plant costs gives the total price per flat for each of the district heating network options available in Hackbridge, see Figure 5.

Figure 5: Total cost per flat of the different district heating networks

Figure 5 shows how it is significantly more expensive to connect the flats with electric heating to the network compared to those with gas heating, because of the costs involved in converting from a “dry” to a

“wet” heating distribution system. It also shows that the energy from waste option is the cheapest option since the costs of the energy generating equipment are borne by the developer of the energy from waste plant. Depending on the different situations the costs of the different energy sources will vary, for example even in Hackbridge it is possible that the owners of the landfill gas site may pay for the conversion of their electricity generation equipment to enable it to harness heat.

Table 7 presents the total cost of setting up each of the different district heating scenarios and connecting the blocks of flats.

£0

£2,000

£4,000

£6,000

£8,000

£10,000

£12,000

£14,000

Cost per flat

District heating network option

Flat types E & H (gas heating) Flat type F (electric heating) Average Hackbridge flat

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Scenario Total cost (£)

Gas CHP & gas back‐up 10,206,872 Biomass CHP & gas back‐up 10,453,700 Biogas CHP & gas back‐up 10,206,872 Gas CHP & biogas back‐up 10,206,872 Biomass CHP & biogas back‐up 10,453,700 Biogas CHP & biogas back‐up 10,206,872

Waste Heat 10,194,872

Energy from waste 9,441,700

Table 7: Total cost to connect the flats in Hackbridge to each of the different district heating network scenarios

It would cost in the region of £10 million to connect the flats in Hackbridge to a district heating network. The type of energy generation equipment used has very little bearing on the cost.

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6 Carbon emission savings achieved by the district heating network

For each energy source modelled in the district heating network, the carbon emission savings were calculated. As can be seen in Table 8, each scenario would achieve carbon emission savings because the different energy sources proposed for the network are less carbon intensive than using either a) grid electricity or b) individual gas boilers.

Scenario Carbon emission intensity

(kgCO2e¹⁶/ kWh)

Grid electricity 0.62

Energy from waste 0.49

Natural gas boiler 0.20

Biomass CHP 0.12

Natural gas CHP 0.08

Biogas CHP 0.00

Biogas boiler 0.00

Waste heat 0.00

Table 8: Carbon emission intensities of the different energy sources in Hackbridge

Using grid electricity to provide heat to the home is significantly more polluting than any other method because the average efficiency of the power stations producing the electricity is low (around 40 %4).

Whilst burning natural gas in an individual boiler to heat the home is less polluting than using grid electricity, it is still more polluting than taking heat from a district heating network which is powered by a natural gas CHP unit.

The ratio of electricity to heat produced by the CHP unit varies depending on the fuel used. Natural gas CHP units produce as much electricity as they do heat. This ratio is much lower for biomass CHP units: for every kWh of heat produced, only 0.25kWh of electricity is produced. This means that, when a CHP unit is sized to meet the heat demand of the district heating network, a lot less electricity can be produced by a biomass CHP unit than the same size natural gas CHP unit. Therefore less grid electricity is offset.

This explains why the heat produced by a biomass CHP unit is more carbon intensive than the heat produced by a natural gas CHP unit, despite biomass fuel being classed as almost carbon neutral¹⁰. Biomass is not classed as completely carbon neutral because of the emissions associated with transporting it. 800 tonnes of woodfuel would be required annually by the CHP unit modelled.

Biogas is classed as completely carbon neutral¹⁰ because its emissions from transportation are considered negligible and, when burned in a CHP unit, it produces heat and electricity in a ratio of 1:1. Therefore the total carbon savings achieved by a district heating network powered by a biogas CHP unit are high.

16 CO2e stands for “Carbon dioxide equivalent”. It describes the total global warming potential of emissions comprising one or more greenhouse gases by equating them to the global warming potential of carbon dioxide.

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Waste heat is also classed as carbon neutral. This is because, as when accounting for a CHP unit’s emissions, the total emissions produced are apportioned to the primary process. In the case of using the waste heat from the landfill gas electricity production, or the pyrolysis plant, any emissions released have already been attributed to the electricity produced.

The energy from waste facility also uses a CHP unit to generate the electricity and heat, hence the carbon emissions are accounted for in the same way as described for a gas or biomass CHP unit. The proposed plant will be large enough to meet the flats’ total heat and electricity demand.

Figure 6: Carbon emission savings per flat achieved by each district heating scenario

Figure 6 shows that the biogas options produce the greatest savings. They produce significantly greater savings than the biomass CHP options because the biomass generator produces much less electricity than the biogas generator hence less grid electricity is offset.

