HVAC&R

Poorly maintained, degraded, and improperly controlled equipment wastes an estimated 15% to 30% of energy used in commercial buildings. Much of this waste could be prevented with widespread adoption of automated condition-based maintenance. Automated fault detection and diagnostics (FDD) along with prognostics provide a cornerstone for condition-based maintenance of engineered systems. Although FDD has been an active area of research in other fields for more than a decade, applications for heating, ventilating, air conditioning, and refrigeration (HVAC&R) and other building systems have lagged those in other industries. Nonetheless, over the last decade there has been considerable research and development targeted toward developing FDD methods for HVAC&R equipment. Despite this research, there are still only a handful of FDD tools that are deployed in the field. This paper is the first of a two-part review of methods for automated FDD and prognostics whose intent is to increase awareness of the HVAC&R research and development community to the body of FDD and prognostics developments in other fields as well as advancements in the field of HVAC&R. This first part of the review focuses on generic FDD and prognostics, providing a framework for categorizing methods, describing them, and identifying their primary strengths and weaknesses. The second paper in this review, to be

The UK building stock accounts for about half of all energy consumed in the UK. A large portion of the energy is consumed by nondomestic buildings. Offices and retail are the most energy intensive typologies within the nondomestic building sector, typically accounting for over 50% of the nondomestic buildings" total energy consumption. Heating, ventilating and air conditioning (HVAC) systems are the largest energy end use in the nondomestic sector, with energy consumption close to 50% of total energy consumption. Different HVAC systems have different energy requirements when responding to the same building heating and cooling demands. On the other hand, building heating and cooling demands depend on various parameters such as building fabrics, glazing ratio, building form, occupancy pattern, and many others. HVAC system energy requirements and building energy demands can be determined by mathematical modelling. A widely accepted approach among building professionals is to use building This work has been made possible by the help, encouragement and support from my supervisors, colleagues, family and friends. Firstly I would like to sincerely thank my supervisory team for the help and guidance they have given me throughout my study period. My heartfelt thanks go to

This paper discusses the suitability of HFC-161 over other refrigerants. Apart from having zero ODP and GWP value of 12, HFC-161 refrigerant can prove a promising alternative to HCFC-22 and various other HCFC refrigerants facing the fate of phase out. Various results are obtained on the basis of COP, discharge temperature, cooling capacity and power consumption. The general finding shows that HFC-161 refrigerant gives better COP, increased refrigeration effects and lower discharge temperatures. The flammability of HFC-161 needs to be addressed while using in air conditioner. A 1.5 TR capacity DC inverter operated air conditioner is to be tested in psychometric test laboratory for Capacity rating and Power consumption test.

Kondensor merupakan komponen vital dari sistem pendingin udara (AC) yang berfungsi untuk mengkondensasi refrigeran. Kondensasi diakibatkan oleh penyerapan panas refrigeran oleh udara yang melewati penukar kalor fin and tube. Tingginya tahanan termal sisi udara oleh karena rendahnya konduktifitas termal menyebabkan rendahnya laju
perpindahan panas. Oleh karena itu, studi ini memfokuskan pada peningkatan laju perpindahan panas konveksi dengan menggunakan longitudinal vortex generator (LVG). Penggunaan vortex generator (VG) berdampak pada peningkatan pressure drop. Untuk mengatasi masalah ini, eksperimen dilakukan dengan menempatkan enam silinder yang
dipanasi di dalam saluran persegi empat. Perbaikan laju perpindahan panas dari silinder ke udara dilakukan dengan menempatkan VG berlubang pada permukaan plat. Susunan VG, jumlah pasang dan kecepatan aliran udara masuk divariasikan. Hasil penelitian
menunjukkan bahwa kenaikan laju perpindahan panas dan pressure drop tertinggi dihasilkan oleh perforated concave delta winglet (PCDW) tiga pasang staggered dengan nilai berturut-turut 46,3% dan 87,5%.

