Guidance on performing Part L2 (2006) assessments

The <VE Compliance> View provides the means to test compliance with the conservation of fuel and power requirements of the UK building regulations, including the 2006 regulations applying in England, Wales and Scotland.

This User Guide covers Part L2, the section of the regulations covering non-domestic buildings in England and Wales. The following guidance is aimed at providing an overview of the implementation of the regulations in the <VE> software.

 

New Part L2 regulations came into force on May 6^th 2006 and apply to non-domestic buildings beginning construction after this date. The regulations requiring designers to demonstrate significant reductions in carbon emissions from building energy use relative to the standards set by the previous (2002) edition of the regulations. This is achieved by performing a detailed analysis of the carbon emissions of two buildings:

The actual building – the building as designed, but subject to standard patterns of occupancy and plant operation, and

The notional building – a version of the building that conforms to standards similar to those applying in the Part L2 (2002) Elemental Method. The notional building is subject to the same occupancy and plant operation patterns as the actual building.

The analysis must demonstrate that the actual building’s carbon emissions improve on those of the notional building by a specified margin – 28% for an air conditioned building. It is this improvement that constitutes the tightening of the regulations in the 2006 edition.

The analysis of carbon emissions must be performed with accredited software applying the National Calculation Methodology (NCM), such as <VE> Compliance or BRE’s SBEM program.

By contrast with the 2002 regulations, where a choice of three compliance routes was offered, the 2006 regulations stipulate a single compliance procedure. This has much in common with the Carbon Emissions Calculation Method (CECM) of the 2002 regulations, but there are important differences including the following:

The actual building’s performance must not merely match, but significantly improve on that of the notional building.

Assessments must be performed under standard occupancy and plant operating conditions. This means that under the new regulations, some of the data entered by the user to model the building for design work has to be replaced by different data for the purpose of compliance analysis.

Requirements on the control of summertime solar gains apply to the actual, not the notional building, and only to rooms without mechanical cooling. In this respect the 2006 notional building sets a slightly less demanding performance target than the 2002 notional building.

In terms of analysis methodology, the most significant change with respect to the 2002 Carbon Emissions Calculation Method is the requirement for standard occupancy and plant operating conditions. The consequence of this is that, in addition to the actual and notional buildings, the designer will usually need to model and analyse (for design and other non-regulations purposes) a third building:

The real building – this is the building as designed, and with the occupancy and plant operation conditions expected to apply in reality, rather than the standard conditions stipulated for Part L2 compliance.

The real building is the building presented in Apache View, where the special conditions required for Part L2 (2006) do not apply.

The testing of carbon emissions constitutes Criterion 1 of Part L2. The full set of criteria is as follows:

Criterion 1 – Achieving an acceptable building CO2 emission rate (BER).

Criterion 2 – Limits on design flexibility: this sets minimum standards for building fabric and system performance.

Criterion 3 – Limiting the effects of solar gains in summer: this imposes limitations on solar gains and temperatures in those parts of the building that are not provided with comfort cooling systems

Criterion 4 – Quality of construction and commissioning: this lays down requirements that the building must meet after construction. (Not covered by <VE> Compliance.).

Criterion 5 – Providing information: certain information must be provided to the owners of the building. (Not covered by <VE> Compliance.).

Users of the <VE> Compliance software are strongly advised to study the official documents defining the regulations.

In the IES <Virtual Environment> all building regulations compliance testing is performed in the <VE> Compliance View. This covers the 2002 and 2006 regulations for England and Wales as applied to both dwellings and non-dwellings, together with their counterparts in Scotland.

The starting point for a compliance analysis, however, is the input of geometrical data in ModelIT. The Template Manager, a central resource available from all Views, is typically used next to set up room system and ventilation parameters. Apache View, while not essential for compliance testing, commonly plays a part in the input of Part L data that is shared by other Apache View application, and Views such as SunCast and MacroFlo may also be invoked. The purpose of this section is to provide an overview of the roles played by the different parts of the <VE> in the compliance testing process.

ModelIT handles the input of the building geometry.

The Template Manager provides facilities for setting room conditions for a range of thermal applications. In the context of Part L2, it also allows the specification of room activities that define the standard occupancy and plant operation conditions that apply in Part L2 (2006). In Part L2 compliance tests these standard conditions automatically override certain of the Space Data settings that would otherwise be taken from the Room Template.

