Phase Change Material Location Research Articles

Parametric analysis of a residential building with phase change material (PCM)-enhanced drywall, precooling, and variable electric rates in a hot and dry climate

Peak electric energy demand inflicts a great stress on the electric grid during the summer in the United States. With most years surpassing its previous year for the warmest year ever recorded, cooling requirements will continue to increase in the coming decades. Energy storage can potentially reduce electric demand. Among different technologies, phase change materials (PCMs) embedded in the building envelope have the potential to shift cooling energy demand away from peak hours. This study performs parametric analysis of PCMs in a relatively new home located in Phoenix, Arizona, USA. The analysis includes PCM location, PCM properties, precooling strategy, and an analysis of natural and forced convection models on the thermal behavior of the house. An extension of a standard forced convection model in EnergyPlus is used to represent the effects of a ceiling fan, which increases heat transfer at wall and ceiling surfaces and shortens the time needed to freeze or melt the phase change materials. Furthermore, the study discusses the use of appropriate setback temperatures to best utilize the PCMs. Overall, the optimal combination of PCMs, convection mode, and precooling schedule can completely shift cooling energy use during a three-hour demand period, producing maximum cost savings up to 29.4%, while increasing the occupant comfort.

Using Thermal Inertia of Buildings with Phase Change Material for Demand Response

Abstract: In recent years, demand response programs have proved useful in managing peak demand and meeting sustainability goals, enabling an efficient use of the smart grid. Heating, ventilation, and air conditioning (HVAC) loads in buildings constitute a large proportion of the total energy consumption of households, and accordingly, a flexible and efficient operation of these devices can aid power utilities in meeting load management objectives while reducing consumer’s electricity bills. With the emergence of promising new technologies, such as phase change materials (PCM), buildings can serve as a virtual thermal energy storage, which improves energy efficiency and also allows occupants to offer grid services like peak demand reduction. The objective of this paper is to establish the effectiveness of PCM as a demand response resource, demonstrating the extent to which it can be used for peak demand reduction. A wide range of scenarios are considered to investigate the impacts of geographical location, PCM melting point, duration of precooling and preheating, setting points of HVAC system, thickness and location of PCM, on the capability of the PCM in reducing or shifting the cooling and heating load. All simulations are performed using the EnergyPlus platform, examining typical residential buildings in five Australian cities: Brisbane, Sydney, Melbourne, Hobart and Perth. The simulation results showed a decrease in the HVAC demand in the buildings with PCM, in all cities, with the highest reductions observed in Hobart and Melbourne. The integration of a 20mm thick PCM in the roof, wall and floor of the building yielded a 21.8% and 16.7% reduction in annual HVAC demand in Hobart and Melbourne respectively, when compared to the building without PCM. However, this is with the assumption that the HVAC system is operating 24 hours a day for a whole year. The PCM-integrated building showed a shift in the HVAC demand in all cities except Perth. A shift by 9 minutes, 3 minutes, 60 minutes and 103 minutes was recorded in the cities of Brisbane, Sydney, Melbourne and Hobart respectively. The simulation results will be used in subsequent research to schedule the HVAC demand using a home energy management system.

Experimental Study of Heat Transfer in a Reduced Scale Cavity Incorporating Phase Change Material Into Its Vertical Walls

In order to really assess the thermal performance of a wall incorporating phase change material (PCM), a reduced scale cavity has been monitored during two heating cycles. For each cycle, the heat source inside the test cell is switched “on” for 5 h and its setpoint is 38 °C and then switched off for 4 h. The outdoor air temperature is kept constant at a low temperature of 20 °C. Two walls are equipped with a PCM layer at different depths in order to study the optimal PCM location. The two other walls are wooden and glass to model a real building. The comparison between the four walls is made based on the absorbed heat fluxes and outside surface temperatures. The results show that the location of the PCM close to the heat source reaches its melting temperature and then reduces the surface temperature. At this location, the PCM layer stores the major part of the inlet heat flux. It takes 10 h to release the absorbed heat flux. However, the PCM layer, practically, does not have an effect on the surface temperatures and absorbed heat fluxes, when it is placed far from the heat source.

Optimal location of PCM layer in building walls under Nanjing (China) weather conditions

The phase change material (PCM) location in the building walls has great effects on the thermal performance improvement of PCM walls. In this paper, a numerical model was built to estimate the optimal PCM locations in the wall during different seasons under Nanjing (China) weather conditions. The heat flux fluctuation reduction rate was used to evaluate the effects of the PCM on the thermal performance of the wall; the optimal PCM location meant the heat flux fluctuation reduction rate was the largest. The heat of fusion of the PCM used in the model was 179 J g−1; it was found that when the phase change temperature range of PCM was 26–28 °C, the optimal PCM locations in Nanjing for spring, summer, autumn, winter and a whole year were 8/16, 2/16, 5/16, 8/16 and 4/16 L, respectively. However, the PCM had great effects only in summer because of its high phase change temperature. It was also found that the optimal phase change temperature ranges for spring, summer, autumn, winter and a whole year were 24–26, 26–28, 24–26, 20–22 and 24–26 °C. Accordingly, the optimal PCM locations were 0/16, 2/16, 1/16, 3/16 and 0/16 L. In addition, the most suitable kind of PCM for a certain location in the wall could also be found.

