Ventilation and air conditioning

What is Part L?

Part L of the Building Regulations concerns the conservation of fuel and power and sets maximum CO2 emissions for buildings. It has been updated as part of the government's legal commitment to implement the European Energy Performance of Buildings Directive (EPBD), which requires all buildings to be given an energy rating and new buildings to meet a minimum standard for energy efficiency.

This push to increase the energy efficiency of buildings through modern construction methods and the Building Regulations has produced more airtight structures. The negative effect of this is that without effective ventilation the indoor air quality will deteriorate and building fabric will be affected.

Part L was revised in conjunction with Part F (ventilation). The amendments to Part L are comprised in four approved documents. These came into force in England and Wales on 6 April 2006 and cover the entire design and construction process of all works carried out on new and existing buildings, both dwellings and non-dwellings.

How does it affect you?

Under Part L, ventilation must be provided to give a good level of indoor air quality without affecting the overall energy rating of the building as calculated by the Standard Assessment Procedure (SAP). It applies when systems are being installed and commissioned.

The use of metering, controls and the commissioning of m&e services such as ventilation and air conditioning are now vital in compliance with the Regulations. There is now a five-step procedure:

• the annual CO2 emission rate of the completed building must not exceed the target set. Approved tools to calculate this target are the Simplified Building Energy Model (SBEM) and approved commercial software including TAS and IES;
• the building fabric and fixed services must meet minimum performance ratings;
• passive ventilation methods must be included to prevent buildings or areas without air conditioning from overheating;
• the building should be built as designed to meet the energy performance;
• the building user must be provided with sufficient information to run it efficiently.

There have been significant changes to the definitions of works and exempt works.

How to comply

• In most cases the building control body must be notified of any work before it is started. This is generally not necessary where the work is minor or involves emergency repairs.
• Plans may also not need to be submitted if work is carried out under an approved self-certification scheme. In these cases, the registered competent person must provide a certificate of compliance on completion of the work.
• The scope of existing competent persons schemes has been widened and more operators have been approved. It is not obligatory that work is carried out by an approved competent person, but can reduce time, costs and admin on projects.
• The submission to a building control body must include the target CO2 emission rate calculated by approved software.
• Contractors must provide sufficient detail about the building, its fixed services and maintenance needs to minimise the amount of fuel and power needed for its operation. This can be done through logbooks that follow templates such as the CIBSE TM 31 Building Logbook Toolkit and can refer to the o&m manuals, plus the health and safety file required by the CDM Regulations.

Part L1 - Dwellings

Part L1 (A and B) cover new and existing dwellings. Dwellings are seen as self-contained units, so buildings containing rooms for residential purposes, such as student accommodation, are not seen as dwellings under Part L.

All properties will have a target CO2 emission rate based on standards set through the SAP calculator, the buildings must then achieve an emission rate that equals or is lower than this target.

The main technical changes for existing dwellings involve a general improvement in the performance standards that are considered reasonable for work on thermal elements and ventilation. The standard for replacement windows, roof windows and rooflights remain unchanged.

Where work involves the full or partial addition of a mechanical ventilation system, the system installed must meet Part F. The system chosen should have a specific fan power rating of 0·8 l/sW for continuous supply and extract systems; or 2·0 l/sW for balanced systems. The heat recovery of these systems should be at least 66%.

Fixed air conditioners should have an energy efficiency rating of at least Class C of the labelling scheme adopted under the Energy Information (Household Air Conditioners) Regulations 2005.

Part L2 - Non-Dwellings

Part L2, Approved Documents A and B, cover non-domestic new and existing buildings. They cover the whole of a building, including any parts that have been altered or designed for separate use, such as living accommodation.

Industrial buildings that are using local air conditioners, but are generally of low energy use and are not air conditioned are exempt from Part L.

Air handling plant installed should be efficient and have effective control systems that can ensure the operation uses only reasonable fuel and power. The system should be capable of achieving a specific fan power at 25% of the design flow rate (no greater than that achieved at 100% of design flow rate). A reasonable way to meet the Regulations for ventilation systems rated over 1100 W would be to include variable speed fans in their installation. This would enable commissioning and give flexibility for future changes of use.

In order to limit air leakage, ventilation ductwork should be made and assembled to be reasonably airtight.

For spaces served by air conditioning, it should be shown that provision has been made to minimise solar gains so that the target CO2 emission rate can be met.

Information sources

The Part L approved documents can be viewed online at: http://www.communities. gov.uk/index.asp?id=1164177

The Charted Institution of Building Services Engineers (CIBSE) has launched the Part L Compliance Toolkit. This is aimed at those involved in the design, installation and use of m&e services and gives a simplified source of what is required under the current regulations and standards.

It covers the four Approved Documents introduced under the second tier of Part L on 6 April 2006, and gives guidance on the standard tests on software and the competence of operators. It also explains the long-term impact on the industry of Part L (2006).

The toolkit includes information on:

• AM10 Natural ventilation in non-domestic buildings;
• Commissioning Code M: Commissioning management;
• TM39 Building energy metering;
• TM22 Energy, assessment and reporting methodology;
• TM31 Building logbook toolkit.