Methods to measure airflow rates using tracer gas in single air handling units are well known. In some buildings however, in particular in Singapore, rooms are often ventilated with two or more units and present large recirculation rates. Large recirculation ratio homogenise the concentrations, so concentrations in supply and extract ducts are close to each other. In addition, these spaces often present a large time constant, so much time is needed to reach steady state. The purpose of this paper is to document an adapted methodology to measure not only the airflow rates provided by each unit, but also the interunits airflow rates and the global ventilation efficiency, The method is illustrated with an example of measurement in an actual building. It is shown that the most accurate method is not the same for small and large recirculation ratios.

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Modeling of vertical ground heat exchangers (GHE) is relatively complex because of the threedimensional transient nature of the problem inside the borehole and in the surrounding ground. Furthermore, the system is characterized by various timescales with rapid changes inside the borehole and slow variations of ground temperature far away from the borehole. Most existing numerical models require important computational resources to adequately represent the short timescale heat transfer occurring in the immediate vicinity of the borehole which warrant their use for annual energy simulations. In this paper, a three-dimensional reduced model (3D-RM), based on domain decomposition and state model reduction techniques, is proposed to reduce computation time and computer memory. Domain decomposition is used to sub-structure the domain and to vary the time-step values in each sub-domain, and state model reduction is applied to each resulting sub-zone. A comparison with a complete threedimensional dynamic model indicates that the proposed 3D-RM model reduces computational time by a factor of about 30 without loss of accuracy. A comparison with experimental results shows that the relatively fast transients occurring in the borehole are well predicted by the 3D-RM model not only for the outlet fluid temperature but also for the tube wall temperatures at different depths.

In conventional air conditioning design, the comfortable range of temperatures is 25 to 27°C, with relative humidity levels of 40 to 60%; these numbers vary only slightly based on a person's race and country. Several studies in tropical climates show that the observed thermal comfort requirement often does not agree with those obtained based on experiments mainly using North American subjects. However, there is no consistent rationale that explains why the comfort requirements are different in a hot climate, suggesting more surveys on thermal comfort may be needed in the tropics. In Asia, there has recently been a rapid and widespread diffusion of air conditioners. Therefore, we conducted a survey to clarify what temperature and humidity level people in Asian countries prefer in order to feel comfortable. Following that research, this article presents the results of a questionnaire survey on the use of air conditioners in houses in hot, dry climates. Nizwa and Rustak, Oman, which are characterized by the hot, arid climate of the Arabian Peninsula, were chosen as survey areas. The questionnaire survey was distributed to students of Nizwa University. Questions were asked about the duration of air conditioner use and the preferred air conditioner temperature setting. In order to determine how respondents felt about their indoor environment, we also asked about the thermal sensations that were experienced while using the air conditioner. In both cities, the mean operating time of the air conditioner was very long. The respondents reported selecting a low temperature setting while sleeping despite the fact that many of them reported that they were cold while sleeping. Ninety percent of respondents reported a cold, cool, or neutral thermal sensation while using the air conditioner, without feeling discomfort.

Ground-coupled heat pumps are highly efficient HVAC systems that provide heating and cooling for buildings. The high initial cost of drilling boreholes is one of the primary reasons that limit the widespread application of a ground-coupled heat pump. It is very important to develop ...

It is essential to investigate person-to-person contaminant transport in mechanically ventilated spaces to improve air distribution design and reduce the infection risk from airborne infectious diseases. This paper provides a systematic study of the effects of ventilation mode, ventilation rate, and person-to-person distance on person-to-person contaminant transport. This study first collected available cases of person-to-person contaminant transport from the literature to create a database. Then this investigation identified the limitations of the existing data and added a number of cases to complete the database. The additional cases were generated by using a RANS-Eulerian model that was validated by experimental data from an occupied office with under-floor air-distribution (UFAD) systems. The database shows that the overall performance of displacement ventilation and the UFAD systems was better than that of mixing ventilation. A higher ventilation rate was beneficial in reducing person-to-person contaminant transport to some extent. Person-to-person contaminant exposure increased rapidly with a decrease in personto-person distance when the distance was smaller than 1.1 m. Generally speaking, person-toperson distance is an important parameter when compared with ventilation mode and ventilation rate.

