Fundamentals of Part L2 2010

The Part L2 (2010) regulations came into force in England on October 1^st 2010 and apply to non-domestic buildings beginning construction after this date (Note April 6^th 2014 onwards should be assessed under the Part L2 (2013) regulations available in VE). The regulations require designers to demonstrate further reductions in carbon emissions from building energy use relative to the standards set by the previous editions 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 the standards defined in the National Calculation Methodology (NCM) Modelling Guide (for buildings other than dwellings in England) 2010 Edition ^[3]. The Notional Building is subject to the same occupancy and plant operation patterns as the actual building.

The analysis of carbon emissions must be performed with accredited software applying the National Calculation Methodology (NCM), implemented in a DSM method such as ApacheSim or BRE’s SBEM program (driven by either the native iSBEM interface or a proprietary interface such as VE-SBEM).

The Actual Building’s performance must 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.

It should be remembered that Part L2 places the requirement for standard occupancy and plant operating conditions on a model. 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 the Apache application, where the special conditions required for NCM analyses are not applied.  In VE Compliance the Real Building is used to create the Actual Building by defining NCM Building Type, Room Types and Activities so that the NCM Template data can be assigned automatically.

 

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

·       Criterion 1 – Achieving the Target Emission Rate (TER).

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

·       Criterion 3 – Limiting the effects of heat gains in summer: this imposes limitations on solar gains but is not in itself evidence that the internal environment of the building will be satisfactory.

·       Criterion 4 – Building Performance consistent with the BER: Quality of construction and commissioning: this lays down requirements that the building must meet after construction. (Not covered by VE Compliance.).

·       Criterion 5 – Providing for energy efficient operation of the building: 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 application. This covers a range of regulations for England, Wales, Northern Ireland, Scotland and Republic of Ireland as applied to both dwellings and non-dwellings.

The starting point for a compliance analysis is the input of geometrical data in ModelIT. The Building Template Manager, a central resource available from all VE applications, is typically used next to set up room system parameters. 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 Building Template Manager provides facilities for setting room conditions for a range of thermal applications. In the context of UK Compliance ratings, it also allows the specification of room activities that define the standard occupancy and plant operation conditions that apply in NCM procedures. In compliance tests these standard conditions automatically override certain of the Space Data settings that would otherwise be taken from the Room Thermal Template.

The Apache application covers thermal applications such as heating and cooling load calculations, and calculation outside the context of ratings. The analysis in this application 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 The Apache module or VE Compliance but for VE-SBEM users it is advised to perform all model setup within VE Compliance. Examples of such shared data include:

·       Constructions

   But for VE-SBEM the following can only be entered in VE Compliance:

·       Location

·       Apache Systems (HVAC)

·       Renewables

 

VE Compliance covers thermal analysis specific to UK ratings analysis (Building Regulations compliance and EPCs).  Some of the data required by ratings is shared with The Apache application, as indicated above, and may be entered or edited in either application. Other ratings-specific data must be entered in the VE Compliance application interface. This includes:

·       Regulatory framework – e.g. Part L2 (2010) (assumed in the list that follows)

·       Building type

·       Room activities (may be specified by means of templates)

·       Data relating to lighting and lighting control

·       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

 

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

The Real Building is the building that you see in the ModelIT and Apache applications. 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 UK ratings analysis. In the Apache application it forms the basis for the analysis of heating and cooling loads and simulations and can be used for analyses beyond the Part L ratings e.g. for thermal comfort assessments.

The Actual Building is the building as designed, but subject to standard patterns of occupancy and plant operation for UK ratings as defined in NCM. The actual building is the building displayed by default in VE Compliance. It has the same geometry and construction as the real building but its activity settings (occupancy, internal gains, heating and cooling set points, hot water consumption rates and minimum ventilation rates) and plant operation conditions are assigned standard settings in VE Compliance as a function of the NCM activities assigned to its rooms. It is also subject to rules governing the calculation of infiltration and auxiliary energy. Aspects of the actual building that are shared with the real building may be edited, it is recommended this is done in the VE Compliance application interface.

The Notional Building is a version of the actual building 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.

Under the SBEM method the notional building for VE-SBEM cannot be viewed in VE Compliance as it is created internally by the BRE SBEM tool.

Users interested in compliance testing only are not obliged to consider the real building as an entity distinct from the actual building. They can thus bypass The Apache application. 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 allows you control over the following aspects of the design, which it shares with the real building.

Data shared between real building and actual building:

·       Location

·       Geometry (including orientation and glazing)

·       Constructions

·       Most system characteristics, including renewables

 

The actual building differs from the real building in terms of its occupancy and plant operation, which for the purpose of UK ratings analysis 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 illuminance levels (these, however, are subject to some flexibility, as well as options on control)

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

·       Minimum ventilation rates

For the purpose of UK ratings analysis, this data (with the exception of certain lighting characteristics) is outside your control and cannot be edited. Note that these attributes are present in the Room Template for review, but the settings appearing there are overridden in the ratings 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: Office (Office: Open)’. 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.

Note: SBEM applies its own NCM Data during calculations but this NCM Data is from the same database as the NCM Thermal Templates used in ApacheSim DSM analyses and is based on the NCM Room Activity assigned.

 

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 Thermal 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 Space Data.

 

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

 

·       System characteristics

 

The Space Data displayed and used in VE Compliance is thus drawn partly from the NCM Template, partly from the Room Thermal Template and partly from user-supplied data, as follows.

 

The data on the Building Regs tab is entirely supplied by the user, with the exception of the NCM Template specifying the NCM activity (which the user may override by unticking the Template checkbox).

 

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 ratings analysis by the room activity, and override the corresponding settings in the room thermal template.

 

The data on the System tab is initially drawn from the room thermal template which can be useful for assigning the HVAC, Auxiliary Vent and DHW systems but all other data will usually be input using Tabular Space Data for each room (or set of rooms).

 

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 system characteristics, which of course do not feature in the room thermal template data.

 

It should be added that wherever the room thermal template is mentioned above, there is (as always) 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 and so the interface makes these inputs inactive to indicate this to the user.

 

System characteristics for the actual building are set by means of Apache Systems, which for SBEM analysis has a modified interface with elements in common with iSBEM. A suitable set of systems should be created and assigned to groups of rooms.

 

The notional building, and the reference building which features in the EPC analysis, are 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 will not be described in detail here. Their derivation is carried out within SBEM.