6.1 Carbon dioxide emissions
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Standard 6.1 focuses on the reduction of carbon dioxide emissions arising from the use of heating, hot water, lighting, ventilation and cooling systems in a new dwelling. The guidance sets an overall level for maximum carbon dioxide emissions in buildings by use of a methodology which incorporates a range of parameters that influence energy use. This means that, for new dwellings, a designer is obliged to consider energy performance as a complete package rather than looking only at individual elements such as insulation or boiler efficiency - a ‘whole dwelling approach’ to energy, which offers a significant degree of design flexibility.
For the majority of new buildings, Standard 6.1 has the greatest influence on design for energy performance. Standards 6.2 to 6.6, in the main, recommend benchmark and back-stop levels to be achieved for individual elements or systems. To achieve compliance with Standard 6.1, it will be necessary to improve upon some or all of these backstop levels or incorporate additional energy efficiency measures, such as low carbon equipment (LCE).
Renewable technologies - Directive 2009/28/EC http://europa.eu/legislation_summaries/energy/renewable_energy/en0009_en.htm promotes the use of energy from renewable sources. Where the dwelling design will include use of renewable energy for heating, Article 13 of the Directive recommends, amongst other measures, consideration of use of the following:
for biomass equipment, conversion efficiencies of 85%
for heat pumps, those that fulfil the minimum requirements of eco-labelling established in Commission Decision 2007/742/EC (amended in 2011 & 2013) establishing the ecological criteria for the award of the Community eco-label to electrically driven, gas driven or gas absorption heat pumps, and
for solar thermal systems, those that are subject to EU standards, including eco-labels and other technical reference systems established by the European standardisation bodies.
High-efficiency alternative systems - Article 6 of Directive 2010/31/EU http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:153:0013:0035:EN:PDF requires that, for all new buildings, the technical, environmental and economic feasibility of high-efficiency alternative systems (such as decentralised energy supply systems using renewable energy, co-generation, district or block heating/cooling and heat pumps) are considered and taken into account in developing proposals.
This should be documented and available for verification purposes and a statement should therefore accompany the building warrant application. Further information on this process is provided in Annex 6.C -'Consideration of High-Efficiency Alternative Systems in New Buildings'.
Conversions - in the case of conversions as specified in regulation 4, this standard does not apply.
Objective - the calculated carbon dioxide emissions (measured in kilograms per square metre of floor area per annum) for the proposed dwelling, the dwelling emissions rate (DER), should be less than or equal to the target carbon dioxide emissions for a ‘notional dwelling’, the target emissions rate (TER).
Summary of procedure - in order to establish the target carbon dioxide emissions rate (TER) for the ‘notional dwelling’ (i.e. a dwelling of the same size, shape and 'living area fraction' as the proposed dwelling), the dimensions and 'living area fraction' of the proposed dwelling and a set of standard values are input into the methodology. To calculate the emissions for the proposed dwelling (DER) a second calculation is carried out where the proposed values are input into the methodology. An alternative way of meeting Standard 6.1 which avoids the use of the calculation methodology is to design to the set of values used for the ‘notional dwelling’. This elemental approach is described in clause 6.1.6.
Standard Assessment Procedure (SAP) - The Government’s Standard Assessment Procedure for Energy Rating of Dwellings (SAP 2012) is the calculation tool which forms part of the UK National Calculation Methodology which conforms with Article 3 of Directive 2010/31/EU on the Energy Performance of Buildings. It is approved to calculate the energy performance and the carbon dioxide emissions of an individual dwelling. At all stages, the conventions in the SAP document should be read in conjunction with the specific guidance given in the clauses to this section. Designers should be familiar with the SAP methodology and their chosen software tool and be able to explain the input and calculation process in the context of the information submitted as part of the building warrant.
Non-domestic use within dwellings - some new dwellings may incorporate surgeries, consulting rooms, offices or other accommodation of a floor area not exceeding 50m² in aggregate, used by an occupant of the dwelling in a professional or business capacity. Where this occurs, the accommodation should be considered as a part of the dwelling.
