Individual heating and cooling systems with
setback controls and DDC shall have optimum
start controls. The control algorithm shall, as a
minimum, be a function of the difference
between space temperature and occupied setpoint,
the outdoor temperature, and the amount
of time prior to scheduled occupancy. Mass
radiant floor slab systems shall incorporate
floor temperature into the optimum start algorithm.
[ASHRAE 90.1:6.4.3.3.3]