Design and Manufacture of a precast PCM enhanced concrete cladding panel for full scale performance monitoring

The overall aim of this study is to develop innovative precast cladding panels for the renovation of Europe’s existing building stock thereby improving their energy performance. Using the mass of a building to store heat and/or cold can reduce the demand on the auxiliary heating and/or cooling systems and hence reduce the overall energy demand of the building. Previous laboratory research has shown that the incorporation of phase change materials (PCMs) into concrete enhances its thermal storage capacity by up to 50%. However in a real application where a PCM-concrete composite material is used in a building to store thermal energy, the effectiveness of the PCM depends on many variables including the form of construction and local climate conditions. In this research study a precast cladding panel formed with PCM enhanced concrete has been developed and manufactured. In order to observe the performance of the PCM-concrete composite panels in a full scale scenario, three demonstration huts have been constructed and instrumented to record internal thermal behaviour. Monitoring of the data is ongoing and shows that the effectiveness of the PCM varies with the seasons. Data recorded during the summer period highlighted that the internal temperature may not drop low enough during the night to solidify the PCM and discharge the stored heat. A further test in which passive ventilation was provided during the night proved to be an effective method of addressing this issue. It is expected that this long term study will enable recommendations to be made on the seasonal benefits of using PCM-concrete to enhance the energy performance of buildings located in climate conditions similar to Ireland. The results of the data analysis will inform a refinement of the panel design prior to installing the panels at a school in the UK which currently has an overheating problem

Prediction of low frequency blood pressure oscillations via a combined heart/resistance model

Low frequency oscillations in blood pressure (BP) can occur due to a feedback pathway between the sensing of BP and the central nervous system (CNS), often termed the baroreflex, affecting both cardiac output (heart-rate and stroke volume) and peripheral resistance. In this paper, an integrated model of both these subsystems is assembled and an analysis technique developed, which shows the conditions under which a limit cycle oscillation can occur. In particular, the role of mean levels of cardiac output and peripheral resistance, previously thought to be relatively unimportant, in establishing and maintaining sustained oscillations, is highlighted. The ultimate aim of this analysis is to assist in the development of diagnostic tests based on measurement of low-frequency blood pressure oscillations

Thermal Mass Behaviour of Concrete Panels Incorporating Phase Change Materials

Phase Change Materials (PCM) have been incorporated into a range of building envelope materials with varied success. This study investigates two different methods of combining concrete and phase change materials to form PCM/concrete composite panels. The first method involves adding microencapsulated paraffin to fresh concrete during the mixing process. The second method involves vacuum impregnating butyl stearate into lightweight aggregate which is then included in the concrete mix design. The primary aim of the study is to determine which method is the most effective way to improve the thermal mass characteristics of a concrete panel in the context of a thermal energy storage system for space heating in a building. The study observes the rate at which the panels absorb and emit heat, ie, the heat flux, and also how the heat flux changes throughout the depth of the panel. The panels are heated in a controlled environment provided by a specifically designed light box. Radiation is used as the heat transfer mechanism. Surface and internal temperatures of the panels are recorded during heating and cooling periods. The data recorded, together with the determined densities and thermal conductivities, are used to compare the thermal mass behaviour of each type of panel and to determine the influence that the method of incorporating a phase change material into a concrete panel has on the effectiveness of the PCM to improve the thermal mass characteristics of the concrete panel. The study highlighted the complexity of thermal behaviour of PCM/concrete composites. The panels containing PCM displayed significantly greater thermal storage capacity despite having reduced thermal conductivity and density. The study concluded that the panel containing lightweight aggregate/PCM composite is more effective at providing additional thermal storage particularly within the first 100mm of depth of an element of structure

Describing Function Approximation For Biomedical Engineering Applications

This paper focuses on the determination of suitable approximations for sigmoid-type nonlinear characteristics, which are common to physiological systems, particularly cardiovascular regulatory systems. These sigmoid nonlinearities have been implicated in the development of limit cycle oscillations in blood pressure. Approximations of the sigmoid are required since the describing function is not calculable for the all representations of the sigmoid characteristic. In this paper, we present a new approximation, which gives a better overall approximation of the sigmoid and hence, can assist the use of describing functions in the diagnostic analysis of cardiovascular function

Thermal Mass Performance of Concrete Panels Incorporated with Phase Change Materials

Using the mass of a building as a thermal storage system can reduce the demand on the auxiliary heating and cooling systems of the building. Concrete combines a high specific heat capacity with a thermal conductivity that is appropriate for the diurnal heating and cooling cycle of buildings. The heat storage capacity of concrete can be enhanced by adding phase change materials (PCMs) which provide a high latent heat storage capacity. However the addition of PCM to concrete reduces the conductivity of the concrete which may affect the ability of a PCM-concrete panel to absorb and release heat within the desired time period. In this study two different methods of combining concrete and phase change materials were used to form PCM/concrete composite panels. The panels were exposed to radiative heat energy in a controlled environment for a specified time period during which the surface and internal temperatures of the panel were recorded. The temperature data together with the measured density and thermal conductivity was used to evaluate and compare the thermal mass behaviour of each type of PCM/concrete composite material. The addition of PCM to the concrete significantly increased the overall thermal storage capacity of the concrete despite reducing the density and thermal conductivity of the concrete

Influence of Ground Granulated Blastfurnace Slag on the Thermal Properties of PCM-concrete Composite Panels

The thermal mass of concrete within a building can be used as an energy storage system and hence reduce the demand on the auxiliary heating and cooling systems in the building. The heat storage capacity of concrete can be enhanced by adding phase change materials (PCMs) which provide a high latent heat storage capacity. However the addition of PCM to concrete reduces the conductivity of the concrete due to the low conductivity of the PCMs. This hinders the efficient utilisation of the additional heat storage capacity provided by the PCM. It is generally understood that the use of ground granulated blastfurnace slag (GGBS) as a partial cement replacement results in a denser cement paste which, for a given aggregate type, increases the conductivity of the concrete. The aim of this study was to determine if the use of GGBS influences the thermal mass behaviour of a PCM-concrete. Two types of PCM-concrete panels were manufactured. Firstly microencapsulated paraffin was added to fresh concrete during the mixing process. Secondly butyl stearate was vacuum impregnated into lightweight aggregate which was then included in the concrete mix. Half of the samples contained 50% GGBS cement replacement and consequently the effect of GGBS on the thermal performance is reporte