Showing papers in "Science and Technology for the Built Environment in 2017"

Design optimization and validation of high-performance heat exchangers using approximation assisted optimization and additive manufacturing

Abstract: The airside thermal resistance of air-to-fluid heat exchangers dominates the overall thermal resistance. On conventional heat exchanger's, fins are required to address such challenges; but their benefits are not limitless and are bound mainly by the tube size and shape. The reduction of the tube characteristic length has favorable impact on compactness and heat transfer. Conventional tubes are typically limited to round, elliptical or flat shapes which result in particular thermal-hydraulic characteristics. The current article has three main objectives. First, discuss the importance of fins on typical air-to-fluid heat exchanger's and how they become unattractive at smaller characteristic lengths with numerical analyses to support this argument from different perspectives. Second, present a proof-of-concept design with small finless tubes and a novel shape that can outperform a microchannel heat exchanger. Third, present a comprehensive analysis with shape optimization leveraging automated computational f...

Update of the scientific evidence for specifying lower limit relative humidity levels for comfort, health, and indoor environmental quality in occupied spaces (RP-1630)

Abstract: Nearly 600 articles were located in citation and keyword searches regarding the effects of humidity on comfort, health, and indoor environmental quality. Of these, around 70 articles reported the effects of low humidity (relative humidity ≤ 40%) and were analyzed in detail. Information in some categories was well chronicled, while other categories had significant knowledge gaps. Low humidity decreased house dust mite allergens. Due to different envelopes, generalizations could not be made for all bacteria and viruses. However, lower humidity increased virus survival for influenza. For comfort, low humidity had little effect on thermal comfort, but skin dryness, eye irritation, and static electricity increased as humidity decreased. For indoor environmental quality, low humidity had nonuniform effects on volatile organic compound emissions and perceived indoor air quality. Across many low humidity studies, ventilation rates and exposure times were noted as confounding variables. A majority of studies that ...

Computational fluid dynamics study on the influence of an alternate ventilation configuration on the possible flow path of infectious cough aerosols in a mock airborne infection isolation room.

Abstract: When infectious epidemics occur, they can be perpetuated within health care settings, potentially resulting in severe health care workforce absenteeism, morbidity, mortality, and economic losses. The ventilation system configuration of an airborne infection isolation room is one factor that can play a role in protecting health care workers from infectious patient bioaerosols. Though commonly associated with airborne infectious diseases, the airborne infection isolation room design can also impact other transmission routes such as short-range airborne as well as fomite and contact transmission routes that are impacted by contagion concentration and recirculation. This article presents a computational fluid dynamics study on the influence of the ventilation configuration on the possible flow path of bioaerosol dispersal behavior in a mock airborne infection isolation room. At first, a mock airborne infection isolation room was modeled that has the room geometry and layout, ventilation parameters, and pressurization corresponding to that of a traditional ceiling-mounted ventilation arrangement observed in existing hospitals. An alternate ventilation configuration was then modeled to retain the linear supply diffuser in the original mock airborne infection isolation room but interchanging the square supply and exhaust locations to place the exhaust closer to the patient source and allow clean air from supply vents to flow in clean-to-dirty flow paths, originating in uncontaminated parts of the room prior to entering the contaminated patient's air space. The modeled alternate airborne infection isolation room ventilation rate was 12 air changes per hour. Two human breathing models were used to simulate a source patient and a receiving health care worker. A patient cough cycle was introduced into the simulation, and the airborne infection dispersal was tracked in time using a multi-phase flow simulation approach. The results from the alternate configuration revealed that the cough aerosols were pulled by the exhaust vent without encountering the health care worker by 0.93 s after patient coughs and the particles were controlled as the aerosols' flow path was uninterrupted by an air particle streamline from patient to the ceiling exhaust venting out cough aerosols. However, not all the aerosols were vented out of the room. The remaining cough aerosols entered the health care worker's breathing zone by 0.98 s. This resulted in one of the critical stages in terms of the health care worker's exposure to airborne virus and presented the opportunity for the health care worker to suffer adverse health effects from the inhalation of cough aerosols. Within 2 s, the cough aerosols reentered and recirculated within the patient and health care worker's surroundings resulting in pockets of old contaminated air. By this time, coalescence losses decreased as the aerosol were no longer in very close proximity and their movement was primarily influenced by the airborne infection isolation room airflow patterns. In the patient and health care worker's area away from the supply, the fresh air supply failed to reach this part of the room to quickly dilute the cough aerosol concentration. The exhaust was also found to have minimal effect upon cough aerosol removal, except for those areas with high exhaust velocities, very close to the exhaust grill. Within 5-20 s after a patient's cough, the aerosols tended to break up to form smaller sized aerosols of less than one micron diameter. They remained airborne and entrained back into the supply air stream, spreading into the entire room. The suspended aerosols resulted in the floating time of more than 21 s in the room due to one cough cycle. The duration of airborne contagion in the room and its prolonged exposure to the health care worker is likely to happen due to successive coughing cycles. Hence, the evaluated alternate airborne infection isolation room is not effective in removing at least 38% particles exposed to health care worker within the first second of a patient's cough.

