Thermal Performance Of Materials Research Articles

Capturing Building Fabric Thermal Performance and Solar Heat Gains Through a Whole House Heat Loss Test – an In-Situ Study in Poland

Determining a building’s “as built” heat loss coefficient (HLC) is one of the key starting points to understand the role of residents’ practices in heating or cooling-related energy consumption. It is also a starting point for white-box modelling of different behaviour scenarios within a given home environment. Co-heating test is a recognised experimental method to evaluate the building’s fabric thermal performance. It involves a quasi-stationary homogeneous heating experiment performed on an unoccupied dwelling. This paper discusses the results of a co-heating test carried out in a low-energy semi-detached house in Wrocław, Poland between 6th-12th December 2021. The periods of different types of solar operation are captured to evaluate HLC: night-time with no solar gains, daytime with direct solar gains, and daytime with only the diffuse component of solar radiation. Internal solar gains in the building are calculated using the TRNSYS simulation program, assuming detailed modelling of the radiation incident on the vertical partitions (including the anisotropy of the diffused radiation component and complex analyses of the sun path geometry inside the building). Based on the results, the HLC values excluding infiltration and ventilation corresponding to different solar operation types are calculated and compared. This contributes to a more nuanced understanding of HLC under different external conditions.

Thermal evolution of CRTS Ⅱ slab track under various environmental temperatures: Experimental study

The environmental temperature plays an important role in thermal performance of materials and structure in CRTS Ⅱ ballastless slab track under operational condition. In this paper, two 1:4 geometric scaled models of five CRTS Ⅱ slab tracks on a simply-supported box girder under three environmental temperatures rising and dropping cases were conducted in a large-scale environmental simulation testing chamber, respectively. In order to study the effect of constraint conditions on the bond of cement asphalt mortar (CAM), the internal temperature distribution, stress and displacement of two scaled models with constraint and freedom boundary conditions are also compared. Results show that the internal temperatures, longitudinal stresses and displacements of the track structure increase nonlinearly within an increase of the environmental temperature. Accordingly, these same responses decrease linearly within a temperature decrease. Most importantly, when the environmental temperature variation is + 26.5℃, the testing axial force at the two ends of the prototype track structure reaches 2,849kN, and the relative longitudinal displacement between the track slab and base plate become larger with a decrease of the environmental temperature, especially for the lowest temperature of −20℃. Moreover, fixed constraint condition decelerates the temperature transfer of the track slab to CAM, since it leads to the larger absolute temperatures and stresses of the track structure compared to the free constraint.

Integrated Testing of Building Fabric Thermal Performance for Calibration of Energy Models of Three Low-Energy Dwellings in the UK

This paper presents the methodology and results of in situ testing of building fabric thermal performance to calibrate as-built energy models of three low-energy dwellings in the UK, so as to examine the gap between as-designed and as-built energy performance. The in situ tests included repeat testing of air permeability (AP) integrated with thermal imaging survey and heat flux measurements of the building fabric elements, along with concurrent monitoring of indoor temperature during the pre-occupancy stage. Despite being designed to high thermal standards, wall and roof U-values were measured to be higher than expected. Thermal imaging surveys revealed air leakage pathways around door/window openings, penetrations and junctions between walls and ceilings, indicating poor detailing and workmanship. AP was found to have increased after the initial test due to post-completion alteration to the building fabric. Though the results did not meet design expectation, they were within the UK Building Regulations. Calibration of energy models with temperature monitoring provided a less extreme energy performance gap than simply replacing the designed values with test results. Insights from this study have reinforced the need for building regulations to require integrated testing of building fabric as part of housing delivery to ensure performance targets are realised.

Insights from in-situ measurement of building fabric thermal performance of three zero energy dwellings in UK

In-situ testing of actual building performance is vital to achieve the UN Sustainable Development Goal 11 (Sustainable cities and communities) in reality, given the growing concern that low energy dwellings often underperform against design specifications. This paper presents the methodology and results of in-situ measurements of the building fabric thermal performance of three zero energy dwellings in the UK, using blower door test (air permeability), heat flux measurement (thermal transmittance/U-value) and thermal imaging survey (heat losses). Despite being designed to high thermal standards, air permeability tests showed that none of dwellings met the design air permeability target, with actual results of 5.4 – 7.5 m3/h/m2@50Pa. Air permeability was found to have increased after the initial test due to post-completion alteration to the fabric, although it remained within the UK Building Regulations requirements. Heat flux measurements showed poor thermal quality of the walls and roof section even for the ‘good’ sections that were measured. Thermal imaging surveys revealed where fabric performance was being compromised. Air leakage pathways were found around door/window openings, penetrations and junctions between walls and ceilings indicating poor workmanship. Insights from this study have reinforced the need to have updated as-built energy models with in-situ performance data to reduce performance gap.