Greatest savings are achieved by connecting the flats with electric heating to the network. This is because their current heat demand is served by grid electricity which is far more polluting than using gas to generate their heat.

0

1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

Carbon emission savings per flat (kgCO2e/yr)

District heating network option

Flat type E (gas heating) Flat type H (gas heating) Flat type F (electric heating)

A district heating network can significantly reduce carbon emissions. A network powered by a biogas‐fuelled system would result in an 80 % reduction in carbon emissions.

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7 Comparing carbon emission savings achieved by district heating networks with those achieved by traditional retrofit.

Once the potential carbon emission savings achieved by the different district heating networks and the associated costs were known, the study then considered if a) a traditional retrofit approach could achieve the same extent of carbon emission savings and b) how the costs of doing so would compare.

The costs and carbon emission savings of the following retrofit measures had been calculated for the

“Formulating a zero carbon strategy for Hackbridge” study:

o Loft insulation

o Draught‐proofing around windows etc.

o Ground floor insulation o Double glazing

o Heat exchange ventilation o Boiler upgrade to A rated unit

o Draught‐proofing floors (silicone sealant around the skirting boards)

o Heating controls (2 channel time clock, room thermostat and cylinder thermostat) o Hot water cylinder lagging

o Hot water pipework on external walls/floors lagging o Thermostatic radiator valves

o New front door to the block of flats o Door draught‐proofing

o Cavity wall insulation

o New A++ rated fridge/ freezer o Energy saving light bulbs o Solar hot water system o Solar photovoltaic panels

Retrofit measures were selected in order to meet the carbon emission savings achieved by the district heating network scenarios. All appropriate retrofit measures were required in order to approach the scale of carbon emission savings achieved by the district heating scenarios, but even when all the retrofit measures were installed the carbon savings were less than connecting the flat to a district energy network.

Table 9 provides a comparison between the different options for retrofitting flats (energy efficiency measures and connection to a district energy network). The costs and carbon savings can be seen for both retrofitting energy efficiency measures and for a district energy network using different energy sources.

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Scenario CO2 savings

(kgCO2)

% reduction in

CO2e emissions Cost (£)

Cost per carbon savings (£/kgCO2e

saved) Retrofitting energy efficiency

measures 2,281,494 34% 18,441,076 8

Biogas CHP & biogas back‐up 5,622,613 84% 10,206,872 2

Biogas CHP & gas back‐up 5,232,970 78% 10,206,872 2

Energy from waste 3,472,276 52% 9,441,700 3

Gas CHP & biogas back‐up 3,220,348 48% 10,206,872 3

Biomass CHP & biogas back‐up 3,182,323 48% 10,453,700 3

Gas CHP & gas back‐up 2,830,706 42% 10,206,872 4

Biomass CHP & gas back‐up 2,792,681 42% 10,453,700 4

Waste Heat 2,645,388 40% 10,194,872 4

Table 9: Comparison of the costs and carbon savings for the different district heating scenarios and retrofitting As can be seen in Table 9, the two biogas scenarios provide the greatest carbon emission savings per pound spent: each kilogram of carbon emissions saved costs £2. The most expensive option is the retrofitting of energy efficiency measures. Each kilogram of carbon emissions saved costs £8; this is twice as expensive as the most expensive district heating option. The waste heat option offers intermediate savings per pound spent (£4 per kilogram of carbon emissions saved).

A comparison of the district heating options and the retrofitting option for the different flat types can be found in Appendix 14.4.

Comparing the results for each flat type, because electric heating is three times more polluting that gas heating, more carbon emissions can be saved per pound spent on the flats with electric heating than those with gas heating. This is despite the extra costs incurred for converting to a “wet” heating system (in the district heating scenario).

For each flat type, the biogas‐fuelled district heating option remains the most cost effective option. The retrofit option remains the most expensive option, although slightly less so for the new flats with gas heating because there is less space on their roofs for solar photovoltaic panels (this is a Hackbridge‐specific issue rather than a UK‐wide issue).

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Lower carbon savings per pound spent are achieved for the newer flats than the older flats, this is because the newer flats are more energy efficient to start with and therefore less CO2 can be saved from district heating. However, the costs of the district heating connection do not change for newer flats.

Retrofitting energy efficiency measures and building integrated renewable energy technologies is a significantly more expensive way to achieve carbon savings than any of the district heating options.

More carbon savings are achieved per pound spent on an electrically heated flat because they are currently significantly more polluting per kWh of heat used than the other two flat types.

More carbon savings are achieved per pound spent on the older flats, because the costs of connection do not vary but the new flats need less heat.

Retrofitting District Heating Systems