Studying the performance of a dehumidifier with adsorbent coated heat exchangers for tropical climate operations

Abstract: A solid desiccant dehumidifier equipped with adsorbent coated heat exchangers has been developed and investigated experimentally. The main component of the solid desiccant dehumidifier included two heat exchangers that were coated with silica gel regular density (RD) type powder in order to increase water adsorption uptake by improving its heat transfer. A series of experiment were conducted to evaluate two key performance indices, namely, moisture removal capacity and thermal performance, under various operating conditions. Results revealed that the reduction of dehumidification process time by 50% can lead to significant improvement of the mean humidity ratio at outlet up to 9.3 g/kg. The maximum moisture removal was found to decrease from 14.8 to 13.2 g/kg with higher airflow rates arising from the reduced residence time of the process air. It was further observed that the water moisture removal was highly affected by inlet humidity ratio. In addition, marked improvement in thermal performance can be a...

Automated fault detection and diagnosis methods for supermarket equipment (RP-1615)

Abstract: Many automated fault detection and diagnostics methods have been developed for application to building mechanical systems over the past 20 years because they have the potential to reduce operating costs and energy consumption by providing early warning of performance degradation faults. Supermarkets could be a very beneficial setting to deploy automated fault detection and diagnostics, particularly in the refrigeration systems, which are major energy users and are known to commonly suffer from significant refrigerant leakage problems. The current article provides an overview of the common mechanical systems deployed in supermarkets, and then describes a comprehensive review of the literature on automated fault detection and diagnostics methods from other systems that could potentially be applied in supermarket settings. A collection of supermarket field data is analyzed in the context of its potential use in automated fault detection and diagnostics methods from other systems. The review includes methods ...

Review and analysis of fuel cell-based, micro-cogeneration for residential applications: Current state and future opportunities

Abstract: Micro-cogeneration or micro-combined heat and power, which can meet both the electrical and thermal needs of the residential sector, is growing and can offer reduced energy usage and emission. Micr...

Human thermal adaptation based on university students in China's severe cold area

Abstract: A field investigation was carried out in a university campus in Harbin winter to study students' thermal comfort and adaptation. Thirty students were selected as the participants. They were tracked and surveyed and their environmental parameters were monitored in dormitories and classrooms. The results show that the indoor air temperatures were close to the upper limit 24°C in ASHRAE 55 Standard (ASHRAE 2013) when the relative humidity and air speed met the standard in both environments. The 90% acceptable temperature range was 19.7°C–23.2°C in dormitories and 16°C–22.4°C in classrooms. Meanwhile, it is found that the participants' thermal responses were evidently discrepant in different built environments. The thermal neutral temperatures were always lower than the indoor temperatures in any heating phase, and they were much lower in classrooms than in dormitories. The mean thermal sensation was basically higher than predicted mean vote (PMV) during the whole space heating period. A thermal adaptation to...

