Mass balance is used to check that the input and output values for your LCA model are balanced, and it is required for EPD verification.
To manufacture the final packaged product, you need to have at least enough raw materials that go into the product and its packaging, and there may also be ancillary materials and waste that need to be accounted for.
It is always good practice to check the mass balance after data collection is done and before you start modelling to ensure there are no gaps or anomalies in the data.
For a simple mass balance of the product stage (A1-A3), the following should be included:
1) Raw materials in
2) Ancillary materials in
3) Packaging materials in
1) Packaged product
2) Waste material
A more complex study could often involve other life cycle stages too, which means that mass balance is more complex as it includes more inputs and more outputs. For example, along with the A1-A3 raw materials (product stage), also inputs and outputs from other stages shall be accounted for, like A4-A5 (installation stage) and B1-B7 (use stage).
For Business license users and above, in One Click LCA software the Mass balance is calculated based on the Mass/unit inputs.
How to use the Mass/unit field?
Datapoints for materials in mass units (‘kg’ …) should have 1 in the mass/unit field.
Datapoints for processes (hot rolling, drilling…) should have 0 in the mass/unit field.
Datapoint for balancing biogenic carbon emissions, should have 0 in the mass/unit field.
If the unit of the data points is in any other unit other than kg, e.g., unit or m3, the mass/unit should be converted to kg and the reference value in kg should be used. The density of the product can be used to calculate the product in m3, for example.
In the case of wood pallets, the weight of 1 unit of pallet is approximately 29.62kg, so that is reference value, as shown below:
If you have both +A1 and +A2 data points declared, please make sure that only one set of data points is declared for mass balance, the other should remain 0, otherwise the software will double count it.
Similarly for construction groups, the mass/unit for the group should be 0, and the mass/unit assigned to the individual constituents of the group.
When you open the Results, you can see the details of how the mass balance is calculated:
The attached example automatic excel calculator can be edited to facilitate your data collection process, or for EPD verification if necessary.