Thermal Building Envelope Research Articles

Reuse of wood biomass ash to improve thermal behavior of gypsum plasters

Huge amounts of waste are generated each year in the world. In addition, the construction sector is one of the larger producers of residues and a huge energy consumer. Thus, architects, engineers and other actors of the building sector should give solutions in order to reduce that problem. In that sense, the idea of finding solutions for the end of the service life of materials, in order to promote circularity, has been studied by several researchers. In this study, biomass wood ash has been used as aggregate for the generation of new eco-efficient gypsum plasters, for its application in new buildings and rehabilitation works. In order to conduct an exhaustive characterization of the new composites, an experimental campaign of the plasters has been conducted: dry bulk density and thermal conductivity of the plasters have been measured. The results showed that it was possible to add up to 25% of wood ash without modifying the water/gypsum ratios. Moreover, thermal conductivity of the plasters has improved up to18% when the ash was added to the mixture. Finally, the effects of using the new gypsum composites in the thermal envelope of buildings was analyzed by its usage in a rehabilitation case study simulation.

Comparing overheating risk and mitigation strategies for two Canadian schools by using building simulation calibrated with measured data

This paper compares the indoor overheating risk of two schools by considering the effect of selected building parameters, under extreme current and future climates, and proposes mitigation strategies. The indoor air temperature measurements were conducted in seven classrooms in two schools constructed in 1960 and 1990. These measurements are used to calibrate the building simulation models of these schools. The study's results show that, in the current extreme year, classrooms on upper floors with larger window-wall ratios WWR (60%) and lower thermal building envelope properties are at a higher risk of overheating. Conversely, in classrooms located on lower floors, or featuring a small WWR (10%), or better thermal properties, no other Climate-resilient measures are needed. Under extreme future years the external roller blind shading, night cooling, and cool roof measures will be necessary for both schools, particularly for last-floor classrooms with south orientation and a 60% WWR in 1960 building.

Thermomechanical characterization and thermal simulation of a new multilayer mortar and a light-weight pozzolanic concrete for building energy efficiency

A brand-new sandwich material has been developed with a pozzolan-granular, plaster composite core and two cement mortar protective layer. The main goal of this study is to test the thermal behavior of a new sandwich material as well as the thermomechanical characteristics of pozzolanic concrete. The effects of granulomere sizes on the thermal properties of sandwich materials, as well as the volume fraction of pozzolan on the thermomechanical properties of lightweight concrete, have been studied. As a reference, mortar and concrete samples were made. The morphology and chemical composition of pozzolan granular were studied using scanning electron microscopy and X-ray fluorescence respectively. An energy building simulation of a prototype by Using TRNSYS simulator software, with variable internal and external walls composition, is performed; in order to evaluate the energy performance of sandwich material and lightweight concrete with optimum mechanical and thermal properties obtained from this work. Experimental results have shown that the incorporation of pozzolan as aggregates in the multilayer material and the concrete improves their thermal behavior. For multilayer material, it was shown that thermal conductivity varies from 0.682 W.m−1.K−1 to 0.42 W.m−1.K−1 for a sandwich sample having a granular size of pozzolan (7–20 mm) compared with reference mortar with 21.17 % mass gain. Concerning effusivity and diffusivity, of the same samples are varied from 723 to 575 J m−2.K−1.s−1/2 and from 3.51 to 2 10–7 m2.s−1 respectively. While for concrete without pozzolanic aggregate compared with a lightweight concrete sample having 100 % of volume fraction of Pozzolan, the thermal conductivity varies from 1.5 W.m−1.K−1 to 0.79 W.m−1.K−1 respectively with 31 % mass gain. Unfortunately, the mechanical performance decreases. The results of the thermal simulation have shown that sandwich material and lightweight concrete might be used in the thermal building envelope and walls. It offers significant reductions in cooling and heating energy consumption of 22 % and 14 %, respectively, as well as a significant yearly decrease in CO2 emissions of roughly 611.57 kg CO2e and 810 KgCO2e. When compared to other common wall materials, the results reveal that the new green construction materials have exceptional self-insulation properties.

