6.1 Carbon dioxide emissions
Standard 6.1 focuses on the reduction of carbon dioxide emissions arising from the use of heating, hot water, ventilation and lighting in new buildings and large extensions. 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 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 building 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 and 6.10, in the main, recommend benchmark and backstop 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 performance measures, such as low carbon equipment (LCE).
The guidance given in support of Standards 6.2 to 6.8 for extensions and alterations should be followed when designing stand-alone buildings of less than 50m2.
Renewable technologies - Directive 2009/28/EC [http://europa.eu/legistlation_summaries/energy/renewable_energy/en009_en.htm] promotes the use of energy from renewable sources. Where a building 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.E - ‘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.
The Simplified Building Energy Model (SBEM) is a 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 for use in carbon dioxide emissions calculations. SBEM has a basic user interface, iSBEM, which includes Scottish compliance parameters for use with this guidance and is available on the National Calculation Methodology website (http://www.ncm.bre.co.uk/index.jsp).
Other tools may be used with the methodology (such as dynamic simulation modelling), particularly where the building is considered to be a complex design. A list of approved calculation tools can be found on the 'Section 6 software' page of the Building Standards Division website. The guidance given here is written in terms of the SBEM calculation tool but the principles and procedures also apply to other calculation tools. Designers should be familiar with the NCM 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.
To comply with the requirements of Standard 6.1, designers should demonstrate that the calculated carbon dioxide emissions for the ‘actual’ building (Building Emissions Rate or BER) do not exceed those which are calculated for a ‘notional' building (Target Emissions Rate or TER). The carbon dioxide emissions are measured in kilograms of CO2 per square metre of floor area per annum.
Outline of process - in broad terms, the way that this process works is described below:
The data defining the actual building is input into an approved software tool and the notional building is generated automatically by applying the National Calculation Methodology (NCM) for Scotland. The notional building has the same size, shape, orientation, conditioning strategy and zone activities as the actual building.
The Target Emissions Rate (TER) for the actual building is generated automatically, with SBEM applying prescribed fabric and services specifications to the notional building (see clause 6.1.4). These are applied to the individual building zones that make up the notional building. Values are assigned automatically based upon both the activity and the conditioning strategy for each zone of the actual building, as input by the designer.
Application of these specifications defines a ‘concurrent notional building’, i.e. one from which a calculated emissions rate is deemed to meet the requirements of this standard. This calculated figure is the TER for the actual building.
The Building Emissions Rate (BER) is generated by applying the designer’s chosen fabric and services specifications for the actual building on a zone by zone basis within the NCM for Scotland. In determining this specification, the fabric and services specifications for the actual building should meet or improve upon the benchmark and backstop levels identified in guidance to Standards 6.2 to 6.6.
If, following full specification of the actual building, the BER is not more than the TER, then compliance with this standard is achieved. If the BER is more than the TER, then the designer should review and improve the construction and building services data in the actual building and determine what measures would be appropriate to reduce the BER. For example, by reducing the air permeability, improving services efficiency or incorporating some ‘enhanced management and control’ features such as power factor correction.
The 'notional' building is created once the design of the actual building has reached the stage where layout, dimensions, site orientation, building services strategy, etc. are known.
At all stages, the conventions in the iSBEM User guide should be read in conjunction with the specific guidance for Scotland given in these clauses. SBEM has much of the input data already embedded in the calculation tool. When 'Scottish building regulations' is selected as the ‘purpose of analysis’ within SBEM, Scottish weather data and the embedded values within the calculation tool are applied to the 'notional' building. The software will automatically generate the 'notional' building from the information provided for the actual building.
In the interests of transparency, key information on the specification used to create the 'notional' building (whether user defined or embedded in SBEM calculation tool) is summarised in the following clauses. Further information, including a full definition of the notional building and explanation of the assessment process is given in the 2015 'National Calculation Methodology (NCM) Modelling Guide for Scotland' http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/techbooks/techhandbooks/ncmg2015.
