Ambient Dry Bulb Research Articles

Effect of roof modification on micro-climate of animal shed

A study was conducted to compare the effect of roof modification with use of polycarbonate plastic sheet and its variable height on micro-climate of growing dairy heifers. The experiment was carried out on three sheds for three seasons, viz. hot-dry (summer) season, hot-humid (rainy) season and winter season. In control group (C), loose housing system was followed and corrugated cemented sheets were used as roofing material. In T1, polycarbonate sheets were used as roofing material with fixed height. In T2, polycarbonate sheets were used as roofing material with adjustable height. Daily ambient temperature (°C), dry and wet bulb temperature outside the shed (macro-climate) and inside the shed (micro-climate), Relative Humidity and Temperature Humidity Index were being recorded twice a day at 9.00 am and 2: 30 pm for three continuous days at fortnightly interval. The average temperature of animal shed was significantly lower in T2 (27.30±0.10), followed by T1 (28.28±0.04) and C (29.46±0.16). In T2 lower temperature of shed than control was recorded during summer. Increasing the height of shed with ridge ventilation might have helped to dissipate heat easily in T2. The overall THI was significantly lower in T2 (76.50 ± 0.16) followed by T1 (77.91 ± 0.05) and higher in control (78.74 ± 0.25), which might be due to less penetration of solar radiation via reflective polycarbonate sheet and higher height of roof in T2. The micro-environment was more conducive and comfortable in T2 than control. Polycarbonate roofing with adjusted higher height may be a desirable choice for animal housing to mitigate heat stress in summer.

The study on plume abatement and water saving of hybrid mechanical draft wet cooling tower

Under strict environmental requirements, the mechanical draft wet cooling tower (MCT) should control the generation of plume and save water resources. In this study, the plume, water saving, and thermal performance of MCT and hybrid MCT are compared through experiments. The main experiment variables include the dry bulb temperature, the relative humidity, the circulating water flow rate, the inlet water temperature, the crosswind velocity, and the crosswind angle. Results show that the hybrid MCT can realize plume abatement and water saving, but its thermal performance will be weakened. The difficulty of plume abatement will be increased at lower ambient dry bulb temperature and higher relative humidity. With the increase of crosswind speed, it is conducive to plume abatement under the crosswind angle of 0°, while that is the opposite under the crosswind angle of 90° and 180°. The working conditions of the hybrid MCT have a great influence on the water saving rate, the water saving rate ranges from 5.9 % ∼ 14.4 % within the scope of this study. Compared to the MCT, the outlet water temperature of the hybrid MCT is increased by about 0.8 ∼ 1 ℃.

Numerical study on performance of hybrid mechanical draft wet cooling tower

To explore the operation mechanism of the hybrid mechanical draft wet cooling tower (hybrid MCT), a 3D model of the hybrid MCT is established. The plume, water saving, and cooling capacity of the hybrid MCT are discussed. The ambient dry bulb temperature, relative humidity, circulating water temperature, and circulating water flow rate are taken as the main variables. Results that the ambient dry bulb temperature and circulating water temperature have the larger impact on the plume abatement and water saving rate, and the relative humidity and circulating water flow rate have relatively small impact. As the ratio of circulating water flow rate in the dry part increases, the water saving rate and cooling capacity of hybrid MCT are enhanced. However, when the ratio of circulating water flow rate in the dry part exceeds 0.4, the variation of water saving rate is not obvious. Based on satisfied plume abatement, by adjusting the airflow resistance in the dry part, the water temperature drop of hybrid MCT can be increased by 0.4 °C.

