An Equivalent and Unified Virtual Battery Modeling Framework for Flexibility Characterization of Building HVAC Systems

TL;DR

This paper introduces a unified virtual battery modeling framework for building HVAC systems, enabling accurate characterization of their operational flexibility for demand response and grid services.

Contribution

It develops a comprehensive VB model for both single-zone and multi-zone HVAC systems, including an aggregation method for simplified, low-complexity modeling.

Findings

VB model accurately captures HVAC flexibility

Effective demand response strategies derived from VB model

Model reduces computational complexity significantly

Abstract

The heating, ventilation and air-conditioning (HVAC) system dominates building's energy consumption and meanwhile exhibits substantial operational flexibility that can be exploited for providing grid services. However, the goal is largely hindered by the difficulty to characterize the system's operating flexibility due to the complex building thermal dynamics, system operating limits and human comfort constraints. To address this challenge, this paper develops an unified virtual battery (VB) modeling framework for characterizing the operating flexibility of both single-zone and multi-zone building HVAC systems, enabling flexible buildings to function like virtual batteries. Specifically, a physically meaningful representation state is first identified to represent building thermal conditions under thermal comfort constraints and a VB model is then established for characterizing the operating flexibility of single-zone HVAC systems. We subsequently extend the VB modeling framework to multi-zone HVAC systems and establish a set of zone-level VB models to characterize the building's zonal operating flexibility. We further develop a systematic method to aggregate the VB models into a low-order and low-complexity aggregated VB model, significantly reducing model and computational complexity. We demonstrate the VB model through demand response (DR) applications and conclude that the VB model can well capture the operating flexibility of building HVAC systems and enable effective DR participation. The DR strategies obtained from the VB model can be efficiently decomposed to zone-level control inputs for maintaining human thermal comfort while achieving near-optimal operation cost.