scholarly journals Mean Operating Temperature (MOT) of Commercial Roof Assembly and Its Impact on the Energy Performance

Buildings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 216
Author(s):  
Sudhakar Molleti ◽  
Logan Carrigan ◽  
David van Reenen
Keyword(s):  
Thermal Resistance ◽  
Thermal Performance ◽  
Operating Temperature ◽  
Energy Performance ◽  
Thermal Design ◽  
The Other ◽  
Temperature Dependent ◽  
Surface Temperatures ◽  
The Mean

In the thermal design of low sloped roofing assemblies, two parameters are overlooked, one is the surface temperature of the roof assemblies which provides the required temperature gradient for heat flow, and the other is the mean operating temperature of the roof assembly, which has direct implications on the thermal performance of the insulation. An in situ field study was conducted in collaboration with Alberta Roofing Contractors Association (ARCA) on their headquarters building located in Calgary, to generate data on the mean operating temperature of the roof assemblies and to determine whether the thermal design of roofing assemblies using conventional methods is an accurate portrayal of in-service thermal performance. For the present study, two roof assemblies insulated with polyisocyanurate insulation, one with a white reflective roof membrane and the other with the black membrane were selected and instrumented. During the monitoring period, the mean operating temperature (MOT) of the roof assembly whether it is calculated as the average of interior and exterior ambient (MOTAIR,) or the average of surface temperatures (MOTSurface), was found to be below 24 °C (75 °F), which opposes the current roof thermal designs that are being designed using label R-value (thermal resistance) of the insulation reported at the mean temperature of 24 °C (75 °F) rather than temperature-dependent thermal resistance. The comparison of two energy transfer theoretical models, QConvention and QMOT, with the measured data indicated that the conventional approach of roof thermal design underestimates the energy performance of the roof assembly on average by 30%. The use of roof surface temperatures and the corresponding temperature-dependent thermal resistance of the insulation as in QMOT has been demonstrated to improve predictions of the energy performance. In addition the loss in thermal resistance due to blowing agent diffusion in polyisocyanurate was evaluated after two years of in situ installation.

scholarly journals Influence of toothbrushing on enamel softening and abrasive wear of eroded bovine enamel: an in situ study

2006 ◽  
Vol 20 (2) ◽  
pp. 148-154 ◽  
Author(s):  
Daniela Rios ◽  
Heitor Marques Honório ◽  
Ana Carolina Magalhães ◽  
Marília Afonso Rabelo Buzalaf ◽  
Regina Guenka Palma-Dibb ◽  
...  
Keyword(s):  
Abrasive Wear ◽  
The Other ◽  
In Situ Study ◽  
Significant Difference ◽  
The Mean ◽  
Student’S T ◽  
Bovine Enamel ◽  
Enamel Layer ◽  
Student’S T Test

This study assessed the surface softening and abrasive wear of eroded bovine enamel with or without the influence of toothbrushing. Five volunteers took part in this in situ study of 5 days. They wore acrylic palatal appliances containing 6 bovine enamel blocks divided in two rows with 3 blocks, which corresponded to the studied groups: erosion without toothbrushing (GI) and erosion with toothbrushing (GII). The blocks were subjected to erosion by immersion of the appliances in a cola drink for 10 minutes, 4 times a day. After that, no treatment was performed in one row (GI), whereas the other row was brushed (GII). The appliance was then replaced into the mouth. Enamel alterations were determined using profilometry and microhardness tests. Data were tested using paired Student’s t test (p < 0.05). The mean wear values (µm) and percentage of superficial microhardness change (%SMHC) were respectively: GI - 2.77 ± 1.21/91.61 ± 3.68 and GII - 3.80 ± 0.91/58.77 ± 11.47. There was a significant difference in wear (p = 0.001) and %SMHC (p = 0.001) between the groups. It was concluded that the wear was more pronounced when associated to toothbrushing abrasion. However, toothbrushing promoted less %SMHC due to the removal of the altered superficial enamel layer.