Prismatic glazing is found in many building applications, such as complex fenestration systems to control solar heat gains and glare and re-direct sunlight to building interior spaces and daylighting (and lighting) systems to enhance their optical and lighting performance. However, modeling and simulation of such prismatic glazing has been a very difficult task due to its versatile and complex geometrics. This article presents the development and validation of a simplified model to compute the optical characteristics and dominant directions of the transmitted and reflected beam rays of sawtooth-like prismatic glazing. The model was based on tracing the average ray and was extensively validated using third-party data derived from ray tracing computer simulations and measurement using integrating spheres and goniophotometers. The model's predictions for the transmittance and reflectance of single and double prismatic panes compared well overall within the accuracy of the third-par...

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Practical correlation for thermal resistance of horizontal enclosed airspaces with downward heat flow for building applications Saber, Hamed H. https://publications-cnrc.canada.ca/fra/droits L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site

The thermophysical properties of foods are required in order to calculate process times and to design equipment for the storage and preservation of food. There are a multitude of food items available, whose properties are strongly dependent upon chemical composition and temperature. Composition-based thermophysical property models provide a means of estimating properties of foods as functions of temperature. Numerous models have been developed and the designer of food processing equipment is faced with the challenge of selecting appropriate ones from those available. In this paper selected thermophysical property models are quantitatively evaluated by comparison to a comprehensive experimental thermophysical property data set compiled from the literature. For ice fraction prediction, the equation by Chen (1985b) performed best, followed closely by that of Tchigeov (1979). For apparent specific heat capacity, the model of Schwartzberg (1976) performed best, and for specific enthalpy prediction, the Chen (1985a) equation gave the best results, followed closely by that of Miki and Hayakawa (1996). Finally, for thermal conductivity, the model by Levy (1981) performed best.

This study investigated experimentally the effects of real fouling material at the air side of the evaporator's heat exchanger coil on the performance of room air-conditioner units as well as the impact of some fouling material compositions on indoor air quality. At the end of the ...

The angle-resolved mean and turbulence characteristics of the axial air flow inside a screw compressor with both male and female rotors have been measured, using a laser Doppler velocimeter (LDV) with high spatial and temporal resolution at different radial and axial locations for speeds of 800-1600 rpm, discharge pressures of 1-1.6 bar and discharge temperatures of 33-90°C. The velocity measurements were performed through a special transparent window fixed near the discharge port. The results confirmed the ability of the LDV technique to characterise the flow inside the compressor working chamber; an angular resolution of 1.5° was able to fully describe the velocity field within the machine. The flow variation between the different working chambers was established as well as the spatial variation of the axial mean velocity and turbulence velocity fluctuation within the working chamber. The effect of discharge port opening on the axial mean and RMS velocities was found to be significant near the leading edge of the rotors causing an increase in the mean and RMS velocities of the order of 4.2Vp in mean (where Vp is the axial pitched velocity) for male rotor and 5.4Vp for, female rotor and this effect is less pronounced on the flow near the root of the rotor. Moreover, to obtain a better understanding of the flow motion, a high sampling rate pressure transducer was used to provide the internal angular static pressure variation. These measurements are used to validate the in-house CFD model of the fluid flow within twin screw compressors which, in turn, allows reliable optimisation of various compressor designs.

