Combined thermal acceptability and air movement assessments in a hot humid climate

In the ASHRAE comfort database [1], underpinning the North American naturally ventilated adaptive comfort standard [2], the mean indoor air velocity associated with 90% thermal acceptability was relatively low, rarely exceeding 0.3 m/s. Post hoc studies of this database showed that the main complaint related to air movement was a preference for ‘more air movement’ 3 and 4. These observations suggest the potential to shift thermal acceptability to even higher operative temperature values, if higher air speeds are available. If that were the case, would it be reasonable to expect temperature and air movement acceptability levels at 90%? This paper focuses on this question and combines thermal and air movement acceptability percentages in order to assess occupants. Two field experiments took place in naturally ventilated buildings located on Brazil’s North-East. The fundamental feature of this research design is the proximity of the indoor climate observations with corresponding comfort questionnaire responses from the occupants. Almost 90% thermal acceptability was found within the predictions of the ASHRAE adaptive comfort standard and yet occupants required ‘more air velocity’. Minimum air velocity values were found in order to achieve 90% of thermal and air movement acceptability. From 24 to 27 °C the minimum air velocity for thermal and air movement acceptability is 0.4 m/s; from 27 to 29 °C is 0.41–0.8 m/s, and from 29 to 31 °C is >0.81 m/s. These results highlight the necessity of combining thermal and air movement acceptability in order to assess occupants’ perception of their indoor thermal environment in hot humid climates.     

A new model based on experimental results for the thermal characterization of bricks

The development of fast and reliable protocols to determine the characteristics of building materials is of importance in order to develop environmentally friendly houses with an efficient energy design. In this article heat flux evolution on different types of clay and concrete bricks has been studied using a guarded hot-plate. The studied bricks were purchased from local commercially available sources and included a solid face brick and a range of honeycombed and perforated bricks. From the data collected a new model to study heat flux is proposed. This model is based on the shape of the typical sigmoidal curves observed for the time dependent heat flux evolution. The model allows the calculation of the thermal resistance (R) and the heat flux in the steady-state (φ_∞). The model also calculates two new parameters, t_B and τ_B. t_B represents the time at which half φ_∞ is attained. This parameter (t_B) has additionally been found to be dependent on the thermal diffusivity and the geometric characteristics of the brick.     

Rebuttal of “Problems in the extreme value analysis”

This paper rebuts claims published in this journal [33] as well as elsewhere [31], [32] and [34]: (a) that improved methodologies for extreme value analysis (EVA) developed over the past 60 years are invalid; (b) that EVA methodologies should revert to the status quo ante 1939; and (c) that, consequently, all regulations and codes of practice for extreme winds should be reassessed. This paper rebuts these claims and shows current EVA methodologies to be valid. The paper also shows that uncertainty due to sampling error, viz. how well a single observed sample represents the random process sampled, dominates over the choice of methodology.     

Uncertainty analysis in building performance simulation for design support

Building performance simulation (BPS) has the potential to provide relevant design information by indicating directions for design solutions. A major challenge in simulation tools is how to deal with difficulties through large variety of parameters and complexity of factors such as non-linearity, discreteness, and uncertainty.The purpose of uncertainty and sensitivity analysis can be described as identifying uncertainties in input and output of a system or simulation tool [1], [2] and [3].In practice uncertainty and sensitivity analysis have many additional benefits including: (1) With the help of parameter screening it enables the simplification of a model [4]. (2) It allows the analysis of the robustness of a model [5]. (3) It makes aware of unexpected sensitivities that may lead to errors and/or wrong specifications (quality assurance) [6], [7], [8], [9] and [10]. (4) By changing the input of the parameters and showing the effect on the outcome of a model, it provides a “what-if analysis” (decision support). [11].In this paper a case study is performed based on an office building with respect to various building performance parameters. Uncertainty analysis (UA) is carried out and implications for the results considering energy consumption and thermal comfort are demonstrated and elaborated. The added value and usefulness of the integration of UA in BPS is shown.     

Thermal analysis of a building brick containing phase change material

This paper presents the thermal analysis of a building brick containing phase change material (PCM) to be used in hot climates. The objective of using the PCM is to utilize its high latent heat of fusion to reduce the heat gain by absorbing the heat in the bricks through the melting process before it reaches the indoor space. The considered model consists of bricks with cylindrical holes filled with PCM. The problem is solved in a two-dimensional space using the finite element method. The thermal effectiveness of the proposed brick-PCM system is evaluated by comparing the heat flux at the indoor surface to a wall without the PCM during typical working hours. A paramedic study is conducted to assess the effect of different design parameters, such as the PCM's quantity, type, and location in the brick. The results indicate that the heat gain is significantly reduced when the PCM is incorporated into the brick, and increasing the quantity of the PCM has a positive effect. PCM cylinders located at the centerline of the bricks shows the best performance.     