scholarly journals Dew frequency across the US from a network of in situ radiometers

2019 ◽  
Vol 23 (2) ◽  
pp. 1179-1197 ◽  
Author(s):  
François Ritter ◽  
Max Berkelhammer ◽  
Daniel Beysens
Keyword(s):  
Similarity Theory ◽  
Bowen Ratio ◽  
Surface Characteristics ◽  
Dew Point ◽  
Energy Budgets ◽  
High Temporal Resolution ◽  
Surface Temperatures ◽  
Dew Formation ◽  
The Mean

Abstract. Dew formation is a ubiquitous process, but its importance to energy budgets or ecosystem health is difficult to constrain. This uncertainty arises largely because of a lack of continuous quantitative measurements on dew across ecosystems with varying climate states and surface characteristics. This study analyzes dew frequency from the National Ecological Observatory Network (NEON), which includes 11 grasslands and 19 forest sites from 2015 to 2017. Dew formation is determined at 30 min intervals using in situ radiometric surface temperatures from multiple heights within the canopy along with meteorological measurements. Dew frequency in the grasslands ranges from 15 % to 95 % of the nights with a strong linear dependency on the nighttime relative humidity (RH), while dew frequency in the forests is less frequent and more homogeneous (25±14 %, 1 standard deviation – SD). Dew mostly forms at the top of the canopy for the grasslands due to more effective radiative cooling and within the canopy for the forests because of higher within the canopy RH. The high temporal resolution of our data showed that dew duration reaches maximum values (∼6–15 h) for RH∼96 % and for a wind speed of ∼0.5ms-1, independent of the ecosystem type. While dew duration can be inferred from the observations, dew yield needs to be estimated based on the Monin–Obukhov similarity theory. We find yields of 0.14±0.12mmnight-1 (1 SD from nine grasslands) similar to previous studies, and dew yield and duration are related by a quadratic relationship. The latent heat flux released by dew formation is estimated to be non-negligible (∼10Wm-2), associated with a Bowen ratio of ∼3. The radiometers used here provide canopy-averaged surface temperatures, which may underestimate dew frequency because of localized cold points in the canopy that fall below the dew point. A statistical model is used to test this effect and shows that dew frequency can increase by an additional ∼5 % for both ecosystems by considering a reasonable distribution around the mean canopy temperature. The mean dew duration is almost unaffected by this sensitivity analysis. In situ radiometric surface temperatures provide a continuous, non-invasive and robust tool for studying dew frequency and duration on a fine temporal scale.

scholarly journals Thermal analysis and post construction verification

2019 ◽  
Vol 38 (1) ◽  
pp. 51-67
Author(s):  
Cormac Flood ◽  
Lloyd Scott
Keyword(s):  
Case Studies ◽  
Thermal Performance ◽  
Building Materials ◽  
Energy Performance ◽  
Research Project ◽  
Content Type ◽  
Thermal Transmittance ◽  
Standard Calculation