Improving the Thermal Performance of Indirect Evaporative Cooling by Using a Wet Fabric Device on a Concrete Roof in Hot and Humid Climates

This study investigated an indirect evaporative cooling system (IECS) to control latent heat loss on roof ponds by increasing the evaporation rates on wet fabric membranes. The cooling potential of the proposed system was experimentally tested in a real environment and it was compared against a roof pond and a floating fiber (gunny bags) to provide an efficient model for buildings in hot and humid climates. Dry bulb temperatures (DBT) are presented for four experimental models. Solar irradiance, ambient and indoor dry bulb temperatures, and relative humidity (RH) were measured for seven days in each of the following climate conditions: hot sub-humid (mean DBT 27.3 °C and mean RH 72%), hot humid (mean DBT 27.1 °C and mean RH 81%), and warm sub-humid (mean DBT 25.2 °C and mean RH 68%). There were no significant variations in thermal performance between the examined devices under hot humid conditions; however, the wet fabric device had superior thermal performance under sub-humid conditions when compared to the other IECSs. In the three climatic scenarios where the proposed system was tested, the wet fabric managed to reduce the indoor air temperature by 6.6 °C, 5.3 °C, and 5.1 °C, respectively, as compared to the outdoor air temperatures.

Analysis and Optimization of Cooling Water System Operating Cost under Changes in Ambient Temperature and Working Medium Flow

The circulating cooling water system is widely used in various industrial production fields, and its operating cost largely depends on external factors, such as ambient temperature and working medium flow. Considering the relative elevation of the heat exchanger, this study establishes a total system operation cost analysis and optimization model based on the superstructure method. The model uses ambient dry bulb temperature, ambient wet bulb temperature, and working medium flow as random variables. Water supply temperature is adopted as the decision variable, and the minimum operating cost of the system is used as the objective function. An analysis of the effect of the three random variables on the operation cost shows that the effect of ambient dry bulb temperature on the operation cost is negligible, and the effect of ambient wet bulb temperature and working medium flow on the operation cost is significant. In addition, a control equation of water supply temperature is established to determine the “near optimal” operation, which is based on the correlation among ambient wet bulb temperature, working medium flow, and optimal water supply temperature. Then, the method is applied to a case system. The operating cost of the system is reduced by 22–31% at different times during the sampling day.

MODELLING THE PERFORMANCE OF A CAMEL MILK STORAGE STRUCTURE WITH EVAPORATIVE COOLING USING ARTIFICIAL NEURAL NETWORK

Storage and marketing of camel milk in arid lands of Kenya is hampered by lack of cold storage facilities. This problem can be alleviated by using storage structures incorporating evaporative cooling whose performance depends on climatic conditions. The objective of this work was to develop an artificial neural network (ANN) to predict cooled milk temperature and cooling efficiency of a locally fabricated cooler. Data were obtained from the cooler which was tested under various experimental conditions. Using some of the experimental data for training, a three-layer feed-forward ANN model based on back propagation Levenberg-Marquardt algorithm was developed using the Neural Network Toolbox for MATLAB®. The optimal model had a 4-4-2 structure with sigmoid transfer function in both layers. The inputs of the model were ambient dry bulb temperature, wet bulb temperature, wind speed and temperature of drip water, whereas the outputs were cooled milk temperature and cooling efficiency. The experimental data set (n=165) was randomly divided into training (75%) and testing (25%) sub-sets. The performance of the ANN predictions was evaluated by comparing the predicted and experimental results. The predictions agreed well with experimental values with mean squared error of 10.2, mean relative error of 4.02% and correlation coefficients in the range of 0.86-0.93. This study reveals that, as an alternative to conventional modelling techniques, the ANN approach can be used successfully for predicting the performance of locally fabricated camel milk storage structures incorporating evaporative cooling in arid pastoral areas of Kenya. The model can be used as a design tool to estimate the sizing and performance of future coolers, as it allows the prediction of the performance of hypothetical coolers designed without a need for time demanding experimentation. This can aid in up-scaling the technology.

Filmwise Condensation From Humid Air on a Vertical Superhydrophilic Surface: Explicit Roles of the Humidity Ratio Difference and the Degree of Subcooling

