# Demand Control Strategies of a PCM Enhanced Ventilation System for Residential Buildings
## 1 Introduction  
To decrease the high energy consumption of the building sector, especially from space heating/ cooling, it is essential to adopt renewable energy and highly energy-efficient building equipment for both new and existing buildings. Renewable energy such as solar energy is usually intermittent energy and highly dependent on outdoor weather conditions, which makes thermal energy storage (TES) more important during the implementation. Phase change material (PCM) as TES for building applications is gaining increasing research interest. The PCM has been proved to be effective for building energy conservation, when integrated into building constructions such as floors [1; 2], roofs [3], ceilings [4; 5], walls [6], and windows [7]. It has also been proved to be effective for building energy conservation and contributes to building energy flexibility for building ventilation systems, such as cooling units [8; 9; 10] and double skin facades [11; 12]. The ventilated window (VW), which was developed by [PERSON] et al. [12], proved to function poorly in cooling a building space during summer, and insufficient for heating the space during winter. Instead, a PCM-enhanced ventilated window (PCMVW) was developed and tested by [PERSON] et al. [13; 14], as seen in Figure 1. It includes a PCM heat exchanger under the ventilated window(VW). The PCM energy storage and heat exchanger is made by parallel PCM plates in a wooden frame and a glass surface [15; 16]. The VW is made by a double layer glass in the outer panel and a single layer glass in the inner panel, which forms a ventilation cavity to allow airflow to go through the window [12]. Compared to the VW and standard window (SW) with fan ventilation, the PCMVW decreases the room air conditioning energy demand by pre-treating the ventilation air, e.g., pre-cools the ventilation air during summer and pre-heats the ventilation air during winter. Investigation of the energy performance of buildings with PCM applications is commonly done by modeling. EnergyPlus as a whole building energy simulation program has been used and proved to be accurate by many researchers concerning PCM modeling in building systems, as the works shown in [17; 18; 19; 20; 21; 22; 23]. Compared to other building simulation programs, the Energylus software has the advantage of combining the PCM applications with various building facilities in a single building system. Moreover, the modeling of PCM in Energylus has been well developed, including Conduction Finite Difference (CondFD) heat balance algorithm, changeable PCM properties along with temperature and PCM temperature hysteresis. The PCM temperature hysteresis was neglected in building modeling for a long period until recently when several researchers included it in building energy calculation [24; 25]. The aforementioned researchers have all successfully modeled PCM in building ventilation systems. However, those models are all based on simple building models and ventilation strategies, and there are not many works concerned directly with the demand control operation, where the building is divided into small sub-thermal zones, and the air conditioning of each room is controlled based on the real-time demand of the room. [PERSON] [25] studied different occupancy patterns and ventilation strategies on the energy-saving potential of buildings with a PCM-enhanced wall system and found out that the occupant pattern, which is directly associated to the HVAC set point, has a big influence on the energy-saving potential. However, those occupancy patterns are based on the assumption that the building is one thermal zone  
Figure 1: The sketch of the PCM-enhanced ventilated window. with one function, and the ventilation strategies are quite simple, and the demand of the room is not considered accordingly in the ventilation strategies. This study is a continuous work based on previous works and their research limits.