Purpose The residential sector in Ireland accounted for 25 per cent of energy related CO2 emissions in 2016 through burning fossil fuels, a major contributor to climate change. In support of Ireland’s CO2 reduction targets, the existing housing stock could contribute greatly to the reduction of space-heating energy demand through retrofit. Approximately 50 per cent of Ireland’s 2m dwellings pre-date building regulations and are predominantly of cavity and solid wall construction, the performance of which has not been extensively investigated at present. Although commitment to thermal upgrade/retrofit of existing buildings may increase under future government policies, the poor characterisation of actual thermal performance of external walls may hinder the realisation of these targets. Thermal transmittance (U-values) of exterior walls represents a source of uncertainty when estimating the energy performance of dwellings. It has been noted in research that the standard calculation methodology for thermal transmittance should be improved. Implementing current U-value calculation methods may result in misguided retrofit strategies due to the considerable discrepancies between in situ measurements and calculated wall U-values as documented in the case studies carried out in this research. If the method of hygrothermal analysis were to be employed as a replacement for the current standard calculation, it could have significant implications for policy and retrofit decision making. The paper aims to discuss this issue. Design/methodology/approach This research project analysed a case study situated in Dublin, Ireland. The case studies offer an account of the in situ thermal transmittance of exterior walls and link these to hygrothermally simulated comparisons along with more traditional design U-values. Findings The findings of this research identify discrepancies between in situ and design U-values, using measurement, hygrothermal simulation and standard method U-value calculations. The outcomes of the research serve as an introduction to issues emanating from a larger research project in order to encourage researchers to understand and further explore the topic. Originality/value It has previously been highlighted that moisture content is linked to the increase in thermal conductivity of building materials, thus reducing the thermal effectiveness and increasing the elemental U-value. Therefore, it is vital to implement reliable prediction tools to assess potential thermal performance values. This paper presents the findings of a critical instance case study in Dublin, Ireland in which an existing west facing external wall in a semi-detached dwelling was analysed, simulated and measured to verify the elemental wall assembly and quantify thermal transmittance (U-value) incorporating the major criteria required for building performance simulation.

Rapid Rhino versus Merocel nasal packs in septal surgery

2011 ◽  
Vol 125 (12) ◽  
pp. 1244-1246 ◽  
Author(s):  
A Hesham ◽  
A Ghali
Keyword(s):  
Standard Deviation ◽  
Pain Score ◽  
Visual Analogue Score ◽  
Nasal Packing ◽  
The Other ◽  
Septal Surgery ◽  
Patient Tolerance ◽  
Operative Complications ◽  
The Mean

AbstractObjective:To compare Rapid Rhino and Merocel packs for nasal packing after septoplasty, in terms of patient tolerance (both with the pack in place and during removal) and post-operative complications.Materials and methods:Thirty patients (aged 18–40 years) scheduled for septoplasty were included. Following surgery, one nasal cavity was packed with Rapid Rhino and the other one with Merocel. Patients were asked to record pain levels on a visual analogue score, on both sides, with the packs in situ and during their removal the next day. After pack removal, bleeding was compared on both sides.Results:The mean ± standard deviation pain score for the Rapid Rhino pack in situ (4.17 ± 1.78) was less than that for the Merocel pack (4.73 ± 2.05), but not significantly so (p = 0.314). The mean pain score for Rapid Rhino pack removal (4.13 ± 1.76) was significantly less that that for Merocel (6.90 ± 1.67; p = 0.001). Bleeding after pack removal was significantly less for the Rapid Rhino sides compared with the Merocel sides (p <0.05).Conclusion:Rapid Rhino nasal packs are less painful and cause less bleeding, compared with Merocel packs, with no side effects. Thus, their use for nasal packing after septal surgery is recommended.

scholarly journals Thermal Performance and Comfort Conditions Analysis of a Vernacular Palafitic Timber Building in Portuguese Coastline Context

2020 ◽  
Vol 12 (24) ◽  
pp. 10484
Author(s):  
Jorge Fernandes ◽  
Ricardo Mateus ◽  
Helena Gervásio ◽  
Sandra Monteiro Silva ◽  
Jorge Branco ◽  
...  
Keyword(s):  
Thermal Performance ◽  
Energy Demand ◽  
Energy Performance ◽  
Subjective Analysis ◽  
Heating And Cooling ◽  
Condition Evaluation ◽  
Timber Constructions ◽  
U Value ◽  
The Difference

The palafitic timber constructions of the central Portuguese coastline are an example of the adaptation to site-specific conditions (climate and sand landscape morphodynamics) using the available endogenous resources. Thus, in a context of environmental awareness and climate change, it is relevant to understand their features/strategies and how they perform. This work analyses the energy performance and thermal condition evaluation of a vernacular timber building–palheiro–from Praia de Mira, through in situ measurements, subjective analysis and energy simulation provided by DesignBuilder/EnergyPlus. The results show a good or satisfactory thermal performance during most of the seasons by passive means only. Despite, it was not possible to guarantee thermal comfort conditions for the occupants during winter. In the energy performance analysis, five scenarios, with different external walls, were compared. In the two scenarios that satisfy the maximum U-value for the climate zone, the current conventional building had a slightly better performance on heating and cooling (less 1.1 and 1.4 kWh/m2, respectively) than the timber building. However, the difference between the two construction solutions is not substantial in the annual energy demand (2.5 kWh/m2, 7.3%), indicating that timber structures are suitable in this mild climate area.

