Biomass meets natural gas

Published:  05 May, 2011

The most cost-effective reductions in carbon-dioxide emissions form biomass boilers is best achieved by supporting them with condensing boilers. Chris Miles and Stefan Gautsch explain why they are the perfect partnership.

The latest announcement on Renewable Heat Incentive (RHI) has given the green light to businesses and private investors seeking more fuel-efficient heating solutions. The impact of the RHI, together with other key CO2-saving initiatives such as the CRC Energy Efficiency Scheme, will revolutionise the take-up of renewable technologies, and the market for biomass boilers looks set to grow considerably in the next five years.

Indeed, with the Government providing its support for businesses and investors looking to reduce carbon emissions, the take-up of renewable solutions is now expected to soar — with the number of industrial, commercial and public sector installations estimated to increase sevenfold by 2020.

Whilst biomass technologies are still relatively new to the UK in comparison to Europe, the role biomass boilers have to play in preparing for a future with reduced fossil-fuel supplies is increasingly important. In the past, it has perhaps been all too easy to take advantage of the rich supplies of coal, oil and gas we have access to in this country.

However, times are changing and with the UK’s natural gas resources predicted to decline massively over the next 30 years, the need for heating solutions that use less energy and emit less CO2 has risen on the agenda. This is especially the case for commercial applications, where organ­isations are responsible for generating heat on a much larger scale and have carbon footprints to manage in line with Government guidelines.

From the viewpoints of fuel security and carbon reduction alone, biomass already makes perfect sense. Compared to most fossil fuels, wood fuel is a competitive source of energy. When used for heating, biomass is the cheapest form of renewable energy there is on a commercial scale. It is also particularly suitable for use in urban fringe areas, where natural gas may be unavailable and reliance on LPG and oil remains high, unless wood fuel is introduced.

At present, two of the primary markets for biomass in the UK include rural estates with forestry and public-sector work, whereby new and retrofit heating-system installations are directly linked to CO2 reduction. The new-build sector is also having a major influence on the market for biomass and other renewable technologies right now as builders progressively have to meet increasingly high levels of the Code for Sustainable Homes.

From an installation point of view, almost all the commercial biomass boilers Econergy [Chris Miles’s company] supplies are fitted in conjunction with Buderus fossil-fuel boilers and sophisticated controls, which enable the two technologies to work efficiently together. Because of the load profile of any demand, 80 to 90% of a building’s heat requirement can typically be met with a biomass boiler sized at 50 to 70% of the peak-load requirement. The lower capital cost of fossil-fuel boilers per kW of output makes them ideally suited for meeting back-up and peak-load demand. This approach gives maximum CO2-emissions reduction per unit of installed cost.

Biomass boilers typically tend to be installed to provide base load for a building. A condensing or standard-efficiency boiler will then be integrated into the heating system to provide back-up for the biomass boiler — the fossil fuel boiler being capable of topping-up what the biomass boiler is not sized to deliver.

This is particularly the case in scenarios where 100% of the building load may only be required for two or three days a year and perhaps 90% of the building load required for five days of the year. As there are few days when the building load is very high and biomass boilers are more costly to install, doubling the size of a biomass boiler to cover a few days of high demand would not be a very cost-effective solution.

Buderus, Econergy, renewable energy, biomass boiler
A biomass boiler in the boilerhouse at Birchen Coppice Middle School in Bromsgrove is supported by condensing boilers.

If an installation were sized for peak demand, a much bigger boiler and buffer tank or multiple biomass boilers would be required for the system to work efficiently, resulting in an unnecessarily high installed cost. In certain scenarios, it therefore makes sense to install a suitable back-up boiler which can easily handle peak-load requirements.

Condensing boilers are a good option to work alongside biomass installations. They have a very high turndown ratio so they can operate for long periods of time at part-load, where their primary function is to back up the biomass boiler from day to day.

Condensing boilers in general are highly efficient and also have very low emissions. This is particularly important when it comes to obtaining planning permission for buildings, as to achieve a good BREEAM rating a building has to have a good source of renewable energy for heating.

Biomass boilers meet BREEAM criteria, but back-up boilers also need to meet minimum requirements for efficiency and NOx emissions. From an investment point of view, condensing boilers strengthen the biomass package. This type of system in its entirety will usually tick all the boxes required to gain a good BREEAM rating and planning permission.

Whilst condensing boilers are a good partner for biomass boilers, non-condensing oil and LPG boilers are just as suitable — especially for installation in remote locations where there may be no access to network gas. Whichever boilers are chosen in a back-up capacity, it is important to make sure they are entirely compatible with the associated biomass boiler.

Specifying the correct controls to link the two technologies is essential to ensure compatibility. Whatever control system is specified, we would always recommend the biomass boiler takes the lead and the back-up boiler is the secondary heating source. It is also important to ensure the buffer tank for the biomass boiler is properly controlled.

With initiatives like the RHI and CRC Energy Efficiency Scheme making renewable technologies a lot more attractive and necessary proposition on a commercial scale, we can expect to see biomass boilers (with the back-up of condensing boilers) gradually becoming more mainstream in the UK. Certainly, designing systems that feature both technologies is a good way to help investors take the next step toward fuel independence, whilst providing peace of mind for a customer base that perhaps is not quite used to biomass technology yet — but will be before too long.

Chris Miles is managing director of Econergy, one of the UK’s leading suppliers of complete biomass heating solutions.

Stefan Gautsch is design engineer for Buderus, part of Bosch Thermotechnology.



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