Possibilities of improving the design of sectional aluminium radiator

The main trend in the development of district heating systems in recent years is a decrease in the temperature of heat carrier, based on the desire to include renewable energy sources in such systems. Despite the ever-increasing demands on the thermal envelope of buildings, lowering the temperature entails the need to increase the area of heating appliances. In turn, this leads to an increase in material consumption of heating systems, increasing their hydraulic resistance and design problems. In order to avoid or at least reduce these negative consequences of the struggle to increase the environmental friendliness and energy efficiency of district heating systems, it is necessary to intensify the heat dissipation of heating appliances. The existing designs of sectional aluminium radiators, which are the most promising for improving their thermal performance, have reached a certain limit in the design, to overcome which it is necessary to change the technology of manufacturing the heat dissipating element of the section. The article shows the reasons for the emergence of such a limit for the existing design of devices, formulates requirements for advanced designs and shows the way to achieve higher thermal performance. The article presents the results of calculations that confirm the presence of the detected limit of thermal performance of existing structures of sectional aluminium radiators. Based on the analysis of existing designs and the identified limits of their further development, a new design of aluminium sectional heating device is proposed, which allows to bypass and overcome the limitations that are characteristic of existing ones. The results of calculations showing the possibilities of intensification of heat transfer of a sectional aluminium device are given. At the same heat output, the dimensions of the proposed radiator will be about thirty percent smaller than the size of existing appliances. The article presents the results of tests of prototypes of sectional radiators of the new design, manufactured using new technology. Devices consisting of seven sections of three sizes in height were investigated: 293 mm, 596 mm, 1097 mm. The results of the study confirmed previous theoretical developments. The tests were conducted in a laboratory certified according to European Union standards at the Institute of Heating and Sanitary Engineering in Radom (Poland).

Influence of heating degree day calculation methods in designing the thermal envelope of buildings

Heating degree day is an essential parameter for estimation of energy demand and consumption in buildings. In the case of hourly temperature data availability, it is more appropriate to use the hourly method to calculate heating degree days. In the situation of reduced meteorological data, other methodologies must be selected for calculation. These methodologies include ASHRAE and UKMO methods. The aim of the present study is to analyse the effect of substitution in the heating degree day calculation method to modify building recommendations of current Chilean thermal building codes, maintaining the transmission heat losses through thermal envelope of buildings, in various geographical locations, with different climatic conditions. Analysing the data obtained from 165 meteorological stations, it has been discovered that there are significant differences in the geographical distribution of heating degree days calculated with ASHRAE and UKMO methods in desert areas, while heating degree days are similar in regions with a more temperate climate with both methods. When there is a significant frequency of days with large daily temperature amplitude, it is more advisable to use the UKMO method for the calculation of heating degree days. For all these reasons, new values of thermal transmittances have been proposed for the opaque elements of the thermal envelopes with the developed methodology. A reduction by up 65% of the values of thermal transmittances are required using UKMO method in desert areas and no variations are required in cold zones. The new values of thermal transmittances proposed will help to improve the energy performance of buildings and to achieve a better adaptation to the climatic conditions.

Evaluation of the Impact of the Envelope System on Thermal Energy Demand in Hospital Buildings

Construction materials and systems for the thermal building envelope have played a key role in the improvement of energy efficiency in buildings. Urban heat islands together with the upcoming rising global temperature demand construction solutions that are adapted to the specific microclimate conditions. These circumstances are even more dramatic in the case of healthcare buildings where the need to preserve constant indoor temperatures is a priority for the proper recovery of patients. A new neonatal hospital, located in Madrid (Spain), has been monitored, and building energy simulations were performed to evaluate the effect of the building envelope on the energy demand. Based on the simulation results, the design of the building envelope was found to be insufficiently optimised to properly protect the building from the external heat flow. This is supported by the monitored results of the indoor temperatures, which went over the standard limit for about 50% of the hours, achieving up to 27 °C in June and July, and 28 °C in August. The results showed, on one hand, that solar radiation gains transmitted through the façade have an important impact on the indoor temperature in the analysed rooms. Heat gains through the opaque envelope showed an average of 8.37 kWh/day, followed by heat gains through the glazing with an average value of 5.29 kWh/day; while heat gains from lighting and occupancy were 5.21 kWh/day and 4.47 kWh/day, respectively. Moreover, it was shown that a design of the envelope characterised by large glass surfaces and without solar protection systems, resulted in excessive internal thermal loads that the conditioning system was not able to overcome.

