MITIE has given the University of Bristol a lesson or two in economics as well as ecology with its new CHP plants.

The University of Bristol has always been ahead of its time. Founded in 1876, it was the first higher education institution in England to admit women on an equal basis to men, and the first to employ a female lecturer.

So it comes as no surprise that, when looking for ways to generate power at its main campus, the university decided to install environmentally friendly combined heat and power (CHP) plant to reduce its carbon footprint.

What may cause some eyebrow raising, however, is the fact that the installation is set to reduce CO2 emissions by 1500 tonnes and save around £300 000 a year.

With CHP units, heat and power (electricity) are generated in a single process. The heat is used for a variety of purposes including water and space heating. Using CHP, electricity can be generated at a lower cost than it can be purchased and CO2 emissions are reduced by more than 30% in comparison with separate generation from power stations and boilers.

The University of Bristol was deemed a good candidate for CHP as it has a high power consumption with several buildings requiring year-round heat. In addition, the university has its own HV ring main with a base electrical load at around 3 MW.

MITIE was employed on a design and build basis to install the units, based on an outline scheme by consultant PB Power.

The university had previously relied on low pressure hot water (LPHW) systems. The CHP installations now feed into these systems, giving the client a heating supply as well. Electrically, the CHP units produce less power than the base load and therefore reduce the power taken from the grid.

The first unit is powered by an eight-cylinder 30-litre gas-fired engine which produces 500 kW of power fed through to the main switchboard of one of the faculties. This provides 500 kW of heat towards the year-round heating requirements for this building. The second unit is powered by a 60-litre V16 gas-fired engine and produces 1160 kW of power and 1500 kW of heat. This CHP unit is connected to the university’s district heating system serving four boiler rooms. In each boiler room, a heat exchanger transfers the heat to the heating system in their respective buildings. In total, both units will generate around 1.6 MW of electricity for the campus.

Spatial constraints proved an issue for MITIE, as the units were installed in operational buildings, with research potentially taking place 24 hours a day. Interfacing the new systems with the existing installations also proved challenging. In both cases, however, the new CHP units were installed in plant rooms recently refitted by MITIE, which was beneficial to the smooth running of the project. John Beardsley, director at MITIE’s engineering division, explains: “The project involved installation work in existing plant areas, passing through occupied and operational buildings. Our knowledge of the campus infrastructure, along with our relationships with the university faculties and staff enabled the project to be completed with a minimum of disruption.”

So is CHP really such hot news for today’s environmentally conscious installations? Martin Wiles, the university’s energy and environmental manager, certainly thinks so: “This is the start of a significant programme of CHP installations at the university,” he says. “With more legislation like the Carbon Reduction Commitment soon to come into force, programmes like this are instrumental in helping to address climate change.”

A CHP off the old block

What is CHP?

Combined heat and power (CHP) is the simultaneous generation of usable heat and power (usually electricity) in a single process.

In its simplest form, it employs a gas turbine and an engine or a steam turbine to drive an alternator to produce electricity, which can be used either wholly or partially on site. The heat produced during power generation is recovered, usually in a heat recovery boiler, and can be used to raise steam for a number of industrial processes, provide hot water, or for space heating.

Because CHP systems make extensive use of the heat produced during the electricity generation process, they can achieve overall efficiencies in excess of 70% at the point of use. The efficiency of conventional coal-fired and gas-fired power stations is typically around 38% and 48% respectively. Efficiency at the point of use is lower still.

What are the pros?

Cost savings vary, but can be between 15% and 40% compared with imported electricity and on-site boilers.
CHP could also provide the largest single contribution to reducing carbon dioxide emissions. Savings in primary energy of 25% or more can be made.

CHP systems can be designed to continue to operate and serve essential loads during an interruption to mains power supplies. They can also supply higher-quality power than the grid, which can be important for projects such as computer data centres.

And the cons?

The payback on investment in CHP is typically more than five years.

Also, CHP is not suitable for every installation. For example, to be cost effective, the system ideally needs to run for a minimum of 4500 hours a year.

What is the government’s CHP target?

The current target for CHP is 10 000 MW by 2010, which remains a key element of the government’s revised Climate Change Programme.

Source

Electrical and Mechanical Contractor