Two-Dimensional Thermal Performance Analysis of a Semi-Transparent Spectral Zirconia Thermal Barrier Coating

2004 ◽  
Author(s):  
Nalini Uppu ◽  
Patrick F. Mensah ◽  
Ravinder Diwan
Keyword(s):  
Heat Transfer ◽  
Thermal Barrier Coating ◽  
Thermal Performance ◽  
Operating Temperature ◽  
Turbine Blades ◽  
The Other ◽  
Ceramic Layer ◽  
Thermal Barrier ◽  
Barrier Coating ◽  
Super Alloy

The performance of an aero engine can be increased in two ways: one by reducing the air requirement for the cooling of the turbine blades and secondly by increasing the turbine inlet temperature (TIT) that is operating temperature of the turbine blades. Taking into account the latter approach the blade material must withstand high temperatures of above 1350°C. For this enhancing purpose, protective coatings called the thermal barrier coatings (TBC) are being employed. The thermal barrier coating mainly consists of two layers; one is the metallic coating MCrAlY, which is the premiere layer over the substrate Ni based super alloy. The other is the ceramic layer made of Yttria Stabilized Zirconia (YSZ). Apart from these two layers, an intermediate layer of Al2O3 is formed by the oxidation of the aluminum in MCrAlY called the diffusion layer which also enhances the adhesion between the two layers. M stands for Nickel or Cobalt. The present study is an investigation on the in-situ thermal performance of TBCs by considering the ceramic layer as a semi-transparent media and varying its thickness and simultaneously increasing the operating temperature on its other boundary surface. The above thermal boundary value problem is modeled in 2-dimensions and solved numerically using the discrete ordinate model for radiative heat transfer in a commercial computational fluid dynamics and heat transfer software. Two samples of Ni based super alloy substrate with dimensions 40 × 100 × 3mm are considered; one sample with a thickness of 0.25 mm ceramic layer and the other sample with 1 mm coating thickness for transient thermal analysis. Simulated transient temperature histories are presented for use in a thermo-mechanical analysis in order to predict the failure modes in the TBC. The temperature distribution in TBC coating mainly depends on the radiative effects combined with heat conduction and convection and radiation at the material boundaries.

scholarly journals AN INFLUENCE OF OUTDOOR TEMPERATURE ON THERMAL PERFORMANCE OF WINDOWS WITH A LOW-EMISSIVITY GLAZING

2003 ◽  
Vol 9 (2) ◽  
pp. 115-121
Author(s):  
Arünas Burlingis ◽  
Birutė Samajauskienė ◽  
Juozas Ramanauskas
Keyword(s):  
Thermal Resistance ◽  
Thermal Performance ◽  
Infrared Radiation ◽  
Heat Losses ◽  
Inert Gases ◽  
Outdoor Temperature ◽  
Surface Temperatures ◽  
Design Values ◽  
U Value ◽  
Value Of It

Heat economy is a pressing issue in all countries with severe climate. The most frequent method to solve the problem is to decrease heat losses in buildings by increasing the thermal resistance of enclosures. The most popular measure to improve windows is the use of low-emissivity coatings and inert gases. The U-value of such glazing unit is mostly dependent on the possibility of coating to reflect IR (infrared) radiation. These coatings are very effective when surface temperatures are high. During service of windows with a change of outdoor conditions (mostly temperature and wind), an U-value of it will suffer changes. The aim of this article is to show an influence of outdoor temperature on thermal performance of windows with a low-emissivity glazing and to determine the differences of declared and design U-values of modern effective windows substantial enough to introduce a concept of a normative design U-value for windows in Lithuania. We have found that differences between declared and design values (under the conditions of Lithuania) reach on average up to 17% for double glazed IG units with one low-E coating. Thus in case of very effective windows, it makes sense to introduce a concept of design U-value for windows in our country.

