2008-05-20
The Building Regulations Part L2 effectively call for sub-metering at any final distribution board in non-domestic premises with a floor area greater than 500 square meters. Ideally, lighting and small power loads supplied from a common board should be metered separately. The Regulations also require automatic meter reading and data collection in buildings with a total floor area greater than 1,000 square meters.
Part L is divided into four documents. L1A and L1B apply to dwellings while L2A and L2B apply to new and existing buildings other than dwellings. The requirements for new and existing buildings are broadly similar although the emphasis is inevitably on ensuring that new buildings are designed to conserve fuel and power.
The requirements – which also apply to fuels such as gas, LPG and oil – are intended to provide a breakdown of energy consumption by different end-use categories – lighting, heating, ventilation, pumps and fans etc. – so that building owners and occupiers can reduce their energy use by 5-10% or more. To achieve this it is suggested that at least 90% of the annual energy consumption for each fuel should be accounted for.
The Regulations call for separate metering for final distribution boards greater than 50kW. Most Type B, three-phase distribution boards are rated 100A or more and would therefore take more than 50kW when fully loaded. So the regulations effectively call for metering at all final distribution boards and even where this is not required, it would be good practice. Furthermore, if a board supplies lighting and small power, these loads should be metered separately.
The Regulations also call for separate metering of motor control centres feeding pumps and fan loads greater than 10kW. Meanwhile individual metering is required for boiler installations greater than 50kW, chiller installations greater than 20kW and electric humidifiers greater than 10kW.
While metering is the normal process for identifying the energy use of different pieces of equipment, L2 does allow for consumption to be calculated by other means, for example, by measuring the run hours of equipment that operates at a known load.
The Regulations also call for the provision of appropriate instructions to enable owners and occupiers to attribute energy consumption to the different end-uses, as part of an overall metering strategy, and compare operating performance with published benchmarks.
Guidance on developing a metering strategy for new buildings is given in General Information Leaflet 65 published by the Government’s Energy Efficiency Best Practice Programme. Guidance is also given in CIBSE Technical Memorandum TM39:Building Energy Metering (a guide to energy sub-metering in non-domestic buildings). This document provides a clear guide to architects, designers and contractors on how to meet the requirements and how to develop a metering strategy for buildings. You can download the document at the bottom of the page.
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