Scottish Government

Appendix 2: Edinburgh Scenario Development and Modelling Results for 2020 with Substantial Biomass Combustion

The scenario for 2020 with substantial biomass combustion has been derived by identifying potential sources from a number of groups of developments. These groups are as follows:

• Future housing developments already identified
• Replacement of demolished housing
• Modification at existing housing
• Schools
• Business development
• Proposals for shops and other similar developments
• Other institutions

The methodology used to estimate emissions from each of these sources is described in detail below. For some development groups, the modeled contributions from biomass with an emission factor of 20g/ GJ was less than 0.1 µgm ^-3 throughout the modeled area and hence, could not be shown on a concentration map.

Housing developments identified in the local plans

The Edinburgh City Local Plan has identified sites throughout the city centre in the areas listed in Table A2.1, whilst the Rural West Edinburgh Local Plan identifies further sites for housing development shown in Table A2.2.

Table A2.1: Housing developments listed in the Edinburgh City Local Plan.

Table A2.2: Housing developments listed in the Rural West Edinburgh Local Plan.

* Housing on these greenfield sites shall not be occupied before the West Edinburgh Tram to Newbridge is operational or its funding has been committed or, in the event of this not being delivered, other strategic (or strategically significant) improvements in public transport accessibility to the area have been secured.

The Council has published The Edinburgh Standards for Sustainable Building¹⁹ as Supplementary Planning Guidance. Priority Standard 1 on energy efficiency states:

"The Council will require all new build developments with floor space of 1000 square metres or more, or ten residential units or more, or a site of 0.5 ha or more to reduce predicted carbon dioxide emissions to a Buildings Emission Rating ( BER) which attains a Target Emissions Rating ( TER) minus 5%."

Priority Standard 2 on on-site renewable energy generation states that:

"The Council will require in all developments, either new build or conversion, with floor space of 1000 square metres or more, or ten residential units or more, or a site of 0.5 ha or more, a minimum of 10% (20% in Areas of major Change developments of 2000 sq m or 20 residential units or more) of its remaining energy requirements to be supplied by on-site renewable energy generation. This on-site renewable energy generation must provide at least a further 10% (20% in AMCs) reduction in the development's CO ₂ emissions. (This CO ₂ reduction is further to that achieved through the improved efficiency priority standard)".

In 2007, the Scottish Buildings Standards Agency produced A Low Carbon Buildings Standard Strategy for Scotland- the Sullivan report²⁰. The Sullivan report recommended for new buildings:

• Net zero carbon buildings (i.e. space and water heating, lighting and ventilation) by 2016/2017, if practical;
• Two intermediate stages on the way to net zero carbon buildings, one change in energy standards in 2010 (low carbon buildings) and another in 2013 (very low carbon buildings);
• The 2010 change in energy standards for non-domestic buildings should deliver carbon dioxide savings of 50% more than 2007 standards;
• The 2010 change in energy standards for domestic buildings should deliver carbon dioxide savings of 30% more than 2007 standards;
• The 2013 change in energy standards for non-domestic buildings should deliver carbon dioxide savings of 75% more than 2007 standards.
• The 2013 change in energy standards for domestic buildings should deliver carbon dioxide savings of 60% more than 2007 standards;
• Backstop levels of U-values and air-tightness for building fabric should be improved in 2010 to match those of Nordic countries, but consideration must be given to the social and financial impact of measures that would necessitate mechanical ventilation with heat recovery in domestic buildings;
• The ambition of total-life zero carbon buildings by 2030.

The report also recommended that consideration be given to developing practical performance standards for existing buildings.

The Target Emissions Rating for any development will depend on the size and design of the building and the heating and cooling system. The Scottish Buildings Standards Agency commissioned Turner and Townsend to undertake a report on The impact on costs and construction practice in Scotland of any further limitation of carbon dioxide emissions from new buildings²¹. Turner and Townsend carried out case studies for typical new detached houses (100 m ² floor area), mid-level flats (80 m ² floor area) and office buildings. They calculated Building Emissions Ratings and Target Emissions Ratings and assessed the potential for improvement resulting from a range of measures including improved insulation and airtightness and the use of biomass and other on-site renewable energy sources. The Turner and Townsend report calculated that the carbon dioxide emissions associated with space and water heating for detached houses and mid-level flats meeting the Target Emissions Rating were 2123 kg/year and 1287 kg/year respectively. Assuming a carbon dioxide emission factor of 51.35 kg/ GJ gross (approximately 57.09 kg/ GJ net ²²), this corresponds to heat demands of 41 and 25 GJ per annum for the detached house and the mid-level flat respectively.

