Often it’s not just individual components of a heating and hot-water systems that are important — a combination of products working together can also greatly increase efficiency. Gary Stoddart of SenerTec explains why pairing CHP with other low-carbon technologies can make sound economic and environmental sense.
From ever-tighter Building Regulations and rising efficiency targets to restrictive budgets and time-poor customers, never has there been more pressure to design a low-carbon and cost-effective heating system.
As is often the case, this increasingly challenging environment is the bearer of innovation, with low-carbon technologies at the forefront. Testament to that is the growth in combined heat and power (CHP) as the core of a hybrid solution, where the fuel source is replaced by a low-carbon technology.
Compared to power produced by CHP, electricity from the grid costs three or four times more than that produced on-site(1) and is subject to transmission losses. Not only that, but by using the heat produced during the generation process, CHP plants can reach efficiency ratings in excess of 80%. The efficiency of gas power stations in the UK ranges from 49% and 52%, meaning that CHP can be over 50% more efficient than traditional heating plant electricity (2). To put that into perspective, UK power generators throw away more heat through their cooling towers than the country’s entire demand for gas-fired heating.
This heat can be used in different ways. For instance, in a standard CHP system design, the CHP unit will provide pre-heated water to water heaters via storage or buffer cylinders.
Innovators within the industry have begun to experiment with how this heat can be used; as a result they are achieving new standards in carbon and energy efficiencies.
A perfect example of this innovation is where CHP has been partnered with ground-source heat pumps.
When the heat from the CHP is not needed to produce hot water, it automatically diverts to the ground-source heat pumps, replenishing the 100 m-deep boreholes from which they take their energy.
This ensures a steady supply of heat during times of high heat demand, and means the full CHP array works hard, even at times of low heat demand — such as during the summer. Meanwhile, modulating gas boilers act as back up during the coldest months. Remotely monitoring performance underpins efficient working of the system, ensuring that the boilers don’t kick in too early, which would take the heat demand away from the CHP and the ground-source heat pumps.
This type of system has been pioneered by the project team behind the regeneration of the Notre Dame Primary School in Glasgow. Here, the carbon and energy savings have resulted in the school coming top when compared to the electrical consumption of schools of a similar size owned by Glasgow County Council.
Five of our Mini-Dachs CHP engines are controlled in two banks and produce 27.5 kW of electricity during the day and 16.5 kW at night to satisfy the requirements of the school buildings. Acting as the lead heat source for hot water, the CHP units work in tandem with Ciat ground-source heat pumps. The back-up gas boilers have, so far, only been required during the very coldest months.
As a result, the school is maximising the electrical efficiency of the system, and the combined running hours of the CHP compensate for the high electrical loads from the ground source heat pumps and their 90.5 kW borehole.
Thanks to the combination of CHP and ground-source heat pumps, the council has calculated that the school will avoid more than 90 t of CO2 emissions annually and will cut running costs by at least £48 200 a year.
As with any heating system, correct sizing to suit the building is essential to get the most out of carbon-saving technologies. In a CHP system, savings are made from electricity being produced by CHP using natural gas rather than purchasing electricity from the grid, plus the generation of heat.
However, because the CHP won’t run if there is no heat demand, it is essential to ensure that a system is sized according to the hot-water base load rather than in line with the requirement for electricity.
While the benefits of incorporating CHP into a heating system are clear, as with all sophisticated technology it is worth seeking expert advice to ensure potential energy and carbon savings are realised. In many cases the manufacturer will be able to offer specialist insight and is equipped to support throughout the project — from the initial site visit to the post-installation assessment and final commissioning stage.
Gary Stoddart is general manager at SenerTec.