Supply Duct Research Articles

A Study on the Characterization of Deposited Dust on HVAC Ducts in Subway Stations

This study used various methods to evaluate duct cleanliness and identify the levels of deposited dust in the HVAC systems of subway stations, as well as identifying the characteristics of the pollution sources at the stations. Levels of deposited dust were determined in two subway stations in Seoul from September 2011 to January 2012. The levels of dust deposited on ducts of the stations were measured by visual inspection, the quantitative vacuum test (VT), and the deposit thickness test (DTT). The VT results confirmed that no subway station exceeded a dust deposit of 1.0 g/㎡, which is the recommended surface contamination limit when using the VT method. However, in some supply ducts, the thickness of the dust layer exceeded 60.0㎛, the recommended surface contamination limit when using the DTT method. The visual inspection indicated that platform pollution in subway station A was higher than in the HVAC and waiting rooms, but the difference was insignificant (p = 0.852). At subway station B, the waiting room had a slightly higher level of deposited dust, but the difference was insignificant (p = 0.438). The inspected areas were divided into HVAC rooms, return lines, and supply lines according to ventilation type. Although all three inspections revealed that return lines had the highest levels of deposited dust, the difference was insignificant. The correlation between the results of the visual inspection and VT methods, and between the results of visual inspection and DTT methods were both significant (p >0.01) with r = 0.815 and 0.818, respectively. It was confirmed that the results of a qualitative visual inspection method corresponded relatively well with the results of the quantitative VT and DTT methods. Analyses of eight heavy metals in the HVAC systems of the subway stations indicated that the inclusion ratios of iron (Fe), zinc (Zn), and magnesium (Mg) were 80.75–93.6%, 2.94–15.64%, and 1.63–1.82%, respectively. Traces of other heavy metals (As, Cd, Cu, Pb, and Cr) were also detected.

Wykorzystanie indeksu termiczno� wilgotnosciowego (THI) do oceny warunk�w termiczno-wilgotnosciowych w oborach wolnostanowiskowych

The objective of this study was to evaluate temperature/humidity conditions in freestall barns with different types of gravity ventilation and to determine the risk of heat stress in cows based on the temperature-humidity index. The study was carried out during summer months (June/July) in two free-stall barns located in north-eastern Poland. The buildings for the study were selected based on the natural ventilation and animal housing systems used. One building was equipped with supply ducts mounted over windows and a roof ridge gap, and the other had flat roof exhaust ducts and side curtain. It was found from this study that the barn having flat roof exhaust ducts and air supply from side curtain was characterized by more favourable temperature/humidity conditions and presented a lower risk of heat stress to cows compared to the barn with roof ridge and air inlets. It was also found that cows in the barn with side curtain had comfortable conditions and those in the roof ridge barn were exposed to mild and moderate stress.

Pool boiling heat transfer on uniform and non-uniform porous coating surfaces

Pool boiling heat transfer experiments were performed using acetone as the working fluid at atmospheric pressure on seven heater surfaces, which can be divided into three types. The first, second and third types refer to the plain surface with poor heat transfer, the open channel surface and uniform porous coating surface with moderate heat transfer enhancement, and the 2-D/3-D porous coating surfaces with significant heat transfer enhancement. The open channel surface and uniform porous coating surface had intercrossed boiling curves, with better performance for the uniform porous coating surface due to the enhanced nucleation heat transfer at small or moderate wall superheats, and better performance for the open channel surface at large wall superheats due to the vapor channel provided. The 2-D porous coating surface with the pitch width of 1.6mm yields the best heat transfer performance and the largest critical heat fluxes among the three 2-D surfaces. The 3-D porous coating surface (TS#7) significantly increases the critical heat flux, which can be 3.7 times of that for the plain surface. Boiling curves were shifted to smaller wall superheat region and critical heat fluxes were increased with increases in liquid subcoolings. Two distinct bubble patterns existed for 2-D/3-D porous coating surfaces: continuously-isolated-bubble-escape pattern at small or moderate heat fluxes, and periodically-large-bubble-escape pattern at large heat fluxes. The hollow well at the heater center and/or the porous stacks exposed in liquid are acted as the liquid supply duct at high heat fluxes. This explains the reason that the porous coating surfaces with periodically varied particle layer thicknesses had larger critical heat fluxes than other heater surfaces.

