On the Interaction between Personal Comfort Systems and Centralized HVAC Systems in Office Buildings

TL;DR

This paper presents a control strategy integrating personal comfort systems with centralized HVAC to improve energy efficiency and occupant comfort, demonstrating significant savings and comfort improvements in various building scenarios.

Contribution

It introduces a Model Predictive Control-based approach for HVAC operation that optimally incorporates personal comfort systems, a novel method for enhancing efficiency and comfort.

Findings

45% energy savings in summer with homogeneous comfort

51% comfort improvement in summer with heterogeneous needs

Significant energy and comfort benefits across different building layouts

Abstract

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.