A credit union may borrow money from any source in an aggregate amount not to exceed 50 percent of the paid-in and unimpaired capital and surplus of the credit union. Loans from the National Credit Union Central Liquidity Facility (12 U.S.C. Sec. 1795 et seq.) shall not be included in computing the aggregate borrowings of a credit union. For the purposes of this division, “certificate for funds” means borrowed money.