Long-Term Monitoring
Performance monitoring is a key function of modern control systems. It can be used for several purposes:
- To detect potential faults, malfunctions etc. at the earliest possible stage so that they can be promptly rectified or prevented.
- To monitor operating conditions and facilitate the planning of maintenance activities.
- To calculate the cost savings achieved.
- To monitor data for CHPQA certification needed for CCL exemption.
Optimisation takes the monitoring and control of the CHP system one step further, and seeks to maximise the economic benefits, by repeated calculation of the costs and benefits of operating the CHP unit. This can be carried out on-line, using continuously updated real-time data, or off-line, using a download or snapshot of data or manual data input.
The logic for carrying out this procedure is not complicated. However, the value of the outputs from a CHP package can change over short periods of time (for example, with changes in site energy demand), making frequent reassessment of the costs and benefits essential. Some of the values are set by external factors. The avoided cost of buying electricity is the main factor affecting the achievable cost savings, and CHP electricity produced during low-cost periods under time of day and seasonal tariffs has less value. At certain times, it may be better to shut down the CHP package, buy electricity from outside sources and provide heat from alternative sources. This is often the preferred option at night, given current night-time electricity tariffs.
When CHP energy is supplied under an energy supply contract, some contractors offer two-tier billing as an incentive for longer and more cost-effective operation. In two-tier billing, a lower rate is enjoyed when more than a certain volume of energy in a given period has been used.
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