All original certificates of competency may be renewed and all renewed certificates of competency may be renewed by the air conditioning air distribution board before the dates of their expiration. Such renewal certificates shall be granted without a reexamination upon the written application of the certificate holder filed with the board and showing that the certificate holder’s purposes and condition remain unchanged unless it is made to appear by affidavit before the board that the certificate holder is no longer competent or entitled to such renewal certificate, in which event the renewal certificate shall not be granted until the applicant has undergone the examination required by section 18-2307.