Thermal conductivity of the materials used in buildings is one of the major factors affecting the heat transfer. Higher thermal conductivity of building walls results in higher heat losses, and in ...order to maintain the same temperature inside a building, energy consumption for heating or cooling increases. To reduce the heat loss, thus decrease the energy usage, materials with lower thermal conductivities should be preferred. Lightweight concretes can be used for this purpose. However, the properties of these concretes may vary depending on the materials used. The main objective of this experimental study is to compare the properties of lightweight concretes produced with different lightweight aggregates. Lightweight concretes in a wide range of unit weights from approximately 300–1800kg/m3 were prepared in the experimental program. Some properties of the concretes containing pumice and expanded polystyrene beads were obtained. Properties of concretes with expanded perlite and autoclaved aerated concrete determined in previous studies are also included in comparisons and discussion. The test results showed that, depending on the amount and type of lightweight aggregate, unit weight of concrete can be reduced and concretes with various physical and mechanical properties of can be achieved. Thermal conductivity was reduced with the use of lightweight aggregates and for all the lightweight concretes considered, a good relationship was obtained between thermal conductivity and unit weight of concrete. Reductions in the compressive strength and modulus of elasticity of concretes have been obtained with decreasing concrete unit weights. The reduction in strength was more for the concrete containing expanded polystyrene beads.Results showed that strong relationships exist between modulus of elasticity and unit weight of concrete. Results showed that strong relationships exist between modulus of elasticity and unit weight of concrete.
District heating (DH) pipes are often older than 20 years and of unknown condition, imposing a strong demand for detailed knowledge about their current state to help cost-effective ongoing renovation ...and reduce water and energy losses. Here, we develop a scalable method that exploits hourly resolved remotely read heat meter data, pipe coordinates, and soil temperature measurements to continuously estimate the heat loss of service pipes. The method does not require the measured or simulated flows in the full system, making it possible to omit the usual step of establishing a complete thermohydraulic network model which is currently hindering implementation on larger scale. By exploiting open-source soil temperature data, the estimated heat loss is normalized to output the transmission coefficient, U, in W/(m∙K), allowing for direct intercomparison between pipes of different length and assessment of timely evolution across seasons. Estimated heat losses are validated by complementary techniques, using simulation of data sets and highly time-resolved data from a test area with additional measurement equipment installed. Finally, a full-scale application is demonstrated over a year on 1089 service pipes, including detection of a spontaneously emerged leakage, revealed through the model sensitivity towards the consequential changes in heat loss coefficient, U.
•A new method is proposed to estimate heat loss from service pipes in operation.•The method is designed focusing on minimal utility data requirements.•Outputs are validated by comparison to reference values from a test area.•Demonstration in full-scale on 1089 service pipes.•Capability to reveal leakage is documented by a real customer example.
An experimental study was conducted to compare laser ignition (LI) and spark discharge ignition (SDI) in an ethylene fueled supersonic combustor operating at a global equivalence ratio of 0.23. The ...Mach number, total pressure, and stagnation temperature of the inflow were 2.92, 2.6 MPa, and 1650 K, respectively. The flame kernel generated by the laser pulses experiences a rapid growth in size when it propagates towards the cavity leading edge and resides there. The cavity recirculation flow plays an important role at this stage because the velocity of it far outstrips the turbulent flame speed. In comparison, the ignition process of SDI is significantly slower because the long pulse duration of the spark discharge decreases the energy density of the plasma and makes the flame kernel more vulnerable to flame quenching. The extra heat loss resulting from the electrodes also delay the ignition process. After reaching the cavity leading edge, the flame kernel forms a small self-sustained flame there. Since the plasmas have transformed into flames, LI and SDI are similar in the aspect of flame propagation. The competition between the chemical reaction and the losses of heat and radicals determines the evolution of the flame. Prior to the reaction zone, the hot products generated by the flame are transported downstream via the cavity shear layer, which reduces the ignition delay time of the fuel/air mixture and promotes the accumulation of radicals in the flame base. The enhanced flame base further accelerates the propagation of the cavity shear layer flame. At the rapid propagation stage, the cavity shear layer flame spreads downstream prior to the flame base because the cavity shear layer dominates the evolution of the flame.
