Off-the shelf solutions

By Mike Lawrence, product line team leader – Commercial Assemblies, Eaton

Electrical wholesalers can offer solutions to many modern requirements for energy sub-metering in buildings with standard catalogue distribution boards and panelboards that include integral metering. This represents added value for the wholesaler and contractor and can deliver a more appropriate solution than metering in the main switchboard.

Understanding the requirements
The UK Building Regulations Part L2: Conservation of fuel and power in buildings other than dwellings, calls for the installation of energy meters so that 90 per cent of the estimated annual energy consumption of each fuel can be assigned to different end-use categories such as lighting, heating, ventilation, pumps and fans. The object is to develop a submetering strategy so that users can identify areas where improvements can be introduced. It is hoped that this will lead to energy savings of at least 5-10 per cent.

The requirements apply to all new buildings with a floor area greater than 500m2, and existing buildings where ‘consequential improvements’ (normally those involving building control approval) are being made. In buildings with a total useful floor area greater than 1000m2 facilities should be provided for automatic meter reading and data collection. As a minimum, the meters used should be capable of communicating kWh information to an external surveillance system.

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. Certificates must be issued by accredited energy assessors who will give the property an energy efficiency rating on a scale of A to G. They will also make recommendations for improvement.

In addition, since October, a Display Energy Certificate (DEC) has been required for larger public buildings. This must be displayed at all times in a prominent place so that members of the public can see the energy efficiency of the building.

Energy Performance Certification does not place any direct requirement for metering but a carefully planned 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.

Landlords’ metering for billing purposes is covered by the Measuring Instruments Directive (MID), which came into effect in October 2006. This is a Europewide standard which has replaced OFGEM approval of meters in the UK (Meters approved by OFGEM before November 2006 can still be manufactured and verified until 2016.) Only meters used for legal transactions need to be MID certified and therefore MID certification has no relevance to compliance with part L2 of the building regulations. MIDcompliant instruments will provide similar standards of accuracy at lower cost where legal transactions are not involved.

According to Part L2, 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 submetering in non-domestic buildings.) This 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.

Metering solutions
There are various approaches to sub-metering. In some cases all metering is provided at the main switchboard. This has the advantage that manual collection of data is easy. However installation of meters in the switchboard can add significantly to the installation cost. Furthermore, each metered load will require a separate feed whereas metering at the final distribution boards means that one supply cable can feed two or more metered loads.

On some sites, MCCB panelboards provide subdistribution to final distribution boards and to loads such as lifts, ventilation or air-conditioning plant. This will require submetering at the panelboard. Bolt-on metering chambers and associated meter packs that can be used to monitor specific loads, are available for panelboards.

Final distribution boards frequently supply more than one type of load (typically lighting and small power). If these loads are metered at the main switchboard or panelboard, it will require separate feeders and probably two distribution boards instead of one.

A variety of solutions is available for metering at the final distribution board:-
• Custom-built boards incorporating metering: This is generally an expensive option.
• Separate meter packs: These are used in conjunction with standard distribution boards and offer a more cost-effective solution available through the wholesaler.
• Distribution boards with integral metering: These are now available as standard products offering a neat and cost-effective solution, also available through the wholesaler.

In each case there are options for a single meter to monitor the entire board, or for split metering to provide separate monitoring of grouped lighting and small power loads. These options are available with both Type A (single-phase) and Type B (three-phase) boards.

It should be born in mind that in some split metering applications, one meter measures one group of MCBways while the second measures the entire board. This calls for external calculation for the second group of MCB-ways. However, better solutions are now available to provide true net readings of the separate grouped loads.

It is recommended that meters always include remote reading capabilities even if these are not put to immediate use. 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 connection, information can be collected directly from the meter. 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 provide a more informative energy monitoring capability.

Eaton solutions
Eaton offers a range of submetering solutions including metering chambers with rapid installation wiring looms for installation alongside its panelboards; separate meterpacks for installation with standard distribution boards; and distribution boards with integral meters for single or three-phase applications.

For single-phase applications the company offers a 12-way metered board, with a preinstalled meter, and an 8+4 way board with a dual-channel meter for separate measurement of grouped power and lighting loads. It also offers a separate meterpack for installation alongside standard Type A distribution boards.

For three-phase applications, Eaton has a number of meterpacks for installation with distribution boards. These include a double meterpack for installation below two boards. This allows a single feeder to supply both boards, via a 125/160A rotary disconnect switch and separate meters. These elements are all pre-installed.

The latest additions to Eaton’s range of sub-metering solutions are 200A smart power and lighting Type B distribution boards which provide separate metering of lighting and power loads. Suitable for both three-phase and single-phase applications, they employ a special smart summing meter which gives true net measurement of grouped power and lighting loads, plus a total for the board, without external calculation.

The new Eaton boards come in four sizes offering from 10 to 24 TP&N ways while a single phasing adapter allows them to be used as 30-72 way singlephase boards. Each size is offered with two meter options – pulsed output or Modbus RS485 communication – and both types can display other parameters such as voltage, current, power factor and maximum demand. They have four earth bars and accessory kits to allow various high integrity earth and functional clean earth configurations to be accommodated.