Last month's revisions to Part L of the Building Regulations – for both dwellings and non-dwellings – will have a profound effect on heating and air-conditioning specification. The Chartered Institution of Building Services Engineers outlines the key changes

Heating and hot water systems

  • Commissioning of heating and hot water systems is being introduced for dwellings. A certificate of commissioning must be issued by the holder of a "recognised qualification".
  • Controls There are new requirements for zone and timing controls and boiler control interlocks. Habitable rooms must be independently controlled, and separate timing controls are required for space heating and water heating systems. Controls should ensure that the boiler only fires when there is demand for heat. Hot water systems incorporating storage vessels should meet the relevant British Standard for insulation and size of heat exchanger, as well as the Waterheater Manufacturers' Association 1999 performance requirements for thermal stores.
  • Instructions These now have to be provided on the operation and routine maintenance of the systems. The information should go to the building owner-occupier.


Carbon performance ratings
Although designers do not have to justify the selection of air-conditioning under Part L, they do have to meet certain standards of performance. Table 11 in Part L2 gives maximum allowable values for the carbon performance ratings in new and existing buildings for air conditioning and mechanical ventilation (ACMV).

For substantial alterations of existing systems, the values in Table 11 or an improvement of at least 10% must be achieved. For replacement systems, the benchmarks in CIBSE TM22: Energy Assessment and Reporting Methodology may be used if designers do not use the formula specified in the Part L document.

Fan power for air-conditioning
For buildings other than offices, the energy used to power the fan must be less than 2 W/litre/second for new systems and less than 3 W/litre/second for systems in refurbished building, or for substantial alterations to an existing system.

Commissioning and testing
A report, including a commissioning plan and confirmation that performance test results meet the approved designs, should be provided by a suitably qualified person, to demonstrate that the work complies with Part L.

Building log book
There is now a requirement for a log book giving details of the installed building services plant and controls, their method of operation and maintenance and details that enable energy consumption to be monitored and controlled.