Influence of the Water Vapour Permeability of Airtight Sheets on the Behaviour of Facade

The air-tightness of the thermal envelope of buildings is one of the measures to reduce their energy demands in order to achieve global warming reduction targets. To this end, airtight sheets with different water vapour permeability characteristics are used. The different products studied are highly dispersed in terms of equivalent air thickness values, leading to confusion. After the analysis carried out, it is concluded that all airtight sheets are vapour barriers. To clarify whether or not these sheets are necessary as vapour barriers, a condensation analysis was carried out on 13 different facades for 3 climate zones with severe winters as defined in Spanish regulations. The results reveal that interstitial condensation occurs in only 7 of the 39 case studies, with the traditional facades of brickwork with render causing the greatest problems if the appropriate products are not used. In these cases, airtight sheets with water vapour barrier characteristics must be applied on the interior face of the insulating material. In all other cases (32), the airtight sheets must be permeable to water vapour if it is looked for a more breathable wall to water vapour and a better control of the interior humidity conditions.

Building moisture diagnosis: Processing, assessing and representation of environmental data for root cause analysis of mould growth

The occurrence of surface condensation and mould can lead to concerns of poor indoor air quality and adverse health implications of occupants. Remedial actions require identification of the root causes, but this can be challenging even for experts. The focus of the research is the development of a diagnostic tool that helps to streamline root cause analysis. The diagnostic method comprises a protocol with guidelines for installation of sensors, easy data collection, and a set of calculations to process environmental information. Environmental parameters collected and calculated from an environmental monitoring exercise of dwellings with and without mould, include physical properties associated with the indoor surface of external walls and surrounding air conditions. The methodology relies on linking specific surface and air environmental parameters together with critical thresholds proposed for the control and avoidance of surface condensation and mould growth in dwellings. These parameters were assessed and used to determine the likely causal factors of a moisture imbalanced environment leading to surface condensation and mould growth; poor thermal building envelope performance, an imbalanced heat-moisture regime, and/or insufficient ventilation. Examples from different scenarios are presented to show the process towards environmental data collection, post-processing to compute and assess pertinent parameters, and the display of environmental conditions in a clear and easy-to-interpret manner. The novel developed system is a time-saving method for processing and represents environmental data. It provides a straightforward building moisture index (BMI) and a systematic diagnostic procedure for environmental assessment and possible causes of mould growth. This helps to support neutral decision making, to identify rectification strategies and direct to more cost-efficient solutions to existing damp and mould problems in buildings.

Thermomechanical study of a sandwich material with ecological additives

New sandwich material was produced using clay-granular cork composite as core material with a protective coating of plaster and cement mortar. The principal purpose of the present work is to evaluate the thermomechanical behavior of the innovative sandwich material experimentally. The effect of volume fraction of plaster and cement mortar coating on the thermomechanical properties of sandwich material has been explored. Samples of clay-granular cork composite were prepared as reference. Asymmetrical Hot Plate method in transient and steady-state regimes has been applied for thermal characterization. Compressive and flexural strengths of sandwich material specimens were tested. The morphology of clay-cork composite was studied using scanning electron microscopy. An energy building simulation of a model house, with variable external wall composition, is performed to evaluate the energy performance of sandwich material with optimum mechanical and thermal properties deduced from this work. Results show that the addition of plaster and cement mortar coating improves the compressive and flexural strength of sandwich material, respectively, from 0.96 MPa to 4.56 MPa and from 2.29 MPa to 3.71 MPa for a sandwich sample having 45% of volume fraction of coating layers compared with clay-cork composite without coating. Unfortunately, thermal performance decreases. Sandwich material samples with the optimum thermal and mechanical performance having 22.5% volume fraction of coating were checked in the current study. Rupture observed mainly during compressive tests occurred mostly by fracture between cork aggregates of the core. Therefore, allowing for targeted improvement of the strength of inter-granular adhesion and the bonding between cork granules. That can ameliorate the mechanical performance of the sandwich material significantly. Results of thermal simulation indicate a potential for the use of sandwich material in the thermal building envelope. It represents very high gains in energy needs of cooling and heating and greenhouses emissions in the range of 31–45% for sandwich material walls compared to Bensmim bricks and conventional bricks walls, showing remarkable self insulation characteristics compared with other wall materials.