To set the target carbon dioxide emissions level, (i.e. the level that should not be exceeded, the TER), refer to the table to this clause. The package of measures for the fuel type for the main space heating of the proposed dwelling is selected. This package of measures is used in the methodology and no improvement factors are applied. In addition, this ‘notional dwelling' is to have the same size, shape (including floor, roof, exposed wall areas and storey heights) and 'living area fraction' as the proposed dwelling. These terms are explained in SAP 2012.
Software vendors providing BRE approved SAP 2012 software [http://www.bre.co.uk/] will incorporate a function that, with ‘Scotland’ selected, automatically generates the target CO2 emissions level once the fuel type is selected and the ‘notional dwelling’ dimensions and 'living area fraction' have been input into the programme.
Measures to calculate target carbon dioxide emissions for the 'notional dwelling' - the measures identified in the tables below are set to deliver, on aggregate, 45% fewer carbon dioxide emissions than the 2007 standards. Whilst it is possible to construct a dwelling using one of the packages of measures (see clause 6.1.6), this table is provided solely for the purpose of setting the target emission rate (TER) for the ‘notional’ dwelling.
It is not necessary that values or elements present in these tables form part of the proposed dwelling. Designers are free to develop cost-effective and appropriate solutions which meet the TER, subject to meeting or improving upon the benchmark and backstop levels identified in guidance to Standards 6.2 to 6.6.
Table 6.1. Main space heating system fuel [1] [2] [3]
| Element or system | Gas (Package 1) | LPG (Package 2) | Oil (Package 3) | Electricity (Package 4) | Biomass [4] (Package 5) |
|---|---|---|---|---|---|
| Walls | U = 0.17 | U = 0.17 | U = 0.17 | U = 0.17 | U = 0.17 |
| Floors | U = 0.15 | U = 0.15 | U = 0.15 | U = 0.15 | U = 0.15 |
| Roofs | U = 0.11 | U = 0.11 | U = 0.11 | U = 0.11 | U = 0.11 |
| Openings [5] | U = 1.4 | U = 1.4 | U = 1.4 | U = 1.4 | U = 1.4 |
| Allowance for thermal bridging [6] | 0.08 x total exposed surface area | 0.08 x total exposed surface area | 0.08 x total exposed surface area | 0.08 x total exposed surface area | 0.08 x total exposed surface area |
| Open flues | None | One | One | None | One |
| Heating system, pump in heated space [7] | Gas boiler room - sealed fan flued 89% efficiency | LPG boiler room - sealed fan flued 89% efficiency | Oil boiler room - sealed fan flued 90% efficiency | Air to water heat pump 175.1% efficiency [8] | Wood pellet boiler 86% efficiency, HETAS approved |
| Heating system controls | Time and temperature zone control +Boiler interlock +weather compensation +delayed start | Time and temperature zone control +Boiler interlock +weather compensation +delayed start | Time and temperature zone control +Boiler interlock +weather compensation +delayed start | Time and temperature zone control | Time and temperature zone control + delayed start |
| Hot water (HW) system | Stored HW (from boiler) separate time control for space and water heating | Stored HW (from boiler) separate time control for space and water heating | Stored HW (from boiler) separate time control for space and water heating | Stored HW (electric immersion) separate time control for space and water heating | Stored HW (from boiler) separate time control for space and water heating |
| Secondary space heating | none | 10% closed wood log-burning room heater [9] | 10% closed wood log-burning room heater [9] | 10% electric | none |
| Heat recovery systems | Instantaneous waste water heat recovery system, 45% efficiency | Instantaneous waste water heat recovery system, 45% efficiency | Instantaneous waste water heat recovery system, 45% efficiency | Instantaneous waste water heat recovery system, 45% efficiency | Instantaneous waste water heat recovery system, 45% efficiency |
| Photo-voltaics | Yes [10] | Yes [10] | Yes [10] | No | No |
Table 6.2. For the 'notional dwelling' in addition all of the following applies in every fuel type
| Windows, doors and rooflights | area 25% of total floor area [11] |