Heat and mass transfer performance comparison between a direct-contact liquid desiccant packed bed and a liquid-to-air membrane energy exchanger for air dehumidification

Abstract: Entrainment of liquid desiccant droplets into the airstream and flow maldistribution are two challenges for liquid desiccant packed beds. Liquid-to-air membrane energy exchangers are novel liquid desiccant exchangers that have the potential to overcome these challenges by using membranes to separate the air and solution flows but have higher heat and moisture transfer resistances. As a new contribution of this study, the heat mass transfer performance of these two exchangers with the same volume and operating condition are compared at two conditions: (1) with the same pressure drop on the air side and (2) with the same total heat/mass transfer area. Results show that liquid-to-air membrane energy exchanger gets up to 13 and 20% higher latent and total effectiveness respectively than the packed bed at the same air pressure drop. Reversely, the packed bed achieves up to 16% higher mass transfer performance than the liquid-to-air membrane energy exchanger with the same heat/mass transfer area. The flow maldi...

Study of a U-tube heat exchanger using a shape-stabilized phase change backfill material

Abstract: This article describes the use of FLUENT software to simulate the heat transfer performance of U-tube heat exchangers in the ground source heap pump using the backfill materials of shape-stabilized phase change materials and crushed stone concrete. In this study, the shape-stabilized phase change material is a mixture of decanoic acid and lauric acid with the following mass concentration compositions: decanoic acid = 60%, silica = 10%, and expanded graphite = 6%. The mixture of shape-stabilized phase change material has a coefficient of thermal conductivity of 1.528 W/(m·K) and a latent heat of 109.2 kJ/kg. From the results of a 12-h simulation of the heat transfer dynamics, the heat exchange for a unit borehole depth of backfilling with shape-stabilized phase change material is 1.223 times the heat exchange for a unit borehole depth of backfilling with crushed stone concrete. In addition, the thermal influence radius of the backfill materials of shape-stabilized phase change material is 0.9 times of that...

HVAC control loop performance assessment: A critical review (1587-RP)

Abstract: This article presents a comprehensive review of control loop performance assessments in the context of building HVAC controls. Few studies are available for assessing HVAC control loop performance using a single control quality factor. A control quality factor should be an objective and quantitative metric with simple-to-interpret criteria and should only use data available from the actual control system, such as the control output. The authors systematically reviewed 34 indices and the associated methods of evaluating control loop performance and cataloged the drawbacks and merits of the different indices. Most of these performance assessment indices are currently used in process control industry applications. There were 14 of the 34 indices selected for further review, due to their particular suitability for implementation in HVAC control loop performance assessment. Finally, the selected 14 indices are implemented for assessments of three regulatory control loops with proportional-integral controllers:...

Thermal comfort investigation of an outdoor air-conditioned area in a hot and arid environment

Abstract: Thermal comfort in hot and arid outdoor environments is an industrial challenging field. An outdoor air-conditioned area was designed and built to host sport and social events during summers 2014 and 2015 in Qatar. This article presents a thermal comfort analysis of the outdoor air-conditioned area using computational fluid dynamics, on-site spectators surveys, and on-spot climatic measurements. The study utilized computational fluid dynamics to develop a thermal comfort model of the outdoor air-conditioned area to predict the thermal comfort of the occupants. Five different thermal comfort indices; mean comfort vote, cooling power index, wet-bulb globe temperature index, Humidex, discomfort index, were utilized to assess the thermal comfort of spectators within the conditioned space. The indices utilized different on site measurements of meteorological data and on-site interviews. In comparison to the mean comfort vote of the sampled survey, all thermal comfort indices underestimated the actual thermal comfort percentage except the wet-bulb globe temperature index that overestimated the comfort percentage. The computational fluid dynamics results reasonably predicted most of the thermal comfort indices values. The computational fluid dynamics results overestimated the comfort percentage of mean comfort vote, wet-bulb globe temperature index, and discomfort index, while the thermal comfort percentage was underestimated as indicated by the cooling power index, and Humidex.

