A developer has filed plans to convert and expand a former Boston Medical Center office building at 615 Albany St. into 24 residential units, through renovation of the existing floors and the addition of one new floor.

Developer Gregory McCarthy is hoping to gain a tax break intended for conversion of office space into residential units - but in downtown, rather than in the South End.

McCarthy bought the building for $3.4 million from the hospital last July, according to Suffolk County Registry of Deeds records. It was once home to the Naval Blood Research Laboratory, which focused on improving preservation and transportation of blood.

His $4-million renovation proposal does not state whether the units will be rented as apartments or sold as condos. Four of the units will be rented or sold as affordable. Overall, The units will range from studios to three-bedroom units.

McCarthy hopes to begin a year of renovation and construction this fall.