ABSTRACT This article assesses the most common architectural and environmental strategies in Ghadames housing in Libya. Preliminary data were collected through field surveys undertaken in July 2013, the hottest and driest season in Ghadames. The surveys investigated the indoor thermal environment and efficiency of energy use in Ghadames housing. The actual mean vote scale was used to investigate occupants’ thermal feeling coupled with recording physical environment and also actual measurements of a number of existing houses. Additionally, objective surveys were conducted to (a) verify the subjective data, (b) provide an overall view of the residents’ life style in the old town, and (c) understand the most significant techniques employed in old dwellings. The subjective survey “questionnaire” distributed among nine new and eight old houses shows that the majority of respondents is satisfied with the number of architectural issues in modern housing design. This general satisfaction excludes the inherited identity of the traditional architecture embedded within the society. On the other hand, occupants are more satisfied with old buildings in regard to indoor environmental conditions, energy consumption, and construction materials. The occupants of old houses expressed their thermal satisfaction with the indoor comfort conditions, but the predicted mean vote, based on measurements and ISO 7730, implied discomfort (hot).The survey also carried out interviews with a number of locals, underlining their personal impressions and preference toward the change of the existing built environment. Findings indicate that, occupants’ satisfaction and perception toward the built environment have not been achieved in new housing developments of Ghadames owing to the lack of understanding of the sociocultural needs of the local community. In addition, a 3D digital model was created for the old town and imparted a full understanding of the building dynamics and physics, explicating the complexity of the compactness of its urban morphologies. The results also showed subjects were feeling neutral to slightly warm in old buildings even when indoor air temperatures reached 32°C.

Humidifiers have been used not only to maintain a comfortable indoor environment, but also to prevent respiratory diseases from worsening due to extremely low humidity. Some evaporative humidifiers (EH) that were considered to be energy efficient have been reported to have problems with microbial contamination. In this study, the microbial contaminations of an EH were verified, and both the germicidal effects and limitations of in-duct ultraviolet germicidal irradiation(ID-UVGI) systems against the contaminations were investigated. A numbers of bacteria and fungi were isolated from the surfaces and drain water of the EH, and airborne microbes that were likely dispersed from the contaminated EH were also detected. Based on the results of monitoring microbes for approximately six months for an ID-UVGI operation, it was found that microbial contamination was reduced but that microbes could still consistently be isolated from the surfaces and drain water. This was likely due to internal contamination of the EH in locations beyond the reach of the ultraviolet C-band (UVC) irradiation. Methods to overcome the limitations of this ID-UVGI system for EH disinfection are thus required.

An urban energy management tool was developed, which is able to predict the heating energy demand of urban districts and analyze strategies for improving building standards. Building models of different Levels of Detail are investigated and analyzed according to their suitability for forecasting energy demand. Based on the specific 3D city model, an input file is generated, which can be read by the building simulation model. Special focus is put on a method for modeling the heating energy demand of the buildings with the fewest input parameters possible, but one which will give reliable forecast results. A simple transmission heat loss method and an energy-balance method were tested. In both cases, there was a good correlation between the measured and calculated annual values for a case study area of over 700 buildings in Ostfildern, Germany. The results also show that a D city model (with low geometrical detail) can be used for energy demand forecasting on an urban scale.

ABSTRACT An analysis of the ventilation effectiveness of a prototype personalized ventilation system of working places named PERMICS-LOS1 (Personal Microclimate System) was made, based on measurements of the air velocity field and of tracer gas concentrations using the decay method. The emphasis of the analysis was mainly on an experimental verification of a parameter based on the relative decrease of tracer gas concentration in the first minute of system operation dC(1) and on local ventilation efficiency using the local air-change index ∊L.. A system analysis was made for several different operating regimes of personalized ventilation, where changes in air quantity and the direction of supplied air in the breathing zone were applied. The results of the experimental analysis were statistically evaluated, compared, and included in the existing database of previous research for use as supplementary values. The performed analysis has confirmed previous findings as well as the connection between the dC(1) parameter and ventilation effectiveness parameters, especially with the local air-change index.

Accurate prediction of soil thermal conductivity is of prime importance in the numerical simulation of heat transmission through soils. This paper focuses upon empirical and semi-empirical prediction methods for soil thermal conductivity. A family of empirical correlations are presented which relate soil thermal conductivity to saturation for five soil types: gravel, sand, silt, clay, and peat. These correlations are developed from a database of measured data available in the literature. Also, a theoretical model of soil thermal conductivity is developed for granular materials composed of rotund particles in an almost dry state. This theoretical model includes the effects of the micro-structure and the conductivity of the solid phase. It explicitly relates soil thermal conductivity to dry density and agrees well with experimental data. This paper also presents a review and discussion of those factors which affect soil thermal conductivity, previously reported prediction methods, and conductivity measurement techniques.

