  It has been shown that the heating, ventilation, and air conditioning (HVAC)
systems of commercial buildings can offer ancillary services to power systems
without loss of comfort. In this paper, we propose a new control framework for
reliable scheduling and provision of frequency reserves by aggregations of
commercial buildings. The framework incorporates energy-constrained frequency
signals, which are adopted by several transmission system operators for loads
and storage devices. We use a hierarchical approach with three levels: (i)
reserve capacities are allocated among buildings (e.g., on a daily basis) using
techniques from robust optimization, (ii) a robust model predictive controller
optimizes the HVAC system consumption typically every 30 minutes, and (iii) a
feedback controller adjusts the consumption to provide reserves in real time.
We demonstrate how the framework can be used to estimate the reserve capacities
in simulations with typical Swiss office buildings and different reserve
product characteristics. Our results show that an aggregation of approximately
100 buildings suffices to meet the 5 MW minimum bid size of the Swiss reserve
market.
