That would become the target of a second, larger borrowing: Moody’s estimates “up to $150 million of potential additional new debt,” which would bring total new financing, at near record-low interest rates, to more than twice the size of Longwood’s last major initiative, the $90 million renovation, replacement, and expansion of hundreds of fountains in the space between the main conservatory building and the Chimes Tower at the southern end of the property.