Abstract The process involving heat and mass transfer during filmwise condensation (FWC) in the presence of noncondensable gases (NCG) has great significance in a large variety of engineering applications. Traditionally, the condensation heat transfer is expressed in the literature as a function of the degree of subcooling—reckoned as the difference between the ambient dry bulb temperature and the condenser wall temperature. However, in the presence of NCG, there exists a finite gradient of vapor mass fraction near the condenser plate, which directly influences the vapor mass flux to the condenser surface, thus limiting the condensation rate. The effects of both these influencing thermodynamic parameters, i.e., the degree of subcooling and the difference of humidity ratio (between the freestream environment and on the condenser plate), have been characterized in this work both experimentally and through a mechanistic model. The vapor mass flux during condensation on a subcooled vertical superhydrophilic surface under free convection regime is experimentally measured in a controlled environment (temperature and humidity) chamber. The mechanistic model, based on the similarity of energy and species transports, is formulated for the thermogravitational boundary layer over the condenser plate and tuned against the experimental results. Further, the model is used to obtain comprehensive data of the condensate mass flux and condensation heat transfer coefficient (CHTC) as functions of the salient thermal operating conditions over a wide parametric range. Results indicate that humidity ratio difference has a more pronounced influence on the condensation mass transfer rather than the degree of subcooling. Regime maps of condensate flux and CHTC show how these can be explicitly identified in terms of the degree of subcooling and humidity ratio difference, regardless of the prevailing thermal and humidity conditions at the freestream and the condenser plate. The mechanistic model thus lends to the development of empirical correlations of condensate mass flux and CHTC as explicit functions of these two parameters for easy use in practical FWC configurations.

An Empirical Investigation of a Modified Gas Engine Heat Pump in Heating and Cooling Mode for the Residential Application

Gas Engine Heat Pump (GEHP) is found as an effective machine among energy conversion systems. However, further improvement of GEHP performance is still indispensable. In the current study, to recycle efficiently the flue gases waste heat of GEHP unit, it is suggested to utilize a condensing heat exchanger. To assess the performance of the proposed GEHP, an equipped test room was designed. The nominal capacity of the current GEHP is about 80 kW for heating and 71 kW for cooling. The experimental investigation was implemented for two common strategies, i.e. heating and cooling modes. The effect of outlet dry bulb temperature of 0 °C, 5 °C, 10 °C and 15 °C for heating, and 25 °C, 30 °C, 35 °C and 40 °C for cooling as well as water outlet temperature of 40 °C, 45 °C and 50 °C for heating and 8.5 °C, 11 °C, 14 °C for cooling on the performance of the GEHP is investigated. The 95% confidence interval has been considered in statistical analysis. In heating mode, results show that the efficiency of the condensing heat exchanger increases during the reduction of water out temperature and it leads to a Coefficient of Performance (COP) enhancement. Additionally, observation indicates that the decrement of the ambient air temperature from 5 to 0 ° C leads to the severe enhancement of fuel consumption of the gas engine. The performance indicators are re-evaluated using the non-condensing heat exchanger. It is concluded that the COP of GEHP with the condensing heat exchanger decreases by the steeper slope versus the reduction of the ambient dry bulb temperature compared to the non-condensing heat exchanger.

Integrated hollow porous ceramic cuboids-finned heat pipes evaporative cooling system: Numerical modelling and experimental validation

The work presented in this paper investigates design, computer modelling and testing of a sub-wet bulb temperature evaporative cooling system for space air conditioning in buildings. The target application of evaporative cooling technology is particularly for geographical regions with hot and dry climate. A laboratory prototype made of integrated finned heat pipes and a water filled hollow porous ceramic cuboids was been built and tested. The design exploits the high thermal conductivity of heat pipes as effective heat transfer device and the good wettability characteristic of porous ceramic material. Key thermal performance metrics of the prototype were modelled and validated experimentally under controlled laboratory conditions of temperature (30, 35 and 40 °C) and relative humidity (35–55%). Under typical dry climates conditions (ambient air dry bulb temperature of 35 °C and relative humidity of 35%), the measured supply air dry bulb temperature was 22.3 °C, which is lower that the ambient air wet bulb temperature, and maximum cooling capacity of approximately 196 W per unit surface area (m2) of wet porous ceramic cuboid. Furthermore, it was shown that the measured prototype cooler wet bulb effectiveness was 1.05 while the dew point effectiveness was 0.73.

