Building Envelope Applications Research Articles

Numerical modelling and experimental validation of pcm-to-air heat exchangers: application of ventilated building envelopes

The earlier applications of phase change material (PCM)-to-Air heat exchangers (PAHXs) reported the insufficient cooling charging energy due to system storage abilities, the profile of inlet air temperature, and the charging duration. This paper proposes a developed PAHX system for building envelope applications utilizing both convective and long-wave radiative heat transfer components. A 2D numerical model was proposed utilizing an apparent heat capacity method to represent the PCM latent thermal storage developing both convective and radiative thermal boundaries. The radiative component was developed to study the effect of the system exposure to the night-time sky during the PCM solidification period. The convective component was comprehensively developed mainly between the storage medium (PCM) and the air channel. A real-scale prototype was constructed for the whole model experimental validation. Field experiments were designed and conducted in the warm temperate climate of Lyon, France during summer. The validation criteria were proposed based on ASHRAE guideline 14. The results of the comparison between simulated data and experimentally obtained data showed that the system temperature was within the accepted range of the proposed criteria.

Development of PCM-to-air heat exchanger for integration in building envelope–modeling and validation

Earlier applications of phase change material (PCM)-to-air heat exchangers (PAHXs) reported the insufficient cooling charging energy needed for complete solidification of the PCM in free cooling systems. Also, the prediction of PAHX performance under low airflow regimes is a system limitation for free cooling applications. Besides, the implementation of the long wave thermal radiation cooling concept has not gained much attention in the free cooling design of PAHX units. This paper reports the development of PAHX system for building envelope applications that promotes the thermal radiation loss to the sky during night-time to maximize the cooling potential. A 2D numerical model has been developed considering the PCM thermal behavior, short and long wave radiation, and convection phenomena. New thermal boundaries of long-wave radiation have been proposed between system elements and the sky temperature. In addition, the model considered various forms of convective heat transfer phenomena. The apparent heat capacity method was used to simulate the thermal storage process. Experimentally obtained data and inter-model comparison were used to validate the proposed model. Two full-scale prototypes of the developed PAHX system were designed and tested under real conditions using two different types of PCMs. A parametric analysis was conducted to investigate the system thermal behavior under various air velocity profiles in the air channel and various inlet air temperature conditions. The results indicate that the building envelope integrated PAHX can use the sky radiation as a cooling source.

Assessing the Potentiality of Animal Fat Based-Bio Phase Change Materials (PCM) for Building Applications: An Innovative Multipurpose Thermal Investigation

In recent years, the implementation of novel solutions aimed at improving thermal energy storage (TES) capability to both energy technologies and building-integrated systems has gained increasing attention. In particular, the application of phase change materials (PCM) is currently gathering worldwide acknowledgment. In this work, the potential of animal fat as a novel bio-based PCM having transition temperature around the ambient temperature is assessed by means of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and extensive temperature monitoring. Results from the TGA showed the differential degradation of the main components of the animal fat during the heating phase, where three different decomposition steps could be noticed. The thermal monitoring and the DSC analysis demonstrated the promising thermal performance of the material, which showed an interesting double transition range globally associated to a melting enthalpy of about 28.94 kJ·kg - 1 . The obtained results demonstrate the promising thermophysical properties of the animal fat blend, which can be considered as a low-cost, biocompatible PCM, particularly with potential application in passive building envelope applications for a wide range of temperature boundary conditions.

Coupling the transient plane source method with a dynamically controlled environment to study PCM-doped building materials

In recent years the combination of latent and sensible thermal energy storage processes within passive and active building components has gathered increasing attention among researchers all over the world. All this considered, an ever-increasing hunger for bridging the gap between chemistry-based characterization methods and engineering-scale monitoring solutions is spreading worldwide, with the aim of developing new experimental procedures allowing to test these advanced systems under realistic operative environmental conditions. In this view, the present paper aims at proposing an innovative characterization procedure for real-scale engineered applications with reference to dynamically variable composites, such as PCM-doped cement-based mixes for building envelope applications. Therefore, in this work, thermally enhanced concretes were produced using micro-encapsulated paraffin and their activation was investigated by means of an innovative experimental technique coupling transient plane source method and controlled environmental dynamic forcing. The dynamic-TPS analysis allowed to produce temperature dependent profiles for three basic material thermal properties, i.e. thermal conductivity, thermal diffusivity and volumetric specific heat. Results show that the proposed methodology is capable of detecting PCM activation within the engineered composites during the imposed hygrothermal cycle, where, for example, the effective thermal conductivity of the composites varied between 40 and 90% amid the melting/freezing process. Furthermore, the transient plane source method also showed to be suitable to investigate PCM dispersion within the composites.

