The issuing officials are hereby authorized to provide, by resolution, for the issuance of refunding bonds for the purpose of refunding any bonds issued under the provisions of this act and then outstanding, either by voluntary exchange with the holders of such outstanding bonds, or to provide funds to redeem and retire such outstanding bonds with accrued interest and any premium payable thereon, at maturity or at any call date. The issuance of such refunding bonds, the maturities and other details thereof, the rights of the holders thereof, and the duties of the issuing officials in respect to the same shall be governed by the foregoing provisions of this act insofar as the same may be applicable. Refunding bonds may be issued by the issuing officials to refund bonds originally issued or to refund bonds previously issued for refunding purposes. The proceeds of the sale of any refunding bonds shall be paid to the State Treasurer and applied to the payment of the principal of, and the accrued interest and premium, if any, on the bonds for the refunding of which such refunding bonds shall have been issued. Notwithstanding the foregoing provisions of this section 12, no refunding bonds shall be issued unless the principal amount thereof plus the interest cost thereon to maturity, as determined by the issuing officials in accordance with accepted financial practice, shall be less than the sum of the principal amount of the bonds to be refunded, plus the interest cost thereon to maturity determined as aforesaid.