Apache View covers thermal applications such as heating and cooling loads calculation, and simulation outside the context of Part L. The analysis in this View applies to the real building, for which all the input data is under your control. Where data is shared between the real building and the actual building, this data may be entered in either Apache View or <VE> Compliance. Examples of such shared data include:

Location

Constructions

HVAC systems

Infiltration

Renewables

 

<VE> Compliance covers thermal analysis specific to the Building Regulations. Some of the data required by the Building Regulations is shared with Apache View, as indicated above, and may be entered or edited in either View. Other regulations-specific data must be entered in the <VE> Compliance view. This includes:

Regulatory framework – eg Part L2 (2006) (assumed in the list that follows)

Building type

Room activities (may be specified by means of templates)

Data relating to lighting energy savings

Heat bridging data

Stage of analysis (Design or As Built)

Data required by the BRUKL compliance calculator, including addresses, system characteristics and air-tightness properties

<VE> Compliance displays data for the actual building by default. The notional building may also be inspected in this View. Facilities are provided for performing compliance simulations, test compliance simulations (on both the actual and notional buildings) and summertime temperature analyses for Criterion 3.

SunCast analyses shading and internal solar penetration, factors which may optionally be taken into account in compliance simulations.

MacroFlo and ApacheHVAC are other Views covering natural ventilation analysis and component-based HVAC system simulation, respectively, that are also available as adjuncts to compliance simulations.

 

Vista provides facilities for viewing the results of <VE> Compliance and other simulations.

The definition, creation and purpose of these three buildings can be summarized as follows.

The real building is the building that you see in Apache View. It is the building as designed, and with the occupancy and plant operation conditions expected to apply in reality, rather than the standard conditions stipulated for Part L2 compliance. In Apache View it forms the basis for the analysis of heating and cooling loads and simulations.

The actual building is the building as designed, but subject to standard patterns of occupancy and plant operation for Part L2 (2006), as defined in NCM. The actual building is the building displayed by default in <VE> Compliance. It is identical to the real building in all respects except occupancy (including associated internal gains and minimum ventilation rates) and plant operation conditions, which are given standard settings in <VE> Compliance as a function of the attributes ‘building type’ and ‘room activity’. Aspects of the actual building that are shared with the real building may be edited either Apache View or <VE> Compliance.

The notional building is a version of the actual building that is modified to conform to a clearly defined set of standards relating to glazing area, constructions and system characteristics. Its purpose is to provide a benchmark or target against which to measure the performance of the actual building. The notional building is subject to the same occupancy and plant operation patterns as the actual building. It can be viewed in <VE> Compliance by switching the Current Model from Actual to Notional. It is created automatically from the actual building, and may not be edited. (One exception to this rule is dealt with below.)

The real building

Users interested in compliance testing only will not need to consider the real building as an entity distinct from the actual building. They can thus bypass Apache View. They should, however, be aware that certain room template attributes are overridden in <VE> Compliance.

Aside from this point, which is covered in more detail below, the real building does not need to be considered further in the context of <VE> Compliance.

The actual and notional buildings, however, can usefully be described in more detail.

The actual building

The actual building allows you control over the following aspects of the design, which it shares with the real building:

Data shared between actual building and real building:

Location

Geometry (including orientation and glazing)

Constructions

System characteristics including renewables

Infiltration rates (permeability)

The actual building differs from the real building in terms of its occupancy and plant operation, which for the purpose of Part L2 (2006) are forced to standard patterns linked to the activity associated with each room. The data in this category is

Activity (NCM Template) Space Data:

Occupancy

Equipment gains

Lighting levels (expressed in terms of illuminance)

Room conditioning (heating and cooling set points and operation periods)

Minimum ventilation rates

For the purpose of Part L2 (2006) compliance analysis, this data is outside your control and cannot be edited. Note that these attributes are present in the Room Template for use in Apache View analyses, but the settings appearing there are overridden in the Part L analysis.

The standard settings for <VE> Compliance are brought into the room by means of a second template called the NCM Template which is applied in combination with the usual Room Template. The NCM Template contains the standard operating conditions (as listed above) associated with the room’s NCM activity. For example, a room assigned the activity ‘Open plan office’ in a building of type ‘Office’ has an NCM Template called ‘NCM Office: Open plan office’. This contains the occupancy and equipment gains, the lighting level and profile, the room conditioning settings and the minimum ventilation regime laid down as standard for NCM assessments of an open plan office. NCM Templates appear in the list of Room Templates in the Template Manager, where they can be examined in detail.

The activity (sometimes called the NCM activity) is assigned to the room on the Space Data Building Regulations tab, and may optionally be specified by means of the corresponding attribute in the Room Template. The activity, which is always associated with a particular building type, exists solely for the purpose of building regulations and is only used by <VE> Compliance. Setting the room activity automatically assigns the correct NCM Template and all the data associated with it. The name of the NCM template, together with that of the room template, can be seen displayed on the General tab of the Space Data dialogue.

