With a SHHE the air flow both sides should be roughly the same, where as with the condenser the water flow can be significantly less than the airflow. Since your HE has much larger piping for airflow than water I suggest it would be better used as the condenser as it appears to be intended.
The surface are of a 1m PD condenser can simply be worked out from the area of a 15mm copper pipe, ie. .015m *pi so only about 0.05m2 (or about 0.5 ft2) double for a duel PD and about 1.5 times if 22mm used rather than 15mm.