Special Issue “Building Thermal Envelope”

The increasing requirements in building thermal and energy performance standards and the need to design nearly zero-energy buildings, while still enhancing the indoor comfort conditions, have led to a demand for more efficient thermal building envelope solutions [...]

Experimental and Computational Study of the Implementation of mPCM-Modified Gypsum Boards in a Test Enclosure

The application of phase change materials (PCM) in the thermal envelope of buildings has proven to be an alternative to reduce energy consumption and to improve thermal comfort conditions. The present work evaluates the thermal behavior of gypsum boards modified with a microencapsulated PCM (mPCM) in a cubic test enclosure, considering the climatic conditions of Santiago de Chile in the September–November period of 2017. The design of the test enclosure was performed considering the minimization of parameters that affect the variation of its inner temperature and favoring the heat flow through the gypsum boards. Experimentally, the results reflect the main effects of the implementation of a mPCM, among which the displacement of the maximum heat load and the decrease in the daily oscillation of the internal temperature of the test enclosure (up to 2 °C) stand out. In addition, the mPCM modified gypsum board was thermally characterized to carry out a thermal simulation of the enclosures using EnergyPlus™. The obtained numerical results agree with those obtained experimentally, including the behavior of the transient heat flux through the gypsum boards. Moreover, it was found that considering a null infiltration rate gives place to unrealistic results, suggesting that this parameter should be controlled.

Energy and carbon balance of materials used in a building envelope renovation

Construction and demolition waste (CDW) are a priority waste stream in EU’s polices, accounting for about 30% of all waste generated. At the same time, according to the EU energy-efficiency directive, existing buildings subject to significant renovation need to be upgraded in their thermal building envelope in order to meet higher energy performance standard. This involves additional building materials and hence increases the CDW generation. This study investigates the energy and CO2 emission balance of building envelope renovation when using different building materials, taking into account the production and end-of-life stages. The study is based on a Swedish case-study building assumed to be upgraded to the passive house standard. Benefits from waste recovering are considered, including construction and demolition wastes. The results show that the selection of building materials can significantly affect the primary energy and CO2 emission balances. Depending on the material alternative the end-of-life primary energy use and net CO2 emission can be reduced by 5%-21% and 2%-24%, respectively, compared to the initial primary energy use and net CO2 emission. Therefore, a careful material choice at the design stage, as well as an efficient waste management, can contribute to reduce primary energy use and CO2 emission associated with energy renovation of existing buildings.

Comparative Life-Cycle Analysis of Building Materials for the Thermal Upgrade of an Existing Building

The existing building stock is estimated to need major renovations in the near future. At the same time, the EU energy-efficiency strategy entails upgrading the energy performance of renovated buildings to meet the nearly-zero energy standard. To upgrade existing buildings, two main groups of measures can be adopted: thermally-improved building envelope and energy-efficient technical devices. The first measure usually involves additional building materials for thermal insulation and new building cladding, as well as new windows and doors. A number of commercially-available materials can be used to renovate thermal building envelopes. This study compares the life-cycle primary energy use and CO2 emission when renovating an existing building using different materials, commonly used in renovated buildings. A Swedish building constructed in 1972 is used as a case-study building. The building’s envelope is assumed to be renovated to meet the Swedish passive house standard. The entire life cycle of the building envelope renovation is taken into account. The results show that the selection of building materials can significantly reduce the production primary energy and associated CO2 emissions by up to 62% and 77%, respectively. The results suggest that a careful material choice can significantly contribute to reduce primary energy use and CO2 emissions associated with energy renovation of buildings, especially when renewable-based materials are used.