| Orientation | all glazing orientated east/west |
| Shading (glazing) | average overshading |
| Number of sheltered sides | 2 |
| Chimneys | none |
| Ventilation system | natural ventilation with intermittent extract fans, 4 for dwellings with floor area more than 80m2, 3 for smaller dwellings |
| Air infiltration (building fabric) | 7m3/h.m2 at 50Pa |
| Hot water cylinder | 150 litre cylinder insulated with standing heat loss of 1.89 kWh/day. Cylinder in heated space, cylinder temperature controlled by thermostat |
| Primary water heating losses (where applicable) | primary pipework fully insulated |
| Low energy light fittings | 100% of fixed outlets |
| Thermal mass parameter | The value identified for the proposed building should be used |
| Party wall heat loss (applicable to cavity separating walls) | 0.0 W/m2K |
| Waste water heat recovery unit (WWHR) | Apply 2 units (shower) in dwellings with floor area more than 100m2, but 1 unit (shower) for smaller dwellings |
Notes:
Where a multi-fuel appliance is proposed, assessment of both TER and DER should be based upon the fuel option with the highest carbon factor (e.g. multi-fuel stove capable of burning coal or wood is assessed as solid mineral fuel).
Where heat is supplied to a dwelling from more than one source, through a generation mix (e.g. community heating using both oil and biomass where heat is provided from both sources simultaneously), the primary heating element within the TER should be calculated pro rata, on the basis of the identified fuel mix. The same mix should be used in calculation of the DER, including any pro rata contribution made by solutions such as CHP. This does not apply where heat demand can be provided solely from one of the identified generating sources, in which case other identified heat sources should be considered as back-up systems and excluded from assessment.
Where solid mineral fuel is proposed for the main space heating system, the TER should be calculated using the values identified for oil as a fuel (package 3). This will require improvements in performance within the DER specification for compliance.
The biomass column should be used not only where biomass fuel is to be used but also for biogas, liquid biofuels, large scale waste combustion from boilers and waste heat from power stations.
U is the average U-value of all openings (windows, doors, rooflights) based on one opaque door of area 1.85m² and U=1.4, any other doors fully glazed. For windows, doors, etc. a frame factor of 0.7, light transmittance of 0.80 and solar energy transmittance of 0.63 are assumed.
For the purposes of setting the TER, a y-value of 0.08 is identified. Note: for DER, this element of calculation must use Htb calculated from length of junctions and individual psi values (see clause 6.2.3).
In the case of gas, LPG and oil, the specified efficiency values for the boiler in the notional dwelling are SEDBUK(2009); distribution temperature 55°C (e.g. radiators as emitters).
Seasonal Performance Factor (SPF) specified for the system includes application of a distribution temperature of 55°C (e.g. radiators as emitters).
The closed room heater included within the fuel package table should be capable of burning wood only, not multi-fuel.
For purpose of calculating the benefit of the PV element in the TER reduction, region is ‘UK average’, orientation ‘SW’, pitch ‘30°’ and overshading ‘no or little’. and kWp is the smaller of:
- dwelling total floor area (in m²) x 0.01, and
- roof area limit.
The roof area limit is to ensure that the PV area does not exceed 30% of the roof area (based on 30° roof pitch and 0.12kWp per m² PV area). In the case of a flat or maisonette the roof area limit is divided by the number of storeys in the block.
If total exposed facade area is less than 25% of the floor area, the area of windows, doors and roofs should be taken as the area of the total exposed facade area.
The second calculation involves establishing the carbon dioxide emissions for the proposed dwelling (DER). To do this the values proposed for the dwelling should be used in the methodology i.e. the U-values, air infiltration, heating system, etc.
