Thermal Transmittance Of Wall Research Articles

Improving the energy performance of a 3D-printed wall using recycled material

In this paper, we present the results of a preliminary experimental campaign conducted on a 3D-printed wall 40 cm thick made of three concrete walls, connected by metal pins and concrete curbs to form three types of cavity - one rectangular and two triangular. The tests were performed in a climatic chamber at the Pietro Pisa Laboratory of the University of Brescia. The wall thermal performance has been evaluated by examining four scenarios in which the cavities have been filled with insulating material made of cellulose-based recycled flakes characterized by a declared thermal conductivity of 0.038 W/mK. The wall thermal transmittance U is measured based on the temperatures and heat fluxes measured through the structure. Based on the degree of filling, the wall thermal transmittance ranges between 1.58 W/m2K for the wall without insulation, and 0.28 W/m2K for the configuration with all cavities completely filled.

Improvement in the Energy Efficiency Label level – PBE Edifica: Case Study of the Community Library of the Federal University of São Carlos (UFSCar) – São Paulo - Brazil

This article describes the application of a method of environmental certification of buildings used in Brazil and named as Brazilian Labelling Program PBE–Edifica. The method was developed by Procel, National Electric Energy Conservation Program, which confers, four Labels of the Energy Efficiency levels of a building, covering the Envelope; the Lighting System; the Indoor Air Conditioning; and the building Overall, which includes all previous levels and bonuses. The levels and scope of the Label apply both in the design phase and after construction or existing building in accordance with the Technical Quality Regulation for the Level of Energy Efficiency for Commercial, Service and Public Buildings, RTQ-C. The efficiency level ranges from A to E, where A is the most efficient and E the least efficient. The method also considers Bonuses that allow improvements in the Overall Classification efficiency. Thus, the objective of the research carried out was to identify the classification of the level of energy efficiency of an existing building on the campus of the Federal University of São Carlos, the Community Library, called BCo, Brazil built in 1995 with an area of 6,947.48 m2. The guidelines of the PBE Edifica using the prescriptive method were applied, and the characterization of the level of energy efficiency was carried out based on data obtained from plans and technical drawings of the building, and through a technical visit to obtain the data for entry into an application, WebPrescriptive. To obtain specific information about the wall's thermal transmittance and roof solar absorbance the PROJETEE application was used. All information processed so the building obtained an Overall classification C. For envelope and lighting level E, and air conditioning level B. To improve the level of efficiency, through bonuses, improvements in the lighting system and the elevator were suggested, resulting in level B for both Lighting and Overall efficiency. Notice that the building, due to its design and construction system does not have the conditions to reach level A of efficiency. In conclusion, we would like to point out that it is feasible to submit the building to the formal labelling process, since the proposed improvements resulted in an Overall Energy Efficiency Rating B. As a contribution for EFFICACY Project, some guidelines to be considered for buildings rehabilitation will be stated, as simulation of thermal insulation in facades and others improvements.

Experimental validation and uncertainty analysis of an innovative IoT infrared sensor for in-situ wall thermal transmittance measurement

This paper presents the development and experimental validation of an Internet of Things (IoT) thermography system for in-situ and real-time monitoring of wall thermal transmittance. The solution proposed has been derived from the upgrade of the Comfort Eye sensor, which is an infrared-based sensor adopted for non-intrusive indoor environmental quality monitoring in occupied buildings. In this work, the system has been used to detect potential building envelope inefficiencies and track building performance trends in a continuous way. The methodology is based on the ISO 9869-2 standard but it has been applied to an entire wall and during its normal functioning without the need of operators. The data management has been performed with a dedicated IoT architecture that allows the synchronised collection of quantities required for transmittance calculation, i.e. indoor and outdoor air temperatures together with the thermographic maps of the wall. The measurement technique has been validated in a real building through the comparison with the results obtained using a heat flux meter (HFM). An uncertainty analysis with Monte Carlo simulation has also been performed to evaluate the overall uncertainty of the method. The values obtained are coherent with those measured with the HFM and the infrared system has proved to be able to provide thermal transmittance measurements with an expanded uncertainty of ±0.038 W m−2K−1 with coverage factor k = 2. The innovative methodology described can be used for U-value estimation without the need for extra measuring tools.

