Citizens Bank has closed an $18 million low-income housing tax credit construction loan for Trinity Northampton Phase Two LP.

The loan will be used to renovate 102 apartments in Harrison Tower, a 12-story building at 860 Harrison Ave. in Boston’s South End neighborhood.

The affordable housing units will include 11 apartments rented to residents at 30 percent of the area’s median income, 69 units for residents at 60 percent of the median income and 22 units for residents at 70 percent of median income.

Originally a dormitory for the Boston City Hospital School of Nursing, the building is located across from Boston Medical Center on the corner of Massachusetts and Harrison avenues.

“Citizens recognizes the crucial need for affordable housing in Greater Boston,” Eva Erlich, senior project manager for developer Trinity Financial Inc., said in a statement. “The Citizens team has been a great partner and has provided critical construction financing for the Harrison Tower development, which will allow dozens of Massachusetts families to live in safe, attractive and affordable housing.”

Trinity Financial Inc. was formed in 1987 by co-founders James Keefe and Patrick Lee.

In mid-2013, Citizens announced a five-year, $1 billion commitment to funding affordable housing and community development projects.

“In a year and a half, we are already more than halfway toward achieving our $1 billion goal and are pleased to be working with leaders in the communities we serve to provide funding for crucial affordable housing projects,” Reza Aghamirzadeh, executive vice president and community development director at Citizens Bank, said in a statement. “The importance of affordable housing in our communities cannot be overstated. Our $1 billion commitment to affordable housing complements the bank’s charitable program, Citizens Helping Citizens, which addresses the key areas of hunger, economic development, financial education and volunteerism as well as housing.”