The Turner and Townsend study indicated that the Edinburgh Standards Priority 1 of up to 5% reduction in carbon dioxide emissions can be readily met by means of increased insulation (above the 2007 requirements), airtightness and low energy lighting. In addition, the further reduction of 20% of a development's carbon dioxide emissions specified in Priority Standard 2 can be achieved readily using biomass. In combination, improved insulation, airtightness and biomass can go a long way towards meeting the recommendations in the Sullivan report.

Potential financial and carbon savings from renewable energy technologies identified in the Edinburgh Standards are shown in Table A2.3 These suggest that biomass will be favoured on cost effectiveness grounds by many developers.

Table A2.3: Potential financial and carbon savings from renewable energy technologies.

The housing mix in the new developments is uncertain. The Council's Policy House 2 is that the Council will seek the provision of a mix of house types and sizes where practical, to meet a range of housing needs, including those of families, older people and people with special needs. For this assessment, it has therefore been assumed that the average dwelling in the new developments will have a heat demand of 30 GJ per annum (taking account of Priority 1). Table A2.4 shows the estimated heat demand for each of the housing developments. The total annual heat demand from these sites is 1153 TJ corresponding to approximately 4.7% of Edinburgh's current heat demand.

It has been assumed here as the worst case that the whole of the heat demand for the new developments will be met by biomass combustion. Two cases have been considered:

1. The heat is supplied to each household through individual boilers ("distributed boilers");
2. The heat is supplied to each household from a small number of centralised boilers ("district heating").

Table A2.4 also shows the annual particulate emission for each development based on a particulate emission factor of 20 g/ GJ and assuming that the biomass boilers have similar efficiency to the gas boilers used in the Turner and Townsend study (91.5%). The emissions are three times greater for an emission factor of 60 g/ GJ. For developments with greater than 500 households and district heating, it has been assumed that the heat is supplied by biomass Combined Heat and Power ( CHP) with 46% thermal efficiency. It has also been assumed that the electricity generated is exported to the grid, rather than used for electrical heating within the development. For the Leith Waterfront development ( WAC 1b), the boiler capacity may exceed 50 MW thermal and so the plant may come under Integrated Pollution Prevention and Control regime. A lower emission factor of 10 g/ GJ has been applied for this plant, corresponding approximately to emission benchmarks for plant of this capacity where best available technology is applied.

Table A2.5 shows the modelled discharge point source discharge characteristics for each of the modelled district heating developments. The thermal capacity of each unit was estimated assuming 30% utilisation for boiler units and 45% utilisation for CHP units. Discharge flowrates at capacity were then estimated assuming a theoretical air requirement of 0.3 kg air per MJ (Chemical Engineers Handbook), 6% excess air and discharge at 100 ^oC. Stack diameters were then selected from the set 0.1 m, 0.2 m, 0.5 m and 1 m based on the natural draught flowrates used in the development of the nomographs ( Appendix 3). It was assumed that large installations (excluding WAC 1b) would have multiple stacks with 1 m stack diameter. The WAC1b effective stack diameter was selected assuming a discharge velocity of 10 m s ^-1. Stack heights above ground were then estimated using the nomographs with the aim of limiting the maximum local contribution to annual mean particulate matter concentrations from each individual plant to less than 1 µg m ^-3. It was assumed that each stack would discharge above a rectangular building 10 m high and 30 m square.

Table A2.4: Heat demand and particulate emissions from new housing developments.

Table A2.5: Modelled discharge characteristics for housing developments with district heating in Edinburgh.

* 10 g/ GJ for plant >50 MW

The emissions for the distributed boiler case were allocated to the nearest 1 km square and were modelled as 1 km x 1 km volume sources, 10 m deep. The Leith Waterfront (Leith Docks) and Granton Waterfront developments extend over more than 1 km ² and so the emissions for these sources have been allocated over several km ² according to the area of the developments.