... The authors are thankful to José Berrondo Mir (Mabe TyP operation's vice president), Agustín Soto (refrigerators engineering's manager), as well as Francisco Antón (I+D manager), for their support to this project, and to the ... 1. Abramson, DS, Turiel, I. and Heydari, A. 1990. ...

ABSTRACT This paper presents a study on HCFC-22 alternative refrigerant mixture flow through capillary tubes, analyzing two different approaches for two-phase flow modeling: separated flow and homogeneous. Simulation results were compared to a large experimental data bank (about 200 different operational conditions/geometries) for R-410A and R-407C flow through capillary tubes for both subcooled and two-phase inlet conditions, obtained in an experimental unit implemented for this study. The comparison showed that both models are suitable for simulation of refrigerant mixture flow in capillary tubes, with the same error level in relation to experimental data.

The cosorption of water vapor and carbon dioxide on BPL activated carbon, silica gel (Grade 40), and 13X molecular sieve were investigated in this study. The explicit analytic equilibrium sorption characteristic equations for cosorption of water vapor and carbon dioxide were obtained from the correlation of experimental data of Hines and Ghosh. The cosorption heats of adsorption were calculated from these equilibrium sorption characteristic equations by applying the method of Sircar. A gas-side-controlled adsorption model, with finite transfer coefficients, for the binary mixture of water vapor and carbon dioxide was derived. In a previous work, the single-blow situation was analyzed illustrating the importance of considering both species simultaneously. This previous work also illustrated that the time scale for CO2 adsorption is much shorter that H2O adsorption. In the present work the model was extended and applied to rotary counterflow regenerative desiccant dehumidifiers, and removal efficiencies were documented, showing the contaminant removal potential of such systems.These results also illustrate that a single desiccant wheel cannot remove both components highly effectively. When the required removal efficiencies are not too high, molecular sieve does have respectable removal efficiencies for CO2 and H2O at lower sorption. However, to have higher removal potentials, a twowheel system appears to be more promising.

Operating rooms often exhibit vertical temperature gradient, radiant asymmetry, local airflows, and local body cooling. The impact of these parameters on the thermal comfort of the occupants can be greatly affected by the type of air-conditioning system used in the room. This work evaluated thermal comfort conditions in an operating room ventilated with a spiral diffuser jet using an instrumented thermal manikin with heated sensors. The objective is to assess the conditions of thermal comfort and local discomfort of the patient and surgical team in this kind of environment using the concept of equivalent temperatures and a manikin with heated sensors. Additionally, the method proposed by Fanger was used to evaluate the thermal sensation. The results showed a very small change in the equivalent temperatures in different parts of the body for the surgeon and nurse. The thermal sensation for the surgeon and nurse simulated by the manikin and using a thermal comfort diagram for equivalent temperature was neutral in the whole body. However, higher equivalent temperatures were found on the heads of the surgeon and nurse because of the heat exchange by radiation from the surgical lights. The local thermal sensation for the patient varied from too cold, cold, and neutral, depending on the body part. Finally, the methodology proposed showed to be very effective for evaluating the thermal comfort conditions in operating rooms when compared to the method proposed by Fanger.

