Data from several oven installations shows that the energy usage varies from 0.404 kWh/kg of baked biscuits to 0.492 kWh/kg of baked biscuits. The energy requirement for baking varies with the product. The energy loss depends on the quality of design and construction of the oven.
The energy used by the oven is predominantly from gas or oil fuel. Electricity is rarely used for baking now, due to its high cost. In a gas/oil fired oven the fuel represents around 95-96% of the total energy usage and electricity (for powering the drive, fans and other electrical systems) about 4-5%.
The energy input to the oven is used primarily to bake the biscuit, to achieve the structure, reduce the moisture content by evaporation and to colour the biscuit. Each type of biscuit requires a certain amount of energy to achieve a good quality result.
In addition to the energy required to bake a good product, energy is lost in several ways:
- By extraction of moist air from each oven zone
- By heat loss through the insulation and outer covers of the oven
- By the return circuit of the oven band
- By heat loss from the flues from a heater module or heat exchanger in an Indirect Fired oven
- By hot air escaping from the oven delivery end
The following is a calculation of heat loss from an actual oven installation (Indirect Radiant oven baking a rotary moulded biscuits)
For product 678.4 kWh 56 %
Heat loss from extraction 220.0 18 %
Heat loss from burner flues 93.1 7 %
Heat loss from return band 87.8 7 %
Est. heat loss of air from oven end 71.0 6 %
Est. loss from thro’ metal, fans etc. 30.0 3%
Heat loss through insulation 20.1 2 %
Heat loss from radiation at oven end 17.0 1 %
Total 1217 kWh 100.0%
The overall oven efficiency is approximately 56%
Of the heat loss through the burner flues, up to 50% can be recovered and used for baking in a Heat Recovery System