Numerical Investigation of the Flow in a Hydrodynamic Thrust Bearing With Floating Disk

In this paper we present a novel method for the numerical simulation of flow in a hydrodynamic thrust bearing with floating disk. Floating disks are commonly employed in turbochargers and are situated between the thrust collar, which is rotating at turbocharger speed, and the static casing. A floating disk reduces wear, improves the skew compensating capacity of the bearing, and is freely movable in the axial direction. The simulation model presented combines a commercial flow solver (ANSYS CFX) with a control unit. Based on physical principles and a predefined axial thrust, the control unit automatically sets the rotational speed of the floating disk, the mass flow of the oil supply, and the oil film thickness between the rotating disk and the casing wall and collar, respectively. The only additional inputs required are the temperature and the pressure of the oil at the oil feed and the turbocharger speed. The width of the computational grid of the thin lubricating oil film in the gaps is adjusted using a mesh-morphing approach. The temperature-dependent variation in viscosity is included in the model. The calculated solution of the flow field in the domain, the oil film thickness, and the resulting rotational velocity of the floating disk are validated against experimental data and demonstrate favorable agreement. The influence of uncertainties in the measurements and the behavior of the systems are thoroughly investigated in parametric studies that reveal the key influencing factors. These are the temperature-dependent viscosity of the oil, the axial thrust, and turbulence effects in the supply grooves and ducts of the floating disk. Using the model presented here, it is now possible to predict design variants for this type of bearing.

Gas-fired instantaneous water heaters with combustion chamber sealed with respect to the room in multi-storey residential buildings—Results of pilot plants tests

In recent years, the literature on HVAC has been predominantly devoted to the problems of increasing the efficiency of buildings, reduction of CO2 emission or ensuring user-friendly indoor air quality. However, in many countries, including Poland, ensuring safety for the users of gas appliances is a key issue. That particularly concerns the gas-fired water heaters with open combustion chamber (Type B). The problem can be solved by replacing the traditional heaters with combustion chamber sealed with respect to the room (Type C) equipped with air supply and combustion product ducts systems. Two pilot plants were built, corresponding with the conditions of a typical Polish multi-storey residential building. During the designing process, the CFD Fluent software was used, making it possible to optimally select the dimensions and configuration of the tested plants. The tests were conducted for different operation variants, during which the appropriate functioning of the appliances was evaluated as well as the energy efficiency of hot water production. Moreover, selected ways of enhancing the operation of such appliances as well as the impact of wind on their work were examined. The experimental results presented in the paper should make it easier to implement gas-fired instantaneous water heaters Type C, particularly in the already-existing multi-storey residential buildings.

Experimental study of heat transfer and air flow in a refrigerated display cabinet

The heat transfer and air flow in a vertical open refrigerated display cabinet loaded with packages of test product was studied in order to analyse unsteady state phenomena. The product and air temperatures in the curtain were measured using tiny thermocouples, air velocity using a hot wire anemometer and PIV (Particle Image Velocimetry). A comparison between the air velocities measured by these two methods shows a good agreement at the internal side of the air curtain. However, these two methods give quite different result at the external side of the air curtain which can be explained by the complex air flow in this region. The temporal variation of the air temperature inside the air curtain is due partly to the “on/off” compressor cycle and partly to the introduction of ambient air via vortices. The latter phenomena contribute to the rapid velocity fluctuations which are greatest in the mixing layer of the air curtain. The product position in the cabinet is a determining factor of its temperature.The convective and radiative heat flux between the products located at the front of the display cabinet and the air was also measured. Near the air supply and return ducts, the convective heat transfer coefficient was higher than between these two positions because of the high instability of air flow near the inlet and return ducts. The radiative exchange is more significant at the top of the display cabinet than at the bottom.

SPEAKER SIDE AIR SUPPLY

A Speaker Side Air Supply Cabinet that has three things that are working together the Speaker Side Air Supply ducts, the Front Air Chamber, and the Bass Horn. The Front Air Chamber takes in air then compress it so that we get a very high sound pressure {sound wave} output, and the Speaker Side Air Supply ducts supply all the air the Front Air Chamber needs. At the same time the Speaker Side Air Supply ducts also supplying air to the Bass Horn working together to eliminate the pull back on the out going sound wave so there is no reduction of the very high sound wave volume output.

