@Stateless(name = "SessionFacade")
 public   class  SessionFacadeBean  implements  SessionFacade, SessionFacadeLocal {
    @PersistenceContext(unitName = "Model")
     private  EntityManager em;

    @Resource(name = "jdbc/modelDS")
     private  DataSource ds;

....
}

<persistence-unit name="Model">
    <jta-data-source>jdbc/modelDS</jta-data-source>
  </persistence-unit>

<persistence-unit name="Model">
    <jta-data-source>jdbc/modelDS</jta-data-source>
  </persistence-unit>
<persistence-unit name="TestModel">
    <jta-data-source>jdbc/testmodelDS</jta-data-source>
  </persistence-unit>