Economic and ecological sustainability of the thermal building envelope: a cross-European perspective

The building sector is crucial to reach the goals of common climate agreements. This paper contrasts three approaches to reduce emissions from typical residential buildings in Central Europe: the instalment of electric heat pumps (eHP), a thicker insulation of the thermal envelope and the encumbrance of a carbon tax. The use of less carbon intense fuels allows major savings of GHG emissions. An insulation thickness of 30 cm leads to GHG emission savings of 8% against a thickness of just 12 cm, while total cost savings (LCC) remain negligible. The introduction of a carbon tax of up to 250 €/t-CO2-eq. does not necessarily result in a reduction of GHG emissions due to increased costs of construction. It was further found that the focus of legal building regulations on heating demand is sufficient for now but needs to be revised as carbon intensities continue to decrease. The heating then reduces its share of the GHG emissions from 85 to 55% for typical residential buildings. The paper closes with a general expression of the lifecycle costs of a building which is dependent on the factors above.

Improving Ventilation Efficiency for a Highly Energy Efficient Indoor Swimming Pool Using CFD Simulations

The operation of a typical indoor swimming pool is very energy intensive. Previous studies have shown that high quality thermal building envelopes, i.e., with high levels of insulation and airtightness, make it possible to rethink conventional ventilation concepts. Due to the reduced condensation risk in and on envelopes of high thermal quality, ventilation design can be optimized for indoor air quality rather than for averting condensation on the facade. This work investigates different air distribution concepts for an existing swimming pool via computational fluid dynamics (CFD) simulations to evaluate their ventilation efficiency. To reduce modelling and computational resources, the velocity and turbulence fields produced by the swirl-diffusers are determined in a set of separate CFD simulations and incorporated into the swimming pool models. The results show that the ventilation efficiency in the examined swimming pool could potentially be improved with various alternative air distribution concepts, therefore improving the indoor air quality. Although the results seem plausible and compare well with the limited measurement data of air humidity, a more formal experimental validation is still needed before generalizing recommendations.

Enameled Glass Panels for Solar Thermal Building Envelopes

The paper presents a novel concept of solar thermal panel specifically intended for building integration, aiming at a higher architectural quality and at a reduction of installation costs. The panel consists of a low-emissivity enameled flat glass as solar absorber and a metallic heat exchanger, which are glued together by an adhesive layer. It features high design flexibility and can be used as roof or façade cladding in combination with common frames and profiles. We analyze the potential of the panel both as uncovered and covered collector by means of efficiency measurements on large-sized prototypes according to ISO 9806. Our results show that panels equipped with black enameled glass can achieve performance values competitive with those of commercial available products (uncovered panel: η0 = 0.75, b1 = 8.05W/m2K, b2 = 1.64J/m3K, bu = 0.043 s/m; covered panel: η0 = 0.74, a1 = 4.26W/m2K, a2 = 0.013W/m2K2). As reported by our optical measurements on small samples, colored glass can exhibit solar absorptance up to 0.93, thus representing an aesthetically appealing alternative to black panels. For its implementation, system integration, operating conditions and design aspects have to be taken into consideration.

Correlation between the morphology of unheated staircase and energy performance of residential buildings

As a side effect of the need for greater energy efficiency of buildings, there is a problem of decrease of the available interior space affected by the reduction in U-value of parts of thermal building envelope, i.e. an increase in thickness of insulating layer, which is especially present in unheated staircase. Having in mind that present methods of calculation of transmission heat losses through elements of thermal envelope include the adjustment factor which regulates designed temperature conditions if the temperature at the colder side of the element of the thermal envelope differs from that of the external environment, this paper strives to demonstrate that in the case of unheated staircases, this fixed value should be reconsidered and treated as a variable depending on the morphology, i.e. form, size and position of the staircase within the building. This problem has been analyzed on the example of Serbian housing stock and relevant national thermal regulations. Three morphological types of unheated staircases have been distinguished within which three models have been defined and examined with respect to variations in number of floors and percentage of glazing. Average temperatures of staircase volume and temperature correction factors were calculated in following temperature modes: stationary that excluded solar gains and ventilation heat losses and gains, and dynamic with variations in air exchange rates and insolation conditions, expressing in all of the cases variations in calculated values of temperature correction factors in comparison to the prescribed fixed value.

