District heating pipes are usually polyurethane-(PUR)-insulated and the outside is protected by a polyethylene (HDPE) casing. The permeability of the cell gases (oxygen, nitrogen, carbon dioxide and cyclopentane) in the PUR foam and in the HDPE casing was determined for a temperature range of 20–60 C (PUR) and 5–40 C (HDPE).
From the results, it was concluded that the casing acts as the main diffusion barrier for carbon dioxide, oxygen and nitrogen, whereas the main diffusion barrier for diffusion of cyclopentane is due to the PUR foam. This conclusion is valid for district heating pipes of small to medium dimensions.
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