When it comes to improving the efficiency of a heating and hot water system, a mix of technologies working together makes a big difference. Here general manager at SenerTec, Gary Stoddart, looks at how combined heat and power (CHP) is maximising savings and shaping the future of hybrid systems.
Hybrid heating systems – which aim to cut energy costs and carbon emissions by bringing low-carbon technologies together as one solution – are becoming increasingly popular among building services engineers.
A recent poll that we carried out among heating engineers, specifiers and end users1 suggested that demand for hybrid heating solutions is on the rise, as two thirds (66 per cent) of heating professionals seek out a way to respond to the heating and hot water needs of increasingly vast and varied property portfolios. More than a third (37 per cent) of respondents said they were considering hybrid systems, while just under a third (29 per cent) said they’d already had experience with them.
Testament to that is the growth in combined heat and power (CHP) as the core of a hybrid solution. Compared to power produced by CHP, electricity from the grid costs three or four times more than that produced on-site2, 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 per cent. The efficiency of gas power stations in the UK ranges between 49 per cent and 52 per cent, meaning that CHP can be approximately 30 per cent more efficient than traditional heating plant electricity3. 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. But innovators within the industry have begun to experiment, 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 metre-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 – for instance, 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 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 Mini-Dachs CHP engines are controlled in two banks and produce 27.5kW of electricity during the day (16.5kW 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, and the back-up gas boilers have, so far, only been required during the very coldest months.
As a result, the school is extracting maximum electrical efficiency from the system and the combined running hours of the CHP compensate for the high electrical loads from the ground source heat pumps and their 90.5kW borehole. The council has calculated that the school will avoid more than 90 tonnes of CO2 emissions annually and will cut running costs by at least £48,200 a year.
As with any heating system, sizing low-carbon technologies to suit the building is essential. To avoid overheating, CHP won’t run if there is no heat demand, so it is wise to size the system according to the hot water base load, rather than in line with the requirement for electricity.
There is a clear trend for increased investment into hybrid heating and hot water systems, which have been shown to reduce carbon and running costs. This trend is powering innovation in the sector – but as with any sophisticated technology, it’s important to seek expert advice from manufacturers who can help to support throughout the project, ensuring potential savings are realised.
For more information please visit www.senertec.co.uk
