Browse Topic: Defoggers
HVAC systems are of critical importance in ensuring passengers’ thermal comfort inside the car cabin as well as safety requirements for defogging functions. These systems involve various components and subcomponents such as blowers, thermal exchangers or actuators, with a wide range of well-known technologies and also new ones on recently introduced innovative products. Currently, within established electrification trends worldwide, the HVAC system is becoming the most important embedded system that can induce major contribution of noise and vibration. These NVH issues can emerge through different transfer paths inside the car cabin possibly causing significant discomfort to passengers. During developments, the NVH issues are mastered and contained by both suppliers according to internal requirements and OEMs according to specifications. However, OEM specifications are mainly defined by overall noise levels and improvements over the years are generally consisting of reducing these specified levels. Furthermore, some HVAC NVH issues may not be well detected when using regular NVH metrics. This raises concerns about the limitations of the regularly used metrics in ensuring specification compliance and, above all, in depicting a subjective assessment at component level. Throughout a statistical analysis of HVAC systems population, this paper first focuses on the discrepancies between the data provided by traditional NVH metrics and subjective evaluations. Then, a deeper analysis involving psychoacoustic metrics provides a relevance overview of the applied metrics depending on the encountered issues and compared to a subjective assessment. Finally, from a responsibility perspective, these findings raise questions about the relevance of regular metrics used by OEMs and the right way to handle HVAC NVH topics nowadays.
The heating, ventilation and air conditioning system is one of the complex systems installed inside the cabin of an automobile vehicle. Each HVAC discipline has specific design requirements in terms of packaging space, performance targets, etc. Technical specifications such as airflow, noise, air distribution, allowable leakage rate vary as per vehicle segment and interior design accordingly. While maintaining the design parameters of HVAC, design engineers often face challenges related to water leakage, air leakage, water infiltration, etc. Controlling these parameters becomes crucial for customer satisfaction and for safety features. Several studies on seal proof technology have been conducted and continue to be conducted, whether for air-based applications, water-based applications, or any other fluid material.The application of sealing technology is spread almost everywhere, from domestic purposes to industrial applications. Similarly, in automotive HVAC, the application of foam packing for sealing doors or reducing leakage plays a crucial role. Different types of material with different cell structures are being used as per application requirements. This study will give insight regarding the application of foam packing, whether for the sealing of doors or the sealing of txv areas. Apart from this, a study was done on defrost leakage, which is a very prominent issue in HVAC. Defrost leakage leads to mist formation during certain climate conditions. The mist issue is mainly related to safety while driving the vehicle. Study on sealing and further detailed study of defrost sealing will give a brief guide to the design engineer in the selection of foam packing according to application within HVAC and surroundings. The application of foam packing in different forms and shapes with the results is presented in this study. Controlling the defrost leakage due to variation in parts is also captured in the study and bench test results provide a fair idea about the selection of foam packing at critical areas like the defrost outlet.
During thermal performance testing, achieving thermal balance between two fluid mediums of any heat exchanger is critical. Heat balance ratio (HBR) measures the heat transfer imbalance between two sides (source and sink) in a heat exchanger and also helps in ensuring accuracy of test data. There could be many factors which may lead to the imbalance in thermal performance of the sample under testing e.g. sensors accuracy, test operating range, sample orientation, hysteresis in the data acquisition systems etc. Therefore, a testing procedure needs to be established to achieve a better heat balance ratio as low as less than ±5%, which accounts for errors during instrumentation processes, flow losses & manual errors during testing. The current experimental study focuses on a typical coolant aluminium brazed heater core product which is used in automotive applications for passenger cabin heating during the cold climate conditions, windshield demisting and defrosting. In this study, three geometrically different heater core samples have been tested inside the calorimeter bench for the measurement of thermal performance and heat balance ratio using the proposed methodology. Heater core inlet air temperature sensor was used for maintaining the inlet temperature parameter. Heater core inlet & outlet air temperature measurement was done using thermocouple (TC’s) grid. Coolant side temperatures are measured using Resistance Temperature Detector (RTD) sensors. This methodology was validated for1:1 Ethylene Glycol+Water mixture and for tube and fin type heat exchanger. The currently existing testing methodologies exhibitHBR in the range of +10% to +30%, whilst the proposed method showed great improvement maintaining HBR less than ±5%& hence the new test method looks promising.
The cabin cool down performance is influenced by heat load, AC system components and Air handling components. The air handling components are AC duct, vane and vent. Design of AC duct vane plays a crucial role in the airflow directivity in cabin which enhances the cabin cool down performance. Simulations are carried out by rotating the vanes manually and requires post process for every iteration. It leads to more time consuming and more number of simulations to achieve the target value. Research articles focusing on automation and optimization of vane articulation studies are scanty. Thus, the objective of this work is to execute the vane articulation study with less manual intervention. A parametric approach is developed by integrating ANSA and ANSYS FLUENT tools. With Direct Fit Morphing and DoE study approach from ANSA delivers the surface mesh model for the different vane angle configurations. This surface mesh model is executed in ANSYS FLUENT for volume meshing, case set-up and post processing. By using journal file manual intervention can be reduced drastically for setting up the volume meshing and case file. A case study is demonstrated in this work for vane articulation exercise with less manual intervention. Further, the analysis can be extended for optimization analysis. This approach helps the designer to freeze the IP duct vane design during the concept phase itself. The same methodology can be extended to freeze the demist/defrost duct vanes.