Proposal of a correction factor for predicting the thermal transmittance of building envelopes in existing buildings accounting for aging and environmental conditions

Thermal transmittance is often considered a constant value in building design and assessment of building performance. However, the thermal transmittance of the building envelope changes as a result of aging and environmental parameters. To accurately evaluate the energy performance of existing buildings, it is important to define the degradation of the thermal performance of the entire wall composition. This study proposes a simple method of calculating the thermal transmittance of a building's envelope, accounting for age and environmental conditions, by applying a correction coefficient to the initial thermal transmittance rather than conducting in-situ measurements. In-situ measurements of wall thermal transmittance were conducted in 40 older buildings using visual observation and the heat flow meter method. By examining the environmental factors that affect deterioration in the performance of insulation in an exterior wall through linear regression analysis, the study found that the correction factor has a high correlation with the type of exterior wall finish, color, surface finishing, pollution source, sea exposure, and the presence or absence of adjacent buildings. Three scenarios are proposed to quantify the correction factor, with the goal of obtaining an optimized model that can predict the thermal transmittance of building envelopes. These scenarios are reviewed based on ISO 15686 and regression analysis, and the scenario with the correction factor that best estimated the measured value is adopted. The thermal transmittance of the walls of older buildings, as estimated by the simple method proposed in this study, shows the best match with the on-site measured results.

Mutual Influence of External Wall Thermal Transmittance, Thermal Inertia, and Room Orientation on Office Thermal Comfort and Energy Demand

Upgrades in building energy efficiency codes led to differences between buildings designed according to outdated codes and those with most recent requirements. In this context, our study investigates the influence of external wall thermal transmittance, thermal inertia, and orientation on energy demand (heating, cooling) and occupant thermal comfort. Simulation models of an office building were designed, varying (i) the thermal transmittance values (0.20 and 0.60 W/(m2K)), (ii) the room orientation (four cardinal directions), and (iii) the wall thermal inertia (approximately 60 kJ/(m2K) for low and 340 kJ/(m2K) for high thermal inertia. The energy demand for heating and cooling seasons was calculated for Ljubljana using EnergyPlus 9.0.0 software. The reduction of the external wall thermal transmittance value from 0.6 W/(m2K) to 0.2 W/(m2K) contributes to significant energy savings (63% for heating and 37% for cooling). Thermal inertia showed considerable potential for energy savings, especially in the cooling season (20% and 13%, depending on the external wall insulation level). In addition, the orientation proved to have a notable impact on heating and cooling demand, however not as pronounced as thermal inertia (up to 7% total energy demand). Comparison of the thermal comfort results showed that when internal air temperatures are identically controlled in all the rooms (i.e., internal air temperature is not an influencing factor), the external wall thermal transmittance, thermal inertia, and room orientation show negligible influence on the average occupant thermal comfort. The simultaneous achievement of thermally comfortable conditions in the working environment and low energy use can only be achieved by simultaneously considering the U-value and thermal inertia.

Thermal Performance Assessment of a Wall Made of Lightweight Concrete Blocks with Recycled Brick and Ground Polystyrene

Hollow concrete masonry blocks made of low strength self-compacting concrete with recycled crushed brick and ground polystyrene as an aggregate (RBC-EP blocks), and their expected structural role as masonry infill in steel frames, has been confirmed in previous research studies, thus the extensive investigation of thermal properties is presented in this paper to fully approve their potential application in practice. The Heat Flow and Temperature Based Method was used to conduct in-situ measurements of the wall thermal transmittance (U-value). The experimental U-values of the wall without insulation varied from 1.363 to 1.782 W/m2·K, and the theoretical value was calculated to be 2.01 W/m2·K. Thermal conductivity of the material used for making RBC-EP blocks was measured in a laboratory by using a heat flow meter instrument. To better understand the thermal performance characteristics of a wall constructed from RBC-EP blocks, a comparison with standard materials currently used and found on the market was performed. Walls constructed from RBC-EP blocks show an improvement of building technology and environmentally based enhancement of concrete blocks, since they use recycled materials. They can replace standard lightweight concrete blocks due to their desired mechanical properties, as well as the better thermal performance properties compared to commonly used materials for building walls.