Internal baffles to reduce the natural convection in the voids of hollow blocks

Hollow bricks are widely used to build facades of light weight and high thermal resistance. The air filled voids within the brick configuration elevates the block’s thermal resistance. Disturbing the natural flow patterns developed inside the voids affects the blocks overall thermal resistance. This paper presents a numerical study for a section of a masonry brick represented by a baffled squared cavity surrounded by a conductive wall of finite thickness. The baffles are attached to the top and bottom sides dividing the void into three regions. The thermal resistance of the partitioned voids depends on baffles length and location. Short baffle develops a stratified region in the central gap and generates two circulation zones near the upper left and lower right corners. Long baffles, on the other hand, splits the flow into three different convection circulation cells, a cell near each side of the cavity and a third in the central gap. Increasing the baffle height increases the thermal resistance of the partitioned cavity for all gap widths. The highest increase in thermal resistance is 53% over the non baffled voids and is achieved with long baffles when located to divide the cavity into three regions of equal widths.     

Heat conduction across double brick walls via BEM

The Boundary Element Method (BEM) is used to compare the steady-state heat and moisture diffusion behaviour across double brick walls provided by two different models: in the first one, the brick wall is assumed to be composed of a set of homogeneous layers bonded together, which is the model frequently used to predict internal condensation; in the second model, the geometrical modelling and hygrothermal properties of the individual bricks are taken into account.The BEM is implemented allowing the use of multi boundaries, which permits the full discretization of the brick cavities.Three different construction solutions are analysed. In the first, the double-brick wall is assumed not to be thermally insulated; in the second, the space between the two layers of bricks is filled with thermal insulation material; in the third solution, both the space between the brick layers and the holes of the inner brick layer are filled with thermal insulating material.     

Steady state theoretical model of fired clay hollow bricks for enhanced external wall thermal insulation

This paper proposes a theoretical model to study the steady state thermal behavior of fired clay hollow bricks for enhanced external wall thermal insulation. The study aims at the development of new materials and structural components with good thermal material properties, with respect to energy saving and ecological design. Thermal insulation capacity of two external walls of different thicknesses, constructed of locally produced bricks, is studied. The basic brick units used for the investigation are small-size bricks with eight equal cavities or recesses and big-size bricks with twelve equal recesses. Their recesses configuration has been varied to perform the assessment. The insulation materials injected within brick recesses during the assessment are granulated cork and expanded polystyrene. The improvement in the thermal performance of the walls will be the result of optimization among the various factors such as brick cavity configurations, integration of insulation within brick recesses and the cavity surface emissivities. So emphasis is given to the study of the impact of these factors singly or in combination on the overall thermal resistance of walls in order to find out the best design solutions to maximize their thermal insulation capacity. Computer modeling and calculations performed, for steady state conditions, show that the increase in hollow brick cavity height contributes to the improvement of the overall thermal resistance of the order of 18–20%. The improvement could significantly increase to the range of 88.64% and 93.33%, if the bricks used are injected with the insulating material. If the cavity surface emissivities are lowered to 0.3, the improvement will be 72.73–78.33%. The results have also shown that replacing the cork by expanded polystyrene (EPS), having lower thermal conductivity, would not improve significantly the overall thermal resistance. This improvement is 9.08% for a wall of small-size bricks having configuration BS2CV and 8.34% for a wall of big-size bricks having configuration BB3CV.     

Towards the identification of worn picks on cutterdrums based on torque and power signals using Artificial Neural Networks

The paper presents an attempt to identify the status of cutters working as an assembly on a multi-tool head. Initial tests covered machining with a single radial tool ( [Gajewski and Jonak., 2007] and [Jonak and Gajewski., 2007]). The time courses of mining power and torque for a multi-tool head with installed radial and tangent-rotational tools were recorded. The tests covered mining with new - sharp - cutters and partially worn cutters. In order to limit the variables influencing the mining process, a model rock block was used for the experiment.The received time courses were used as input variables for the Artificial Neural Network (ANN). For this purpose, mining power and torque signals statistical parameters were established: variance, skewness, and kurtosis. The status of mining cutters (sharp or worn) was the input variable Artificial Neural Network. Multilayer perceptron (MLP) structure networks, verified in the previous identification tests ( [Gajewski and Jonak, 2006] and [Gajewski, 2005]), were used for analysis.     

