Using PCM to improve building's thermal performance

Due to EU and worldwide high energy consumption of the buildings stock, it is important to take measures to reduce these needs and, consequently, reduce the EU energy dependency as well as the greenhouse gas emissions. To improve the behaviour of the buildings, concerning thermal comfort of the occupants and energy performance, it is necessary to reduce the thermal amplitudes, the winter heat losses, the summer heat gains and to store the energy from solar gains. The thermal insulation and the thermal inertia play an important role in this. The use of phase change materials (PCM) is a way of achieving thermal mass without increasing the weight of the buildings and simultaneously improving the thermal comfort conditions inside buildings, by increasing thermal energy storage. The good thermal characteristics of PCM can be used, in new and existing residential or office buildings, as a passive way of saving energy and reducing running costs for both heating and cooling seasons. Therefore it is possible to achieve an adequate behaviour of buildings reducing the energy needs, using solar gains, night cooling and off-peak electricity and, at the same time, increasing the comfort conditions inside the buildings, reducing temperature fluctuations and peak temperatures. In the Mediterranean Countries the selection of the type and amount of PCM to be used is a challenge due to the different characteristics needed to achieve an adequate behaviour of the buildings during winter and summer periods. In this study, the use of micro and macro-encapsulated PCM in buildings was studied to evaluate the annual behaviour and to identify the amount of PCM needed to ensure a suitable thermal and energy performance of the buildings.The work was partially funded by the European Union (COST Action COST TU0802

Assessing the thermal performance of phase change materials in composite hot humid/hot dry climates: an examination of office buildings in Abuja-Nigeria

PhD ThesisThe aim of this study is to investigate the possibility of using Phase Change Materials (PCM) in improving indoor thermal comfort while conserving electricity in office buildings in the composite Hot Humid/Hot Dry climate of Abuja, Nigeria. The first stage is a quantitative investigation of electricity consumption in 15 Nigerian office Buildings. Purpose-built mechanically cooled office buildings are selectively chosen across major Nigerian cities and climates. The surveyed data is analysed and used to construct a hypothetical office building as a base case. Scientifically validated software DesignBuilder v3 and EnergyPlus V6 and V7 are used for the parametric analysis of simulation results. The building simulations are used in two stages, firstly to test passive and climatically responsive scenarios to reduce electricity consumption then secondly to study the potential benefit of incorporating PCM in the building fabric and its effect on thermal comfort and electricity conservation. Results show that cooling, lighting, and appliance loads account for approximately 40%, 12% and 48% respectively of electricity consumption in the buildings audited. Power outages are frequently experienced necessitating alternative power usage. A data collection method is presented for energy auditors in locations where alternative back-up power is essential. Simulation results indicate that the magnitude of energy saving can be achieved by optimizing the passive and climate sensitive design aspects of the building and an electricity saving of 26% is predicted. Analysis indicates that it is difficult to achieve thermal comfort in office buildings in Abuja without mechanical cooling. Adding such a PCM to the building fabric of a cyclically cooled mechanical building may alleviate indoor discomfort for about 2 hours in case of power outage and is predicted to save 7% of cooling load. Cyclic cooling is the cooling of the interiors long enough to maintain comfort for a maximum duration within the working hours. The use of lightweight partitions instead of the heavyweight ones common in Nigeria is shown to a 2-fold improvement in consumption. Adding a PCM to light-weight partition walls with transition temperature of 24°C, conductivity of 0.5W/m K, and a thickness of 10mm gives the best predicted energy savings.Petroleum Technology Development Fund (PTDF), Nigeria

Overheating in English dwellings: comparing modelled and monitored large-scale datasets

Monitoring and modelling studies of the indoor environment indicate that there are often discrepancies between simulation results and measurements. The availability of large monitoring datasets of domestic buildings allows for more rigorous validation of the performance of building simulation models derived from limited building information, backed by statistical significance tests and goodness-of-fit metrics. These datasets also offer the opportunity to test modelling assumptions. This paper investigates the performance of domestic housing models using EnergyPlus software to predict maximum daily indoor temperatures over the summer of 2011. Monitored maximum daily indoor temperatures from the English Housing Survey's (EHS) Energy Follow-Up Survey (EFUS) for 823 nationally representative dwellings are compared against predictions made by EnergyPlus simulations. Due to lack of information on the characteristics of individual dwellings, the models struggle to predict maximum temperatures in individual dwellings and performance was worse on days when the outdoor maximum temperatures were high. This research indicates that unknown factors such as building characteristics, occupant behaviour and local environment makes the validation of models for individual dwellings a challenging task. The models did, however, provide an improved estimate of temperature exposure when aggregated over dwellings within a particular region

