Condensing the bonuses of using greener boilers
All boilers for biofuel are now technically advanced. Superior in environmental performance, they are able to almost entirely substitute heating systems based on fossil fuel energy.
Through their ability to offer automatic control and their adaptation to computers, they mainly operate like conventional heating systems.
Condensing liquid biofuel boilers, proven since 2000, have two distinct heat exchangers.
The first is a newly developed seven pass steel design; the second is a high-grade plastic tubular arrangement.
The flue gases leave the seven pass design at temperatures lower than 90 deg C and are extracted from the tubular arrangement at temperatures below 50 deg C.
The introduction of outside combustion air through the plastic tubular exchanger lowers the flue gas temperature below dew-point, meaning there is no need for return heating system water temperature to be lower than 50 deg C.
In a B100 biofuel R-Series condensing boiler, the B100 biofuel is kept at temperatures just above freezing in an external or bunded vessel, then piped to a pre-heat tank within the R Series boiler, from which it passes to the burner.
B100 biofuel is developed from organic material and burns with the same maximum condensing efficiency as fuel oil and natural gas. Condensing B100 biofuel boilers achieve 92-97 per cent GCV efficiency.
About 12 litres of air is needed for each litre of B100 biodiesel, so the volume of hot flue gases represents a substantial use of energy.
This is partly in the form of sensible heat due to the elevated temperature of the gases, and partly as latent heat in the water vapour.
R Series condensing boilers are designed to recover much of the heat in the flue gases and consequently operate at much higher efficiencies.
If the flue gases are cooled down to their dew point, which is 50 deg C for B100, much of the latent heat, as well as the sensible heat, can be recovered.
The R Series boiler, designed to operate permanently in the condensing mode, uses corrosion-resistant plastic materials for all of the condensing heat exchange and contains limestone granules to treat the acidic condensate before safe disposal.
One litre of B100 biofuel is equivalent to 8.4 kWh. For a year-round condensing boiler, there is an output of 7.75 kWh per litre - rising to 8.1 kWh in mid-winter.
In the typical London weather pattern, the biofuel R Series boiler may be used to meet the base load throughout the year. A second fossil fuel boiler will meet the extra demand of the peak winter months.
Additionally, both boilers can have dual fuel B100 and fossil fuel capability to give an in-built standby facility. Each boiler has its own header with in-built four-port valve and shunt pump. This guarantees minimum water flow and temperature control.
Single and group boilers can use a balancing and sedimentation vessel or a low-velocity header as a neutral heat outlet. Any number of circuits, in order of priority, can then be served from the boilers.
Harry Howard is technical director at Atlantic Boilers
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