Thermal Inertia Characterization of Multilayer Lightweight Walls: Numerical Analysis and Experimental Validation

The thermal inertia properties of construction elements have gained a great deal of importance in building design over the last few years. Many investigations have shown that this is the key factor to improve energy efficiency and obtain optimal comfort conditions in buildings. However, experimental tests are expensive and time consuming and the development of new products requires shorter analysis times. In this sense, the goal of this research is to analyze the thermal behavior of a wall made up of lightweight concrete blocks covered with layers of insulating materials in steady- and transient-state conditions. For this, numerical and experimental studies were done, taking outdoor temperature and relative humidity as a function of time into account. Furthermore, multi-criteria optimization based on the design of the experimental methodology is used to minimize errors in thermal material properties and to understand the main parameters that influence the numerical simulation of thermal inertia. Numerical Finite Element Models (FEM) will take conduction, convection and radiation phenomena in the recesses of lightweight concrete blocks into account, as well as the film conditions established in the UNE-EN ISO 6946 standard. Finally, the numerical ISO-13786 standard and the experimental results are compared in terms of wall thermal transmittance, thermal flux, and temperature evolution, as well as the dynamic thermal inertia parameters, showing a good agreement in some cases, allowing builders, architects, and engineers to develop new construction elements in a short time with the new proposed methodology.

Wall heat loss recapture evaluation of transpired solar collectors for different climates: A European case study

In the present paper, the performance of the transpired solar collector (TSC) is evaluated for several European cities with different climates. Two primary outputs, the solar air heating, and the recapture of transmission heat loss through the walls were analysed. The wall heat loss recapture can be considered as an important factor for energy saving in buildings, which has not been studied before. RETScreen and SWift are two building simulation tools available for the design and evaluation of transpired solar collectors. Another primary aim is to investigate the detailed mathematical approach that describes the heat transfer process of the physical model for each simulation tool. Results of the models were analysed to predict the performance of TSC in delivering heated air for ventilation applications, and the ability of the partial recapture the transmission heat loss from the warm building interior. Solar radiation, heating degree days, wall thermal transmittance, and air flowrate are the key parameters that influence the heat transfer process. The findings indicate a promising result of using TSC as a dynamic insulation solution for energy savings which can reach up to 55 [kWh/(m2·year)] at high air flowrate 180 [m3/(h∙m2)] for some climates besides the main duty which is the solar air heating.

Thermal performance of double brick wall construction on the building envelope of high-rise hotel in Malaysia

The study discusses the impact of building double brick wall construction on the thermal performance of building façade in Malaysia. The Sunway Hotel, nestled within the heritage city of George Town in Penang, has been selected as a case study. Characterised by its simplicity and mass-produced construction, special attention is given to its double brick wall façade. The study comprises of two parameters for the façade thermal performance measurement on the west wall façade. The first measurement employs systematic calculation of the wall thermal transmittance (U-values) and proceeds with the calculation of the Overall Thermal Transfer Value (OTTV). This calculation is meticulously undertaken to incorporate the previously calculated U-values for both the opaque and transparent elements of the double brick-wall façade unit. Secondly, the study records variations in the façade average external surface temperature using time-sequential thermography from 1200 to 1800 in response to the diurnal variation in solar radiation. Concerning the results of these two analyses, the finding informs the thermal performance of a double brick wall based on the requirement of the local standards MS 1525:14 and energy efficiency in the tropical climate of Malaysia.