Contribution to flashover modelling: Development of a validated numerical model for ignition of non-contiguous wood samples

A computational model of flashover is presented that closely follows the experimental setup at CNRS-ENSMA-Poitiers. A propane burner with thermal power of 55 kW is used as a primary source of fire and square beech wood samples (30 mm×30 mm×5 mm) as fire spread targets. The computational model describes the wood pyrolysis with a progress variable. Using the conservation of heat fluxes at the solid–gas interface, the thermal diffusion in the wood samples is coupled with the convective and the radiative heat transfer in the ambient gas phase. The incoming heat flux at the upper surface of the wood samples reaches values between 20 and 30 kW/m². With the ignition and subsequent combustion of the pyrolysis volatiles, the heat flux increases by approx. 12 kW/m². The results show that the ignition of the wood samples is triggered at an approx. surface temperature of 650 K. Due to large local variations in incident heat flux, significant differences in the ignition times of the wood samples are observed. The comparison of the calculated and the experimentally measured temperature shows a good agreement for the first wood sample and the model predicts the ignition time very well. But for the second and the third wood samples the model overpredicts the temperature, which leads to a premature ignition of these wood samples.     

A Round Robin Test for buildings energy performance in Italy

The energy policy in Europe regarding buildings and the energy efficiency sector are regulated by two directives: 2002/91/CE - EPBD and 2006/32/CE - EEESD [1] and [2].The CEN has elaborated a standard to revise all European normatives about building energy performance and HVAC plants. The “CEN Umbrella” CEN/TR 15615 [3] includes a new version of EN ISO 13790:2008 [4] and a new standard about heating plant, use and contributions of renewable energy sources. Furthermore, the CEN Standard provides a software version for technicians.In this paper we present a Round Robin Test between a selection of softwares applied to an Italian case study. The selected calculation methodologies, range from research packages to extra-simplified software. Furthermore, the Italian procedure described in UNI TS 11300 [5] has been analyzed and considered as the reference for all other calculation methodologies.The results of the Round Robin Test show the relationship between thoroughness of data input and energy evaluation accurancy. The more the input data is affected by uncertainty, the less precise is the energy efficiency calculation. On the other hand the energy performance of building evaluation accurancy depends on the aim of the simulation: the energy audit, the energy design or the energy labeling (certification).     

Optimization of the configuration of 290 × 140 × 90 hollow clay bricks with 3-D numerical simulation by finite volume method

This paper is aimed at finding the optimum configuration of the number of holes and their arrangement for the 290 × 140 × 90 hollow clay bricks with 3-D numerical simulation by a home-made code with finite volume method. Seventy-two kinds of configurations with different hole number and arrays are chosen elaborately and their equivalent thermal conductivities are numerically predicted. In addition, the effects of the hole surface radiation and the indoor–outdoor temperature difference on the equivalent thermal conductivity are also investigated. The major findings are as follows. The radiation of the hole surfaces makes heat transfer enhanced and the equivalent thermal conductivity enlarged in some extent, ranging from 25.8% to 4.6%. The optimum configuration has eight holes in length, four holes in width and one holes in height, whose equivalent thermal conductivity is the lowest and of 0.400 W/(m K),which is only 59% of the highest thermal conductivity of the all cases studied. When the indoor–outdoor temperature difference varies from 50 °C to 20 °C, the equivalent thermal conductivity of the 72 kinds of hollow bricks does not vary too much, usually within ±5%. Especially, the equivalent thermal conductivity of the optimum configuration holds no change within this variation range of indoor–outdoor temperature difference.     

Influence of secondary settling tank performance on suspended solids mass balance in activated sludge systems