Figure A2.1 shows the modelled contribution to particulate matter concentrations from the identified housing developments for emission factors of 20 g/ GJ and 60 g/ GJ for both distributed and district heating.

Figure A2.1: Modelled contribution to particulate matter concentrations from new housing developments in 2020 in Edinburgh.

The predictions for district heating are based on the assumption that heat will be supplied via district heating from a small number of biomass boilers or CHP systems. Generally, the predicted impact is restricted to small areas close to the biomass installations. The maximum contribution to ground level annual mean concentrations is generally predicted to be less than 0.5 µg m ^-3 from these sources. For district heating assuming a larger emission factor of 60 g/ GJ, the larger emissions have been taken into consideration when estimating stack heights so that the modelled stack heights are considerably greater than for the 20 g/ GJ case. The predicted area of impact is substantially greater than for the 20 g/ GJ emission factor case. Nevertheless, the maximum contribution to ground level annual mean concentrations is generally predicted to be less than 1 µg m ^-3 from these sources, except on the seaward side of the WAC 1b development in Leith.

Generally, the predicted impact assuming a distributed boiler case with the 20 g/ GJ emission factor is restricted to small areas close to the biomass installations. However, the impact is greater where there are large numbers of new houses in Leith and Granton. The maximum contribution from these sources to ground level annual mean concentrations is almost 2 µg m ^-3. The distributed boiler case for an emission factor of 60 g/ GJ shows a maximum contribution from these sources to ground level annual mean concentrations is predicted to be almost 5 µg m ^-3.

Replacement of demolished housing

Table 3.3 in the main text indicates that the current domestic heat demand satisfied by fossils fuels and electricity in Edinburgh is 13554.4 TJ per annum. Part of the existing housing will be demolished or substantially renovated and replaced by housing meeting the Council's Priority Standards: it has been assumed here that 5% of the housing stock is replaced by 2020 (cf PB Power 5% replacement by 2025). The energy demands of the new houses will be less than the existing houses. Typical annual heat demands for UK households for space and water heating are 63.8 GJ per household ²³ compared to 30 GJ assumed here for new household heat demands. The overall heat demand will be reduced if demolished or renovated houses are replaced on a like for like basis by 359 TJ per annum. The annual heat requirement for the replacement properties will be 319 TJ, approximately 1.3% of Edinburgh's current heat demand. If the heat demand for the new properties is met by biomass boilers with particulate emissions of 20 g/ GJ of heat provided then the annual emission will be 6.37 tonnes. For an emission factor of 60 g/ GJ, the emission will be three times greater.

We have no information about where demolition and renovation will take place. The particulate emissions have therefore been allocated across the city in proportion to population based on 2001 census data.

The contribution to annual mean concentrations from this source is predicted to be less than 0.1 µg m ^-3 for appliances with emission factors of 20 g/ GJ. Figure A2.2 shows the predicted contribution from replacement houses fitted with biomass boilers with emission factors of 60 g/ GJ. The predicted contribution remains less than 0.2 µg m ^-3 throughout Edinburgh, with the highest concentrations in the city centre.

Figure A2.2: Modelled contribution to particulate matter concentrations from replacement housing developments in 2020 assuming an emission factor of 60 g/ GJ.

Existing houses

The PB Power study Powering Edinburgh into the 21 ^st Century²⁴ suggested that there would be little conversion to biomass in the existing housing. However, Edinburgh has a range of housing types. Many of the more affluent areas such as Murrayfield and the Grange have large houses and villas with large gardens that may be particularly suitable for biomass conversion. Many of the houses in the Rural West Edinburgh area may also be suitable for conversion and may have access to inexpensive supplies of biomass. The suburban areas on the outskirts of the city may also have some potential. Areas of tenements in the most densely populated areas may be less suitable because of the space requirements.

In this study, we have assessed the potential for conversion to biomass on the basis of population density throughout Edinburgh in 2001 as follows:

Overall, it is estimated that this would lead to conversion of 3.6% of the existing housing stock. It has also been assumed that biomass would then meet 3.6% of the current domestic heating demand for the city (481.8 TJ per annum) (2.0% of Edinburgh's total heat demand). Assuming a particulate matter emission factor of 20 g/ GJ for these installations provides an estimated annual emission of 9.63 tonnes. For an emission factor of 60 g/ GJ, the emission will be three times greater.