Are the energy savings of the passive house standard reliable? A review of the as-built thermal and space heating performance of passive house dwellings from 1990 to 2018

The Passive House (PH) standard is a voluntary quality assurance standard focused upon maximising the health and wellbeing of occupants, whilst reducing space heating demand to a very low level. To meet the PH standard, well-defined criteria have to be met. However, given literature that suggests a ‘performance gap’ for energy savings, the question remains, how well do PH dwellings perform in situ? This paper presents results from in situ building fabric thermal performance measurements, along with a comparison between the design intent and the measured space heating energy used by over 2000 newly built and retrofitted PH dwellings. The results reveal the in situ thermal performance of the building fabric is close to the design predictions. Within space heating measurements, a standard deviation of up to 50% has to be attributed to the broad spectrum of user behaviour; this is not specific for PH, but a general observation. Despite this, the average values for the PH developments ranged within the uncertainty of the demand calculations. With over 2000 PH dwellings averaging a space heating energy consumption of 14.6 kWh/(m2a), the in situ performance is close to the original design intent and extraordinary low compared to the consumption in ordinary buildings. The results suggest the PH standard is capable of producing dwellings in a verifiable manner. This means, on average, the in situ thermal performance of the building fabric and the energy consumption for space heating match the design intent, i.e. there is no significant ‘performance gap’.

Measuring and modelling retrofit fabric performance in solid wall conjoined dwellings

There remains a significant number of occupied and uninsulated solid wall dwellings in the UK. Deep retrofit is often required for these buildings to become energy efficient but it is difficult to determine how these buildings will respond to retrofit without a detailed understanding of their fabric thermal performance Greater certainty can however be achieved by combining theoretical models and practical field tests, prior to the design of retrofit programmes. This type of approach can then be used to inform and optimize the design of retrofit interventions. This paper presents results from a series of in situ fabric performance tests undertaken on two no-fines concrete, conjoined dwellings pre- and post-retrofit and demonstrates how empirical data can be used to inform and calibrate the thermal performance of dynamic simulation models (DSMs). This is a particularly pragmatic calibration method as it eliminates the need for actual weather data, which is expensive and prohibitive to collect and collate. The DSM inputs and outputs were compared with those obtained from Standard Assessment Procedure (SAP) calculations. The results illustrate how the fabric performance of no-fines concrete can vary between similar house types within the same development. This research also validates the effectiveness of the calibration methodology that uses the whole house Heat Transfer Coefficient (HTC) as the qualifying metric. Furthermore, results also emphasize the importance of appropriately characterizing the physical properties of existing buildings before designing retrofit strategies. This paper contributes to the growing knowledge base concerned with the energy performance gap. In this instance, SAP predicts higher absolute savings then measured in situ which is problematic when assessing the financial viability of retrofits.

Magnitude and extent of building fabric thermal performance gap in UK low energy housing

This paper presents new evidence from a nationwide cross-project meta-study investigating the magnitude and extent of the difference between designed and measured thermal performance of the building fabric of 188 low energy dwellings in the UK. The dataset was drawn from the UK Government’s national Building Performance Evaluation programme, and comprises 50 Passivhaus (PH) and 138 non-Passivhaus (NPH) dwellings, covering different built forms and construction systems. The difference between designed and measured values of air permeability (AP), external wall/roof thermal transmittance (U-value) and whole house heat loss were statistically analysed, along with a review of thermal imaging data to explain any discrepancies. The results showed that fabric thermal performance gap was widespread especially in terms of AP, although the magnitude of underperformance was much less in PH dwellings. While measured AP had good correlation with measured space heating energy for PH dwellings, there was no relationship between the two for NPH dwellings. The regression analysis indicated that for every 1 m3/h/m2 reduction in designed air permeability, the gap increased by 0.8 m3/h/m2@50 Pa. Monte Carlo analysis showed that likelihood of AP gap was 78% in NPH dwellings designed to 5 m3/h/m2@50 Pa or lower. The study provides useful evidence for improving the fabric thermal performance of new housing through in-situ testing.