Validation of the Criteria for Initiating the Cleaning of Heating, Ventilation, and Air-Conditioning (HVAC) Ductwork Under Real Conditions

Dust accumulation in the components of heating, ventilation, and air-conditioning (HVAC) systems is a potential source of contaminants. To date, very little information is available on recognized methods for assessing dust buildup in these systems. The few existing methods are either objective in nature, involving numerical values, or subjective in nature, based on experts’ judgments. An earlier project aimed at assessing different methods of sampling dust in ducts was carried out in the laboratories of the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST). This laboratory study showed that all the sampling methods were practicable, provided that a specific surface-dust cleaning initiation criterion was used for each method. However, these conclusions were reached on the basis of ideal conditions in a laboratory using a reference dust. The objective of this present study was to validate these laboratory results in the field. To this end, the laboratory sampling templates were replicated in real ducts and the three sampling methods (the IRSST method, the method of the U.S. organization National Air Duct Cleaner Association [NADCA] and that of the French organization Association pour la Prévention et l’Étude de la Contamination [ASPEC]) were used simultaneously in a statistically representative number of systems. The air return and supply ducts were also compared. Cleaning initiation criteria under real conditions were found to be 6.0 mg/100 cm2 using the IRSST method, 2.0 mg/100 cm2 using the NADCA method, and 23 mg/100 cm2 using the ASPEC method. In the laboratory study, the criteria using the same methods were 6.0 for the IRSST method, 2.0 for the NADCA method, and 3.0 for the ASPEC method. The laboratory criteria for the IRSST and NADCA methods were therefore validated in the field. The ASPEC criterion was the only one to change. The ASPEC method therefore allows for the most accurate evaluation of dust accumulation in HVAC ductwork. We therefore recommend using the latter method to objectively assess dust accumulation levels in HVAC ductwork.

Design and Fabrication of a Flat-Plate Multichannel He-Cooled Refractory HX for Divertor Applications

A flat-plate He-cooled divertor would provide a flat surface facing the plasma, would minimize the number of otherwise complex sub-modules needed to cool large areas, and could greatly reduce the complexity of the coolant manifold systems.We recently designed and manufactured a unique flat-plate multichannel refractory metal heat exchanger (HX) that employs open-cell refractory foam to enhance heat transfer from the heated plate to the helium coolant. The structural material of the flat-plate HX box (102 mm wide and 165 mm long) is powder metallurgy molybdenum. Three flat-plate HX boxes were fabricated, two with a heated surface plate made of 4-mm thick Mo, TZM, and one 3-mm thick W. Four supply- and five return ducts, each 4.8 mm wide by 61 mm long run parallel underneath the heated plate. A thin sheet of Mo-foam (˜2 mm × 70 mm × 80 mm; H/W/L) is sandwiched between the ducts and the heated plate. Advantages of using foam are detailed in a separate paper in these proceedings. The supply ducts push helium up towards the heated plate and then circumferentially through the foam into the neighboring return ducts. Key to optimizing the design was achieving uniform helium flow upwards to the heated plate along the entire length of the supply ducts, while simultaneously minimizing end-effects due to the short active duct length (˜80 mm). A series of geometric features were designed to obtain relatively uniform flow distributions throughout the HX box. Here we report on the final design based on CFD analysis and thermo-structural finite element.

Application of Danckwerts-type boundary conditions to the modeling of the thermal behavior of metal hydride reactors

The paper presents a model-based investigation of a metal hydride reactor applied as a solid state hydrogen storage device. The elements of a metal hydride reactor are hydrogen supply duct, internal hydrogen distribution, hydride bed, reactor shell and the flow domain of the heat transfer fluid. Internal hydrogen distribution and hydride bed are porous media. Therefore, hydrogen flows through non-porous and porous regions during its reversible exothermic absorption and endothermic desorption, respectively. The interface between porous and non-porous regions is a discontinuity with respect to energy transport mechanisms. Hence, Danckwerts-type boundary conditions for the energy balance equation are introduced. Application of the first and second law of thermodynamics to the interface reveals that temperature jumps may occur at the hydrogen inlet but are not allowed at the hydrogen outlet. Exemplarily the loading behavior of a metal hydride storage tank based on sodium alanate is analyzed. It is demonstrated and experimentally validated that only Danckwerts-type boundary conditions predict the important cooling effect of the inlet hydrogen on the exothermic absorption process correctly.