The contribution to annual mean concentrations from this source is predicted to be less than 0.1 µg m ^-3 for appliances with emission factors of 20 g/ GJ. Figure A2.3 shows the predicted contribution from existing houses fitted with biomass boilers with emission factors of 60 g/ GJ. The predicted contribution remains less than 0.2 µg m ^-3 throughout Edinburgh, with the highest concentrations in the suburbs surrounding the city centre.

Figure A2.3: Modelled contribution to particulate matter concentrations from replacement heating in existing houses in 2020 assuming an emission factor of 60 g/ GJ.

Schools

The Edinburgh City Local plan identifies current school proposals that involve the development of new sites (Table A2.6).

Table A2.6: Current proposals for new school developments.

In addition, the Rural West Edinburgh Plan identifies the potential need for a new primary school at North Kirliston.

The Council also has a number of proposals to rebuild schools on their existing sites. The Council has agreed a public private partnership to build eight schools by 2010. Biomass fuel has been identified as the preferred primary source of heating for seven of the schools as a solution to meeting the Council's carbon target. The eighth school, Tynecastle, will be heated by the waste heat from the adjacent North British Distillery.

The gross internal floor area of primary schools in Edinburgh is 274184 m ²: the floor area of secondary schools is 286545 m ². There were 24714 primary school pupils and 19454 secondary school pupils in 2007 ²⁵. Service sector fuel use for space and water heating in 2005 was typically 5327 GJ gross per hectare of floor space ( BERR data). The annual heat demand for primary schools is thus 146.1 TJ: for secondary schools the annual heat demand is estimated to be 152.6 TJ. If this heat demand is met by biomass combustion with particulate emission factor of 20 g/ GJ the annual emission from schools would be 6.0 tonnes. The total emissions have been allocated to each school in Edinburgh in proportion to the number of pupils.

Each of the primary school boiler discharges was modelled as a point source with stack diameter 0.5 m and stack height 12 m above ground next to a rectangular building 10 m high and 30 m square. The discharge temperature was assumed to be 100 ^oC and the discharge velocity was 1.4 m s ^-1. These conditions broadly correspond to a 400 kW boiler. Each of the secondary school boiler discharges was modelled as a point source with stack diameter 0.5 m and stack height 14 m above ground next to a rectangular building 10 m high and 30 m square. The discharge temperature was assumed to be 100 ^oC and the discharge velocity was 2.6 m s ^-1. These conditions broadly correspond to a 700 kW boiler.

Figure A2.4 shows the modelled contribution to particulate matter concentrations from biomass installations in all schools in Edinburgh assuming an emission factor of 60 g/ GJ. The predicted contribution is less than 0.1 µg m ^-3 over most of the city, with higher concentrations in the vicinity of the schools. The maximum predicted contribution was less than 0.5 µg m ^-3. If the boilers operated with an emission factor of 20 g/ GJ, the maximum predicted contribution was less than 0.2 µg m ^-3.

Figure A2.4: Modelled contribution to particulate matter concentrations from all schools in Edinburgh in 2020 assuming an emission factor of 60 g/ GJ.

Business development

Table A2.7 shows the business opportunity sites identified in the Local Plans for Edinburgh City and Rural West Edinburgh. Service sector fuel use for space and water heating in 2005 was typically 5327 GJ gross per hectare of floor space ( BERR data). The heat demands have been estimated on this basis. The total heat demand calculated for these developments is 1084 TJ, corresponding to 4.4% of Edinburgh's current heat demand. It has been assumed here as the maximum impact case that the whole of the heat demand for the new developments will be met by biomass combustion.

Table A2.7 also shows the annual particulate emission for each development based on a particulate emission factor of 20 g/ GJ. For developments with annual heat demands greater than 30 TJ, it has been assumed that the heat is supplied by biomass CHP with 50% thermal efficiency. It has also been assumed that the electricity generated is exported to the grid, rather than used for electrical heating within the development.

Table A2.7: Current proposals for new business developments.

Floorspace values in italics are estimated on the basis of a 2 storey building occupying half the available land area.