Characterization of thermal performance, flux transmission performance and optical properties of MAX phase materials under concentrated solar irradiation

In this study, thermal performance and optical properties of MAX phase materials subjected to high concentrated flux are characterized. A new indoor facility is developed that allows for investigation of the independent effect of irradiance and temperature on the thermal performance of the material. Two MAX namely, Titanium Aluminum Carbide (Ti2AlC) and Chromium Aluminum Carbide (Cr2AlC) are examined in this study. Both materials are exposed to high concentrated homogenized flux in the range of 527.2 kWm−2 – 917 kWm−2 for 1000 s and 3000 s using a high flux solar simulator while their temperatures are maintained at 60 °C ± 5 °C via water-cooled heat flux gage. Materials’ surface characterization before and after irradiation is carried out using X-ray diffraction, scanning electron microscopy and X-ray fluorescence analysis. It is found that both materials have excellent resistance to high concentrated flux, but that Ti2AlC shows higher light scattering due to the oxidation of its surface. It is also found that the variations in the optical properties over time do not depend on the selected incident flux level. The thermal performance of Ti2AlC and Cr2AlC was found to varies in the 0.56 – 0.68 and 0.60 – 0.67 range, respectively, for selected flux levels. Flux transmission performance of both materials is not affected by exposure to high concentrated flux.

NUMERICAL SIMULATION OF RELATIVE HUMIDITY IN A MASONRY WALL APPLYING THREE DIFFERENT WATERPROOFING MEMBRANES

The analysis by numerical simulations can be applied to building materials subjected to different climatic conditions to envisage the influence of environmental factors in terms of drying time, water absorption and thermal performance of materials. Currently there is a wide variety of new building materials used for insulation, waterproofing and rehabilitation, each contributing in a specific way to constructions improvement during their service life. In time, every building is subjected to degradation due to the action of environmental factors. One of these is water due to its continuous acting under all forms of aggregation: vapour, liquid, solid, each having particular influence on the building s elements. The present paper highlights a numerical simulation of hygrothermal waterproofing characteristics for three different membranes applied on a brick masonry basement wall. The simulation was performed using WUFI2D 3.2 computer software. The information extracted from the analysis results made reference to the materials performance while subjected to moisture transfer processes.

Measuring thermal performance in steady-state conditions at each stage of a full fabric retrofit to a solid wall dwelling

The methodology used for measuring the thermal performance of fabric retrofit systems which were applied to a solid wall UK Victorian house situated within an environmental chamber is explored in detail. The work describes how steady-state boundary conditions were approximated, then repeated at the Salford Energy House test facility. How established methods of measuring the fabric thermal performance of buildings in situ were adapted to test the effectiveness of retrofit measures within a steady-state environment. The results presented show that steady-state boundary conditions enable the change in fabric heat loss resulting from the retrofit of a whole house or individual element to be measured to a level of accuracy and precision that is unlikely to be achieved in the field. The test environment enabled identification of heat loss phenomena difficult to detect in the field. However, undertaking tests in an environment devoid of wind underestimates the potential reduction in ventilation heat loss resulting from an improvement in airtightness, and hides the susceptibility of retrofit measures to various heat loss mechanisms, such as wind washing. The strengths and weaknesses of the methods employed, the Energy House test facility, and a steady-state environment, for characterising retrofit building fabric thermal performance are demonstrated.

Thermal performance evaluation and comfort assessment of advanced aerogel as blown-in insulation for historic buildings

Research and development of cost-effective, high-performance thermal insulation materials for the construction sector has to be focused on their final application. In particular, solutions for refurbishing historic buildings, which represent 40% of the European building stock, have to offer a good compromise between environmental quality, energy efficiency and conservation aspects. In this paper, the experimental assessment of an insulation material based on aerogel technology, recently developed in the European project EFFESUS, is presented with regard to the material's thermal performance, compatibility with historic fabric and reversibility. The overall results obtained in laboratory testing on a real-size mock-up and in a real-world case application indicate that the new material is a promising solution for retrofitting historic buildings, thanks to its thermal properties, easy application, reversibility and material compatibility.

