There are a number of drivers affecting energy performance in modern buildings, some of which impact upon the work of the electrical design engineer, challenging him to produce cost-effective solutions but also presenting new business opportunities. Mike Lawrence, product line team leader - commercial assemblies at Eaton, explains
Principal among the drivers affecting energy performance is the Building Regulations Part L2: Conservation of fuel and power in buildings other than dwellings. This calls for sub-metering so that at least 90% of the estimated annual consumption can be attributed to specific end-use categories.
Some energy metering systems offered by manufacturers are complex and costly. However, the solution does not necessarily have to be so complex. Sometimes it is possible to install a relatively simple, cost-effective system that is future-proofed to allow more advanced automatic metering and trending (AM&T) systems to be introduced later.
Energy Performance Certificates
Since October 2008 an Energy Performance Certificate (EPC) has been required by law for any new building or any building sold or rented. First introduced for domestic premises, the requirement was extended in April 2008 to cover large commercial properties. Then in October it became applicable to all buildings, or parts of buildings, when they are "built, sold or rented". In addition, since October a Display Energy Certificate (DEC) has been required for prominent display in larger public buildings.
The EPC and DEC are among a number of interrelated requirements of the European Energy Performance of Buildings Directive (EPBD).
Energy Performance Certificates must be issued by accredited energy assessors. They will give the property an energy efficiency rating on a scale of A to G, similar to the ratings used for domestic appliances. The assessors will also give recommendations for improvement.
While the requirements for Energy Performance Certificates do not impose any direct requirements for metering, a carefully-planned sub-metering strategy will enable building owners or occupiers to monitor energy usage, identify significant trends and assess the effectiveness of measures taken to implement the energy assessors' recommendations.
Building Regulations L2
The UK Building Regulations Part L2 was also driven by the Energy Performance of Buildings Directive. It is published as two documents, L2A covering new buildings and L2B covering existing buildings.
The key requirements affecting sub-metering are:-
- Energy meters should be installed so that at least 90% of the estimated annual energy consumption of each fuel (electricity, gas, LPG, oil etc.) can be assigned to various end-use categories such as lighting, heating, ventilation, pumps and fans.
- Reasonable provision of energy meters in existing buildings can be achieved by following the recommendations of Cibse Technical Memorandum TM39:Building Energy Metering (A Guide to energy sub-metering in non-domestic buildings.)
- Reasonable provision of energy meters would be to install sub-meters in any building greater than 500m2.
- In buildings with a total useful floor area greater than 1000m2, facilities should be provided for automatic meter reading and data collection.
The objective is to develop a sub-metering strategy so that users can identify areas where improvements can be introduced to achieve energy savings of 5-10% or better.
TM39 is an updated version of Cibse General Information Leaflet 65 (GIL65):Metering energy use in new non-domestic buildings, which can be downloaded free of charge from www.cibse.org/pdfs/GIL065.pdf.
The L2 requirements apply to premises with a floor area greater than 500m2 and existing buildings where "consequential improvements", normally involving Building Regulations approval, are being made. This includes separate buildings on multi-building sites.
Specific recommendations are made for plant and equipment for which separate metering should be provided as follows:-
- Motor control centres feeding pumps and fan loads greater than 10kW
- Boiler installations greater than 50kW
- Chiller installations greater than 20kW
- Electric humidifiers greater than 10kW
- Final electricity distribution boards greater than 50kW
This last recommendation is especially pertinent because the majority of distribution boards are rated higher than 50kW.
There are various approaches to sub-metering. In some cases all metering is provided at the main switchboard. This has the advantage that meters are all in the same location so manual collection of data is easy. However, on some sites MCCB panelboards provide sub-distribution to final distribution boards and to loads such as lifts, ventilation or air-conditioning plant. These will require sub-metering at the panelboard.
Final distribution boards frequently supply more than one type of load (typically lighting and small power). If these loads are metered separately back at the main switchboard or panelboard, it will require separate feeders and probably two distribution boards instead of one. If, however, metering of the grouped loads can be carried out at the distribution board it is possible to use a single feeder.
Different solutions are available at the final distribution board:-
- Custom-built boards incorporating metering. This is generally an expensive solution.
- Separate meter packs installed below, or alongside, standard distribution boards offer a more cost-effective solution.
- Distribution boards with integral metering are now available as standard products.
In each case there are options for a single meter to monitor the entire board, or for split metering to provide separate measurement of grouped lighting and small power loads. These options are available with both Type A (single-phase) and Type B (three-phase) boards. However, it should be noted that in some split metering applications one meter monitors the entire board. This calls for external calculation for one group of MCB-ways.
It is recommended that meters should always include remote reading capabilities. As a minimum this should be a pulsed output offering remote measurement of kWh. A better solution is a Modbus design that provides information via an RS485 connection. With Modbus RS485 communication, information is read directly from the meter and some data registers, such as peak demand, can be re-set remotely. If the meter is connected to an effective energy management system (EMS/BMS), it can deliver a more informative energy monitoring capability. Specifiers and installers do not need to go to the expense of custom-built distribution boards and panelboards to ensure compliance with Building Regulations Part L2. A range of metering solutions is now available for type A and type B boards including add-on meter packs for use with standard distribution boards and distribution boards with integral metering capabilities. The design of these units minimises the amount of on-site work for the contractor and the standardised design allows boards to be sourced through the normal electrical wholesaler network.
Where greater sophistication is required, ethernet connectivity can be used to integrate the sub-metering into a comprehensive energy management architecture for effective monitoring, control and management of the complete energy infrastructure in large sites. Eaton's Power Xpert software allows energy use to be monitored and trends identified so that systems can be optimised to reduce energy costs and achieve a more efficient system.
For further information see www.poweringbusinessworldwide.tv