Sizing a bioenergy boiler
The design load of the boiler must be accurate - it will save you money, time and trouble! It is strongly advisable that only experienced and knowledgeable biofuel staff be appointed to this job.
An inaccurate design load will lead to reduced efficiency, higher emissions and increased fuel use.
It is important not to overspecify the size of the boiler to prevent inefficiency. Although some systems can regulate their range of operation very well, typically during low-load (<25%) there is excessive air and a regular 'on-off' cycling.
The peak load requirement will be needed for a short time (during the coldest part of the year) and the summer load can be very low depending on your requirement. Experience has shown that a biofuel boiler should cover 50-60% of the maximum system load, which translates to approximately 85% of the heating need being supplied by the biofuel boiler (see graph below). A peak load boiler - normally the existing oil/gas boiler, or a renewable source such as solar water heater, covers the extra capacity.
It is also very common in smaller units to manage for variation by storing hot water using an accumulator tank. The volume of storage should be about 40-60 times the boiler heat output in kW.