Correct design of vertical borehole heat exchanger systems through the improvement of the ASHRAE method

Abstract: In this article, the ASHRAE method for borehole heat exchanger field design is deeply discussed in order to trace its theory and physical meaning. The aim of the article is corroborate previous studies in order to demonstrate that the current version of the method is not suitable for a reliable sizing of the borehole field since the criteria for calculating the temperature penalty term fail to large extent from a correct estimation. Based on the above findings (demonstrated by a comprehensive comparison with reference results pertaining a vast number of borefield configurations), a new version of the temperature penalty calculation procedure is presented that is able to maintain the ASHRAE formalism and simplicity while enhancing the accuracy of the design results.

Experimental evaluation of transcritical CO2 refrigeration with mechanical subcooling

Abstract: Transcritical CO2 booster refrigeration systems have seen a growing interest in recent years as they can provide two-stage refrigeration with R744, which has a global warming potential of 1.0, as the working fluid. However, the efficiency of these systems, particularly in transcritical operation, is often not as good as the efficiency of comparable conventional equipment. One possible way to improve performance in hot climates is through the use of a mechanical subcooler. This study describes laboratory testing of a lab-scale transcritical booster system, with and without mechanical subcooling and in transcritical and subcritical operating modes. In addition, a new steady-state model for generalized vapor compression systems was developed and is presented here. The model is used to simulate the system tested in the current article. The testing showed a significant improvement in both capacity and efficiency at all operating conditions with the subcooler. The solver was able to match capacity, power, and e...

Comparative performance study on liquid desiccant dehumidification with different packing types for built environment

Abstract: Packed liquid desiccant dehumidification systems are regarded as energy-saving and environmentally friendly technologies compared with conventional dehumidification technologies. The packing type plays a significant role in the system performance, but comparative studies of the different types are limited. First, this article investigates the dehumidification performance of liquid desiccant dehumidification with three packing types: corrugated structured, S-shaped polyvinyl chloride, and globular-shaped polypropylene. Then, the operation performance of solar-assisted liquid desiccant air-conditioning systems with different packings is simulated. A commercial building in Hong Kong was chosen as the case study. Results show that each specific packing surface area and structure determines the dehumidification performance by significantly influencing the liquid/air contact area and time. The enthalpy and moisture effectiveness of the corrugated structured packing were found to be 1.69 and 1.60 times those of ...

Effects of process air conditions and switching cycle period on dehumidification performance of desiccant-coated heat exchangers

Abstract: This study investigated the dehumidification effect of silica gel and sodium polyacrylate desiccants coated on fin and tube heat exchangers under various humidity and temperature conditions. In the system, the two desiccant-coated heat exchangers are periodically operated in mass equilibrium states between dehumidification and regeneration processes. The corresponding cyclic switching times between the two processes are investigated to determine suitable switching times that will further improve the operational efficiency of the system. The experimental results show that while water at a temperature of 50°C was supplied during the regeneration process, the sorption ability was greater and the vapor was discharged in a shorter period of the regeneration process for the sodium polyacrylate desiccant than for silica gel. Thus, the moisture sorption ability of sodium polyacrylate in the system is superior to that of silica gel under the same operational conditions. Suitable cyclic switching times for both des...

Energy use predictions with machine learning during architectural concept design

Abstract: Studies have shown that the actual energy consumption of buildings once built and in operation is often far greater than the energy consumption predictions made during design—leading to the term “performance gap.” An alternative to traditional, building physics based, prediction methods is an approach based on real-world data, where behavior is learned through observations. Display energy certificates are a source of observed building “behavior” in the United Kingdom, and machine learning, a subset of artificial intelligence, can predict global behavior in complex systems, such as buildings. In view of this, artificial neural networks, a machine learning technique, were trained to predict annual thermal (gas) and electrical energy use of building designs, based on a range of collected design and briefing parameters. As a demonstrative case, the research focused on school design in England. Mean absolute percentage errors of 22.9% and 22.5% for annual thermal and electrical energy use predictions, respectively, were achieved. This is an improvement of 9.1% for the prediction of annual thermal energy use and 24.5% for the prediction of annual electrical energy use when compared to sources evidencing the current performance gap.

