Combined heat & power Reaping the benefits of CHP A very effective way of assessing load is by producing a load duration curve
To correctly size CHP, an
organisation must understand for how long a particular demand exists
2. Load
LoadFollowing CHP units have the ability to modulate, or change their output in order to meet fluc- tuating demand. These CHP units can be set up to track either the electrical or thermal demand pro- file. The decision to track thermal or electrical load depends on the heat to power ratio of the site and associated energy costs. When following the electricity demand, the implications of possible heat dumping into the atmosphere via heat trim or heat dump radiators have to be fully analysed.
3. Electricity export
Another way to deal with excess electricity is to export to the
// The author is the sales and marketing director at ENER-G Combined Power Ltd. //
power grid, however this must be carefully evaluated as it can have significantly lower value than elec- tricity consumed on site. Another strategy is to employ multiple CHP units instead of one larger one. Using the former strategy, an operator would set up a series of units to cascade to meet energy demand during times of peak demand. One unit would meet the baseline while smaller plants would provide excess needs.
Load duration curve to size CHP To correctly size a CHP, an organ- isation must understand how long a particular demand exists for. A very effective way of assessing load is by producing a load dura- tion curve. (See diagram above) This load duration curve shows heat load for one year and how two CHP units can be used in con- junction with each other. One 180kWe unit operates for 6,000 hours each year, and the other 90kWe one runs for 5,000. Load duration curves can also be used very effectively to analyse a site’s existing electrical demand.
Since installing a gas-fired ENER-G cogeneration system in April 2012, medical device manufacturer LifeScan has reduced its carbon footprint at its Inverness site by 625 tonnes per year. This is equivalent to the environmental benefit of removing more than 200 cars from the road or of the carbon dioxide sequestered annually by 512 acres of forest. LifeScan Scotland, a Johnson & Johnson-owned company, manufactures blood glucose monitoring devices and the Inverness facility is a key research and development location for the global group. M&E building services consulting engineers Hulley & Kirkwood was commissioned by LifeScan to carry out the initial feasibility study to reduce overall carbon emissions and to cut energy related costs. Following its report, CHP was considered to be the most viable and efficient solution with the greatest carbon saving, and ENER-G was selected to undertake the CHP project.
After analysis and detailed specification, ENER-G designed, manufactured and installed a 230kWe CHP system, which has been integrated with the site’s boiler network system to supply the manufacturing facility with low-temperature hot water, as well as power. The system is fully containerised and includes roof-mounted dry air coolers.
Carbon emissions at the site have reduced by 21 per cent, and electricity consumption is down by more than half (53 per cent), lowering the energy bill by 27 per cent. As a large site, LifeScan is subject to the CRC Energy Efficiency scheme and the CHP system is making a substantial contribution towards its CRC performance. LifeScan recognises the need for regular CHP maintenance and has taken out a fully comprehensive operation and maintenance package with ENER-G. This provides a range of services, including 24-hour remote monitoring, a dedicated site engineer and all inclusive parts and labour required to rectify faults or repairs for the contract term. Following the success of the CHP installation and the high performance and savings achieved, LifeScan took the decision to purchase another CHP unit from ENER-G, which has been installed in the Inverness site’s phase 3 building. Jason Whitley, LifeScan’s facilities senior project engineer, said:
“We are continually seeking ways to raise our environmental performance and this move to on-site generation of power is a key element of our carbon- cutting strategy. We are very pleased to be partnering with ENER- G, which is able to provide us with a total service – from initial design to long-term care of the systems – ensuring our commitment to a sustainable future.
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HVR | July 2014 | 25
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