  Most modern HVAC systems suffer from two intrinsic problems. First, inability
to meet diverse comfort requirements of the occupants. Second, heat or cool an
entire zone even when the zone is only partially occupied. Both issues can be
mitigated by using personal comfort systems (PCS) which bridge the comfort gap
between what is provided by a central HVAC system and the personal preferences
of the occupants. In recent work, we have proposed and deployed such a system,
called SPOT.
  We address the question, "How should an existing HVAC system modify its
operation to benefit the availability of PCS like SPOT?" For example, energy
consumption could be reduced during sparse occupancy by choosing appropriate
thermal set backs, with the PCS providing the additional offset in thermal
comfort required for each occupant. Our control strategy based on Model
Predictive Control (MPC), employs a bi-linear thermal model, and has two
time-scales to accommodate the physical constraints that limit certain
components of the central HVAC system from frequently changing their set
points.
  We compare the energy consumption and comfort offered by our SPOT-aware HVAC
system with that of a state-of-the-art MPC-based central HVAC system in
multiple settings including different room layouts and partial deployment of
PCS. Numerical evaluations show that our system obtains, in average, 45% (15%)
savings in energy in summer (winter), compared with the benchmark system for
the case of homogeneous comfort requirements. For heterogeneous comfort
requirements, we observe 51% (29%) improvement in comfort in summer (winter) in
addition to significant savings in energy.