Flexible short-tube orifices were designed to decrease their diameter as the pressure differential across them increases under high outdoor temperatures. A series of tests for an R-22/lubricant mixture (mass fraction of oil 1.2%) were performed with two flexible short-tube orifices to develop flow data over a range of typical air conditioner operating conditions. One short tube had a modulus of elasticity of 7063 kPa and the other a value of 9860 kPa. Both short tubes had identical lengths (14.5 mm), entrance diameters (2.06 mm), and exit diameters (2.46 mm). The tests included both single-and two-phase flow conditions at the inlet of the flexible short tube. Upstream pressures were varied from 1179 kPa to 2144 kPa, which corresponded to saturated condensing temperatures of 29.4 to 54.4°C. Experimental results were presented as a function of pressure, subcooling/quality, evaporating pressure, and modulus of elasticity. Mass flow rates were compared with those of a rigid short tube. The flow rate through the flexible shorttube orifices was strongly dependent on the condensing pressure, subcooling/quality, and modulus of elasticity (which, in effect, changed diameter at different upstream pressures) of the shorttube material. However, the flow rate showed little dependence on the evaporating pressure. An empirical flow model was developed using the experimental data. This flow model was then combined with an airconditioning system simulation model. Results from the model indicated that the flexible short tube provided approximately 2 to 3% higher capacity than the fixed expansion devices at temperatures lower than 25°C and higher than 45°C. However, the flow control with the flexible short-tube orifice was not as good as with a thermal expansion valve.

The angle-resolved mean and turbulence characteristics of the axial air flow inside a screw compressor with both male and female rotors have been measured, using a laser Doppler velocimeter (LDV) with high spatial and temporal resolution at different radial and axial locations for speeds of 800-1600 rpm, discharge pressures of 1-1.6 bar and discharge temperatures of 33-90°C. The velocity measurements were performed through a special transparent window fixed near the discharge port. The results confirmed the ability of the LDV technique to characterise the flow inside the compressor working chamber; an angular resolution of 1.5° was able to fully describe the velocity field within the machine. The flow variation between the different working chambers was established as well as the spatial variation of the axial mean velocity and turbulence velocity fluctuation within the working chamber. The effect of discharge port opening on the axial mean and RMS velocities was found to be significant near the leading edge of the rotors causing an increase in the mean and RMS velocities of the order of 4.2Vp in mean (where Vp is the axial pitched velocity) for male rotor and 5.4Vp for, female rotor and this effect is less pronounced on the flow near the root of the rotor. Moreover, to obtain a better understanding of the flow motion, a high sampling rate pressure transducer was used to provide the internal angular static pressure variation. These measurements are used to validate the in-house CFD model of the fluid flow within twin screw compressors which, in turn, allows reliable optimisation of various compressor designs.

A comparison between energy performance, simulated by means of the EnergyPlus building simulation programme, of two air systems (all-air and fan coil) and radiant heating and cooling floors/ceilings is developed in this work for various European climates

Car passengers' comfort plays an increasing role not only from the feel good or travel comfort point of view but also from the transportation safety perspective where the driver's thermal comfort is of crucial importance. The main components that affect optimal comfort are HVAC vents. The article focuses on the assessment of a performance of a side dashboard car vent with adjustable horizontal vanes which allow changing the air jet direction vertically along with a complete shut-off. A new measurement methodology capable of simulating the real car ventilation system conditions fitted with a vent tested. The flow pattern was first studied with the smoke visualisation then using a two-wire CTA probe. Jet orientations and boundaries were identified for particular vent setups ; those are fundamental in assessment of the vent performance. Average air speed and turbulence intensity were determined. Results show that the actual jet direction differs substantially from the direction that was set by the vanes and that further research may lead to a new and improved design of automatic control of a zonal ventilation system and can contribute to a more accurate control of passengers' comfort.

Energy use in buildings, transportation systems and lighting networks represents a significant contribution to the overall energy consumption in urban and suburban areas. This paper presents a method to evaluate the energy consumption of suburban neighborhoods from these three points of view, aiming to highlight the most relevant variables linking urban form and neighborhoods energy consumptions. The method includes three parts: 1) a computational approach combining dynamic simulation tools and a database of building typologies to determine the energy consumed in heating; 2) an empirical approach to assess the energy consumed by transportation systems (four purposes of travel are taking into account: work, school, leisure and shopping); and 3) a simplified approach to calculate the energy consumed by public lighting. Results from the application of the method to three characteristic suburban neighborhoods in Belgium are presented along with a life cycle energy assessment of buildings. A sensitivity analysis was conducted to determine the effects of building and neighborhood characteristics and of building inhabitant behavior on calculated energy consumption. Results from the analysis show that building insulation, building distribution, heating system management and neighborhood location are critically important factors in the energy efficiency of suburban residential areas.

