The amount of any loan made under section 1511(a) of this title with respect to a project described in that section shall not exceed 50 percent of the cost of such project; except that if the loan is made to a person proposing to make application of the resources of the reservoir involved primarily for space heating or cooling or process heat for one or more structures or facilities then existing or under construction, the loan may be in any amount up to 90 per centum of such cost. In any event no loan shall be made in an amount in excess of $3,000,000.