Design of a Cold Plate Tester for Accurate Measurement of Thermal Performance

2005 ◽  
Author(s):  
Nikhil Lakhkar ◽  
Madhusudan Iyengar ◽  
Michael Ellsworth ◽  
Dereje Agonafer
Keyword(s):  
Thermal Resistance ◽  
Thermal Performance ◽  
High Performance ◽  
Heat Dissipation ◽  
Thermal Design ◽  
Junction Temperature ◽  
Cold Plate ◽  
Expected Performance ◽  
Cold Plates ◽  
Effective Heat Transfer Coefficient

With the continuing industry trends towards smaller, faster and higher power devices, thermal management has become an extremely important element in the development of computer products. The primary goal of a good thermal design is to ensure that the chip can function at its rated frequency, while maintaining its junction temperature below the specified limit, to ensure reliable operation. The use of a heat sink or cold plate to manage the external thermal resistance has been well documented in the literature. However, the measurement of thermal performance of today state-of-the-art cold plates is challenging because of the low value of thermal resistance that they offer to heat dissipation. In this paper, the design of a tester apparatus for such high performance cold plates is presented. The expected performance of the tester is modeled numerically for a heat flux of 250 W/cm2, and for a range of footprint areas of 100-400 mm2. The analysis study is supported by a detailed uncertainty analysis that utilizes a Monte Carlo simulation approach. It was observed that the sum of random and repeatable errors could be controlled to within ±7.5% even for a very high performance cold plate with an effective heat transfer coefficient of 200,000 W/m2-K dissipating 250 W/cm2, with assumed errors in other relevant parameters.

scholarly journals Quantifying the aggregate thermal performance of UK holiday homes

2016 ◽  
Vol 38 (2) ◽  
pp. 209-225 ◽  
Author(s):  
David Johnston ◽  
David Farmer ◽  
Dominic Miles-Shenton
Keyword(s):  
Thermal Performance ◽  
Energy Performance ◽  
Evidence Base ◽  
Small Sample ◽  
Performance Gap ◽  
Design Intent ◽  
The Uk ◽  
The Way ◽  
A Performance

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.

scholarly journals Experimental Investigation of Thermosyphon Thermal Performance Using Different Filling Ratio

2021 ◽  
Vol 39 (1A) ◽  
pp. 34-44
Author(s):  
Talib Z. Farge ◽  
Samar J. Ismael ◽  
Rawad M. Thyab
Keyword(s):  
Experimental Investigation ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Heat Dissipation ◽  
Operating Temperature ◽  
Input Power ◽  
Filling Ratio ◽  
Working Fluid ◽  
Distilled Water ◽  
Percentage Decrease

The present work investigated the thermal performance of thermosyphon by using distilled water as a working fluid at different filling ratios (50%, 60%, and 70 %). The thermosyphon was manufactured from a copper tube with outer and inner diameters (26 and 24) mm, respectively. The thermosyphon was tested experimentally at different input power (100, 200 and 300) Watt. The operating temperature of the oil was chosen below 85°C. Experimental results revealed that the filling ratio of 60% exhibited the best heat dissipation at the highest operating temperature. While the low operating temperature and 50 % filling ratio show better heat dissipation. Further, it was found that the thermal resistance of the thermosyphon was obviously decreased with increasing the input power. The percentage decrease in the thermal resistance of the thermosyphon at a filling ratio of 0.6 was 14.6 % compared with that filling ratio of 0.5 at an input power of 300 W.

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