Best practice guidelines for integrating Combined Heat and Power (CHP)

There are a number of benefits of integrating combined heat and power (CHP) with existing site systems. Efficiency can be maximised by fully exploiting the waste heat from electricity generation and the payback period is determined by CHP running time and utility rates. CHP capacity must be matched to site demand to be economically viable and to deliver financial returns.

Below, we take a look at some of the best practice guidelines you should follow when integrating your combined heat and power (CHP) with local sites and applications.

Determine the correct size for your system

CHP is sized to meet base-level demand - the constant demand for heat and electricity when the site is operational. Intermittent excess demand for heat is met by conventional boilers, while excess demand for electricity is met by power from the grid.

To size a system accurately, the current energy profile must be calculated to determine base and peak demand levels. With a Building Energy Management System (BEMS), this is relatively straightforward. Records of heating, cooling and electricity usage over a year will indicate base and peak demand. Without a BEMS, utility bills are a good starting point, but half-hourly meter readings are preferable. Regular reading of meters will provide additional data. A further option is short-term monitoring – installing temporary metering to measure the data over a designated period, from which the load profiles can be estimated.

Weather also influences the need for heating. The collected data will show real demand for specific dates, but not long-term averages for that day of the year. ‘Degree Days’ are based on mean observations and are used to adjust the data to produce normalised estimates for consumption for each day. These are used to calculate expected base-level and peak demand. By having this information to hand, you will be able to correctly size your CHP system and deliver maximum uptime for your customers.

Investigate and establish economic viability

The Carbon Trust estimates that ‘4,500 hours of high and constant heat demand is needed to make CHP economical.’ This is an average of 12.3 hours every day or 86.5 hours for a 5-day week

In summer, heating may not be required, but rejecting heat to the atmosphere wastes money. An absorption chiller connected to the system can use CHP waste heat to produce chilled water for cooling and air conditioning systems (trigeneration). If trigeneration is being considered, normalised data for cooling demand must also be included in the base level calculations.

For economically marginal cases, other factors can influence the decision to invest in CHP. Excess electricity exported to the grid generates revenue and taxes can be reduced by adopting low-carbon energy sources. CHP can be part of an emergency electricity supply, helping to reduce capital expenditure and high running cost by using dedicated standby generators. CHP can also meet planning requirements for inclusion of renewable and low-carbon energy sources when developing a site.

Integrate your existing systems

To successfully integrate a CHP system with your existing on-site equipment, you need to understand how existing heating and cooling equipment can work alongside CHP. You should also align this knowledge with your targets and establish why you are connecting your CHP with local sites and applications.

• For integration with existing boilers, CHP is connected in series before the boilers to preheat water. At base-level demand, no further heating is required
• For replacement heating solutions, CHP is placed in parallel with one or more boilers. It is the lead source for the system and meets base-level demand
• For integration with existing chilled-water cooling, an absorption chiller is connected into the chilled water circuit
• For electricity, CHP is integrated with existing supplies as the primary source. Excess demand is met by the grid connection. The electricity supply required (e.g. 3-phase low voltage) must be included in the CHP specification.
• To export surplus electricity, a Distributed Generation Connection is required. This is arranged with the CHP supplier and local electricity distribution network operator. To sell electricity requires membership of a Feed-in Tariff (FIT) scheme for renewables or a Power Purchase Agreement (PPA) with an electricity supplier.

Once the system is specified, physical integration must be considered through a site survey. Equipment housing, access and security requirements will need evaluation alongside environmental factors such as generator noise.

Minimise disruption and downtime

Careful planning reduces disruption. For existing heating and cooling circuits, much of the CHP installation can be completed without interrupting supply. Electrical connections will also involve some limited supply interruption.

Meanwhile, support and maintenance services are critical to maximising CHP efficiency and reliability. A good supplier proactively minimises unplanned downtime through:

• Automatic monitoring to detect potential problems before they occur
• Remote management to optimise performance
• Responsive engineering teams for maintenance and fault resolution

Conclusion

Integrating CHP with your existing on-site applications doesn’t need to be difficult. By following these best practice guidelines, you will be able to maximise energy efficiency and create a greater return on investment. Once the CHP plant has been integrated, you should monitor usage and measure consumption, as well as reevaluate the base load requirement from time-to-time. This will help you to give the best service to your customers.

Takeaways

• Base-level demand and sizing must be considered to assess economic viability and decide if installing CHP is appropriate.
• Careful installation planning can minimise the disruption involved.
• Proactive support, maintenance and management minimises unplanned downtime.