Exploiting the benefits of biomass boilers
The wood pellets shown here deliver at least five times more heat per cubic metre than wood chips — but are unlikely to be locally sourced.
Most boiler suppliers and manufacturers offer a biomass option — but what is driving the demand for biomass, and how can you ensure a successful installation? Ian Bradley has some pointers.As the Inter-Governmental Panel on Climate Change releases its latest report and Gordon Brown turns green, it would appear that the subjects of global warming and carbon emissions are once again at the top of everyone’s agenda — both in the realms of politics and building services. One of the noticeable effects of this trend has been the increased specification of biomass boilers and heating systems. So what are the drivers behind the installation of biomass? Reduction targets
The primary driver in the UK is the attempt to meet the Government’s target of a 60% reduction in carbon-dioxide emissions by 2050. Alongside that target, the EU target of a 20% reduction by 2020 is also having an effect. A recent report by Ernst & Young suggests that the 20% reduction is certainly economically achievable and that as much as 50% reduction is technically achievable. However, the present Government is talking about an 80% reduction. Faced with that prospect along with the Code for Sustainable Homes and the revised Building Regulations, more and more specifiers and engineers are turning to sustainable and renewable heating systems —particularly in the public sector. But why biomass? That is an interesting question. In the realm of public procurement, biomass is certainly seen as a key plank in the fight against global warming, climate change and carbon-dioxide emissions. Although heat pumps are used for space heating, solar systems generally aren’t, so biomass once again comes to the fore. Reports show that after capital costs are taken in to consideration, biomass is approximately a third of the cost of oil and two-thirds the cost of natural gas. Also, after energy conservation measures, biomass heating is the cheapest way to reduce energy bills and reduce carbon emissions. Amongst farmers, country estates and rural businesses, where access to wood is relatively easy, there is a definitely an aspirational AGA-style factor — where a ‘showing-off’ to neighbours and friends comes into play. Pitfalls to avoid
So what do you need to keep in mind when installing a biomass system, and what are some of the pitfalls that need to be avoided? The first thing to think about is objective behind the installation. Is a biomass boiler being installed to meet targets for reducing carbon-dioxide emissions, is it part of a fuel cost reduction strategy or is it to help with the planning process? The answer to those questions will help set the scene for the next part of the planning process, and that is looking at what is actually required from the system. Design issues include the peak heat loss and the physical distribution, including the number of buildings to be served and their location. A fuel strategy should also be devised, with, perhaps, biomass meeting the base load and fossil fuel to provide support for peak load and standby. The next part of the process — and vital to the correct specification of a biomass system — is space and access for the biomass boiler plant. This is not simply a matter of working out where to put a boiler but also where and how the fuel will be stored. If the wood fuel is to be delivered by truck, access and how the fuel will be delivered must be considered. For example, pellets can be blown into a hopper, whereas wood chips need to be tipped from a truck. Both methods present challenges for the specifier and architect — which links neatly on to the issue of fuel supply. Suppliers
Unlike gas or oil there are very few nationwide suppliers of wood fuel. Fuel is usually sourced locally, so a supplier needs to be found at the design stage to ensure that the right type of boiler, hopper and delivery facilities are in place. Where the project is new build, this process will certainly be a simpler than for a retrofit. Biomass tends to be better suited to new build, as the design constraints are more easily dealt with, and space issues for fuel storage and delivery can be less of a problem. There are obviously cost and availability decisions to be made at this point, and working in partnership with a fuel supplier will ensure the continuity of both fuel quality and supply. So what type of fuel is best? Fuels
Wood chip costs about 1 to 3 p/kWh and is suited to applications from 10 kW to 5MW. It has a relatively low energy density (600 kW/m3) but can be used with an automatic feed for 24-hour operation. In large-scale applications, it is certainly the most economic fuel type — but the set-up for receiving deliveries is vital. Local authorities can convert council wood waste into chips. Wood pellets are about twice the price of chips, but have a much higher energy density — about 3450 kW/m3. They can be transported across great distances and be delivered by blower. That said, they are expensive and are unlikely to be locally sourced, so the additional carbon cost will need to be part of any green calculation. As with wood chips, quality is critical to a successful system. What of the future of biomass boilers? The technology is certainly proven and mature. It is well established across continental Europe, Scandinavia and Canada and offers the opportunity for substantial reductions in carbon emissions. Biomass boilers often enable planning mandates to be met more cheaply and their overall economics are better than fossil fuel in many cases — so biomass is certain to be a major strand in the UK’s drive for developing the use of renewable-energy sources. Ian Bradley is managing director of MHS Boilers.