Automation and optimization of in-situ assessment of wall thermal transmittance using a Random Forest algorithm

Reducing energy consumption and greenhouse gases emissions is among the main challenges of building sector. It is therefore crucial to know the characteristics of envelopes. There are experimental methods to determine thermal transmittance, but limitations are presented. By using techniques of artificial intelligence, this article solves the limitations of current methods by predicting correctly the thermal transmittance value of ISO 6946 and the building period of a wall with monitored data. The methodology used is extrapolated to any country: 163 real monitorings and 140 different typologies of walls have been combined to generate the dataset (22,820 items). The results show the optimal operation of the Random Forest algorithm because both the thermal transmittance of ISO 6946 and the building period are determined by using the most common methods: the heat flow meter method and the thermometric method. This study makes progress towards more automatized processes to characterize thermal transmittance.

Lowest thermal transmittance of an external wall under budget, material and thickness restrictions: An integer linear programming approach

This paper deals with the minimization of a building's external wall thermal transmittance, with the aim of improving the energy efficiency of the building. The wall's thermal transmittance must abide by the current legislation, but also suit the limitations of other construction parameters, mainly budget and thickness, but also time limit, workforce, number and thickness of the layers and availability of materials depending on the approach.The optimization is achieved formulating an Integer Linear Programming (ILP) problem involving the parameters mentioned above. Therefore, any available ILP solver can be run to obtain the best combination of the different materials and thicknesses for the layers, in order to minimize the thermal transmittance. This paper presents a case study of a common but representative external wall consisting of 6 layers, with more than 670,000 possible combinations of materials and their thicknesses. The study concludes with a comparison of the lowest thermal transmittance obtained for a selection of budget and thickness combinations for the mentioned wall.

Monitoring the hygrothermal and ventilation performance of retrofitted clay brick solid wall houses with internal insulation: Two UK case studies

This work assesses the hygrothermal and ventilation performance of two ‘hard-to-treat’ historic, clay brick, solid wall houses that are internally insulated. Retrofit A is a two bedroom bungalow with the addition of internal plasterboard and air cavity and Retrofit B is a 5 bedroom house with sheep wool, phenolic and plasterboard insulation. To evaluate the long term performance of the retrofit measures, the testing is carried out 7 and 8 years respectively after completion. The first part of the work investigates whole building hygrothermal performance, ventilation and internal conditions. It was found that both retrofits are operating below specification in regards to their ventilation performance. An in-situ performance based specification for mechanical ventilation via CO2 monitoring is proposed. The second part focuses on the hygrothermal behaviour of the clay brick wall assembly. Both presented high relative humidity within critical layers of the wall make up. In Retrofit A the wall thermal transmittance was found to be much higher than designed due to inappropriate construction detailing while Retrofit B showed excellent thermal performance and minimal effects of thermal bridging.

A new simple method to measure wall thermal transmittance in situ and its adaptability analysis

The Simple Hot Box - Heat Flow Meter Method is proposed to measure the wall thermal transmittance conveniently in situ with the high accuracy on the basis of the previous study, while it avoids the heavy equipment of the Hot Box Method and overcomes outdoor and indoor thermal environment limitation of the Heat Flow Meter Method. According to these, this study mainly analyzed the determination method of the hot box dimension and the effect of the heating temperature by the numerical simulation. Results shows due to the local heating from the hot box, the wall can be divided to four zones with the different thermal characteristics, where a one-dimensional heat transfer zone is the optimum one to past the thermocouples and heat flow meters. With increasing the hot box dimension, the one-dimensional heat transfer zone increases linearly and the heat dissipation zone is constant, defining the minimum hot box dimension. The minimum dimension increases linearly with increasing the wall thickness or equivalent thermal conductivity. When temperature difference is more than 20°C, its effect can be ignored on the minimum dimension. And the maximum system error decreases by up to 4.4–7.5% with the temperature difference increasement from 10°C to 30°C. Taking wall thickness, wall equivalent thermal conductivity, temperature difference as variables, a regression formula is obtained to determine the minimum box dimension and the recommended values of the hot box dimension are also offered.