Quantifying the aggregate thermal performance of UK holiday homes

In the UK, there are approximately 330,000 holiday homes spread across a large number of mainly privately owned sites. These homes are often sited in exposed locations, are poorly insulated and are generally heated using expensive fuels, such as electricity or LPG. There is also a lack of empirical evidence available on the in situ energy performance of these homes. Consequently, it is not possible, given the existing evidence base, to determine whether these homes suffer from the same scale of building fabric thermal ‘ performance gaps’ (between assumed and realised in situ performance) that have been documented for newbuild UK housing. This paper presents the results obtained from undertaking detailed in situ thermal fabric tests on five new holiday homes. Whilst the size reported here is small, the results indicate that a ‘ performance gap’ exists for all of these homes. Results obtained indicate that this gap appears narrower than that documented for newbuild UK housing. The results also suggest that the scale of the ‘ gap’ may be more a consequence of the way in which the design intent of these homes has been determined, i.e. a ‘ prediction gap’. Practical application: This paper presents the results obtained from undertaking detailed building fabric thermal performance tests on a small sample of new holiday homes. The results of these tests indicate that although a building fabric thermal performance ‘ performance gap’ exists in all of the holiday homes tested, the results suggest that the ‘ gap’ is much smaller than that documented for new build UK housing and may be more of a consequence of the way in which the design intent of these homes has been determined, i.e. a ‘ prediction gap’, rather than a ‘ performance gap’ between assumed and realised in situ performance. These results could be used by industry to develop more appropriate prediction tools that are relevant to holiday homes.

The Building Fabric Thermal Performance of Passivhaus Dwellings—Does It Do What It Says on the Tin?

The Passivhaus (or Passive House) Standard is one of the world’s most widely known voluntary energy performance standards. For a dwelling to achieve the Standard and be granted Certification, the building fabric requires careful design and detailing, high levels of thermal insulation, building airtightness, close site supervision and careful workmanship. However, achieving Passivhaus Certification is not a guarantee that the thermal performance of the building fabric as designed will actually be achieved in situ. This paper presents the results obtained from measuring the in situ whole building heat loss coefficient (HLC) of a small number of Certified Passivhaus case study dwellings. They are located on different sites and constructed using different technologies in the UK. Despite the small and non-random nature of the dwelling sample, the results obtained from the in situ measurements revealed that the thermal performance of the building fabric, for all of the dwellings, performed very close to the design predictions. This suggests that in terms of the thermal performance of the building fabric, Passivhaus does exactly what it says on the tin.

Crowd-sourced building intelligence: the potential to go beyond existing benchmarks for effective insight, feedback and targeting

In the UK benchmarking, as defined by CIBSE TM46 [CIBSE. 2008. TM46 Energy Benchmarks. London: CIBSE], has been implemented through report and display mechanisms such as Display Energy Certificates (DECs). Bruhns, Jones, and Cohen [2011. “Cibse Review of Energy Benchmarks for Display Energy Certificates – Analysis of DEC Results to Date.” CIBSE. Accessed January 31, 2013. http://www.cibse.org/index.cfm?go=page.view&item=2346.] have shown that while some TM46 benchmarks can reflect total actual building energy consumption, in education buildings, the ratio of electricity and fossil fuel use is less well represented. This has been attributed to changes in occupant behaviour, equipment use and fabric thermal performance that have not been reflected in updated benchmarks. The headline data available through DECs therefore may not offer sufficient insights or motivation to encourage identification of opportunities for energy reduction measures [Godoy-Shimizu, D., P. Armitage, K. Steemers, and T. Chenvidyakarn. 2011. “Using Display Energy Certificates to Quantify Schools’ Energy Consumption.” Building Research & Information 39: 535–552]. Intelligent buildings could generate crowd-sourced databases of building energy data to offer these insights and provide sufficient disaggregation of energy data to identify systems or measures that impact energy consumption. Anonymous crowd-sourced data may also be able to offer contemporary benchmarks based on current data with sufficient depth to identify areas for improvement, help develop new methodologies for building design and operation and challenge orthodox architectural and engineering practice. This article explores the opportunities and limitations of a crowd-sourced database of building intelligence through analysis of the school data in the CarbonBuzz and DEC databases.

Bridging the domestic building fabric performance gap

It is recognized that there is often a discrepancy between the measured fabric thermal performance of dwellings as built and the predicted performance of the same dwellings and that the magnitude of this difference in performance can be quite large. This paper presents the results of a number of in-depth building fabric thermal performance tests undertaken on three case study dwellings located on two separate Passivhaus developments in the UK: one masonry cavity and the other two timber-frame. The results from the tests revealed that all the case study dwellings performed very close to that predicted. This is in contrast with other work that has been undertaken regarding the performance of the building fabric, which indicates that a very wide range of performance exists in new-build dwellings in the UK, and that the difference between the measured and predicted fabric performance can be greater than 100%. Despite the small non-random size of the sample, the results suggest that careful design coupled with the implementation of appropriate quality control systems, such as those required to attain Passivhaus Certification, may be conducive to delivering dwellings that begin to ‘bridge the gap’ between measured and predicted fabric performance.

