The structure of the unit is critical and determines the amount of thermal and acoustic insulation achieved. Thermal insulation is vital to the efficiency of the unit and is required to prevent thermal bridges: these cause condensation to build on the surface of the casing and can damage both the house and the unit itself.
The thermal insulation inside the unit determines the acoustic comfort of the inhabitants. This is very important for a unit designed to work 24 hours a day, 7 days a week.
The unit structure can be made from metal sheet with insulating mat; double sheet panelling with insulating material on the inside (normally EPS, polystyrene, fibreglass or polyurethane foam); self-supporting EPP (expanded polypropylene); or from coated sheet EPP.
The sheet structure is inexpensive and easily made, but it has very limited thermal and acoustic insulation. This system also suffers from unavoidable thermal bridges and so is not used in any high quality products.
The double panelled structure guarantees good thermal and acoustic insulation. Furthermore, it is solid, it does not need investment, and the inside is easily cleaned. However, localised thermal bridges are unavoidable, especially where the external and internal sheets are in contact with each other.
Additionally, the air flow is not well ducted like in EPP structures and this causes strong turbulence, inefficiencies and added noise.
Over time, the collection and discharge of condensation causes issues, because condensation builds on the metal walls and the sheet interstices, dripping outside the unit. This moisture compromises the insulation between the panels and can lead to the growth of mould. Furthermore, because the insulating materials are not visible inside the panels if, during the production process, some filling problems occur, it will compromise the quality and create thermal bridges. Being air-tight is always critical, in particular referring to the seal life.
The EPP (expanded polypropylene) self-supporting structure guarantees good thermal and acoustic insulation, without external thermal bridges (unless the connections between the fittings of the distribution network's piping are poorly made).
Normally this type of structure is designed to improve the internal air-flow, reduce turbulence and ensure that the collection and discharge of condensation, as well as the air tightness, are optimal. Unfortunately, to obtain a self-supporting structure, in particular for larger units, the EPP density must be very high during the entire production process. This greatly reduces the thermal and acoustic insulation.
The EPP structure with coated sheet guarantees the best thermal and acoustic insulation as it has the advantages of both the coated sheet and EPP types.
The external supporting structure is made of coated sheet, for strength and ease of installation, while the internal components in contact with the two air flows are made solely of EPP. Furthermore, with this casing the internal airflow is superior, reducing turbulence.
Compared to the EPP self-supporting structure it is moulded with the ideal density maximising the thermal and acoustic insulation.