Residential Trash Compactor

Household packaging waste takes up far more volume than its mass warrants. With limited storage space in a kitchen, that volume is what forces people to take the bin out — frequently, and long before the bin is actually full of anything.

The project set out to develop a bin capable of compressing plastic waste at a ratio of 3:1. Requirements were gathered and weighted, and the one that came out on top was price — the target was a product that could retail under 4,500 DKK. Every subsequent decision was made against that constraint.

The work ran under Aalborg University's Problem Based Learning model, with input from students and from Nordværk, the regional waste management company, to frame the problem against how waste is actually handled.

Rather than assume a compaction force, the group ran an experiment to determine the pressure actually required to compress household plastic waste to the target ratio. That measurement — not a guess — became the input that sized the motors, the gearing and the structure.

Existing products on the market were surveyed, the complications of compressing mixed waste were analysed, and concepts were generated through function/means trees and a morphological chart before a design was chosen against the weighted requirements.

Hitting the price target meant treating manufacturing as part of the design. The group contacted manufacturers for quotes on the specially designed parts and on casting moulds for in-house production of sub-components, built a bill of materials for the standard parts, and calculated production time and cost for the finished product.

The calculations show the compactor delivers the 10 kPa required to compress waste at 3:1, and the finite element analyses — validated by convergence studies — show it does so without critical failure.

The final production cost came out at 822.11 DKK, comfortably inside the 4,500 DKK retail target that had been the highest-weighted requirement in the specification.