Secondary settling is the final step of the activated sludge-based biological waste water treatment. Secondary settling tanks (SSTs) are therefore an essential unit of producing a clear effluent. A further important function of SSTs is the sufficient thickening to achieve highly concentrated return sludge and biomass within the biological reactor. In addition, the storage of activated sludge is also needed in case of peak flow events (Ekama et al., 1997). Due to the importance of a high SST performance the problem has long been investigated ( [Larsen, 1977], [Krebs, 1991], [Takács et?al., 1991], [Ekama et?al., 1997], [Freimann, 1999], [Patziger et?al., 2005] and [Bürger et?al., 2011]), however, a lot of questions are still to solve regarding e.g. the geometrical features (inflow, outflow) and operations (return sludge control, scraper mechanism, allowable maximum values of surface overflow rates). In our study we focused on SSTs under dynamic load considering both the overall unsteady behaviour and the features around the peaks, investigating the effect of various sludge return strategies as well as the inlet geometry on SST performance. The main research tool was a FLUENT-based novel mass transport model consisting of two modules, a 2D axisymmetric SST model and a mixed reactor model of the biological reactor (BR). The model was calibrated and verified against detailed measurements of flow and concentration patterns, sludge settling, accompanied with continuous on-line measurement of in- and outflow as well as returned flow rates of total suspended solids (TSS) and water.As to the inlet arrangement a reasonable modification of the geometry could result in the suppression of the large scale flow structures of the sludge-water interface thus providing a significant improvement in the SST performance. Furthermore, a critical value of the overflow rate (q_crit) was found at which a pronounced large scale circulation pattern develops in the vertical plane, the density current in such a way hitting the outer wall of the SST, turning then to the vertical direction accompanied with significant flow velocities. This phenomenon strengthens with the hydraulic load and can entrain part of the sludge thus resulting in unfavourable turbid effluent.As a representative case study an operating circular SST most commonly used in practice was investigated. Focusing on the sludge return strategies, it was found that up to a threshold peak flow rate the most efficient way is to keep the return sludge flow rate constant, at 0.4Q_MAX. However, once the inflow rate exceeds the threshold value the return sludge flow rate should be slowly increased up to 0.6Q_MAX, performed in a delayed manner, about 20-30 min after the threshold value is exceeded. For preserving the methodology outlined in the present paper, other types of SSTs, however, need further individual investigations.     

Local thermal sensation and comfort study in a field environment chamber served by displacement ventilation system in the tropics

This paper presents a study of local thermal sensation (LTS) and comfort in a field environmental chamber (FEC) served by displacement ventilation (DV) system. The FEC, 11.12 m (L)×7.53 m (W)×2.60 m (H), simulates a typical office layout. A total of 60 tropically acclimatized subjects, 30 male and 30 female, were engaged in sedentary office work for 3 h. Subjects were exposed to three vertical air temperature gradients, nominally 1, 3 and 5 K/m, between 0.1 and 1.1 m heights and three room air temperatures of 20, 23 and 26 °C at 0.6 m height. The objective of this study is to investigate the mutual effect of local and overall thermal sensation (OTS) and comfort in DV environment. The results show that in a space served by DV system, at OTS close to neutral, local thermal discomfort decreased with the increase of room air temperature. The OTS of occupants was mainly affected by LTS at the arm, calf, foot, back and hand. Local thermal discomfort was affected by both LTS and OTS. At overall cold thermal sensation, all body segments prefer slightly warm sensation. At overall slightly warm thermal sensation, all body segments prefer slightly cool sensation.     

Experimental and numerical investigation of a hollow brick filled with perlite insulation

The present study is focused on the investigation of the effective thermal properties of a modern vertically perforated masonry unit filled with perlite insulation. Based on measurements and numerical calculations, the thermal performance of the new hollow brick was determined. The authors suggest to use the following parameters for this building material: equivalent heat capacity equal to 855.1 J/kg K, equivalent heat conductivity equal to 0.09 W/mK and equivalent density equal to 653.15 kg/m³. The dependence of the equivalent thermal resistance of the whole wall made of this brick and mortar, is shown for different mortar joint thicknesses. All results, presented in this paper, can be used in energy balance calculations for buildings made of masonry unit.     

Strength and thermal conductivity in lightweight building materials

Pumice can be used in bricks and concrete to produce lightweight building materials with high porosity, high thermal insulation and resistance to earthquake motion. The paper presents ongoing research to design a structural lightweight concrete and brick using Nevşehir pumice. The testing of four different brick types is reported. The density, thermal conductivity, compressive and tensile strengths and Young’s elastic modulus indicated that these lightweight materials had significant advantages as a construction material in earthquake-prone areas.      

Assessment of coconut fibre insulation characteristics and its use to modulate temperatures in concrete slabs with the aid of a finite element methodology

This paper presents the assessment of coconut fibre thermal characteristics and its use to modulate temperatures in concrete slabs in the construction industry. Fibre is abundantly available in tropical regions, extracted from the husk of coconut fruits and manufactured at 115.54 MPa to obtain specimens. A first thermal conductivity of k = 0.048 (W/m K) is obtained by solving the heat diffusion equation with experimental temperatures as boundary conditions. A second value k = 0.0499 (W/m K) is obtained by solving the Fourier's law by using a known heat flux and temperature histories in the specimen. The maximum error between the first and second k values was 3.8%. However, the k = 0.048 (W/m K) was used for numerical analysis.Experimental work was done to find density and heat capacity, 174 kg/m³ and 2600 J/kg K, respectively. Further numerical work was carried out to modulate temperature in concrete slabs. This showed that fibre put on the concrete external surface allows room temperatures to fall within the comfort range. Density, thermal conductivity and heat capacity of coconut fibre were varied in a wide range to investigate the sensitivity of temperature to such changes. This showed that temperature can be considered sensible only to thermal conductivity variations.     

