The best data available should be used where there are multiple data sources for a given meter. Care should be taken with invoices (for fiscal meters) to ensure they are based on actual meter readings rather than estimates, and that half hourly data is complete over the reporting/operational period. Manual meter reads taken regularly (say monthly) can be used as a check, particularly on the fiscal meters.
Energy may be supplied indirectly to a facility through on-site bulk storage, such as for biomass, oil or LPG. In this case the supplier's delivery notes do not represent the facility's actual consumption between deliveries. Ideally, there would be a meter downstream of the storage facility to measure energy consumption. Where this does not exist inventory level adjustments between deliveries can be used to supplement the delivered volumes.
If data is missing from the reporting period, a reporting period mathematical model can be created to estimate the missing data. The M&V Plan should establish a maximum rate of data loss and how it will be measured, as well as a methodology to estimate missing or erroneous data. However, baseline data should not be estimated; where data is missing the baseline period may be changed.
A more comprehensive set of guidance on metering strategy is provided in CIBSE TM39 - Building Energy Metering (2009). This provides best practice guidance for energy metering and sub-metering in non-domestic buildings. The objectives of the guidance are to ensure that the metering strategies: > Gather accurate and useful energy consumption data (kWh) > Determine where the energy is used (site, building, tenancy, activity area, etc.) > Provide this information, in a user-friendly format, to whoever needs it, in order to: • manage buildings and improve operational efficiency • isolate 'separable uses' and other items not typically included in energy benchmarks • take account of renewable energy systems by measuring their performance > Document the metering strategy in the building logbook |
The methodology comprises 10 steps: 1. Select the TM39 boundary 2. List all energy imported and exported across the boundary 3. List all energy-using items within the boundary 4. Decide which items should be metered 5. Select appropriate meter for each item 6. Decide location(s) of meter(s) 7. Decide how meters are to be read 8. Review the metering strategy 9. Specify, implement and commission the metering 10. Document the strategy For systems which are not directly metered, then 'CIBSE TM22 - Energy assessment and reporting method' (2006) can be used to help estimate consumption. |