Why Part L is no longer good value

Is Part L, the bit of building regulations which deals with energy and power, really delivering good value for the construction industry? In this context value doesn’t just equate to cost - though clearly Part L has financial consequences - but more to ensuring a broad public confidence in the buildings we build doing what we say they do.

Part L Conservation of Fuel and Power, is the foundation of UK sustainability regulation. It’s the minimum standard for new build, the reference standard for building refurbishment, the benchmark for planning carbon policy and the “cornerstone” for BREEAM Excellent and Outstanding ratings.  It’s oft quoted though understood by a relative few practitioners.

To start its worthwhile understanding what Part L “is” and in this context I mean Criterion 1 of Part L2A.  It’s a carbon emissions calculation methodology. The results then allow you to bench mark and compare regulated carbon emissions between new buildings and compare your actual building to the required Part L standard.

Regulated carbon emissions include emissions from lighting, auxiliary equipment (fans and pumps), heating, cooling and hot water. Equipment plugged into the smaller power network, process loads, lifts and computers are excluded.  Furthermore to allow a fair comparison between buildings, occupancy profiles are standardised so it doesn’t consider the real occupancy of the building.

The origins of the Part L calculation as a simplified energy modelling tool didn’t envisage its current day use

With this simple introduction it’s evident that a Part L calculation will not provide a realistic indication of a building’s true energy consumption as it doesn’t consider all the energy uses and it’s unlikely a user will mirror the standard occupancy profile (see CIBSE TM 54: 2013 evaluating operational energy performance of buildings at the design stage for more details).

If we understand that Part L simply calculates the carbon emissions for a new building’s regulated load, does it do this accurately and fairly? Let’s examine a few of the anomalies:

• It’s a one off calculation based on current data.  No cognisance is made of the building’s operational carbon or energy use over its lifespan. In theory grid electricity carbon content will reduce to around 50g/kWh in 2030, currently the figure is 517g/kWh. This will lead to completely different technical solutions to those promoted today.
• Energy associated with LTHW and CHW pumping is modelled as a fixed figure. While small adjustments can be made for pump control (3 options are available) if the building has 1 or 1,000 pumps it makes no difference to calculation.
• A heat network with a remote energy centre containing a gas fired combined heat and power (CHP) plant is modelled using a different methodology than a building containing the same technical solution in a local plant room. An efficient CHP plant in a building with a large heat demand will result in a much better result than the same building served with the same CHP plant from a heat network.
• Heat network connections normally ignore the significant pump energy used to distribute the hot water round the network to the building.
• Lighting is assessed by how efficiently it is supplied not how much you use. So if you lower the lighting level in a space it will not make an equivalent improvement in Part L.    

The origins of the Part L calculation as a simplified energy modelling tool didn’t envisage its current day use nor the need to demonstrate continued carbon improvement. As we progress to zero carbon buildings or more immediately address the GLA planning policy target of a 40% improvement in Part L 2010 we need a more precise, flexible  methodology with the ability to take a longer term view.

David Bownass is sustainability director at WSP