Feasibility experiment on the simple hot box-heat flow meter method and the optimization based on simulation reproduction

This paper proposes a simple hot box-heat flow meter method (SHB-HFM) and verifies its feasibility by an in-situ measurement of wall thermal transmittance. The experimental results show that even under very unfavorable test conditions, the test error of the wall thermal transmittance by the SHB-HFM is only −5.97% relative to the design value, which proves that the SHB-HFM has the adequate test accuracy, thereby proving that this method is feasible. And through arranging reference test sensors, 15 cm up and down from the central primary test sensors, the test errors due to location deviation increase to −8.14% and −9.60% respectively, which basically meets the accuracy requirement and thereby demonstrates the SHB-HFM has an acceptable tolerance for the in-situ operation. To further explore the influence of various factors on the test accuracy, a mathematical model is established and verified by the experimental data. The simulation results indicate that the perfect in-situ measurement conditions do not improve the measurement accuracy obviously, while moderately enlarging the box dimensions or simultaneously arranging heat flow meters on the inner and outer surfaces is more effective in improving the test accuracy.

A quantitative methodology to evaluate thermal bridges in buildings

The use of multi-layer walls with high thermal resistance values is widely used to reduce heat losses in buildings during wintertime. Nevertheless, it is extremely important to treat also weaker components of the envelope such as doors, windows and all the various thermal bridges, otherwise the efforts in increasing walls thermal resistance can be vanished.If the improvement of the thermal performance of windows and doors has reached a significant development and a high level of standardization, the same is not true for the corrections related to thermal bridges, which therefore require a specific analysis in the design phase.Thermal bridges, of whatever nature, are therefore a crucial point in the energy analysis of the building envelope. The analysis on existing constructions can be performed on site with thermographic techniques that describe in first approximation the qualitative energy performance of the building and put in evidence the main heat losses.The paper proposes a methodology to perform a quantitative analysis of some types of thermal bridges, through simple thermographic surveys and subsequent analytical processing. From the simple measurement of the air temperature and the analysis of the thermogram, the thermal bridge effect can be estimated as a percentage increase of the homogenous wall thermal transmittance. This term is obtained without further information on the structure of both the thermal bridge and the stratigraphy of the wall.The analytical methodology – which was validated with experimental and numerical analyses – is described and the results of surveys on different types of thermal bridges are reported. This method represents a quick and effective tool to define the actual heat loss of high-insulation buildings and to evaluate the benefits in treating thermal bridges.

Thermal Transmittance of Concrete Block Walls with Core Insulation

Thermal transmittance values (U-values) of concrete block walls, with and without core insulation, tested at three laboratories are summarized. Insulations were perlite, vermiculite, expanded polystyrene (EPS) beads, and EPS inserts. Measured U-values are compared to values calculated using the isothermal planes method. For empty core concrete block walls with known concrete thermal conduc tivity, measured U-values were within 10% of calculated values. However, for walls with core insulation, measured U-values differed by 0% to 40% from calculated values. Sensitivity of wall thermal transmittance to changes in block configuration, con crete thermal conductivity, and fill thermal conductivity is discussed.

On the calculation of the [formula omitted] of walls containing slotted bricks or blocks

The thermal transmittance of walls containing slotted bricks or blocks has been studied using a finite element computer program. The results are compared with conventional calculation methods, and a new manual method based on a more realistic model of heat flow in slotted blocks is proposed.

Thermal transmittance of walls obtained by measurement on test panels in natural exposure

The results are given of measurements of heat flow through walls exposed to the weather in sheltered to moderate exposure and facing due north. Many of the results are published for the first time and are presented with test data already available in the literature to give a complete summary of the work carried out in Britain on heat transmission in winter through naturally-exposed walls. It is proposed to discuss the results in detail in a following paper.