Towards a Brazilian standard for naturally ventilated buildings: guidelines for thermal and air movement acceptability

The Brazilian Federal Government has been recently promoting energy-conservation initiatives, most notably the ‘Thermal Performance in Buildings – Brazilian Bioclimatic Zones and Building Guidelines for Low-Cost Housing’ and the ‘Federal Regulation for Voluntary Labelling of Energy Efficiency Levels in Commercial, Public and Service Buildings’. These new regulations provide information for designers based on Brazil's climate requirements, with specific advice related to lighting systems, HVAC and the thermal envelope of buildings. Nevertheless, requirements for naturally ventilated indoor environments appear as an open category without clear criteria. To address this, the paper proposes guidelines for naturally ventilated environments in which specific thermal and air movement acceptability goals must be achieved. The guidelines are based on results from field experiments in non-residential naturally ventilated buildings in different climatic zones as well as drawing on other studies. The proposed guidelines consider occupants' adaptive potential as well as thermal and air movement acceptability. Combining thermal acceptability with air movement acceptability is a key design challenge. Permissible operative temperature ranges are based on the ASHRAE 55 adaptive comfort standard, and minimum air velocity requirements within the occupied zone are specified. Considerations also included ‘active’ occupants and specific control over openings and fans. Le Gouvernement fédéral brésilien encourage depuis peu les initiatives en faveur des économies d'énergie, et tout particulièrement les initiatives « Performances Thermiques des Immeubles – Zones Bioclimatiques Brésiliennes et Directives de Construction pour les Logements à Faible Coût » et « Réglementation Fédérale pour l'Etiquetage Volontaire des Niveaux de Rendement Energétique des Immeubles Commerciaux, Publics et de Services ». Ces réglementations nouvelles fournissent aux concepteurs des informations basées sur les exigences climatiques du Brésil, et s'accompagnent de conseils spécifiques relatifs aux systèmes d'éclairage, aux systèmes CVCA et à l'enveloppe thermique des immeubles. Néanmoins, les exigences relatives aux environnements intérieurs à ventilation naturelle apparaissent comme une catégorie ouverte sans critères clairs. Pour traiter ce problème, le présent article propose des directives pour les environnements à ventilation naturelle dans lesquels des objectifs spécifiques d'acceptabilité thermique et en matière de circulation d'air doivent être atteints. Ces directives sont basées sur les résultats d'expériences de terrain menées dans des immeubles non résidentiels à ventilation naturelle dans différentes zones climatiques, mais s'appuient également sur d'autres études. Les directives proposées prennent en considération le potentiel adaptatif des occupants aussi bien que l'acceptabilité thermique et en matière de circulation d'air. Réussir à combiner l'acceptabilité thermique et l'acceptabilité en matière de circulation d'air pose un problème de conception essentiel. Les plages de température de service admissibles sont basées sur la norme de confort adaptatif ASHRAE 55, et les exigences minimales quant à la vitesse de l'air dans la zone occupée sont précisées. Ont également été pris en considération les occupants « actifs » et les commandes spécifiques des ouvertures et des ventilateurs. Mots clés: confort adaptatif acceptabilité de la circulation d'air directives de conception ventilation naturelle occupants satisficing [stratégie de prise de décision] acceptabilité thermique confort thermique

Development of windows based on highly insulating aerogel glazings

Within a finished and a current EU project, research and development are being carried out on the use of monolithic silica aerogel as transparent insulation in windows. Results related to the window application will be presented here. At the thermal envelope of buildings, the window area is the weakest part with respect to heat loss, but at the same time, this area also provides advantages, e.g., solar energy gain. Glazing prototypes have been made of aerogel tiles of about 55×55cm2 (fabricated within the EU projects). The tiles are evacuated rapidly and easily sealed between two glass panes and a specific rim seal. A heat-treatment phase (after the supercritical CO2 drying) of the aerogel is currently being developed in order to improve its optical quality. This step increases the solar transmittance by ∼6 percentage points. For glazing prototypes with an aerogel thickness of ∼15mm, a center heat-loss coefficient of <0.7Wm−2K−1 and a solar transmittance of 76% have been obtained.