Optimised dynamic control philosophy for improved performance of mine cooling systems

Mine workers require substantial cooling and ventilation to work in a safe and habitable environment. Deep level mine cooling systems were identified as significant energy-intensive consumers to supply such cooling. Mine cooling systems can make up to 25% of a mine’s total electricity consumption. Coupled with increasing electricity costs, deep level gold mines are struggling to remain competitive. Literature reveals a need for a simple and practical solution to optimise deep level mine cooling systems for improved system performance. In this paper, an optimised dynamic control strategy is presented to optimise the control of mine cooling systems. An integrated dynamic temperature set point algorithm and ambient dry-bulb (DB) temperature prediction model was formulated, implemented and verified. The optimised dynamic control model, when compared to existing control practises, attained a chiller coefficient of performance (COP) improvement and compressor power reduction of 7% and 4% respectively. Implementation results also showed a power demand reduction of 45.7% during the evening high electricity cost period. This strategy demonstrated to be simple and cost effective while showing significant performance improvements for South African mines.

Effect of heat stress on rumen temperature of three breeds of cattle.

Thirty-six steers (12 of each Angus, Charolais, and Brahman) with an initial BW of 318.5±6.7kg were used in a 130-day study. Two treatments were imposed: un-shaded and shaded (3m2/animal; 90% solar block shade cloth). On day 1, steers were administered with rumen temperature boluses. Rumen temperatures (T RUM) were obtained at 10min intervals over the duration of the study to determine differences in T RUM between Bos indicus and Bos taurus cattle. Six feedlot pens (162m2) were used with six steers (2/breed) per pen with three pens/treatment. Ambient dry bulb temperature (T A; °C), relative humidity (RH; %), wind speed (WS; m/s) and direction, and solar radiation (SR; W/m2) were recorded at 10min intervals. Rainfall (mm) was collected daily at 0900h. From these data, black globe temperature (BGT; °C), temperature humidity index (THI), heat load index (HLI), and accumulated heat load (AHL) were calculated. Individual T RUM were converted to an hourly average and then mean hourly T RUM were converted to a mean within hour T RUM across the 130days. Rumen temperatures were analyzed using an autoregressive repeated measures model. The model analyzed the effect of breed (P<0.0002), treatment (P=0.3543), time of day (hour, h; P<0.0001), breed × treatment (P<0.3683), breed × h (P<0.0001), treatment × h (P<0.0001), breed × treatment × h (P=0.0029), pen within treatment (P=0.0195), and animal × breed × treatment within pen (P=0.1041). Furthermore, there were breed × treatment × hour differences in T RUM (P=0.0036), indicating that Bos indicus and Bos taurus regulate T RUM differently.

Seasonal variation of mitochondria activity related and heat shock protein genes in spermatozoa of Karan Fries bulls in tropical climate

The study was conducted the seasonal effect on mitochondria activity-related genes [Succinate dehydrogenase (SDH), Citrate synthase (CS) and mitochondrial transcription factor-A (TFAM)] and heat shock protein (HSP) genes in spermatozoa of Karan Fries (Tharparkar X Holstein Friesian) bulls. Five (n = 5) adult healthy bulls were selected from Artificial Breeding Research Centre of National Dairy Research Institute, Karnal. Thirty (30) ejaculates were collected during summer and winter using artificial vagina (42–45 °C). The ambient temperature, relative humidity, dry and wet bulb temperatures were recorded during the study. Total RNA was isolated by Trizol method. The mRNA expression of SDH, CS and TFAM was lower during summer compared to winter season. The expression of HSP70.1, HSP70.2, HSP90 and HSP105 was higher (p < 0.05) during summer than winter season. However, the expression of HSP70.8 was non-significantly higher during summer season. The physical analysis of semen (volume, motility, live spermatozoa, hypo-osmotic swelling test, concentration, acrosome integrity, total sperm out, major abnormalities) was affected significantly (p < 0.05) by the summer season. The antioxidant enzymes (glutathione peroxidase, superoxide dismutase, glutathione reductase and total antioxidant capacity) and malondialdehyde (product of lipid peroxidation) concentration were estimated higher (p < 0.05) during the summer season than winter. The semen quality of Karan Fries bulls is affected considerably during summer season in tropical climatic conditions.