The application of heat pipe heat exchangers to improve the air quality and reduce the energy consumption of the air conditioning system in a hospital ward—A full year model simulation

Research was conducted to study the effect of heat pipe heat exchangers on the existing air conditioning system of a hospital ward located in Malaysia, a tropical region. The present research employs the transient system simulation software (TRNSYS) to study the hour-by-hour performance of the system in terms of supply duct air and indoor air conditions in the ward space. Fieldwork study showed that the existing air conditioning system operating in the Orthopaedic Ward, University of Malaya, Malaysia is not capable of providing the desired supply duct air and indoor air to the space. Therefore, the possibility of improving the air conditioning system by adding heat pipe heat exchangers was investigated. The impact on energy consumption, power savings, supply duct air and indoor air with heat pipe heat exchangers incorporated in the air conditioning system were simulated and the results were compared with the existing system. Based on the present research, the system with the added eight-row heat pipe heat exchangers is recommended to provide convenient and healthy air into the ward space according to the ASHRAE recommendations. Moreover, it was found that by applying the new design, a considerable amount of energy and power could be saved.

CFD Analysis of Performance of a Reconstruction Plan of Smoke Control System in Metro Station

There are plenty of pipes to be arranged in subway station platform. Optimizing the air-conditioning system ducts is especially important because of its large size. Due to the location of stairs and the size of ducts, the platform exhaust ducts of a Shanghai subway station were laid out within the range from the stair to the end of the platform which probably can’t exhaust smoke effectively in fire. In reconstruction plan, air supply ducts and discharge ducts are connected and valves are added. Air supply pipe can be changed into discharge duct by controlling the valves. The smoke extraction performances of the original plan and the reconstruction plan are analyzed with the CFD numerical simulation. The results show that the reconstruction plan can make up the shortcoming of the original plan and contribute to the layout of pipes in new platform.

Operational characteristics of residential and light-commercial air-conditioning systems in a hot and humid climate zone

Forced-air space-conditioning systems are ubiquitous in U.S. residential and light-commercial buildings, yet gaps exist in our knowledge of how they operate in real environments. This investigation strengthens the knowledge base of smaller air-conditioning systems by characterizing a variety of operational characteristics measured in 17 existing residential and light-commercial air-conditioning systems operating in the cooling mode in Austin, Texas. Some key findings include: measured airflow rates were outside of the range recommended by most manufacturers for almost every system; actual measured cooling capacities were less than two-thirds of rated cooling capacities on average; hourly fractional operation times increased approximately 6% for every °C increase in indoor–outdoor temperature difference; and lower mean indoor surrogate thermostat settings and higher supply duct leakage fractions were most associated with longer operation times. The operational characteristics and parameters detailed herein provide insight into the magnitude of the effects of HVAC systems on both energy consumption and indoor air quality (IAQ) in residential and light-commercial buildings.

Chute Aerators. II: Hydraulic Design

Chute aerators are applied if cavitation damage on spillways is expected or observed. The aerator efficiency is usually described with the ratio of the air discharge entrained through the air supply ducts and the water discharge, which does however not account for the resulting air concentration distribution within the flow or for air detrainment. The present study investigates the streamwise development of the air transport along the flow downstream of chute aerators. Based on an extensive test program in which six governing parameters were systematically varied, the development of the average and the bottom air concentrations is provided up to the self-aeration point. Based on this information, an optimization of aerators in terms of increased air entrainment and reduced detrainment rates is possible, by assuming minimum required air concentrations. The main parameters influencing the air transport downstream of aerators are the approach flow Froude number, the deflector angle and the chute bottom angle.

Optimierung der Luftführung eines Bandtrockners mittels Strömungssimulation

Uneven drying often occurs in belt dryers which leads to an increase in energy consumption and a decreased throughput. To optimise the system a fluid flow simulation was performed aided by computational fl uid dynamics (CFD), supported by actual measurements. The installation of guiding plates and the optimised adjustment of the flaps inside the air supply duct can provide an effective approach for a better air supply.

A Study on the Application of a Ceiling Plenum Ventilation System in an Apartment House

Currently, an air change rate (0.7 h-1) and spring cooler installation must be considered when building an apartment house in Korea, in order to comply with the Building Standards and the Fire Service Act. In accordance with a series of legal requirements for Korean apartment houses, the improvement of the availability of ceiling space and space for working ease is required in apartments by installing a new ventilation system in the ceiling space to accommodate a spring cooler. In this study, a new ventilation system is suggested, called the ceiling plenum ventilation system. To introduce this system in the residential section of a residential-commercial complex building, a constant air volume system or combination air volume system with a 150 mm supply opening and branch duct must be used. For residential-commercial complex buildings with lower ceilings or for general apartment houses, the effective area of the supply opening of the rooms and the air supply duct at the total heat exchanger side must be increased and a combination air volume system must be used.

