This paper presents a simulation study of an active energy storage device intended to enhance building operation. This device -which is designed for installation in the ceiling plenum of an office, a mechanical room or in other convenient locations- consists of an arrangement of several panels of a phase-change material. It may be charged or discharged as required with an air stream passing between the panels, thus operating as a PCM-air heat exchanger (PCM-HX). The first part of the paper focuses on the design of the PCM-HX. Several design configurations are evaluated; investigated parameters include the PCM-HX dimensions, the number of air channels and airflow rates. The paper also includes an experimental validation of the PCM model. Performance criteria that were considered in the parametric study include the amount of stored heat, the time needed to charge discharge the PCM storage and the overall energy density of the device. The second part of the paper evaluates different control strategies aimed at reducing peak demand and the size of HVAC system. The impact on peak load of a linear ramp for the temperature setpoint is investigated: it was found that a two hour linear ramp in temperature setpoint -together with a PCM-FIX configuration with six air channels- can reduce the peak heating load by 41% as compared to a benchmark case without the PCM-HX. Crown Copyright (C) 2019 Published by Elsevier B.V. All rights reserved.