Fundamentals of Part L2 2021
New Part L2 regulations came into force in England on June 15th 2022 (29th March 2023 for Wales) and apply to non-domestic buildings beginning construction after this date. 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)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 View, where the special conditions required for NCM analyses are not applied.
The testing of carbon emissions constitutes regulations 24, 25, 25B, 26, 26C, 27 and 27C of Part L2 as follows:
- Regulation 24 requires the Secretary of State to approve a methodology of calculation of the energy performance of a building. Approved tools for implementing this methodology for new non-domestic buildings are the Simplified Building Energy Model or other software tools approved under the Notice of Approval. Calculation methodologies are set out in Section 1 and Section 2 of the approved document.
- Regulation 25 requires the Secretary of State to approve minimum energy performance requirements. These requirements are in the form of a target primary energy rate and a target emission rate. The targets are set out in Section 1 of this approved document.
- Regulation 25B. The Secretary of State considers that a building has a very high performance rate for the purposes of the definition of a nearly zero-energy building if both of the following are met.
- The building meets the target emission rate required under regulation 26.
- Both: i. An analysis is made of the technical, environmental and economic feasibility of using high efficiency alternative systems, which include decentralised energy supply systems based on energy from renewable sources.
ii. This analysis is considered as required by regulation 25A.
- Regulations 26 and 26C. A newly constructed building must be shown to meet regulations 26 and 26C by producing calculations to show that the building meets both of the following.
- Target primary energy rate.
- Target emission rate.
Section 2 of this approved document sets out how to produce these calculations.
- Regulations 27 and 27C.Both before and after a newly constructed building is built, a notice must be given to the building control body of the calculations.
This testing is also subject to:
- Consideration of high efficiency systems: as schedule L2 and section 3 (Regulation 25A) the feasibility of high-efficiency alternative systems must be considered for new buildings including systems include renewable energy, CHP, district heating/cooling and heat pumps);
- Constraints on U values : as schedule 1(a) and section 4 (table 4.1) minimum U-values must be met;
- Constraints on system performance : as schedule L1(b) and section 5, 6 including Boilers, Heaters, CHP, Water heaters, Comfort cooling, Circulators & pumps, Mechanical ventilation (SFP), Heat recovery, Lighting, Lighting controls, Building controls, On-site electricity generation & storage, District heat networks & community heating
- Limits on solar gains: for residential elements this is covered by Approved doc O (4.16), for non-residential elements by 4.17, 4.18;
- Commissioning as section 8 (not covered by VE Compliance);
- Providing certain information as section 9 (not covered by VE Compliance).
Users of the VE Compliance software are strongly advised to study the official documents defining the regulations.