This paper describes the development of a model-based optimization procedure for the synthesis of novel heating, ventilating, and airconditioning system configurations. The optimization problem can be considered as having three suboptimization problems: the choice of a component set; the design of the topological connections between the components; and the design of a system operating strategy. In an attempt to limit the computational effort required to obtain a design solution, the approach adopted in this research is to solve all three subproblems simultaneously. The computational effort has been further limited by implementing simplified component models and including the system performance evaluation as part of the optimization problem (there being no need, in this respect, to simulate the system performance). The optimization problem has been solved using a Genetic Algorithm (GA) that has data structures and search operators specifically developed for the solution of HVAC system optimization problems. The performance of the algorithm and various search operators has been examined for a two-zone optimization problem, the objective of the optimization being to find a system design that minimizes system energy use. In particular, the performance of the algorithm in finding feasible system designs has been examined. It was concluded that the search was unreliable when the component set was optimized, but if the component set was fixed as a boundary condition on the search, then the algorithm had an 81% probability of finding a feasible system design. The optimality of the solutions is not examined in this paper but is described in an associated publication (Wright and Zhang 2008). It was concluded that, given a candidate set of system components, the algorithm described here provides an effective tool for exploring the design of novel HVAC systems.

... Among all the refrigerants tested, R-134a had the highest initial absorption rate and solubility in POE under the test conditions. For the blended refrigerants, the differential solubility of individual refrigerant component depended on its par-tial pressure and its vapor pressure. ...

A review of published studies of numerical techniques for air filter performance simulation shows that there are two general approaches to such simulations. One describes gases flowing through filter media as continuous fluids, influenced by the macro properties viscosity, density, and pressure. The alternate approach treats gases as molecules in random motion, impacting their own kind and solid surfaces on a micro-scale. The appropriate form for a given filter medium and operating condition depends on the gas properties and the Knudsen number (Kn) of the smallest fibers in the filter medium simulated. When no fiber Kn exceeds 0.01, the Navier–Stokes equation and finite-volume solutions should simulate filter media pressure drop and particle capture reliably, if correct particle and fiber boundary conditions, including “slip” at boundaries, are employed. In addition, fibrous media geometry must be modeled in enough detail to make simulation results match experimental data. Part I of...

Heat exchangers are usually designed in such a way that they do not operate in the transition region. This is usually due to a lack of information in this region. However, due to design constraints, energy efficiency requirements or change of operating conditions, heat exchangers are often forced to operate in this region. It is also well known that entrance disturbances influence where transition occurs. The purpose of this paper is to present experimental heat transfer and pressure drop data in the transition region for fully developed and developing flows inside smooth tubes using water as the working fluid. The use of different inlet disturbances were used to investigate its effect on transition. A tube-in-tube heat exchanger was used to perform the experiments, which ranged in Reynolds numbers from 1 000 to 20 000, with Prandtl numbers being between 4 and 6 while Grashof numbers were in the order of 10 5. Results showed that the type of inlet disturbance could delay transition to a Reynolds number as high as 7 000, while other inlets expedited it, confirming results of others. For heat transfer, though, it was found that transition was independent of the inlet disturbance and all commenced at the same Reynolds number, 2 000-3 000, which was attributed to secondary flow effects. NOMENCLATURE A Area [m 2 ] D Diameter [m] f Darcy-Weisbach friction factor h Enthalpy [J/kg]

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Practical correlation for thermal resistance of horizontal enclosed airspaces with downward heat flow for building applications Saber, Hamed H. https://publications-cnrc.canada.ca/fra/droits L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Practical correlation for thermal resistance of horizontal enclosed airspaces with downward heat flow for building applications Saber, Hamed H. https://publications-cnrc.canada.ca/fra/droits L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site