The fabric and services specification of the notional building are assigned on a zone by zone basis. There are two specification categories identified which are based upon the conditioning strategy assigned to the actual building by the designer:
heated and naturally ventilated, or
heated and mechanically ventilated or heated and cooled.
The zone by zone approach allows designers greater flexibility, assigning the mechanically ventilated or cooled specification only to those zones where such solutions are proposed or required in an otherwise heated/naturally ventilated building. This sets a TER which is moderated by a less heavily serviced strategy, encouraging buildings with a reduced overall energy use and carbon dioxide emissions.
The following table outlines the standard notional building zone specifications for fabric and fixed building services, depending on the zone conditioning strategy. Some elements are further varied based upon the activity type defined for each zone within SBEM. The full definition of the notional building and explanation of the assessment process is given in the 2015 'National Calculation Methodology (NCM) Modelling Guide for Scotland' http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/techbooks/techhandbooks/ncmg2015.
Table 6.1. 'Notional' building - fabric and fixed building services values for TER
|Element||Zone heated & naturally ventilated||Zone heated & mechanically ventilated/cooled|
|Roof (U-value, W/m2.K)||0.18||0.16|
|Wall (U-value, W/m2.K)||0.23||0.20|
|Floor (U-value, W/m2.K)||0.22||0.2|
Window (U-value, W/m2.K
1.8 (10% FF)
1.6 (10% FF)
Rooflight (U-value, W/m2.K)
1.8 (15% FF)
|Vehicle access and similar large doors||1.50||1.50|
|Pedestrian doors and high usage entrance doors||2.20||2.20|
|Thermal capacity of element||Refer to NCM Modelling guide for details.|
|Thermal bridging - Junctions||Refer to NCM Modelling guide for details.|
|Air Permeability (m3/hr.m2)||5||3|
|Lighting Efficiency (Luminaire lumens/Circuit watt)||60||65|
|Occupancy control (Yes/No)||Yes||Yes|
|Daylight control (Yes/No)||Yes||Yes|
Heating and DHW (% efficiency)
Fuel(s) for actual building applied to the notional building.
Refer to NCM Modelling guide for details.
|Central Ventilation (SFP, W/l/s)||N/A||1.8|
|Terminal Unit (SFP, W/l/s)||N/A||0.4|
|Heat recovery (% efficiency)||N/A||70%|
|Variable speed control of fans, pumps and circulators (Yes/No including multiple sensors)||Yes||Yes|
|Photovoltaic Panels (% of floor area)||4.5%||4.5%|
In certain buildings, air permeability is further differentiated by building size. Refer to NCM Modelling Guide http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/techbooks/techhandbooks/ncmg2015.
The following information should be input and should reflect the design of the actual building:
size and shape, internal layout and dimensions (see clause 6.0.12)
activity type and fixed building services for each building zone (and therefore the same activity type parameter values)
orientation - the 'notional' and actual building have the same orientation
areas of building envelope elements
construction build-up of elements to complement U-values embedded in the SBEM calculation tool.
The following assertions are applied within the NCM when calculating the carbon dioxide emission rate for the ‘notional’ building:
the heating fuel(s) specified for the actual building are applied to the ‘notional’ building
the amount of glazing in the notional building is not the same as in the actual building. It is assigned on a zone by zone basis as a percentage of the external wall and roof based upon the glazing type for that activity within the NCM activity database. Information on this is set out in the NCM Modelling guide http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/techbooks/techhandbooks/ncmg2015
any services not covered by Section 6 are not assessed (for example emergency escape lighting and specialist process lighting)
thermal bridge heat loss is based upon the same geometry as for the actual building.
Low carbon equipment element of the TER - the concurrent specification for the ‘notional’ building includes an element of low carbon equipment (LCE) represented, as a proxy, by the inclusion of roof mounted photovoltaic panels, expressed as a fixed percentage of the building gross internal area. This is included to assist in reducing the TER, in recognition of both the recast Directive 2010/31/EU on the energy performance of buildings and Directive 2009/28/EC which promotes the use of energy from renewable sources. It is intended to encourage designers to consider the incorporation of LCE within design proposals, where this is considered an appropriate and cost-effective part of the overall building solution.
