Green Retrofits Act This bill reauthorizes a Department of Housing and Urban Development (HUD) water and energy conservation demonstration program through FY2027. Prior to its FY2019 expiration, the program allowed HUD to execute agreements with specified entities to reduce utility costs through improvements at multifamily subsidized housing projects. The reauthorization makes a number of changes to the original program, including increasing the cap on eligible residential units from 20,000 to 35,000 and extending the cap on agreement terms from 12 to 15 years. The bill also creates a green retrofit program that allows HUD to provide grants or loans to owners of multifamily subsidized housing projects. The grants or loans must be used to perform in-home health and green retrofits to the property.