Heating and Ventilating

The environmental and cost benefits derived from combined heat and power (CHP) are dependent on operation and maintenance contracts going beyond just ensuring reliability, suggests Colin Porter
CHP is enjoying something of a renaissance at the moment. However, there are a number of key issues to be addressed when running CHP plant if the benefits are to be maximised. Not least of these is that those responsible for operating and maintaining the plant have a key role to play, so it makes sense to fully harness the specialist expertise available.

CHP can be a significant investment so it is important to maximise plant availability and running hours. Economically, once CHP is running, the incremental benefit of, for example, generating electricity from CHP compared with importing electricity from the grid can be significant - and this focuses the mind on maximising availability of CHP and minimising downtime.

Plant runs reliably
Typically, a CHP maintenance contract will, at a minimum, be designed to ensure the plant runs reliably. It may also have key performance indicators (KPIs) relating to availability of heat and power. However, we believe that a truly comprehensive operation and maintenance agreement needs to go beyond these basic performance parameters.

For example, with CHP there can be long lead times for spares, so the service provider needs a good understanding of which components are most likely to fail and a stock of critical spares to avoid being caught out. In parallel, there are many benefits to deploying a remote monitoring system, along with the ability to re-start the CHP safely from a remote location.

Reliability also depends on security of fuel supply and while most large energy users have expertise in the procurement of fossil fuels, newer fuels such as biomass are less familiar. Therefore, if biomass is being considered it is sensible to work with a service provider that can ensure a consistent and available fuel supply of fuel and assistance with schemes such as the Renewable Heat Incentive (RHI) and Renewable Obligation Certificates (ROCs).

There are also additional measures that can be taken to maximise investment in CHP. These include optimising run-times so the CHP is operating when it delivers the most benefits, such as when the gas and electricity price relationship is above an agreed value. At other times, electricity import tariffs may be low enough to make it more favourable to switch off the CHP and import electricity. This can often be a complex decision requiring consideration of a range of factors.

Electrical and heat loads will also influence the extent to which it is favourable to run the CHP. For example, operators need to consider the amount of heat required in the facility, in order to minimise wasting excess heat - and be aware of any potential impacts on CHPQA assessment. Good quality CHP status retains key advantages, such as Climate Change Levy costs on gas procured for the CHP.

Other important considerations include how much electricity is to be exported (and at what price) and any physical export restrictions on the export capacity; plus the impact on efficiencies of running at less than full power output (influenced by ambient temperatures).

Modified to optimise performance
Plant design can also be modified to optimise performance: including the addition of absorption cooling and/or a thermal store to maximise the operating pattern of the CHP. Furthermore, it's essential this situation is reviewed regularly as heat usage by buildings or processes can vary seasonally, or with changes in use of the facility.

Where there is a fall-off in demand, perhaps due to a reduction in manufacturing capacity or closure of a building, it may be possible to generate income from unused power generation capacity through the Short Term Operating Reserve (STOR). This mechanism by the National Grid to back up shortfall in supply usually requires participants to offer at least 3MW of standby generation or load reduction. However, our company has developed innovative aggregation contracts that enable smaller sites to be grouped together to create a combined load of 3MW.

In addition, if the CHP plant has surplus capacity for all or some of the time, there may be opportunities to export some of the steam, hot water, chilled water or power to nearby organisations via an energy network and generate additional revenue to subsidise the operation of the plant.

We manage various CHP units from gas engines for buildings and energy networks to gas turbines for major industrial users. Each system has a bespoke model to optimise running of the plant that takes account of the bespoke requirements of the end user. In fact, we believe it is the responsibility of the service provider to consider all of the options available and identify opportunities for innovation.

Operated correctly, exploiting specialist technical know-how and experience, CHP can significantly reduce energy costs and environmental impact. The key is to choose the right partner to ensure maximum benefits.

The author is is business manager with Cofely Industrial Energy Services