Carbon dioxide diffusion in district heating pipes

Measurements on the cell gas composition of old district heating pipes insu lated with carbon dioxide-blown polyurethane foam and still in use, are rep orted. The pipes had been in use for up to more than eight years at the lat est date of measurement. The effective permeability coefficients for carbon dioxide in the district heating pipes at room temperature were calculated to be in the range 1.5 to 5.3.10(-16) mole.m(-1).s(-1).Pa-1. For carbon dio xide, the major part of the resistance to diffusion was found in the polyet hylene casing. The influence of the dimension of the district heating pipe and the temperature of the polyethylene casing is discussed.