Development of novel form-stable composite phase change materials and integration in building for thermal regulation

The integration of phase change materials (PCMs) into building components has attracted in-creasing interest in stabilising indoor temperatures by enhancing the thermal energy storage (TES) capacity and decreasing temperature swings, which lead to an improvement in buildings' thermal comfort and energy efficiency. Gypsum board, with the advantages of low cost and ease of placement, has wide applications for ceiling or wall covering. Thus, PCMs have great potential to be incorporated into gypsum board to improve the energy performance of buildings. However, the application of PCMs has been remarkably restrained by their poor shape stability during the phase change process. Accordingly, a challenge to practical application is that the PCM leak from the building materials. Moreover, due to its low thermal conductivity, the low heat transfer rate of normal PCM also acts as a block upon the wide utilisation of its enormous TES capacity benefits. As yet, very little research has been conducted to study the performance and benefits of using PCMs in real houses, especially in combination with thermal insulation. This study aims to overcome the above issues by containing PCM in porous diatomite material to develop form-stable composite PCM (FSPCM) and study the influence of using FSPCM in max-imising the TES capacity of gypsum board for improving the thermal performance of houses. Test results showed that the produced FSPCM with 48.7 wt.% of diatomite enhanced the thermal conductivity of PCM by 63.7% and eliminated the leakage issue above the PCM melting point. Experimental studies were conducted to develop an energy storage gypsum board by incorporating 40 wt.% of FSPCM in the board. An experimental study and a numerical investigation were conducted to investigate the feasibility of using the FSPCM board as a retrofitting solution to a model house in Sydney, Australia. Furthermore, the effectiveness of the combined use of FSPCM board and thermal insulation in improving the energy efficiency of residential houses was investigated

Analysis of energy requirements versus comfort levels for the integration of phase change materials in buildings

This paper investigates the importance of the design parameters when looking at possible energy savings and comfort enhancement in a building using Phase Change Materials (PCMs). Computer based simulations are performed using a simulation software for modelling a house and its thermal behaviour over a year. It is found that by varying the heating set point and the phase change (melting) temperature range of the PCM, significant changes can be observed. Some poor scenarios show that the integration of PCM can increase both the discomfort (up to 6% more discomfort hours) and the energy requirements (up to 25% more energy needed). On the other hand, appropriate scenarios bring significant energy savings (up to 33% less energy needed) and comfort enhancement (up to 31% less discomfort hours). This highlights the strong need for a clever design when integrating PCM into buildings. The goal is to find a trade-off between energy savings and comfort enhancement. The PCM with a phase change temperature range between 21 °C and 26 °C shows the best results. The study is based on climate conditions for Auckland City in New Zealand but most of the conclusions drawn can be applied to any climate. © 2015 Elsevier Ltd

TOWARDS THE DEVELOPMENT OF PERFORMANCE BASED GUIDELINES FOR USING PHASE CHANGE MATERIALS IN LIGHTWEIGHT BUILDINGS

Incorporating Phase Change Materials (PCMs) in construction materials can increase the thermal mass of a building. With this increase in thermal mass, PCMs are known to reduce the heating and cooling loads of a building significantly. During the past 10 years, studies have estimated potential reduction of energy consumption of buildings between 10 and 30 percent. This wide range is due to the large number of parameters that effect energy consumption and make the process of selecting the optimal type and amount of PCM challenging. In fact, extensive engineering studies are generally necessary to determine the practicality of PCM in any specific case. As a result, architects and engineers are reluctant to use PCM because of the lack of such a comprehensive study. In the United States, eight climate zones are identified on the basis of annual degree heating and degree cooling days. For a given building in a given climate, there exists an optimal melting temperature and enthalpy that can reduce the energy consumption and the payback period. In this research, the optimal properties of PCM boards are determined for all 15 representative cities. Additional topics discussed in this research are the sensitivity of the optimal properties of PCM and the effect of the average cost of energy on the selection of PCM. The effect of six independent variables on the performance of PCM boards is presented in detail and the climate types where PCM boards perform optimally are narrowed down. In addition, a new procedure is presented to study the temporal and directional melting and solidifying trend of the PCM placed in buildings. The energy consumption and hourly data for the PCM enhanced buildings are determined numerically using the Department of Energy software EnergyPlus, which calculates the energy consumption for heating and cooling a building under any climate and operation schedule. The software is run on a computer cluster for a wide range of properties from which the optimal values are extracted. The findings from this research suggest that, there are only a few climate types within the United States where the use of PCM boards in lightweight buildings are viable. While the market potential for PCMs in building energy improvements can be significant, its acceptance is hindered by its extraordinary high cost. Analysis of the performance of PCM boards against six independent variables suggests that the internal load is a crucial factor in determining the optimal performance of PCM. Therefore any guideline on the selection of proper PCM should be formulated predominantly on the basis of internal load and the internal mean air temperature