The exceptions to entering the dwelling specific values are:
it may be assumed that all glazing is orientated east/west
average overshading for glazing may be assumed if not known. 'Very little' shading should not be entered
2 sheltered sides should be assumed if not known. More than 2 sheltered sides should not be entered
where secondary heating is proposed, if a chimney or flue is present but no appliance installed, the worst case should be assumed i.e. a decorative fuel-effect gas appliance with 20% efficiency as secondary heating. If there is no gas point, an open fire with 37% efficiency should be assumed as secondary heating burning solid mineral fuel for dwellings outwith a smokeless zone and smokeless solid mineral fuel for those that are within such a zone.
All other values can be varied, but before entering values into the methodology, reference should be made to:
the back-stop U-values identified in guidance to Standard 6.2, and
guidance on systems and equipment referenced in guidance to Standards 6.3 to 6.6 and the Domestic Building Services Compliance Guide for Scotland http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/techbooks/techhandbooks/dbscgs .
Where a building contains more than one dwelling (such as a block of flats or terrace of houses) the average carbon dioxide emissions for the proposed block or terrace (DER) may be compared to the average target CO2 emissions (TER) for the ‘notional block or terrace'.
The average emissions for the block or terrace is the floor-area-weighted average for all the individual dwelling emissions, i.e.:
{(emissions1 x floor area1) + (emissions2 x floor area2) + (emissions3 x floor area3) + …)} ÷ {(floor area1 + floor area2 + floor area3) + …}
The degree of flexibility which is provided by averaging out building emissions should be used carefully. It is not intended that one or more dwellings are super-insulated (in a building consisting of dwellings) so that another may be constructed with a high percentage of glazing.
Where subject to Standard 6.1, communal rooms or other areas in blocks of dwelling (which are exclusively associated with the dwellings) should be assessed either by:
a SBEM calculation using the methodology and guidance to Standard 6.1 for non-domestic buildings, or
ensuring that the glazing does not exceed 25% of the total communal floor area of the building; and the U–values, thermal bridging, air infiltration values equal or better than those given for the gas 'notional dwellings' (package 1 in the table to clause 6.1.2).
However where the common areas are less than 50m2 in total these rooms or areas may be treated as a stand-alone building and are not therefore subject to Standard 6.1.
Where a dwelling is designed to one of the packages of measures in the table to clause 6.1.2, it can be considered to reduce carbon dioxide emissions to the same level as by use of the methodology, calculating and comparing DER with TER.
In using a package of measures east/west orientation, average overshading for glazing and 2 sheltered sides may be assumed for the proposed dwelling.
The simplified approach may still be used where there are minor deviations in the values input that will clearly achieve the same or a better level of emissions. For example:
a boiler with a higher SEDBUK efficiency
a ground source heat pump instead of an air source heat pump
where secondary heating forms part of the TER calculation, a secondary space heating system of equal or better performance (e.g. a closed, biomass-burning room heater)
area of openings between 20% and 25% of total floor area (windows, doors, rooflights, and roof windows)
a declared air infiltration of 7m3/h.m2 @ 50 Pa or lower
a hot water cylinder with a declared heat loss figure (BS 1566-1: 2002) not exceeding 1.89 kWh/day
This simplified approach should not be used where there is any deviation from values in the table which will result in higher CO2 emissions. An example of this is where the proposed dwelling has more than 4 extract fans or windows of a poorer U-value. Likewise, if some elements offer poorer performance and others offer higher performance, the simplified approach should not be used.
This approach should also not be used where there is a likelihood of high internal temperature in hot weather or where air-conditioning is proposed. Reference should be made to the guidance to Standard 6.6.
Note that an Energy Performance Certificate (EPC) will still be required, on completion of the dwelling, to meet Standard 6.9.
Conservatories of less than 50m2 in area are stand-alone buildings, thermally separated from the dwelling. A dwelling to which one is attached should be assessed as if there was no conservatory proposed.
For conservatories and other ancillary stand-alone buildings of 50m2 or more subject to Standard 6.1, a SBEM calculation using the methodology and guidance to Standard 6.1 for non-domestic buildings should be provided, applying the standards set for domestic buildings in all other respects.