Performance assessment and gained operational experiences of a residential scale solar thermal driven adsorption cooling system installed in hot arid area

In this study, performance assessment of a residential scale size solar thermal driven adsorption cooling system installed in hot arid and dusty area at Upper Egypt, and, in operation since summer 2012 until now is carried out experimentally for four years in operation, moreover, the gained operational experiences are presented. The system performance is expressed in term of the solar collectors' field thermal efficiency, actual chiller chilling capacity, the temperature of cold-water outlet from the chiller, chiller coefficient of performance (COP) and cooling-water temperature outlet from the cooling tower. The system performance results show that the daily solar collector efficiency during the reported period was ranged from about 50% to 78%. While, the average chiller COP was varied from 0.4 to 0.64 in combination with average chilling power ranged from 3.6 to 6.42kW and average chiller outlet cold water temperature ranged from 19°C to 12.12°C correspondence to cooling tower outlet cooling water temperature ranged from 31.4°C to 23.4°C, respectively. In the cooling session of 2014, a 50kW cooling capacity wet cooling tower is integrated into the system, and the measurements show that the outlet water temperature from the cooling tower is about 23.4°C at ambient air dry bulb temperature of 35.7°C and wet bulb temperature of about 19°C. Consequently, under this new heat rejection condition, the chiller average cooling capacity and COP reaches were 6.42kW and 0.64 with a chilled water temperature of 15°C. Clearly from the system operation period, the heat rejection through the re-cooling sub-system has the main significant impact on the system performance in the hot arid areas. Therefore, it should be based on alternative heat sink recourses with appropriate cost performance techniques.

Efficiency analysis of semi-open sorption heat pump systems

Sorption systems traditionally fall into two categories: closed (for chilling and heat pumping) and open (for dehumidification). Recent work has explored the possibility of semi-open systems, which can perform heat pumping or chilling while utilizing ambient humidity as the working fluid of the cycle, and are capable of being driven by solar, waste, or combustion heat sources. The efficiencies of closed and open systems are well characterized and can be accurately determined from four temperatures (one for each of the main components—desorber, absorber, condenser and evaporator). In this work, the performance potential of semi-open systems is explored by adapting expressions for the efficiency of closed and open systems to the novel semi-open systems. A key new parameter is introduced, which involves both the ambient dry bulb and ambient dew point temperature, since both are critical to semi-open absorber operation. The dew point temperature is necessary to capture the absorption performance, while the dry bulb temperature is needed to calculate sensible heat transfer with surrounding air.

Performance assessment and transient optimization of air precooling in multi-stage solid desiccant air conditioning systems

Renewable energy is one of the most promising solutions to both energy and global warming crisis. Energy consumption can be minimized considerably by utilizing solar energy in air conditioning systems operation. One of the popular solar air conditioning technologies is desiccant air conditioning. Nonetheless, conventional desiccant air conditioning systems have a relatively low coefficient of performance (COP). In consequence, two-stage desiccant air-conditioning systems are proposed to improve desiccant air conditioning systems’ COP. Moreover, a recently commercialized cooling method named Maisotsenko cooling cycle which is capable of cooling air near to its dew point temperature is considered to be integrated within the proposed multi-stage desiccant cooling systems.In this paper, three new two-stage desiccant air conditioning systems incorporating Maisotsenko cooling cycle are proposed and investigated in details for hot and humid climates such as UAE. Furthermore, air precooling is considered to improve two stage desiccant air conditioning systems’ COP. Moreover, full transient analysis and optimization are carried out in UAE within June–October. The proposed system can minimize the required solar heating during noon time as the ambient air dry bulb temperature rises. Average COP of the system during electricity load peak hours (10:00–14:00) for all five considered and combined months is 1.77. Average rate of heat input required to operate the system and average building cooling load are determined to be 100.3kW and 46.2kW, respectively. Therefore, system average COP is computed to be 0.46.

Gas turbine evaporative cooling evaluation for Lagos – Nigeria

Evaporative cooling is widely recognised as one of the available gas turbine power augmentation tools. Due to its inherent characteristics evaporative cooling is thought as being only effective in geographic areas with high ambient air dry bulb temperature and low relative humidity. This paper clarifies, via literature review and thermal modelling examples, the fact that there is still potential for evaporative cooling in high temperature and relative humidity areas. The paper also estimates the maximum cost of the evaporative cooling installation that will yield a positive return of investment to plant owners in the decision of retrofitting evaporative cooling systems for the particular location of Lagos in Nigeria. In consequence power plant operators, especially those whose power generation assets are located on coastal environments, should be aware of the prospective benefits associated with such cooling technology.