Whilst there is no requirement for the actual building to include LCE, designers should be aware that other aspects of building specification would require to be improved should such an element be absent. Similarly, the presence of a larger LCE element within the actual building would enable other elements of specification to be lowered, subject to the minimum values for building fabric and services set out in guidance to Standards 6.2 to 6.6.
The BER is calculated by using the values and efficiencies input by the designer in the SBEM calculation tool. There are, however, provisions that limit the flexibility of design. These are:
backstop measures given in the guidance to Standards 6.2 to 6.6, and
when display windows are present in the actual building, they are not copied across into the ‘notional’ building.
The first of these measures is intended to limit energy demand, particularly where LCE may offset rather than reduce energy consumption. The second allows the provision of display glazing but requires designers to compensate for the additional heat loss from such elements by improving specification of other elements of the actual building.
Certain management features offer improved energy efficiency in practice, while others have this potential if appropriate action is taken. Where these management features are provided in the proposed building, the BER can be reduced by an amount equal to the product of the percentages given in the table below and the CO2 emissions for the system(s) to which the feature is applied:
Table 6.2. BER Adjustment Factors
|Central power factor correction to achieve a power factor of at least 0.9||0.010|
|Central power factor correction to achieve a power factor of at least 0.95||0.025|
Automatic monitoring and targeting (AMT) with alarms for out of range values
For example, if the total CO2 emissions in a gas heated building were 60kg/m2/annum and 20kg/m2/annum are due to electrical energy consumption without power factor correction, the provision of correction equipment to achieve a power factor (pf) of 0.95 would enable the BER to be reduced by 20 x 0.025 = 0.5kg/m2/annum. The revised BER would then be 59.5kg/m2/annum.
Credit can only be taken where the feature is applied.
Where, rather than making a staged warrant application, a new building shell and fit-out are the subject of separate building warrant applications, the final specification of building systems may not be known. However it remains important to ensure that such a building, if intended to be heated or cooled (other than by heating provided solely for the purpose of frost protection) will still be constructed to limit carbon dioxide emissions.
In such cases, the calculation methodology should still be used to show that the building shell, as proposed, can comply with Standard 6.1. This should be done by identifying an example specification for any uninstalled services needed for occupation and use of the building and using this in the calculation. This specification should:
be compatible with the intended building end use and servicing strategy. Assessment should be based upon the most energy intensive solution associated with the proposed building use (e.g. that a shell building for commercial/office will be air conditioned), and
recognise the available utilities provided to the site.
A TER/BER comparison can then be carried out. In specifying the building shell, reference should be made to the maximum U-values and air-tightness levels identified in clauses 6.2.4 and 6.2.6.
Whilst the NCM will assess shell and fit-out installations on a zone-by-zone basis, full details of the example specification, identifying uninstalled services, should form part of information with the building warrant and should identify, in particular, any installed low carbon equipment proposed to meet the Target Emissions Rate. This will provide information to any party considering subsequent fit-out work on the expected level of performance of remaining building services needed to demonstrate compliance of the finished building prior to occupation.
Use of continuing requirement - where Standard 6.1 applies to a building, the verifier can issue a continuing requirement with a building warrant for a shell building. This will mean that the subsequent fit-out, whether subject to a building warrant or not, demonstrates that the final building also complies with Standard 6.1 by having calculated emissions which do not exceed the TER declared for the shell building. In demonstrating this, the same edition of the NCM used for the shell building calculation may be used for the BER calculation for the final building.
This will also result in the production, under Standard 6.9, of an Energy Performance Certificate on completion of the final building. This must be produced using the edition of the NCM which is current at the time works are completed.
Dependant upon the final specification of the building, additional provisions may be needed to meet the carbon dioxide emissions standard at building fit-out phase. Accordingly, those involved in the further development of a shell building are advised to consider early assessment of the building, as constructed, to determine the extent to which such provisions may be needed at fit-out.
Similarly, when considering either separate building warrants for shell and fit-out or a single, staged warrant, an early assessment of the implications each route may have on the design and specification of the initial building is recommended.