In one aspect, a mass exchanger having an air inlet, air outlet, airflow generator, and a tubular membrane assembly. The tubular membrane assembly includes an inlet header, an outlet header, and a plurality of tubular membranes. The tubular membranes have side walls configured to facilitate mass transfer between air contacting the tubular membranes and working fluid in the tubular membranes. The inlet header includes an inlet header body having inlet header body openings with inlet end portions of the tubular membranes extending in the inlet header body openings and inlet header potting connecting the inlet end portions of the tubular membranes to the header body. The outlet header includes an outlet header body having outlet header body openings with outlet end portions of the tubular membranes extending in the outlet header body openings and outlet header potting connecting the outlet end portions of the tubular membranes to the header body.