Future energy loads
It is important to define, as accurately as possible, the future energy loads that will need to be met by the CHP plant, and by other energy supply plant, both existing and new. The energy demand data need to be subdivided to a high level of detail – preferably down to daily demand profiles: these may differ according to time of the year, day of the week etc. For heat use, the demand must be subdivided according to the different heat load temperatures and other demand conditions, e.g. high or low-pressure steam; pressurised hot water requirement.
The initial feasibility study is unlikely to have been based on sufficiently detailed data, and new measurements may be required, particularly if existing site metering is limited or of dubious accuracy.
Specific data requirements include:
- Electricity demand data. In some instances, the electricity supplier may be able to provide a load profile for a 24-hour period, for a week or even for a whole year. Where this is not an option, electrical current flows can be measured using non-intrusive clamp-on meters linked to a data logger. Where load profiles are derived for a short period only, it is important to recognise that they represent only a snapshot of the current situation at one particular time of year. Careful interpretation is necessary to account for production and non-production periods, variations in production trends, seasonal changes in electricity demand etc., and to generate the appropriate annual, seasonal or daily profiles.
- Heat demand data. Heat loads can be more difficult to assess, particularly steam loads. It may, therefore, be necessary to carry out a detailed survey of heat users, including the type and grade of heat used in each case, and to combine this with hourly or half-hourly readings of boiler fuel or steam/heat meters over a typical 24-hour period. The required heat load values can be derived from, for example, fuel flow rates and system loss calculations. Again, it is important to remember that the measurements taken represent the situation at one particular point of time. As with electricity, careful interpretation is needed to generate appropriate annual, seasonal and daily load profiles.
- Likely future changes in demand. It is important to assess the likely effect of future changes in demand. These will usually be associated with the implementation of energy efficiency measures, the introduction of new production or other facilities, discontinued processes, or changes in operation/organisation. Heat loads, in particular, are likely to be reduced by the future implementation of energy conservation measures or by the introduction of local metering, charge allocation and other incentives for plant operators/energy users.
Consumption data forecasts are needed for the expected lifespan of the potential CHP plant – preferably a minimum of ten years. If demands are forecast to change in the future, then data for each year should be provided wherever possible. The greater the level of detail provided at this stage, the greater the potential accuracy of the subsequent financial evaluation.
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