Using electricity and heat generated by the same installation is an effective way to increase efficiency in buildings — and also cut costs. In co-generation systems, the fuel, in this case gas, is used to generate electricity using a small gas turbine and the waste heat is used to heat the building and provide hot water.
Wirral Metropolitan College, near Liverpool, is setting a good example in this field. The college has four campuses located around Birkenhead in the Wirral. By the end of the year, it will be using gas to cover most of its Twelve Quays campuses own day-to-day heat and electricity needs.
Reducing dependence on
electricity prices
The sharp increases in electricity and gas prices, in the UK in recent years, make this transition a worthwhile investment for the college. ‘This is a demonstration project which is receiving funding from the local authorities as part of an extremely low energy agenda,’ says George Norrie, Technical Director at Scotia Energy, the project designers and integrators. Wirral Metropolitan College is the first public institution to benefit from a multi-million regeneration programme for the town of Birkenhead, just across the Mersey from Liverpool. Its new Wirral Waters campus is the first building completed as part of the redevelopment.
‘There’s a substantial initial outlay, but in the long term the 12 Quays campus will be able to slash energy consumption, CO2 emissions and costs — we estimate savings of over £55,000 per year after an amortization time of about 6 years,’ says Mr Norrie. This is made possible by co-generation technology, which in this case runs on gas along with thermal heat storage and electrical battery storage. This is much more efficient than, for example, oil or gas boilers.
The initial project assessment also considered using an electric heat pump, but this was decided against, due to the higher cost of generating heat than when using a gas turbine combined heat and power solution. This also provided greater CO2 savings. The college will now draw minimum power from the public grid and will make particularly efficient use of the gas, which it burns in its own installation. This will also reduce the electrical load on the local electrical infrastructure, allowing additional capacity elsewhere. There will also be significant maintenance savings over the costs for the existing heating system.
Combined plant for optimum efficiency
The college, which has around 3000 students, has installed two 65kWe Combined Heat and Power (CHP) Units and thermal and electrical battery storage as elements of a co-generation plant. One CHP unit will supply heat and electricity around the clock, while the other will only run during the day in winter to best match the heating and electrical demand profiles when students are in class and the heat and electrical consumption is at its highest. The phase change thermal and Tesvolt electrical batteries store energy during periods of low demand and supplement the heating and electrical systems when the demand is high.
The college is in use 40 weeks a year from 7am to 11pm. As the amount of electricity and heat generated over the course of a day does not always correspond to the level of demand, a battery storage system and thermal storage system are in place to absorb surplus quantities and re-supply them later on. The thermal storage system takes up heat generated by the first, continuously running unit at night and then supplies it during the day as needed. The electrical battery storage system does the same for surplus electricity.
The two co-generation units also give the project an extra layer of financial security. If one of the machines is unavailable, the other can ensure that the supply is maintained until they are both in operation again.
During the summer holidays in July and August, when electricity and heat requirements are much lower, the college will draw energy from the grid and the co-generation plant will be shut down. The low energy demand over the summer makes this more cost-efficient, and it also reduces maintenance requirements and extends the service life of the installations. Depending on the cost of imported electricity in the future it is possible to run the CHP in electrical mode only, by blowing off the heat and generating electricity during the summer if found attractive.