Vulnerability of U.S. Residential Building Stock to Heat: Status Quo, Trends, Mitigation Strategies, and the Role of Energy Efficiency

abstract: Thermal extremes are responsible for more than 90% of all weather-related deaths in the United States, with heat alone accounting for an annual death toll of 618. With the combination of global warming and urban expansion, cities are becoming hotter and the threat to the well-being of citizens in urban areas is growing. Because people in modern societies (and in particular, vulnerable groups such as the elderly) spend most of their time inside their home, indoor exposure to heat is the underlying cause in a considerable fraction of heat-related morbidity and mortality. Notably, this can be observed in many US cities despite the high prevalence of mechanical air conditioning in the building stock. Therefore, part of the effort to reducing the overall vulnerability of urban populations to heat needs to be dedicated to understanding indoor exposure, its underlying behavioral and physical mechanisms, health outcomes, and possible mitigation strategies. This dissertation is an effort to advance the knowledge in these areas. The cities of Houston, TX, Phoenix, AZ, and Los Angeles, CA, are used as test beds to assess exposure and vulnerability to indoor heat among people 65 and older. Measurements and validated whole-building simulations were used in conjunction with heat-vulnerability surveys and epidemiological modelling (of collaborators) to (1) understand how building characteristics and practices govern indoor exposure to heat among the elderly; (2) evaluate mechanical air conditioning as a reliable protective factor against indoor exposure to heat; and (3) identify potential impacts from the evolving building stock and a warming urban climate. The results show strong associations between indoor heat exposure and certain health outcomes and highlight the vulnerability of elderly populations to heat despite the prevalence of air conditioning systems. Given the current construction practices and urban warming trends, this vulnerability will continue to grow. Therefore, policies promoting climate adaptive buildings features, as well as better access to reliable and affordable AC are needed. In addition, this research draws attention to the significant potential health consequences of large-scale power outages and proposes the implementation of passive survivability in regulations as one important preventative action.Dissertation/ThesisDoctoral Dissertation Engineering 201

Computational modelling of latent heat storage systems with integrated phase change materials in building applications