Thermal load mitigation and passive cooling in residential attics containing PCM-enhanced insulations

Residential attics has the potential to be one of the most energy efficient building components by combining thermal processes of attic floor insulation, attic air space, ventilation in attics, and solar collecting roof decks. Large amounts of solar energy collected by the roofs in cooling-dominated and mixed climates generate excess cooling loads, which need to be removed from the building by the space conditioning systems. This paper investigates potential ways to improve the thermal design of the residential home attics to minimize the cooling energy consumption in the cooling-dominated and mixed climates. Dynamic thermal characteristics of thick attic floor insulations and blends of phase change materials (PCMs) with insulations are analyzed. Both approaches can provide notable reductions of thermal loads at the attic level. In addition, a significant time shift of peak-hour loads can move a major operation time for air conditioning system from the daytime peak hours to nighttime low demand hours. A reverse heat flow direction can be observed during the day in the case of really thick layers of bulk insulation or PCM-enhanced insulations, compared to the rest of the building envelope components. This effect may provide free passive cooling to the building, and can be very useful in locations of double electrical tariffs with high daytime peak-hour electric energy rates and less-expensive off-peak energy cost. In both of the above cases, an addition of PCM to the bulk insulation brings substantial performance enhancement not available for traditional insulation applications. This paper presents a short overview of dynamic material characteristics and energy performance data necessary for future dynamic applications of different configurations of the attic floor insulation and PCM-insulation blends in residential homes. A series of whole-building scale and material scale numerical simulations were performed on a single story ranch house to analyze potential energy savings and optimize location of PCM within the attic insulation.

Effects of PCM state on its phase change performance and the thermal performance of building walls

To figure out the effects of PCM location on the thermal performance of building walls, the effects of the state of a kind of salt hydrate phase change material (PCM) on its phase change performance were researched by the differential scanning calorimeter (DSC) tests and the cooling experiments. The three different PCM states are the not-melted state, the partially-melted state, and the fully-melted state, respectively. The experimental results showed that PCM state had great effects on the degree of supercooling and the phase change performance of PCM. When the PCM was in the partially-melted state before cooling, it was able to release the latent heat quickly, while when the PCM was in the fully-melted state before cooling, its degree of supercooling was large. Because the temperature ranges of PCM during the thermal cycles were different when the PCM was placed in different locations in the wall, the PCM location had significant effects on its state, and as a result, on the phase change performance of PCM and the thermal performance improvement of building walls.

On the importance of the location of PCMs in building walls for enhanced thermal performance

Phase change materials (PCMs) are used to enhance the thermal storage capacity of building walls. PCM incorporation into building walls poses several design challenges; a critical one being the integration method (e.g., micro- vs. macro-encapsulation) as well as the location of PCMs within the volume of the walls. Such location is critical for wall performance in terms of controlling heat transfer rates for purposes of energy conservation and peak load shifting. This paper highlights the dependence of wall thermal performance on PCM location leading to the most optimal PCM location for the system under study. In this study, PCMs were incorporated in walls via “thermal shields” where the PCM material was encapsulated in polyethylene flat bubbles “sandwiched” between two layers of protective aluminum foil. This system is herein referred to as “PCM thermal shield (PCMTS)”. The thermal performance of the walls with and without PCMTS was evaluated experimentally using a dynamic wall simulator. PCM thermal shields (PCMTSs) were placed within the wall insulation at varying distances from the internal surface of the bounding wallboard, which happened to be the bounding layer furthest from the heating sources of the simulator. For the system under study, the results showed that the optimal location for a PCMTS was at a distance of 1/5L from the internal surface of the bounding wallboard, where L was the thickness of the insulation cavity. At this location, the average peak heat flux reduction and load shifting time were approximately 41% and 2h, respectively, when compared to the peak heat fluxes across walls without PCMTS.

Thermal analysis of a building brick containing phase change material

This paper presents the thermal analysis of a building brick containing phase change material (PCM) to be used in hot climates. The objective of using the PCM is to utilize its high latent heat of fusion to reduce the heat gain by absorbing the heat in the bricks through the melting process before it reaches the indoor space. The considered model consists of bricks with cylindrical holes filled with PCM. The problem is solved in a two-dimensional space using the finite element method. The thermal effectiveness of the proposed brick-PCM system is evaluated by comparing the heat flux at the indoor surface to a wall without the PCM during typical working hours. A paramedic study is conducted to assess the effect of different design parameters, such as the PCM's quantity, type, and location in the brick. The results indicate that the heat gain is significantly reduced when the PCM is incorporated into the brick, and increasing the quantity of the PCM has a positive effect. PCM cylinders located at the centerline of the bricks shows the best performance.