Building integrated photovoltaic (BIPV) glazing is currently regarded as a promising building material with a wide range of benefits. Photovoltaic combined vacuum glazing is a relatively new ...innovative concept in BIPV glazing. On the other hand, photovoltaic combined hybrid vacuum glazing (PVCHVG) is a rarely studied topic in which an air gap exists between vacuum glazing and photovoltaic glazing to form an insulated glazing unit. This paper investigates the overall energy-saving performance of a CdTe-based semi-transparent PVCHVG. A dynamic simulation model was developed and validated with an outdoor experiment to explore the energy-saving performance of the PVCHVG under five different climate conditions in China, and the results were compared with commonly used window systems. The results indicated good insulation properties against both heat loss and heat gain due to the combined action of vacuum glazing and semi-transparent photovoltaic glazing. Compared to clear single-glazing and double-glazing window systems, PVCHVG can save overall energy consumption up to 59.39% and 39.97% in heating-dominated region, and 76.33% and 73.766% in cooling-dominated region, respectively. Furthermore, the PVCHVG window system generated electricity with a good performance ratio and total system efficiency ranging from 85.7% to 85.78% and 7.45%–7.55%, respectively, considering five climate conditions.
•A CdTe-based STPV glazing combined hybrid vacuum glazing is investigated.•A dynamic simulation model is developed and validated with an outdoor experiment.•It poses inferior heat loss and heat gain in 5 distinct climate conditions in China.•The energy-saving potential is better in cooling than heating-dominated regions.•Key performance parameters for the window PV system are discussed.
The aim of this work was to evaluate the diurnal patterns of physiological responses and the thermal regulation of adult Nellore bulls. Six 30-mo-old Nellore bulls (669 ± 65 kg BW) were randomly ...assigned to four 6-h periods in a Latin Square design such that measurements of each animal cover a 24-h cycle. Meteorological variables (air temperature, relative humidity, local solar irradiance, ultraviolet radiation, wind speed and black globe temperature) were recorded at regular one-minute intervals with an automated weather station. Respiratory rate, ventilation rate, oxygen, carbon dioxide, methane, saturation pressure, air temperature of the exhaled air, saturation pressure in the air leaving the ventilated capsule placed over the animal surface, hair coat, skin surface and rectal temperature were assessed. The thermal equilibrium was determined according to the principles of the first law of thermodynamics using biophysical equations. Animals were evaluated in an area which was protected from solar radiation, rain, and had a range of ambient air temperature between 20.57 ± 0.07 and 30.86 ± 0.07 °C. Percentage of O2 and CO2 in the exhaled air changed moderately (P < 0.0001) throughout the 24 h, which resulted in an average metabolic heat production of 151.45 ± 13.60 W m-2. At the largest thermal gradient (TS - TA; from 24:00–07:00 h), heat transferred by long wave radiation and surface convection corresponded to near 60% of the metabolism. At 11:00 h the ambient temperature approached 29 °C and latent heat became the main way to cool the body. From this time until 17:00 h, cutaneous evaporation represented approximately 53% of total heat loss. In conclusion, results of the present study seem to be a good indicator of lower energy expenditure for body thermal regulation, high heat tolerance and adaptation of Nellore cattle to the tropical environment.
•Circadian period of thermal equilibrium of Nellore cattle was investigated.•Average of metabolic heat production of Nellore bulls was 151.45 ± 13.60 W m-2.•Air temperature above 29 °C, cutaneous evaporation is the main way to mantain Nellore's thermoregulation.•Respiratory evaporation present minor significance for thermal regulation of Nellore.
The foam-structured reactor is one which has hitherto been regarded as of great potential for industrial applications in the field of solar thermochemistry. The utilization mode of ceramic foam has, ...generally, a significant impact on energy conversion and storage efficiency. This study establishes a numerical model, coupled with computational fluid dynamics and dry reforming of methane reaction kinetics, to find the optimal structural parameters of the ceramic foam. A local thermal non-equilibrium model coupled with the P1 approximation has been developed to address the heat-transfer problems, and the non-Darcy flow effect has been considered to calculate the momentum dissipation in the porous zone. Based on ample simulation examples, the effects of porosity and foam cell size on the reaction temperature, surface heat loss, thermal efficiency, CH4/CO2 conversion, H2/CO yield, carbon deposition, and solar-to-chemical efficiency are illustrated in detail. The results indicate that using the ceramic foam with high porosity and large cell size is able to attain the best thermochemical characteristics, of which the validity can be assured, insofar as the various operating conditions in this study are concerned. Furthermore, as compared to the best single-layer structure, the application of the optimized double-layer foam structure is a more effective solution, which is able to further improve the energy storage efficiency by a remarkable 9.23%.
