When a building is operated with night set-back, it
is not necessary to condition the building until the last
person leaves in the evening. But the system must be
restarted in the morning so that optimum conditions are
reached before the beginning of the business day. It is
not difficult to determine an appropriate time to let the
system begin to drift in the afternoon, but morning
warm-up (or cool-down) can require substantial time
and energy.