A novel building material with low thermal conductivity: Rapid synthesis of foam concrete reinforced silica aerogel and energy performance simulation

With the increasing number of commercial buildings in the United States, the energy consumption for space air conditioning is continuously rising. Considering the external building envelope an important role to generate cooling and heating loads, we developed a new high performance building material for building envelope application. Hence, a novel foam concrete reinforced SiO2 aerogel (FC-SA) material was synthesized via sol-gel technique, vacuum impregnation method and rapid supercritical drying process. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric / differential scanning calorimetry (TG-DSC), N2 adsorption-desorption test (BET) and transient plane source method (TPS). The prepared composite had a high degree of aerogel filling (74% volume of matrix) and the aerogel component still maintained a porous nanostructure. Besides, FC-SA showed a large specific surface area of 405.3 m2/g and high pore volume of 1.28 cm3/g. Meanwhile, the introduction of aerogel has little effect on the mechanical strength of the matrix material. According to the test results, the thermal insulation performance of foam concrete has been found greatly improved with silica aerogel composition. The thermal conductivity of FC-SA composite was measured as low as 0.049 W m−1 K−1 at room temperature (30 °C), which was a 48.4% decrease from foam concrete. Finally, the energy saving simulation results showed that in cold and hot areas, the use of FC-SA to replace traditional concrete materials can greatly reduce both of energy consumption and cooling water consumption.

Bio-based insulation materials and their hygrothermal performance in a building envelope system (ETICS)

Bio-based insulation materials (such as wood or hemp) are emerging as a promising alternative in building envelope applications, aiming at improving in-use energy efficiency. When compared to common insulation materials (rock and glass wool or petrol-based foams) bio-based materials present the advantage of being renewable, with a low embodied energy and CO2 neutral or negative. Moreover, these materials have a distinct hygrothermal performance, as the sorption/desorption of water vapour in their porous structure, in dynamic equilibrium with their surrounding environment, constantly modifies their hygric and thermal properties while causing energy transfers itself. In this paper, the hygrothermal performance of two different bio-based materials in outdoor conditions is evaluated. The first is an innovative light-weight composite made from corn pith and alginate. The second a commercially available wood insulator. The materials are tested alone and as components of external thermal insulation systems (ETICS) and compared to a conventional polystyrene foam. The results show how the sorption process influence the hygrothermal performance of the materials when the surrounding conditions are modified. When subjected to cyclic changes in temperature and relative humidity, the bio-based materials tested show a lower temperature variation than polystyrene. This is in part due to their lower thermal diffusivity, but also to the water absorption and desorption mechanisms occurring within the materials, which were measured by the change in mass of the materials during the tests. The differences in the thermal performance were more noticeable when the insulation materials were tested alone than when these were tested as a part of an ETIC System.

Snapping Facades: Exploring Elastic Instability for the Building Envelope

This article presents an alternative dynamic facade actuation mechanism utilizing the deformation of snapping instability without continuous force application. Based on analytical and numerical studies prior to fabrication, a prototype snapping facade is built and its proof of concept is demonstrated for the proposed snapping-induced motion. The snapping facade provides a novel way to exploit elastic instability in dynamic building-envelope applications. Further development of the system for practical applications will include the study of different materials for the snapping beams and shading membranes as well as the energy-performance benefits of the snapping facade system.

Life cycle analysis (LCA) and life cycle cost analysis (LCCA) of phase change materials (PCM) for thermal applications: A review

Thermal storage systems development is under significant concern focusing mainly to the thermal energy storage use for thermal applications. On the other hand, the investigation of phase change materials (PCMs) in the building sector was tested consisting a very promising field of research and development. A number of substances have been tested as potential PCMs; however, only few of them have been further developed for commercial purposes. This is attributed to a number of thermophysical barriers, which make the applications of PCMs in buildings difficult. Several studies have examined the potential of PCM use, either incorporated into building envelopes or in heating and cooling applications. Regarding building envelope applications, PCMs are used to mainly ensure indoor thermal comfort and contribute to energy performance. The positive impact of PCMs on the building's annual cooling and heating loads in various climate zones is a common conclusion. Concerning heating and cooling applications, the main idea has been to substitute the storage medium with PCMs, which have higher storage capacity. Hence, the use of PCMs can be considered as scientifically mature, although there are still technical, environmental, and economic barriers. The present study is the state of the art of the existing research of PCM for thermal applications taking into consideration environmental (based mainly on life cycle analysis methodology) and economic performance (accounting to life cycle cost analysis methodology) criteria, while excluding solar power generation applications.