Oil retention in a microchannel type condenser and its effects on heat transfer rate performance and on the pressure drop

Abstract: Oil retention in a microchannel type condenser was measured and its effect on heat transfer rate performance and pressure drop were analyzed for refrigerants R410A and R134a condensation. The heat exchanger was a 2-pass aluminum louvered-fin type consists of multiports rectangular channels with hydraulic diameter of 0.06 inch (1.7 × 10−3 m). The refrigerants and Polyolester oil mixtures were studied at saturation temperature from 85 to 130°F (29 to 54°C) and oil mass fraction (OMF) was varied from 0 to 6 wt.%. Oil retained in the condenser was found to be strongly dependent on the OMF and it was measured up to 11% of its internal volume. The oil retained for high mass fluxes were higher than those for low mass fluxes. The effect of mass flux on the oil retention was small for low OMFs but became more evident for OMFs of 3 wt.% and higher. The oil penalized the heat transfer capacity by as much as 10% when the OMF was 3 wt.%. For medium temperature of 105°F (41°C) the heat transfer capacities were fairly c...

Moisture buffering, energy potential, and volatile organic compound emissions of wood exposed to indoor environments

Abstract: This is the author’s version of the article published in Science and Technology for the Built Environment.

Study to identify computational fluid dynamics models for use in determining HVAC duct fitting loss coefficients

Abstract: This article presents results from a systematic study to establish whether computational fluid dynamics techniques are capable of predicting pressure drop in close-coupled five-gore elbows having nominal diameters of 203 mm (8 in.) and turning radii r/D = 1.5. The close-coupled elbow combinations comprised either a Z-shape or a U-shape. In every instance the duct length separating the center-points of the elbows was systematically varied. An experimental program was likewise conducted to verify the computational fluid dynamics predictions, and data from the measurements are included. Zero-length pressure loss coefficients were predicted using five two-equations Eddy Viscosity Models including the standard k-ϵ, the Realizable k-ϵ, RNG k-ϵ, standard k-ω, and SST k-ω models, as well as the Reynolds Stress Model, and compared to the experimental data. The two-equation turbulence models predicted incorrect trends when applied to flow in U- and Z-configuration ducts. However, the Reynolds Stress Models with enh...

Sizing heating, ventilating, and air-conditioning systems under uncertainty in both load-demand and capacity-supply side from a life-cycle aspect

Abstract: Uncertainty in HVAC system sizing exists as there is a lack of accurate information at the design stage to predict a building's peak load demand and not enough operational data to predict system operating cost and energy performance. Instead of dealing implicitly with the uncertainty through a choice of safety factor in the standardized sizing procedure, which tends to lead to excessive oversizing as design engineers are prone to minimizing professional risk, a sizing framework that is based on uncertainty analysis has been proposed, which addresses uncertainties directly in the sizing procedure and increases the transparency of sizing in terms of risk management. However, current studies focus on uncertainty on the load demand side, but neglect uncertainty on the cooling capacity supply. Therefore, the current article proposes a study on the uncertainty on the cooling supply side and shows its importance for correct HVAC system sizing. Based on this, a new sizing strategy is developed that will size HVAC...