89 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Υπολογιστική Μηχανική”Ο σκοπός αυτής της διπλωματικής εργασίας είναι να εκτιμήσει την επίδραση θερμικών συστημάτων, τα οποία ενσωματώνουν υλικά αλλαγής φάσης, με την ανάπτυξη υπολογιστικών εργαλείων. Στην εισαγωγή, μια σύντομη θεώρηση καταλήγει στο ότι, ο σύγχρονος τρόπος ζωής απαιτεί μεγάλες ποσότητες ενέργειας στον κτιριακό τομέα, ούτως ώστε να καλυφθούν οι ανάγκες φωτι- σμού και θερμικής άνεσης. Τα συστήματα αερισμού, θέρμανσης και κλιματισμού καταναλώνουν, ίσως, την περισσότερη ενέργεια, και για τον λόγο αυτό η απόδοσή τους παίζει σημαντικό ρόλο στην εξοικονόμηση ενέργειας. Μία, σχετικά, νέα γενιά εφαρμογών μπορεί να καταστήσει τα συστήματα αυτά πιο αποδοτικά. Οι εφαρμογές αυτές υιοθετούν την χρήση υλικών αλλαγής φάσης. Τα υλικά αυτά μπορούν και συσσωρεύουν ενέργεια υπό την μορφή λανθάνουσας θερμότητας. Με τον τρόπο αυτό επιτυγχάνεται η θερμοκρασιακή ομοιομορφία. Επίσης, η αποθηκευμένη θερμότητα μπορεί να χρησιμοποιηθεί σε μελοντικό χρόνο. Τα υλικά αυτά, ο τρόπος λειτουργίας τους, καθώς και τα ιδιαίτερα χαρακτηριστικά τους μελετώνται στο δεύτερο κεφάλαιο. Στις περιπτώσεις που μελετώνται, οι κτιριακές εγκαταστάσεις θερμαίνονται λόγω της ηλιακής ακτινοβολίας. Επίσης, λόγω θερμοκρασιακών διαφορών, παρατηρούνται φαινόμενα φυσικής συναγωγής. Για τους λόγους αυτούς, ο ρόλος του τρίτου κεφαλαίου είναι να λειτουργήσει ως μια εισαγωγή σε φαινόμενα μεταφοράς και ρευστοδυναμικής. Επιπροσθέτως, θα αποδειχθεί, ότι η αναλυτική επίλυση του θερμοκρασιακού και του ροϊκού πεδίου είναι αδύνατη, συνεπώς η αριθμητική προσέγγιση κρίνεται απαραίτητη. Στοιχεία της υπολογιστικής μεθόδου των πεπερασμένων όγκων θα κλείσουν το κεφάλαιο αυτό. Στο τέταρτο κεφάλαιο, λαμβάνει χώρα η υπολογιστική μελέτη δύο περιπτώσεων. Αρχικά, περιγράφεται η πειραματική μελέτη συστήματος περσίδων, στο οποίο έχει εγκατασταθεί υλικό αλλαγής φάσης. Εν συνεχεία, αναλύονται τα χαρακτηριστικά του υπολογιστικού μοντέλου. Τελικά, παρουσιάζονται τα αποτελέσματα της προσομοίωσης, τα οποία παρέχουν ικανοποιητική συμφωνία με τις τιμές του πειράματος, παρέχοντας πιστοποίηση στο υπολογιστικό εργαλείο. Στο δεύτερο σκέλος, μελετήθηκε ένα νέο σύστημα, το οποίο αποτελείται από περιστρεφόμενες περσίδες. Οι περσίδες ενσωματώνουν ένα στρώμα μονωτικού καθώς και υλικό αλλαγής φάσης. Εκτιμήθηκε η επίδραση του συστήματος στην θερμική συμπεριφορά εξωτερικού τοιχώματος, υπό δύο διαφορετικές κλιματικές συνθήκες. Τα αποτελέσματα δείχνουν ευνοϊκή επίδραση έναντι σε περιπτώσεις χωρίς την εγκατάσταση του συστήματος. Ωστόσο, προτείνονται συμπληρωματικές προσομοιώσεις και βελτιώσεις στο υπολογιστικό μοντέλο, για την εξαγωγή περαιτέρω χρήσιμων συμπερασμάτων. Τέλος, γενικά συμπεράσματα και προτάσεις για μελλοντική δουλειά κλείνουν αυτή την διπλωματική. Τα υλικά αλλαγής φάσης παρουσιάζουν θετικό αντίκτυπο σε κτιριακές εφαρμογές, ενώ το υπολογιστικό εργαλείο, που αναπτύχθηκε, δείχνει να έχει δυνατότητες εξέλιξης.The purpose of this thesis is to assess the effect of thermal systems that incorporate phase change materials, with the development of a computational tool. In the introduction, a brief consideration concludes, that the modern way of life requires large amounts of energy in the building sector, in order to meet the needs of lighting and thermal comfort. The ventilation, heating and air conditioning systems consume more energy, and therefore their performance plays a significant role in saving energy. A, relatively, new generation of applications can make these systems more efficient. These applications adopt the use of phase change materials. These materials can store energy in the form of latent heat. Thereby, it is necessary to study their behaviour, their advantages and, also, their limitations. In addition, previous works were investigated. This contributed in gaining insight and, also, a valuable fashion to treat the heat capacity: the effective heat capacity method. These topics are discussed in the second part. The investigated cases in this work, present complicated features: the buildings are heated with thermal radiation, natural convection is observed and multi-layer objects are employed. Hence, the role of the third chapter is to serve as an introduction to heat transfer phenomena and fluid dynamics. It is discussed, that an analytical approach on the temperature and flow fields is impossible. Hence, the computational method of finite volume will close this chapter The fourth chapter presents the computational study of two cases. Initially, the experimental study of a blind, which integrated a phase change material, is described. Then, the characteristics of the numerical model are presented. Eventually, the results of the simulation show a very good agreement to the experiment, verifying the method. Furthermore, a new developed system is investigated under two different environment conditions. This system consists of slats, in which an insulation layer and a phase change material are embedded. It will be installed on walls of existing building to improve their thermal characteristics. The results show the beneficial role of the specific applications in the summer period. More tests should be performed to obtain more useful information for winter days as well. In addition, an overview reveals the positive and negative features of this method, and countermeasures are suggested. Finally, general remarks of this work with comments and overall observations conclude this work. Thermal energy storage systems have, in general, a positive impact and we can gain the most out of them with careful design. The presented numerical method is considered suitable to simulate heat transfer phenomena and future simulation work is outlined.Ιωάννου Νικόλαο