•The significance of foam structure to thermochemical characteristics is revealed.•CFD coupled with DRM kinetics determines reactor characteristics.•Ceramic foam with high porosity and large cell size refines system performance.•The optimized structure could yield efficiency gains of 10–28%.•Double-layer structure further improves energy storage efficiency by 9.23%.
Nowadays, with the advancement of construction technology, saving energy use of the building has been considered as one of the fields of environmental sustainability. The use of green cover and ...plants on the buildings is a suitable passive method that leads to the replace reduced urban green spaces and reduce the problems caused by the effect of the urban heat island (UHI) and improve the energy performance of buildings by reducing the indoor temperature, regulating humidity and creating thermal insulation. The objective of this study was to evaluate the reduction of energy consumption through the green walls of an educational building in Gorgan (Csa climate). For this purpose, first, a building designed on the university site, and the effects of two methods of constructing green walls by using three different plant species were simulated. For comparison, thermal data of a building with a direct green facade in the same climate was measured as an experimental sample, and the results were used in the simulation. The effects of using two methods of a green wall with three different plant species (Sedum, Parthenocissus tricuspidata, Hedera helix) were simulated, which Sedum has had better results than other species. The final results showed that the latent heat of the building is increased by green walls and less significant heat is generated in the environment than buildings without green cover. Also, in buildings with living green walls, compared to buildings with direct green facades, the thermal transmittance of the wall is reduced due to more material layers. The results show that some types of green walls reduce heat loss, and finally the total energy use of the building. The green wall has a more efficient effect on the buildings with a simple form and the limited number of interior spaces. In general, depending on the variables of each building, the use of green walls with plant species is different. It is better for a building before design, to determine the most appropriate method of constructing a green wall and plant species to reduce the energy usage according to project factors and climate type of the region.
The Heat Loss Coefficient (HLC) characterizes the envelope efficiency of a building under in-use conditions, and it represents one of the main causes of the performance gap between the building ...design and its real operation. Accurate estimations of the HLC contribute to optimizing the energy consumption of a building. In this context, the application of black-box models in building energy analysis has been consolidated in recent years. The aim of this paper is to estimate the HLC of an existing building through the prediction of building thermal demands using a methodology based on Machine Learning (ML) models. Specifically, three different ML methods are applied to a public library in the northwest of Spain and compared; eXtreme Gradient Boosting (XGBoost), Support Vector Regression (SVR) and Multi-Layer Perceptron (MLP) neural network. Furthermore, the accuracy of the results is measured, on the one hand, using both CV(RMSE) and Normalized Mean Biased Error (NMBE), as advised by AHSRAE, for thermal demand predictions and, on the other, an absolute error for HLC estimations. The main novelty of this paper lies in the estimation of the HLC of a building considering thermal demand predictions reducing the requirement for monitoring. The results show that the most accurate model is capable of estimating the HLC of the building with an absolute error between 4 and 6%.
Natural gas pressure drops in city gate stations, in the natural gas distribution network, and bypassing through throttle valves. On the other hand, sudden gas pressure drop causes extreme ...temperature drop. To prevent natural gas from being hydrated in city gate stations, a water bath heater is used, leading to heating natural gas before the pressure reduction stage.
The main consequence of this research is the consideration of the challenge of low thermal efficiency in water bath heaters and the high potential of flue gases, which leads to the preheating of the gas by heat loss recovery and consequently improving the energy performance of the whole system.
In this study, a heat pipe heat exchanger was laboratory designed and constructed by using the ε-NTU method. The heat exchanger performs to recover partly the waste energy of flue gas emitted to the environment through heat pipes. This has been investigated in several experiments, based on conducted studies, measured data from a city gate station during a year, and also corresponding the experimental results with real conditions. In addition, to determine energy saving in fuel consumption, the city gate stations process was simulated in HYSYS software and evaluated according to gas temperature in new conditions.
As major findings applying heat pipes reduces natural gas consumption by 510,132 SCM a year; it also annually prevents 756 tons of CO2 from being emitted off a city gate station.
•The challenge of low thermal efficiency in water bath heaters is considered.•A heat pipe heat exchanger was laboratory designed and constructed by using the ε-NTU method.•The heat exchanger performs to recover partly the waste energy of flue gas through heat pipes.•The results show that applying heat pipes reduces natural gas consumption by 510,132 SCM a year.•It also annually prevents 756 tons of CO2 from being emitted off a city gate station.
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