It is recognized that not all tenants of public housing will qualify for home ownership. Some who qualify may elect not to purchase units of public housing. Additional public housing will be required in the future to replace the units sold to tenants. To meet the need, the Authority shall develop replacement plans. If necessary, a funding commitment shall be obtained from the U. S. Department of Housing and Urban Development or other source. All funds realized in the sale of public housing units in excess of the costs of the homeownership plans developed and approved pursuant to this chapter shall be committed to the purchase of replacement public housing units.