Modular heating/cooling coil design and coil flow connector

A modular heat exchanger system comprising at least a primary heat exchanger having two parallel manifolds with a chosen plurality of heat exchange tubes running therebetween, the manifolds defining a liquid pathway therein within which baffles are provided to produce a serpentine path through the manifolds and heat exchange tubes of the exchanger, one of the manifolds being an intake manifold and the other being a return manifold having a terminal return chamber, the chamber feeding into a return tube extending through the manifold and exiting the opposite end thereof, the tube being of smaller diameter than the manifold and creating an annular channel therearound through which liquid flowing through the exchanger is routed, said return chamber having a closable open end and the system further including a secondary heat exchanger having two parallel manifolds with a chosen plurality of heat exchange tubes running therebetween, the manifolds defining a liquid pathway therein within which baffles are provided to produce a serpentine path through the manifolds and heat exchange tubes of the exchanger, one of the manifolds being an intake manifold and the other being a return manifold having a closable open ended terminal return chamber, the chamber feeding into a return tube extending through the manifold and exiting the opposite end thereof, the tube being of smaller diameter than the manifold and creating an annular channel therearound through which liquid flowing through the exchanger is routed, and an intake chamber at the opposite end of the manifold which is joined to the return chamber of the primary exchanger, in a manner where, upon blocking access between the return tube and return chamber of the primary exchanger, liquid from the return chamber of the primary exchanger flows into the intake chamber of the secondary exchanger, with access between the return chamber and return tube in the primary exchanger being blocked by a spool shaped flow connector comprising a small diameter tube having two end flanges, one of which seats within the return chamber of the primary exchanger and lies against the baffle defining the chamber and the other end of which rests within the intake chamber of the secondary exchanger and seats against the baffle defining same.