The Approved Document (AD) Part L has been extensively revised to provide guidance in support of the Building Regulations that came into force in October 2010, and these are firmly aiming sights at ‘zero carbon’ new buildings. The desire, as shown in Figure 1, is that all new homes should be ‘zero carbon’ from 2016, and non-domestic buildings from 2019, with rather less firm ambitions for the existing building stock (even though this probably contributes more than 90% of the real carbon challenge).
Fig. 1 : The expectation for building performance
The principal elements of Part L have not altered but there are some significant developments in how different types of building will be treated, and there is a strengthening of areas such as compliance to ensure that there is less of a gap between buildings as they are designed, and buildings as they are constructed and operated. This article will concentrate on non-domestic buildings and mainly on AD Part L2A – Conservation of fuel and power in new buildings other than dwellings.
The development of AD Part L 2010 has led to changes not just in the expectations for buildings’ thermal performance but also the methods that may be applied to comply with the requirements. As each iteration of the AD is developed, there is a greater emphasis on meeting the requirements based on carbon emissions from buildings, rather than providing a prescriptive set of design attributes. The aim is to achieve an overall national average reduction in CO2 emissions of 25% compared with Part L 2006 standards. However, some building types will be expected to achieve more than this – and others less – with the intention of delivering the national target when applied across the building mix, and of trying to ensure that all new nondomestic buildings achieve the required level of improvement at approximately the same cost of carbon mitigation.
Establishing the benchmark
As with Part L 2006, for each new building a Target CO2 Emission Rate (TER) is evaluated that relates to a minimum acceptable building performance. This number represents the minimum energy performance requirement for a new building where the annual energy use is converted into equivalent emissions of carbon dioxide per year, per square metre of the total useful fl oor area of the building (kg/sq m/year). The National Calculation Methodology (NCM) provides the standard for the TER calculation, and the 2010 revisions are reflected in the Simplified Building Emission Model (SBEM) software as well as in other approved modelling software (as listed at www.ukreg-accreditation.org) that comply with the NCM. Unlike the previous AD (2006), the target emission rate from the building is the notional building emission rate based on a building designed to meet 2010 requirements with standardised fabric thermal performance, usage patterns, plant efficiencies and fuel CO2 emission factors. (And not, as previously, a reduced value based of a building designed under the 2002 regulations).
There are five criteria in Part L (see Figure 2) but only the first criterion is a regulation (the remainder are guidance), and this criterion is the fundamental requirement that the BER must not be greater than the TER. This reliance on guidance is a principle of the AD, which aims to limit prescriptiveness and encourage innovation to meet the requirements (whilst also limiting worst case performance of individual building elements and systems).
One of the most important changes for the evaluation of building performance under the 2010 revision is that there is better discrimination in the categories of building types and activities. SBEM (and compliant modelling software) offers 29 different building types (such as retail, secondary school and launderette) and this is used together with an appropriate choice of one of more than 70 activity areas (such as classroom, laboratory or meeting room) to define the operational characteristics of individual spaces.
The combination of building types and activity are used by the calculation method to define appropriate values of:
- Occupation densities and associated sensible and latent gains
- Heating and cooling set-points
- Set-back temperatures for unoccupied periods
- Lighting standards
- Fresh air ventilation requirements
- Heat gains from equipment
- Humidity requirements
- Hot water requirements.
The application of values more closely describing the actual project will allow the notional building to better represent a benchmark for the building under consideration. When modelling the spaces, the fenestration of the notional building is now categorised as one of three types: side-lit, for use with buildings such as offices; top-lit, for warehouses; and no-lit, for buildings such as performance theatres. They are intended to create a more representative notional building. Improved definition of glazing will assist in evaluating new limits on solar gain per unit area of the façade of a new building, with the intention of limiting the need for air conditioning, or to reduce the required capacity for installed systems. A limiting criterion has been added that applies to any space that is occupied and/or has mechanical cooling where the solar gain (aggregated from April to September) must be evaluated and checked against a benchmark value. This overcomes the anomaly of the previous regulations, where naturally ventilated spaces with high gains would struggle to comply whereas the same spaces with mechanical cooling were exempted. For designers to achieve the greatest flexibility and to encourage innovative applications – including external shading, solar control glass and thermal inertia – an approved Dynamic Simulation Model (DSM) would be needed (in place of SBEM). The freely downloadable NCM modelling guide  provides a useful (and accessible) reference to explore how the detail of the notional building is modelled.
