Monitoring & Advisory Systems
To enable the CHP package to operate safely and effectively without supervisory staff, most units are fitted with a monitoring system that checks a range of operating parameters at regular intervals (usually every few minutes). The data collected can be either stored for later review or passed on immediately.
The main purposes of the monitoring system are:
- Plant condition monitoring – to check the reliability and performance of the CHP package, and to assist in planning unit maintenance.
- Plant performance monitoring – to check the inputs and outputs and to monitor the unit’s energy efficiency.
The overall objective of plant monitoring is to ensure regular review of the data collected and use of the information to maximise the cost savings achieved.
An advisory system is an effective tool for providing a rapid review of the energy and flow data collected, and for advising on the optimum operating mode of the unit. The advisory system needs to contain data relating to the costs and values of the energy inputs and outputs, such as the cost of fuel, the avoided cost of purchased electricity, and the avoided costs of providing heat to the site. The system would also contain information relating to the overall maintenance costs of the CHP package, usually expressed as a cost per operating hour or per unit of electrical output. By using this information in conjunction with up-to-date data on the unit’s performance and the site’s energy demands, an advisory system can make recommendations on the most cost-effective mode of operation.
For example:
- At night-time, particularly outside the winter period, the cost of purchasing electricity from external, conventional sources can be quite low. If the sum of the fuel and maintenance costs associated with operating the CHP package exceeds the cost of the alternative option – buying electricity and using fuel to provide heat – it is clearly uneconomical to operate the CHP package.
- If the site heat load falls, and the only way to continue operating the CHP unit is to dump heat, it may be more economical to run the unit at lower output or to shut it down, and to purchase electricity from external sources.
In most cases, the factor having the greatest influence is the cost of purchased electricity from external sources, and this varies from time to time according to the selected tariff. The use of a fixed tariff, where the timing of tariff changes is known in advance, usually enables the advisory system to predict periods when shutting down the CHP unit is the more cost-effective option.
Because the CHP package is usually unmanned, any advisory system should be used in such a way that its recommendations can be promptly reviewed and acted on. Where a site operates some form of Building Energy Management System (BEMS), both the CHP package controls and the advisory system can be installed as components of the BEMS. This allows the CHP package to be controlled in a way that maximises the cost benefits.
In most cases, the CHP package supplier will offer a remote monitoring and advisory service. This is usually based on the use of a telephone line to transmit data between the site and the supplier’s monitoring and control centre. This approach ensures that the condition of the CHP package is effectively monitored and that it is controlled to achieve maximum cost benefits. The system can also be configured to avoid a pattern of frequent stops and starts, as this may be harmful to the equipment.
Other Topics
Previous: Plant Control
Next: Staff Training