The Influence of Different Hydrophobic Agent on the Water Absorptivity of Foam Concrete

Foam concrete products had high absorption rate due to a large number of bubbles dispersion in it.which has serious effects upon the overall thermal performance of material and the durability of construction.Three methods were studied which includes Organic Silicon hydrophobic agent、High fatty acids hydrophobic agent and hydrophobic agent F in order to reduce the water absorption rate.Results show that the water absorption rate was reduced significantly with mixed High fatty acids. The water absorption rate drops of 68.2%, and the organic silicon is in a second place , and the hydrophobic agent F is the worst.

A simple, scalable and low-cost method to generate thermal diagnostics of a domestic building

Traditional approaches to understand the problem of the energy performance in the domestic sector include on-site surveys by energy assessors and the installation of complex home energy monitoring systems. The time and money that needs to be invested by the occupants and the form of feedback generated by these approaches often makes them unattractive to householders. This paper demonstrates a simple, low cost method that generates thermal diagnostics for dwellings, measuring only one field dataset; internal temperature over a period of 1week. A thermal model, which is essentially a learning algorithm, generates a set of thermal diagnostics about the primary heating system, the occupants’ preferences and the impact of certain interventions, such as lowering the thermostat set-point. A simple clustering approach is also proposed to categorise homes according to their building fabric thermal performance and occupants’ energy efficiency with respect to ventilation. The advantage of this clustering approach is that the occupants receive tailored advice on certain actions that if taken will improve the overall thermal performance of a dwelling. Due to the method’s low cost and simplicity it could facilitate government initiatives, such as the ‘Green Deal’ in the UK.

Co-heating test: A state-of-the-art

Several studies have shown that the actual energy performance of buildings can differ significantly from its designed value. An important part of this performance is constituted by the building fabric's thermal performance. A common method to evaluate the latter for an actual building is the co-heating test. The co-heating test comprises a quasi-stationary heating experiment followed by linear regression analysis of aggregated building performance data. This paper reviews related research work and cristallises the current state-of-the-art. The physical phenomena working behind the scenes of the generally assumed simplified heat balance are discussed. Statistical constraints generally prevent these from being uncovered fully during the analysis. Multiple linear regression is proposed as the most sensible method to analyse co-heating measurement data. A novel way to visualise such analysis, deduce building performance data graphically and compare different co-heating test results is presented.

Effect of Surrogate Aggregates on the Thermal Conductivity of Concrete at Ambient and Elevated Temperatures

The accurate assessment of the thermal conductivity of concretes is an important part of building design in terms of thermal efficiency and thermal performance of materials at various temperatures. We present an experimental assessment of the thermal conductivity of five thermally insulated concrete specimens made using lightweight aggregates and glass bubbles in place of normal aggregates. Four different measurement methods are used to assess the reliability of the thermal data and to evaluate the effects of the various sensor types. The concrete specimens are also assessed at every 100°C during heating to ~800°C. Normal concrete is shown to have a thermal conductivity of ~2.25 W m−1 K−1. The surrogate aggregates effectively reduce the conductivity to ~1.25 W m−1 K−1 at room temperature. The aggregate size is shown not to affect thermal conduction: fine and coarse aggregates each lead to similar results. Surface contact methods of assessment tend to underestimate thermal conductivity, presumably owing to high thermal resistance between the transducers and the specimens. Thermogravimetric analysis shows that the stages of mass loss of the cement paste correspond to the evolution of thermal conductivity upon heating.

Economic efficiency of social housing thermal upgrade in Mediterranean climate

The age of European existing building stock and the very low growth rate make energy retrofit a critical issue at the moment. The spreading of good practices is strongly hampered by their cost effectiveness.National legislation thermal requirements for retrofitting works play a fundamental role. If they are too strict, the initial economic investment could be too high if compared with energy savings achievable.The paper refers to a case study of improving fabric thermal performance of stone masonry buildings located in Cagliari – Italy. They were built in 1950s.The economic feasibility of different energy efficiency retrofits is evaluated. Two different scenarios are analyzed: the former according to the earlier Italian legislation (valid from 2006 to 2008), the latter according to the latest and strictest measures (valid from 2010).The results show that heavy thermal performance upgrades, even though compulsory, are not completely cost-effective in a mild Mediterranean climate area as far as payback time is concerned. National subsidy policies can improve the economic return on the investment. The impact of present Italian incentives has also been evaluated.