Analysis of the convective heat exchange effect on the undisturbed ground temperature

The ground temperature is an important parameter for several applications such as ground source heat pumps, agricultural greenhouses and ground energy storage systems. This paper describes a numerical model based on 1D transient heat conduction equation, using the energy balance on the soil surface as a boundary condition. The absorbed solar radiation by the soil, the convection heat transfer between the soil and the ambient air, as well as the long wave radiation exchange between the soil and the sky have been considered. An hourly simulation over a whole year (8760h) with 1h time step has been conducted using real meteorological data including global solar radiation, ambient dry bulb and dew point temperatures as well as the wind velocity. The model has been validated against measurements and analytical calculations for a site located in Montreal (Canada). The model is applied to investigate the effect of convective heat flux, calculated using three different correlations on the deep ground temperature for different climates. It has been found that in general, McAdams (1954) and Kusuma (2004) correlations can be used for different climates with relatively good agreement between measurements and calculations.

Impact of different light sources on broiler rearing environment

Broiler production is highly dependent on the use of artificial light. The light source may affect the effectiveness of housing conditions due to increasing ambient temperature and concentration of noxious gases. This research aimed to evaluate the effects of different bulb types on the thermal, aerial, and acoustic environment of broiler aviaries. The experiment was carried out at a commercial broiler farm in Dourados, Mato Grosso do Sul State, Brazil. Three aviaries were used, and two flocks of male broilers from Cobb® genetic strain were reared from the first day to slaughter. Each aviary was equipped with a different light source, comprising the adopted treatments (A1 - incandescent light bulb, control; A2 - sodium vapor light bulb; A3 - fluorescent light bulb). The aviaries were divided into nine quadrants, and the environmental data (ambient dry bulb temperature and relative humidity), litter surface temperature, CO2 and NH3 concentrations, and bird sound pressure behavior were recorded in each quadrant. The aviary with incandescent light presented higher air and litter temperatures, and concentration of gases than the other tested alternatives. It also presented higher level of sound pressure in the second week of the growing period; however, from this period up to slaughter, there was no effect of the light source on the results of broiler sound pressure level.

Numerical modeling of the drift and deposition of droplets emitted by mechanical cooling towers on buildings and its experimental validation

A CFD numerical modeling for simulating the drift emitted by mechanical cooling towers located in built-up urban areas is presented. The averaged Navier–Stokes equations for the air motion are discretized through a finite volume method, with the k–ɛ model to simulate the turbulent flow. An appropriate set of boundary conditions is employed, in order to avoid the non-homogeneity problem in the Atmospheric Boundary Layer (ABL). A Eulerian–Lagrangian model is used to simulate the air–water droplet motion, taking into account the effects of evaporation. The results are validated with experimental data of the deposition of droplets emitted by a pilot cooling tower, obtained through a technique based on water sensitive papers. Local meteorological data are measured through a meteorological tower adjacent to the cooling tower. The present study shows the influence of variables such as the ambient dry bulb temperature, the ambient specific humidity and the droplet exit temperature from cooling tower on the water droplet deposition and on the size of the affected area for mechanical cooling towers. The numerical procedure has proved useful for obtaining the outlined objectives.

Solid Desiccant Cooling System Employed with Ventilation Cycle: A Sensitivity Analysis

For better use of evaporative cooling techniques in humid climate, employment of desiccant cooling system (DCS) can be a suitable option. Desiccant augmented evaporative cooling system may be employed for energy saving in buildings in place of conventional vapour compression based cooling system. This article presents a sensitive analysis of DCS simulated under the humid climate of Mumbai, India. Mathematical computations have been performed using outdoor specific humidity, ambient dry bulb temperature and room supply temperature. A sensitive analysis considering some important forcing parameters was conducted. It was observed that the “effectiveness” of direct evaporative cooler to be predominantly high influencing parameter compared to others, for the performance of DCS.