• • • ENERGY EFFICIENCY • • •
How to maximise your CHP efficiency
After installing a containerised gas generator and various combined heat and power (CHP) components, Rotherham Hospital achieved an overall energy efficiency of 90.2% in just 30 days. The system offers a total heat recovery of 1545 kW and is the prime source of heating for the hospital. Scott Tamplin, sales manager for diesel and products at energy and transportation expert Finning UK & Ireland, explains how operators can maximise their CHP efficiency
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onventional electricity generation is inefficient – energy is often lost during transmission, which can make it costly to run solely on energy from the National Grid. Using conventional boilers to heat facilities is also inefficient, because heated gases are released into the atmosphere via the boiler’s flue. In both cases, the costs are eventually passed onto the user in the form of increased energy bills. One solution is generating heat and power on site using a CHP unit. This process involves converting a single unit fuel – often gas – into electricity and heat that can be harvested and reused.
Designing for efficiency Operators can improve CHP efficiency by selecting certain parts and fuels during the design of their CHP package. A reciprocating engine requires little modification, other than alterations to the compression ratio and ignition system to improve performance and reduce emissions. Operators will also need to install recovery units to recapture heat from the combustion system, exhaust, lube system and intercooler.
When selecting a gas fuel, the higher and lower heating values (HHV/LHV) are important considerations. The HHV is the total amount of heat retrieved following combustion, including latent heat stored in the water vapor. The LHV is the amount of heat available after heat of vaporisation and this is deducted from the HHV to determine the maximum amount of recoverable heat. LHV operating efficiencies are higher than HHV, because fewer British Thermal Units (BTUs) are being factored into the efficiency equation.
Therefore, best practice would be that operators choose a gas fuel based on the LHV rather than the HHV.
Operators can improve efficiency further by incorporating power factor correction (PFC) equipment into their electrical systems. PFCs maintain the level of reactive power consumption, minimising waste energy and saving electricity.
Sizing correctly
A common cause of reduced CHP efficiency is incorrect sizing. If the unit is too small, it won’t provide the full cost savings because it cannot generate sufficient power to meet demand. If the unit is too large, it will struggle to meet its minimum load threshold to operate efficiently. The machine will also turn itself off if it falls below certain site parameters.
Operators should size their CHP to meet the base load. Calculating the base load means understanding the specific site heat conditions and completing an economic feasibility study. Any data loggers and measuring equipment must be calibrated in advance and onsite readings should be distributed around the facility. There are several tools available that help operators choose the right generator size, including SpecSizer.
Maintenance and servicing Once a CHP system is installed, operators can maintain performance and efficiency with regular servicing.
Simple issues like a lack of lube can raise engine temperatures, reduce efficiency and increase the risk of machine downtime. More serious problems like the inclusion of non-genuine or counterfeit parts can be dangerous, particularly if the high-pressure unit rejects the components. When devising a maintenance regime, operators can improve efficiency and safety by selecting parts that have been approved by the original equipment manufacturer (OEM). Choosing a
16 ELECTRICAL ENGINEERING • FEBRUARY 2022
robust servicing contract and working with qualified, experienced engineers is also essential. As part of their servicing schedule, operators should also regularly change the generator engine’s oil and assess its various fluids.
Introducing hydrogen
As the energy landscape transitions towards net zero, the role of green hydrogen in the UK’s gas networks is expected to increase — something that will undoubtedly impact gas-powered CHP systems. With Finning and Caterpillar, it is now possible to install CHP systems that run on natural gas and are also capable of operating with up to 25% hydrogen with minor modification. Furthermore, some dedicated products can be configured to operate on up to 100 per cent hydrogen for sites with a dedicated hydrogen infrastructure. With Rotherham Hospital achieving over 90% efficiency in just 30 days, CHP is clearly a beneficial technology. Operators can maximise their returns by regularly maintaining their machines, sizing them appropriately and being selective with parts and fuel.
electricalengineeringmagazine.co.uk
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