Not all the Space Data is set by the NCM Template. Just as in Apache View, each room in <VE> Compliance has a Room Template, and this sets the parts of the Space Data that are not covered by the standard activity settings – namely

User-supplied Space Data:

System characteristics

Measures to improve the efficiency of lighting systems

Infiltration rates

The Space Data displayed and used in <VE> Compliance is thus drawn partly from the NCM Template and partly from the Room Template, as follows.

The data on the Room Conditions tab is drawn entirely from the NCM Template. These parameters, which include set points and operation times for heating and cooling plant and hot water demand, are fixed for Part L2 by the room activity, and override the corresponding settings in the room template.

The data on the System tab is drawn entirely from the room template. The system parameters are under your control, and may be adjusted as part of the process for achieving compliance.

The data on the Internal Gains tab is, with one permitted exception, drawn from the NCM Template. Occupancy and equipment gains form part of the standard pattern for the activity. Lighting gains and power consumptions must also follow the pattern laid down for the activity, but here it is permitted to adjust these figures downwards for the actual building if this can be justified on the basis of lighting system efficiency. It is also permitted to implement daylight-linked lighting control by means of formula profiles. This option is described in more detail in the appropriate section of the User Guide.

The data on the Air Exchange tab is drawn partly from the room template and partly from the NCM template. The NCM template stipulates ventilation rates for the activity, and these appear as Auxiliary Ventilation air exchanges, replacing any air exchanges of this type appearing in the room template. Other types of air exchange – those of type Infiltration and Natural Ventilation – are taken from the room template.

By applying these rules, <VE> Compliance automatically sets the attributes that are laid down by the room’s NCM Activity, while giving you control over those aspects where good design can produce energy and carbon savings – namely system performance, infiltration (air-tightness) and ventilation strategies involving the use of outside air for cooling. To this list can be added improvements to the building fabric, and to system characteristics, which of course do not feature in the room template data.

It should be added that wherever the room template is mentioned above, there is (as usual) the option to override the template settings manually in individual rooms or groups of rooms. However, NCM template settings cannot be overridden in this way, except in the special case of lighting gains.

System characteristics for the actual building (which it shares with the real building) are set by means of Apache Systems. A suitable set of systems should be created and assigned to groups of rooms. The ‘UK NCM system data wizard’ facilitates this process and allows the system characteristics to be specified using an iSBEM-like interface.

The notional building

The notional building is derived automatically from the actual building according to rules laid down in the NCM methodology. These rules are set out in full in the official documents and what follows is a summary.

The notional building settings represent standards of construction and system efficiency that are similar to those applying in the Elemental Method of Part L2 (2002).

The location and geometry of the notional building (with the exception of glazing and door area) are copied from those of the actual building:

Glazing in the notional building is modified to conform to standard facade area percentages depending on the building type, and there are particular rules applying to areas of display glazing, doors (of two kinds) and smoke vents.

The notional building is assigned standard constructions for external elements – walls, roofs, floors and glazing. A special rule applies to ground floor constructions. In broad terms the notional building constructions conform to the standards of the 2002 regulations. Where the actual building has spaces that are designated ‘Unheated roof’, ‘Unheated buffer space’ or ‘Glazing cavity’ – indicating spaces that form part of the building envelope rather than the occupied areas – these spaces are absorbed into the elements by which they connect to the occupied areas in the notional building, which are assigned the appropriate standard constructions.

Rooms in the notional building are assigned the same NCM Templates as their counterparts in the actual building, so that the occupancy, gain and plant operation regime in each room conforms to the appropriate NCM Activity.

In the notional building, Space Data that is not covered by the NCM Activity (and which in the actual building is set by means of the Room Template) is also set by the NCM Template, which in respect of these attributes contains the data stipulated in the official notional building definition. In particular, infiltration rates are set in conformance with the Part L2 (2006) standards of air-tightness as interpreted by BRE TM 23.

Three types of systems may be present in the notional building, depending on the type of room conditioning used in the actual building:

Heating and natural ventilation,

Heating and mechanical ventilation, or

Air conditioning

For each type of system, standard efficiency characteristics are laid down in the official notional building definition. In <VE> Compliance, the three types of system appear as Apache Systems named

NCM notional heating + nat vent system

NCM notional heating + mech vent system

NCM notional air conditioning system

Rooms which in the actual building are served by an Apache System of a given type (as indicated by the ‘Cooling mechanism’ setting) are assigned the appropriate NCM notional building system in the notional building.