An open-source automated continuous condition-based maintenance platform for commercial buildings

Abstract: Many studies have documented that retro-commissioning provides energy savings ranging between 10 and 30%; in some cases, more than 50% of a building's energy consumption. Over the past two decades, retro-commissioning has evolved from being mostly a manual process to using functional testing to a semi-automated process of using monitored data to identify operational problems. Many of the issues that the retro-commissioning process identifies relate to the inability to manage and maintain building systems and controls associated with those systems. Even though retro-commissioning has proven to be cost-effective, only a small fraction of the buildings are commissioned and many buildings that are commissioned only implement a fraction of recommend retro-commissioning actions. Two primary reasons for lack of interest in retro-commissioning is a perception that: (1) retro-commissioning is expensive and (2) many retro-commissioning measures lack persistence. Many cities in the United States are mandating that s...

Prediction of undisturbed ground temperature using analytical and numerical modeling. Part I: Model development and experimental validation

Abstract: The interaction of buildings and ground source heat pump systems with the surrounding ground is quite important for design and energy calculation procedures. This article describes a one-dimensional finite volume numerical model that can be used to estimate the undisturbed ground temperatures under various ground covers—short grass, tall grass, bare soil, concrete, and asphalt; and a two-harmonic analytical model, which requires minimum computational time and is intended for engineering application. The analytical model relies on five model parameters: annual average ground temperature, two temperature amplitudes, and two phase lags to estimate the ground temperatures. The parameters are estimated using the numerical model results. This article presents experimental validations of both models: Nineteen geographically and climatically diverse measurement sites, covered by short grass or tall grass, are chosen for validating the models for a 1-year period using weather data at the sites. Validation results ...

Evaporation of Al2O3-water nanofluids in an externally micro-grooved evaporator

Abstract: Nanofluid is a mixture of liquid and solid phase nano-sized particles that shows a high thermal conductivity compared to its base fluid. With micro-grooves being a good method to increase the surface area for heat transfer, there is potential for nanofluid together with microgrooves to improve the performance of cooling systems. This article aims to study the effect of an externally micro-grooved surface on evaporation of aqueous nanofluids and discuss its potential application. In order to prepare a stable nanofluid, the duration time required for ultrasonication, which is a common technique in the preparation process of nanofluid, was first investigated. Next, experiments were conducted to investigate the effect of the micro-grooved surface on the evaporation rate of the nanofluids under different environmental conditions. Results show that the advantage of the enhanced thermal properties of nanofluids can only be manifested by the presence of micro-grooves. The use of a heat exchanger with nanofluids t...

Assessment and improvement of indoor environmental quality in a primary school

Abstract: This study reports levels of indoor environmental quality variables before and after installation of heat recovery ventilation in a primary school located in an urban area in Izmir, Turkey. A CO2-based modeling was performed to determine the required flow rates that would comply with an international ventilation standard, followed by computational fluid dynamics modeling for best airflow distribution in a classroom. Temperature, CO2, PM2.5, and total volatile organic compounds were found at undesired levels, among which relative humidity, CO2, and PM2.5 were improved after the intervention. Reductions in the mean and maximum concentrations were 29% and 68% for CO2 and 29% and 46% for PM2.5. This intervention study was a part of the city-wide main project that aimed to increase awareness of the students and their families, teachers, and staff regarding importance of indoor environmental quality in both at school and home due to its possible effects on children's health and academic performance, one of the ...

Detailed velocity profiles in close-coupled elbows—Measurements and computational fluid dynamics predictions (RP-1682)

Abstract: This article presents a systematic study to measure detailed velocity profiles in close-coupled five-gore elbows having nominal diameters of 305 mm (12 in) and turning radii r/D = 1.5, and to, likewise, predict the velocity profiles using computational fluid dynamics. The purpose of the testing was to study the physics of the flow in complex geometries and to provide data that can be used to verify the accuracy of computational fluid dynamics modeling predictions. The close-coupled elbow combinations comprised either a Z-shape or a U-shape configuration. In every instance the duct length separating the center-points of the elbows was systematically varied. Detailed velocity profile measurements were performed at one traverse plane located one duct diameter upstream of the first elbow and at one duct diameter downstream of the second elbow, and at various axial locations in the straight section between the close-coupled elbows. Velocity profiles results are compared to computational fluid dynamics Reynolds...

