Sizing Biomass Boilers
There are many factors to consider when sizing a biomass boiler. Beyond an EPC and property size there are off-peak and peak loads to consider.
Oversizing biomass boilers
Past Government schemes, such as the RHI, have generated an interest in oversizing biomass boilers to earn more subsidy returns and whilst this may not have caused issues for every operator, it could be costing more money than it’s bringing in.
If the heat produced by a biomass boiler cannot be dissipated and the boiler is continually overheating or short cycling (stopping and starting), there will be excessive wear on many of the boiler components.
Excessive heat in the combustion chamber will cause wear and damage to firebricks and refractory bricks as well as seals, fire ropes, grates and de-ashing systems, in some cases, warping and damage to the boiler steel itself.
As well as causing wear and damage, oversizing biomass boilers is also hugely inefficient. A biomass boiler can be likened to a combustion engine, like a car, it’s more efficient running at a steady pace on a motorway compared to the stopping, starting and idling in cities. The most inefficient process in the heating cycle of a biomass boiler is ignition, so if your boiler is turning on and off many times an hour you’ll experience energy use with lower efficiency.
Our experts optimise biomass boiler plants across the UK
Undersizing biomass boilers
Understanding peak and off-peak loads is vital to correctly sizing a biomass boiler. In some cases the boiler is used for process heat, so the peak load may be quite constant, however it’s more common that heating systems have variable heat demands, meaning the boiler will have peak load times where it’s working very hard and off-peak times where its not.
An undersized biomass boiler can’t meet demand, so will run continuously without breaks, reducing the life span of the boiler and its components.
It’s worth noting that modern, quality biomass boilers can modulate their heat output meaning that they can run at a lower heat output when demand is low or run at full capacity when heat demand is high.
How can you tell if your biomass boiler has been undersized?
If a biomass boiler is undersized, i.e the heat demand i greater than the boiler can provide, then you will have excessive operating hours but a cold property or lack of heat for a process.
How do you fix an undersized system?
Cascading
Adding a boiler to your system (cascading), allows boilers to share duty when heat demand is low and work together during high demand periods to produce the heat required.
Buffer stores
Buffer stores are an ideal solution for applications where there is a large peak load, e.g hotels, where there is a very high demand for water in the morning and evening, but for a short amount of time. Adding or increasing the capacity of buffer stores allows for heat to be produced over a longer period of time and stored ready to meet demand. If you had a 120kW boiler with buffer tanks, you could meet a 150kW peak load demand, the buffers allow the 120kW boiler to produce a large volume of heat during times of low demand and store this in anticipation of high demand times.
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