Numerical simulation by the FVM of coupled heat transfers by conduction, natural convection and radiation in honeycomb’s hollow bricks

This paper presents a detailed numerical study, in steady state regime, of the interaction between two dimensional heat transfers by conduction, natural convection and radiation in double hollow bricks formed by two honeycomb walls separated by an air layer. The air motion in all cavities of the system is laminar. The left and right vertical sides of the hollow bricks are considered isothermal and maintained at different constant temperatures. The top and bottom horizontal sides are assumed to be adiabatic. The governing equations are solved using the finite volume method (FVM) and the SIMPLE algorithm. The impact of the thickness of the air layer on the global heat flux through the structure is discussed. The simulation results show that the variation of the overall heat flux through each hollow brick as a function of the temperature difference ΔT between the vertical sides of the system is almost linear for the different types of double hollow bricks considered. This linear thermal behaviour allowed the generation of appropriate overall heat exchange coefficients that permit fast and accurate prediction of heat transfers through the hollow bricks without solving the complex system of equations governing the coupled heat transfers. Comparison of the performance of different types of double hollow bricks is made.     

Energy and emergy based cost–benefit evaluation of building envelopes relative to geographical location and climate

This paper presents an environmental evaluation of building envelopes, made of three different technologies: a traditional air-cavity wall, a plus-insulated wall (with an external cork covering), and a ventilated wall (with external brick panels fixed on extruded frames). An environmental accounting method, namely Emergy Evaluation (EE), was performed for assessing environmental resource use (energy and material flows), both directly and indirectly, for the construction of a façade (1000 m²). Then, energy use during the building lifetime was assessed as a constant inflow to the building depending on the thermal skills of building envelopes, besides thermal efficiency of air-conditioning system. In particular, this energy inflow is needed for maintaining constant indoor climate conditions (18 °C) and has to balance heat dissipation through envelopes (heat loss in winter and heat gain in summer). Outcomes were compared with an Energy Analysis (EA) based on an embodied energy accounting. Finally, costs for manufacturing walls (with enhanced performance) and benefits (energy saving) were compared in a unique balance, through both EA and EE. Moreover, outcomes were obtained for three scenarios corresponding to three geographic locations (Berlin in northern Europe, Barcelona on the Mediterranean coast and Palermo in the south of Italy). Results highlighted that performances of building envelopes depend on technologies relative to external climate conditions. Different environmental accounting methods, such as EE and EA, provided outcomes with some difference that are not contradictory to each other but complementary.     

The Nile monitor (Varanus niloticus; Squamata: Varanidae) as a sentinel species for lead and cadmium contamination in sub-Saharan wetlands

Wetland pollution is a matter of concern in sub-Saharan Africa. Though regularly exploited, the Nile monitor (Varanus niloticus), a large amphibious lizard, is not threatened. This work aims at assessing the value of this varanid as a sentinel species in surveys of environmental contamination by metals. Lead and cadmium quantifications were performed by graphite furnace-atomic absorption spectrophotometry in bone, intestine, kidney, liver and muscle in 71 monitors from three unevenly polluted sites in Mali and Niger, plus a reference site. The effects of sex, size and fat reserves as well as factors related to the sampling strategy (tissue sampled, sampling site) were studied with a mixed linear model. Metal contamination is moderate at the four sites but clear differences nevertheless occur. Lead levels are generally maximal in bone, with a gender-independent median value 320 ng.g⁻¹. Median cadmium concentrations never exceed 70.2 ng.g⁻¹ in females (kidney) and 57.5 ng.g⁻¹ in males (intestine). Such levels should have no detrimental effects on the monitors. Lead and cadmium levels in muscles are generally below 200 and 20 ng.g⁻¹, respectively, and should provoke no health hazard to occasional consumers of monitor meat. Metal organotropisms are consistent with those observed in other studies about Squamates: for lead: bone > [kidney, intestine, liver] > muscle in males and [bone, kidney] > [intestine, liver] > muscle in females; for cadmium: [liver, intestine, kidney] > [bone, muscle] for both genders. Females are more contaminated, especially in their kidneys. In this tissue, median values in ng.g⁻¹ are 129.7 and 344.0 for lead and 43.0 and 70.2 for cadmium, for males and females, respectively. Nile monitors can reveal subtle differences in local pollution by metals; moreover, the spatial resolution of the pollution indication that they give seems to be very sharp. The practical relevance of this new tool is thus validated.