Pipework and other components should be insulated after the safety pressure test, but usually before prolonged running of the plant, since it is very difficult to remove water and frost once it has formed. Only the low-pressure piping is insulated, where it does not form part of the evaporator, i. e. after the expansion valve, where this may be outside the cooled space, and from the evaporator back to the compressor.
Insulants for pipework and curved pressure vessels can be obtained ready shaped, so that they fit tightly to the surface. All surfaces should be quite dry before the material is applied, even if the adhesive is a water-based emulsion, and the water or other solvent must be given ample time to dry or set before any outer wrapping is applied.
Any air spaces within the insulation should be avoided, since this air will contain moisture, which will condense and freeze, leading to early deterioration of the insulant.
The essential part of the insulation system is the vapour barrier, which must be complete and continuous over the outer (warm) surface.
The application of insulating materials is a specialist trade and justifies careful supervision and inspection.
Much use is made of flexible foamed plastic material, which can be obtained in tubular form for piping up to 114 mm diameter and in flat sheets of various thicknesses for tailoring onto other shapes. This material has a vapour-tight outer skin, but must be sealed at all joins and the ends. The manufacturers are helpful in advising users.
Posted in Refrigeration and Air Conditioning