Superporous Intelligent Hydrogels for Environmentally Adaptive Building Skins

ABSTRACTThis work explores responsive hydrophilic polymers for convergent functions of climate control with architectural material systems. In buildings, the transition across exterior and interior space occurs through the envelope, which is an enclosure system that mediates heat, light, air and moisture transfer functions. Conventional building envelopes are typically constructed to form a barrier that insulates and hermetically separates outdoor and indoor conditions. The dynamic environmental responses of superporous intelligent hydrogels are shown to be beneficial at the interior layer of a double-skin glazing system for building envelope applications. If the hydrogels are integral to the building envelope system, then various environmental functions (such as natural daylighting, heat transfer, airflow and moisture control) can be achieved through integrated actuators to result in improved building energy performance.The composite embodiments emulate bio-analytical functions when embedded microbore-tube water channels serve as actuators for swelling and deswelling kinetics respectively. Each prototype is conceived in response to hot-arid climate contexts. The prototype presented here is a lightweight ventilation cooling and daylighting system. Initial prototypes are inserted into an environmental test-bed that is consequently divided into two chambers to represent an outdoor and indoor condition. The input chamber includes controllable heat and light elements that affect the dynamics of the hydrogel system. The output chamber on the opposite side of the prototype division includes temperature, humidity and photo sensors that are connected to an Arduino board for data collection. Dependent upon the environmental conditions of chamber two, a control program actuates small hydro-pump to saturate the gels with water.The initial results provide correlations between mechanical (elasticity) and thermal (conductivity) properties. Current work in progress includes documentation of average rates for sorption-desorption kinetics and correlations between saturation loading and visible transmittance. The physical test data will also be integrated into building-scale energy performance simulations and hygrothermal transfer numerical analysis for building envelope compositions. The embedded material logic of the hydrogel is exploited in an architectural configuration for a convergence of prior building mechanical system and building envelope functions. The current work demonstrates a highly promising application of soft-skin membranes for much needed reductions in energy consumption within the building sector.

Study of coupled transient radiation-natural convection heat transfer across rectangular cavities in the vicinity of low emissivity thin films for innovative building envelope applications

The coupled natural convection-radiation heat transfer across cavities is an extremely important research issue commonly encountered in many innovative building envelope applications. Extensive both experimental and numerical studies were conducted to analyse the natural convection flow coupled with radiation heat transfer across vertical and inclined rectangular cavities, proposing accurate empirical or regression correlations according to the particularities of the studied cavity problem. Nevertheless, there is a lack of correlations accurate and adapted enough to model coupled natural convection-radiation across cavities in the vicinity of low emissivity surfaces. The present work aims to cover this subject, through an exhaustive numerical analysis validated and evaluated enough with the use of experimental data. A numerical model is firstly updated to simulate infrared radiation and convective heat transfer across a sophisticated innovative building envelope prototype, while 8 different approximations have been implemented in the model in order to evaluate a variety of available correlations on the subject. Formerly the numerical approach presented here used available experimental data for the same prototype. The air’s temperature experimental data served as input to the model boundaries in order to exactly impose the same initial conditions for obtaining the results. Furthermore, experimental data regarding the temperature on the sample’s interfaces were used for validating the proposed theoretical model. Satisfactory enough agreements are observed between the theoretically simulated and experimentally measured temperatures and the model is afterwards evaluated to determine the most accurate approximation. Finally, the numerical study presented in this paper concluded in the proposition of 2 new updated correlations to model natural convection across vertical cavities in the vicinity of low emissivity surfaces with the perspective to further support their implementation into Computational Fluid Dynamic (CFD) codes.

Translucent marbles for building envelope applications: Weathering effects on surface lightness and finishing when exposed to simulated acid rain

Marble thin panels are widely used for external building envelope application, due to their original light transparency effects during day-time and night-time. Considering their application in polluted environments and the interaction with aggressive agents, the aesthetical characteristics of this element could be compromised by degradation processes. To investigate such changes, experimental ageing test analyzing the effects of acid rain aggression on different marble samples is carried out in this research. Marbles’ reactions are studied in terms of: lightness, gloss, and Distinctness Of Image. The main findings demonstrate how the acids hugely degrade both the marble typologies and quantify the modifications.