Table A2.8 shows the modelled discharge point source discharge characteristics for each of the modelled developments. The thermal capacity of each unit was estimated assuming 30% utilisation for boiler units and 45% utilisation for CHP units. Discharge flowrates at capacity were then estimated assuming a theoretical air requirement of 0.3 kg air per MJ (Chemical Engineers Handbook), 6% excess air and discharge at 100 ^oC. Stack diameters were then selected from the set {0.1 m, 0.2 m, 0.5 m and 1 m} based on the natural draught flowrates used in the development of the nomographs ( Appendix 3). It was assumed that large installations would have multiple stacks with 1 metre stack diameter. Stack heights above ground were then estimated using the nomographs with the aim of limiting the maximum local contribution to annual mean particulate matter concentrations from each individual development to less than 1 µg m ^-3. It was assumed that each stack would discharge above a rectangular building 10 m high and 30 m square.

Table A2.8: Modelled discharge characteristics for business developments in Edinburgh.

Figure A2.5 shows the modelled contribution from new business developments in Edinburgh if they were heated by biomass installations with an emission factor of 20 g/ GJ or 60 g/ GJ. The predicted contribution for emissions factors of 20 g/ GJ is less than 0.1 µg m ^-3 over most of Edinburgh, with higher contributions in the vicinity of the larger developments. The maximum contribution to annual mean concentrations was predicted to be 0.6 µg m ^-3. The predicted contribution for emissions factors of 60 g/ GJ is more than 0.1 µg m ^-3 over a substantial part of Rural West Edinburgh, with higher contributions in the vicinity of the larger developments. The maximum contribution to annual mean concentrations was predicted to be 1.1 µg m ^-3.

Figure A2.5: Modelled contribution to particulate matter concentrations from biomass installations in new business developments in Edinburgh.

Shopping and related proposals

The Edinburgh Local Plans identify a number of shopping and related proposals (Table A2.9). Service sector fuel use for space and water heating in 2005 was typically 5327 GJ gross per hectare of floor space ( BERR data). The heat demands have been estimated on this basis in Table A2.9. The total heat demand calculated for these developments is 75 TJ, corresponding to 0.3% of Edinburgh's current heat demand. It has been assumed here as the maximum impact case that the whole of the heat demand for the new developments will be met by biomass combustion. Table A2.9 also shows the annual particulate emission for each development based on a particulate emission factor of 20 g/ GJ.

Table A2.9: Current proposals for retail developments.

Table A2.10 shows the modelled discharge point source discharge characteristics for each of the modelled developments. The stack discharge characteristics were estimated following the method used for business developments, above.

Table A2.10: Modelled discharge characteristics for retail developments in Edinburgh.

The modelled contribution from emissions from new redevelopments fitted with biomass heating is generally less than 0.1 µg m ^-3 throughout Edinburgh except in the immediate vicinity of the retail developments.

Other institutions

Table A2.11 lists other institutions that may be suitable candidates for biomass heating. We have provisionally estimated the capacity of the boilers, and derived estimates of the annual heat demand and potential particulate emissions if biomass boilers or CHP were installed. The estimates have been based on 30% utilisation for biomass boilers and 45% utilisation for CHP. The total heat demand was estimated to be 564 TJ, approximately 2.3% of Edinburgh's current heat demand. Table A2.11 also shows the annual particulate emission for each development based on a particulate emission factor of 20 g/ GJ. For developments with annual heat demands greater than 30 TJ, it has been assumed that the heat is supplied by biomass CHP with 50% thermal efficiency. It has also been assumed that the electricity generated is exported to the grid, rather than used for electrical heating within the development.

Table A2.11: Other institutions viable for biomass heating.

Table A2.12 shows the modelled discharge point source discharge characteristics for each of the modelled developments. The stack discharge characteristics were estimated following the method used for business developments, above.

Table A2.12: Modelled discharge characteristics for other potential biomass installations in Edinburgh.

Figure A2.6 shows the modelled contribution from biomass installed in identified institutions in Edinburgh if they were heated by biomass installations with an emission factor of 60 g/ GJ. The predicted contribution is more than 0.1 µg m ^-3 over a substantial part of the city, with higher contributions in the vicinity of the larger developments.

Figure A2.6: Modelled contribution to particulate matter concentrations from biomass installations in other institutions in Edinburgh assuming an emission factor of 60 g/ GJ.