Once the design of the new building is complete, a copy of the predicted Building Emission Rate (BER) must be lodged with the Building Control Body (BCB), along with the specifications that will enable the building to meet the TER. This is to allow the BCB to identify aspects of the design that may materially affect the eventual performance of the building and so allow key attributes to be monitored through the whole project development. Following construction of the building, the as-built BER must now match or exceed the as-designed BER. This would include input from building permeability tests and performance details that have altered during the procurement and construction process. The SBEM software that generates the BER will identify the design features that are critical to achieving compliance. If changes are made to the specifications lodged with the BCB, a list of changes must be handed over with a certificate signed off by a ‘suitably accredited’ energy assessor. Developers have the freedom to vary the specification, so long as the same overall level of CO2 emissions is achieved or bettered. This may be seen as one of the most significant elements of Part L 2010, and looks set to fundamentally change approaches to ‘value engineering’ and alterations to specifications as construction progresses. This is an attempt to ensure that the actual building and its carbon emissions match those presented at the design stage.
The new Non-domestic Building Services Compliance Guide replaces the Non-domestic HVAC Compliance 2007 guide, and the guide now encompasses lighting as well as pumps for heating and cooling systems.
It clearly states that ‘it is important to note that many of these recommended minimum standards will need to be exceeded if the building regulations target carbon dioxide emission rate (TER) for new buildings is to be met’, and so these values should not be used as design ‘rules of thumb’. The values of minimum seasonal efficiencies for heat generating plant have been slightly enhanced (by a few per cent) to take account of expectations of improved operation and biomass boilers are now explicitly included (75% seasonal efficiency compared with 86% for individual gas boilers).
Minimum standards for pumps have been included in this section in recognition of their making up a significant part of the background continuous energy use.
Lighting systems for principal areas in buildings have had minimum efficiency lifted by nearly 20% to 55 luminaire lumens per lamp watt and display lighting must be at a minimum 50% more efficient than the 2006 regulations at 22 luminaire lumens per lamp watt.
Operation and post-occupancy
There has been much discussion as to how well buildings truly perform once they are occupied when compared to the design expectation. Part L requires that ‘effective controls be provided’. This includes controls to ensure that if a building has heating and cooling, they cannot operate simultaneously in a given space with default condition for central plant being ‘off’.
To provide a strong motivation to ensure that buildings perform as expected, commissioning and log books will play an increasingly important role. A commissioning plan should be handed to Building Control at the design stage that may use templates of BSRIA’s Model Commissioning Plan to document the process. On handover of the building, the owner should receive a building log book which contains information about the fixed building services and their maintenance requirements ‘so that the building can be operated in such a manner as to use no more fuel and power than is reasonable in the circumstances’. The log book should also include all the information used to calculate the TER and BER.
Recommendations contained in the Energy Performance Certificate (issued on construction of a new building) must also be included so that the owner is aware of any steps that can be taken to further improve the energy performance of the building. Energy efficiency levels claimed for any fixed building service should have test data certified by a notified body. Part L 2010 documentation states that it is ‘reasonable’ for Building Control to accept this information at ‘face value’.
Metering of energy consumed continues to be a requirement, with a new rule that ‘output of any renewable electrical energy generation system is to be separately monitored’. The methods for monitoring are set out in CIBSE’s TM39: Building Energy Metering 2009.
Fig. 2 : The five criteria for Part L2B Compliance
The elephant in the room
It is widely accepted that if the UK is to meet it’s emissions reduction aspirations, there is a need to address the performance of existing buildings.
Under Part L2B: Existing non-domestic Buildings, the basic principle for existing buildings continues to be that whenever building work is carried out, elements of this work should meet certain minimum standards. There is no CO2 target given, except for very large extensions to existing buildings. However, when carrying out building works, there is a requirement to make additional improvements to the fabric and services of the whole building to improve its energy consumption, and ensure the building complies with Part L.
The factors that trigger these consequential improvements are the same as for Part L 2006. Part L 2010 documentation states that the improvements should be ‘practical and economically feasible’, and sets out examples of these. Potential improvements include upgrading heating, cooling or air handling systems that are more than fifteen years old; or installing energy metering.
The new regulations will provide an incremental improvement on the performance of new buildings, with the aim of reducing carbon emissions by 25% compared with 2006 values. Lessons have been learnt from the experience in applying previous regulations, resulting in a more representative benchmarking procedure whilst enhancing the opportunities for measurable innovation.
By providing greater emphasis on properly informed building commissioning and operation, and through evidencing actual building performance, the actual outcomes may have more chance of meeting the aspirations set in the virtual world of computer models. Time (and practice) will tell if this increment is enough in the quest for 2019 ‘zero carbon’.
© Tim Dwyer
With thanks to Mitsubishi Electric for providing material for this article.