Manufacture and multi-physical characterization of aluminum/high-density polyethylene functionally graded materials for green energy building envelope applications

An aluminum/high-density polyethylene (HDPE) functionally graded material (FGM) has been fabricated as an essential component of a multifunctional building envelope for high performance of energy efficiency and sustainability. The mass production of the FGM was realized by using coarse aluminum (Al) particles and fine HDPE powder through a vibration-sedimentation process. The gradation of the FGM across its thickness direction was analyzed by developing a modified Rice method, from which five different uniform Al-HDPE samples were made to characterize the material properties of the five sub-layers of the FGM. The mechanical and thermal physical properties of the FGM such as Young's modulus, Poisson ratio, thermal expansion coefficients and thermal conductivities were obtained by various experimental characterizations. A prototype FGM panel with water tubes embedded was fabricated by the vibration and sedimentation combined approach and the thermal efficiency of the FGM panel was evaluated. Under an irradiation level of 620w/m2 and a water flowing rate of 60ml/min, a 22.3°C water temperature increase and an average 18.7°C surface temperature decrease of the FGM panel were achieved, which demonstrates that significant PV conversation efficiency improvement can be realized for both electricity generation and heat collection by the presented FGM panel. The presented fabrication procedures and the associated experimental characterization methods and results can serve as a baseline for quality control of the manufacture of the green energy building envelope materials.

Low-cost phase change material as an energy storage medium in building envelopes: Experimental and numerical analyses

A promising approach to increasing the energy efficiency of buildings is the implementation of a phase change material (PCM) in the building envelope. Numerous studies over the last two decades have reported the energy saving potential of PCMs in building envelopes, but their wide application has been inhibited, in part, by their high cost. This article describes a novel PCM made of naturally occurring fatty acids/glycerides trapped into high density polyethylene (HDPE) pellets and its performance in a building envelope application. The PCM–HDPE pellets were mixed with cellulose insulation and then added to an exterior wall of a test building in a hot and humid climate, and tested over a period of several months. To demonstrate the efficacy of the PCM-enhanced cellulose insulation in reducing the building envelope heat gains and losses, a side-by-side comparison was performed with another wall section filled with cellulose-only insulation. Further, numerical modeling of the test wall was performed to determine the actual impact of the PCM–HDPE pellets on wall-generated heating and cooling loads and the associated electricity consumption. The model was first validated using experimental data and then used for annual simulations using typical meteorological year (TMY3) weather data. This article presents the experimental data and numerical analyses showing the energy-saving potential of the new PCM.

Integrated Thermal-Energy Analysis of Innovative Translucent White Marble for Building Envelope Application

Marble is a natural material, used in the construction field since antiquity. It has always been used to communicate monumentality and solidity. Nowadays new technologies permit marble to express new languages: particularly, translucent marble technology overturns the concept of solidity. The main issue to address is the lack of thermal-energy performance of such a thin stone layer as the only facade component. Conversely, Bianco Carrara and Statuario marbles, for instance, have intrinsic benefits as natural cool materials, due to their high solar reflectance and thermal emissivity. Thus, this paper analyzes the thermal-energy and environmental behavior of marble facade for a new designed building in New York City. An integrated analysis of the energy performance of the marble skin is performed through a preliminary experimental characterization, carried out for two different types of naturally white marble, for comparative purposes. Then, a dynamic simulation model of the building is developed to evaluate year-round benefits and drawbacks of the translucent marble envelope in terms of indoor thermal comfort and air-conditioning requirement. The analysis showed how the proposed marble facade is able to decrease the energy requirement for cooling up to 6%, demonstrating possible relevant perspectives for marble-based facades, even in energy-efficient buildings.

Air filtration with moisture and frosting phase changes in fiberglass insulation—I. Experiment

A laboratory apparatus has been constructed to subject fiberglass insulation to one-dimensional moist airflow and heat transfer with temperatures from 20 to −20°C. Using this apparatus, the effects of air exfiltration and infiltration on the heat and moisture transport characteristics within a medium density fiberglass insulation material are investigated experimentally for one-dimensional transient conditions. The experimental results, which are typical of cold climate building envelope applications, indicated that the adsorption process had a significant influence on the temperature distribution over much of the warm portion of the slab during air exfiltration shortly after the tests began. Furthermore, for all of the air exfiltration tests carried out, the majority of the moisture and frost accumulation was within the insulation slab adjacent to the cold surface. For air infiltration, it was discovered that the drying rate was substantially higher for lower airflow rates.