Algorithm for explicit solution to the three parameter linear change-point regression model

Abstract: Linear change-point models (also known in the building industry as energy-signature models) are commonly used for the monitoring and verification of whole building energy consumption. They have pro...

The accuracy of mapping the airstream of jet fan ventilators by fire dynamics simulator

Abstract: Jet fan ventilators are often applied for smoke control and support for pollutant dispersal in large enclosures, especially in tunnels and car parks. In the design phase, computational fluid dynamics techniques are most often used to verify the fire safety level afforded by the application of jet fans. However, reliable design based on computational fluid dynamics requires a validation of jet fan airstream modeling. To predict these flows, this investigation evaluated the performance of four turbulence models using large-eddy simulations by comparing the simulation results with the experimental data of both horizontal and sloped jet fan guide vanes. The axial velocity was examined and simulations were prepared with fire dynamics simulator software, from the National Institute of Standards and Technology, which is the most popular program for fire simulations, although it is often criticized for inaccurate mapping of ventilation jet fan airstreams. In addition, this investigation analyzed the computing cos...

Multi-objective optimization of thermo-acoustic devices using teaching-learning-based optimization algorithm

Abstract: This paper presents three case studies based on a multi-objective optimization approach to optimize the performance of thermo-acoustic devices by obtaining the best possible set of geometrical characteristic parameters. In case study 1, the performance of a thermo-acoustic refrigerator is measured in terms of three objectives namely, acoustic cooling load (ΦC), coefficient of performance (COP) and acoustic power loss (W02). Each objective is assigned a weight to facilitate suitable user-defined significance. The case study 2 aims to optimize a thermoacoustic prime-mover. The influence of stack position and its length, resonator length, plate thickness and plate spacing are considered as design variables. Two objectives namely, pressure amplitude (P) and frequency (f) are considered as objectives for multiobjective optimization of the thermo-acoustic prime-mover. In case study 3, the performance of a thermo-acoustic engine is measured in terms of five objectives namely, work output (W), viscous loss (Rv), ...

Defrosting performance on hydrophilic, hydrophobic, and micro-patterned gradient heat transfer surfaces

Abstract: In the current article, differences in drainage rates and defrosting effectiveness were explored for surfaces of differing wettability. Both patterned and nonpatterned surfaces were explored. Seven surfaces were examined in all—an uncoated, untreated aluminum plate (Sample 1), an identical surface treated with a hydrophilic coating (Sample 2), a surface containing evenly spaced microchannels with and without a hydrophobic coating (Samples 3 and 4), and a surface containing a microstructural roughness gradient with and without a hydrophobic coating (Samples 5 and 6). Cyclical tests consisting of three frosting/defrosting events were performed on each sample. Each cycle consisted of 1 hour of frost growth, followed by 10 minutes of defrost and drainage. The frost layer was grown on the surface inside an environmental test chamber under controlled operating conditions. The surface temperature, air temperature, and relative humidity were recorded to ensure that constant conditions were maintained during each ...

Low-energy LED lighting heat gain distribution in buildings, part 1: Approach and pilot test

Abstract: Lighting heat gains are a significant contributor to space cooling load in buildings and it is important to determine the lighting heat gain distribution—specifically, the fraction of convective and radiative heat gains, as well as the fraction of conditioned space and plenum space heat gains Traditional lighting's heat gain distribution has been determined and the data are available on the ASHRAE Handbook However, there is a lack of relevant data for the light-emitting diode lighting heat gain As the light-emitting diode technology and application are rapidly growing, the need to identify light-emitting diode lighting heat gain becomes highly demanded In this project (ASHRAE RP-1681), 14 commercially available light-emitting diode lighting luminaries’ heat gain distributions were determined through systematically designed experiments The split between the convective heat gain and the radiative heat gain, and the split between the conditioned space heat gain and ceiling plenum heat gain were determin