Run-Around Energy Recovery System for Air-to-Air Applications Using Cross-Flow Exchangers Coupled with a Porous Solid Desiccant—Part I: Model Development and Verification

Heat and moisture transfer between supply and exhaust air streams are investigated for a run-around system in which the coupling material is a desiccant coated solid that is transported between two exchangers. The finite volume method is used to solve the governing partial differential equations of the cross-flow heat exchangers in the supply and exhaust ducts under steady state operating conditions. The outlet air properties are calculated for several inlet air operating conditions and desiccant properties. The accuracy of the model is verified by comparing the simulations with well-known theoretical solutions for a single cross flow heat exchanger and a liquid coupled run-around system. The difference between the analytical predictions and numerical model for sensible effectiveness for each exchanger and the run-around system were found to be less than 1% over a range of operating conditions. The model is also verified by modifying the boundary conditions to represent a counter flow energy wheel and comparing the calculated sensible, latent and total effectiveness values with correlations in the literature. Part II of this paper will investigate the sensible, latent and total effectivenesses during simultaneous heat and moisture transfer.

A fuzzy logic procedure for ventilation control in case of fire in long tunnels

Ventilation is a crucial element while managing fire events in tunnels. This paper deals with ventilation strategies to be applied in case of fire in a long tunnel. The Frejus road tunnel has been considered as an application. This is a single tube road tunnel with semi-transversal ventilation. Ordinary and emergency ventilations are operated by using dedicated supply and extraction ducts. The optimal configuration of the ventilation system depends not only on the fire size and its location, but also on the pressure at the portals (which is an important factor in the case of a long tunnel), the traffic, etc. In this paper, some particular scenarios are analyzed. These scenarios correspond to particular fire locations, fire sizes, pressure and temperature at the portals, and traffic. Fuzzy-logic approach is applied in order to generalize the results obtained in these scenarios, so that any event can be managed. Some transient simulations are performed in order to test the control strategy. The values of input parameters selected for the test cases are not coincident with those selected to build the control strategy. Transient simulations allows one to check not only the extension of the tunnel portion occupied by smoke, but also the time required to confine the smoke front.

Energy efficiency enhancement of natural rubber smoking process by flow improvement using a CFD technique

A non-uniform flow and large temperature variation in a natural rubber smoking-room cause an inefficient use of energy. Flow uniformity and temperature variation can be improved by using a computational fluid dynamics (CFD) simulation. The effects of the size, position and number of gas supply ducts and ventilating lids which were at the inlets and the outlets of the smoking-room were investigated. The optimal rubber smoking-room of size 2.6m×6.2m×3.6m contains 154 50mm-diameter hot gas supply ducts, and four 0.25×0.25m and four 0.25×0.20m ventilating lids. The velocity distribution of this model in the rubber-hanging area was rather uniform. The average monitoring temperature of 54 positions was 62.1°C. This model could reduce the temperature variation by a factor of three from the original room model, i.e., from 15 to 5.5°C. In a further study, the heat input of an appropriate room model was finely adjusted to obtain a suitable temperature (60°C) for the smoking process. It was found that an appropriate heat supply at this temperature is 11kW. At this rate, the temperature variation is 5.3°C. This improved model should help the rubber smoking cooperatives to achieve at least a 31.25% saving in energy.

Particle loading rates for HVAC filters, heat exchangers, and ducts

The rate at which airborne particulate matter deposits onto heating, ventilation, and air-conditioning (HVAC) components is important from both indoor air quality (IAQ) and energy perspectives. This modeling study predicts size-resolved particle mass loading rates for residential and commercial filters, heat exchangers (i.e. coils), and supply and return ducts. A parametric analysis evaluated the impact of different outdoor particle distributions, indoor emission sources, HVAC airflows, filtration efficiencies, coils, and duct system complexities. The median predicted residential and commercial loading rates were 2.97 and 130 g/m(2) month for the filter loading rates, 0.756 and 4.35 g/m(2) month for the coil loading rates, 0.0051 and 1.00 g/month for the supply duct loading rates, and 0.262 g/month for the commercial return duct loading rates. Loading rates are more dependent on outdoor particle distributions, indoor sources, HVAC operation strategy, and filtration than other considered parameters. The results presented herein, once validated, can be used to estimate filter changing and coil cleaning schedules, energy implications of filter and coil loading, and IAQ impacts associated with deposited particles. The results in this paper suggest important factors that lead to particle deposition on HVAC components in residential and commercial buildings. This knowledge informs the development and comparison of control strategies to limit particle deposition. The predicted mass loading rates allow for the assessment of pressure drop and indoor air quality consequences that result from particle mass loading onto HVAC system components.