It is particularly easy to get tunnel vision as a domain expert, and focus only on the improvements one could provide in their area of expertise. To make matters worse, many Original Equipment Manufacturers (OEMs) are silo-ed by domain of expertise, unconsciously promoting this single mindedness in design. Unfortunately, the successful and profitable development of a vehicle is dependent on the delicate balance of performance across many domains, involving multiple physics and departments. Taking for instance the design of a Heating, Ventilation & Air Conditioning (HVAC) system, the device’s primary function is to control the climate system in vehicle cabins, and more importantly to make sure that critical areas on the windshield can be defrosted in cold weather conditions within regulation time. With the advent of electric and autonomous vehicles, further importance is now also placed on the energy efficiency of the HVAC, and its noise. During the development of the defrost mode of an HVAC, the first priority is to satisfy the certification tests for defrost performance, verifying the vehicle’s safety. Since no realistic prototype of the vehicle interior can be built in early stages, this can lead to an increased mass flow rate through the HVAC defrost registers, and consequently increased noise levels from the HVAC. Furthermore, the complexity of the windshield and defroster topography is not considered in detail at the early design stage, resulting in dead zones and hindering visibility. Limited testing focusing mainly on passing defrost regulations leads to more defrost noise, and complaints from consumers. In this paper, we will present a novel Computational Fluid Dynamics (CFD) method to digitally design quiet HVAC systems through virtual defrost performance certification with reduced development time. Using this method, we will show that simulation can be used to drive early stage optimization of both defrost performance and noise in a CAD based parametric optimization.
SAE J3078/5 specifies a test method for testing defrosting systems. It is applicable to off-road self-propelled work machines as defined in SAE J1116 and agricultural tractors as defined in ANSI/ASAE S390. The full list of machines covered is included in Table 1.
Nowadays development of automotive HVAC is a challenging task wherein thermal comfort and safety are very critical factors to be met. HVAC system is responsible for the demisting and defrosting of the vehicle’s windshield and for creating/maintaining a pleasing environment inside the cabin by controlling airflow, velocity, temperature and purity of air. Fog or ice which forms on the windshield is the main reason for invisibility and leads to major safety issues to the customers while driving. It has been shown that proper clear visibility for the windshield could be obtained with a better flow pattern and uniform flow distribution in the defrost mode of the HVAC system and defrost duct. Defroster performance has received significant attention from OEMs to meet the specific global performance standards of FMVSS103 and SAE J902. Therefore, defroster performance is seriously taken into consideration during the design of HVAC system and defroster duct. The HVAC unit provides hot air to the defroster duct which is blowing high velocity air to the windscreen to clear the frosting. Currently as a traditional defrost duct design process, multiple flow simulation needs to be carried out for various design configurations of defrost duct through CFD analysis until the performance targets are achieved during the design cycle and it is very time consuming. In this paper, the focus is to develop defrost duct modelling using parameterization technique and optimize the defrost duct system to meet the performance requirements through robust optimization Design for Six Sigma (DFSS) methodology to reduce the design time, cost, size and weight of the system. Parametric modelling technique is used for designing the defrost duct through design software to reduce the design time for simulation. A 3-dimensional model (3D) of a car cabin with full a HVAC system was developed using Star-CCM+® to predict the performance of the system in the windshield. DFSS methodology helps in finding out the optimized design factors of defrost duct to meet the performance targets such as pressure drop, airflow and velocity at windshield aim points simultaneously. The optimized defrost duct design results were compared with the baseline defrost duct design results and the improvement in performance results is achieved by more than 60%.
In this study, we developed the defrost performance evaluation technology using the multi-objective optimization method based on the CFD. The defrosting is one of the key factors to ensure the drivers’ safety using the forced flow having proper temperature from HVAC during drive. There are many factors affecting the defrost performance, but the configurations of guide-vane and discharge angles in the center DEF(defrosting) duct section which are main design factors of the defrost performance in automotive, so these were set to the design parameters for this study. For the shape-optimization study, the discharge mass flow rate from the HVAC which is transferred to the windshield and the discharge areas in the center defrost duct were set to the response parameters. And then, the standard deviation value of mass flow rate on the selected discharge areas checking the uniformity of discharge flow was set to the objective function to find the optimal design. The results on the windshield from optimization analysis were quantified from some kind of standards to evaluate the defrost performance, in particular, the important parts on it to secure the drivers’ safety as specified FMVSS103, to which the weighted value has been assigned. From this process, it is possible to quantify the defrost performance with various automotive models, and to find the optimized design. In case of using these methods, it is possible to reduce the calculation time, and to effectively analyze the results by controlling the design parameters systematically. These methods also make it possible to check the performance rapidly, and to propose the optimal design through the analytical verifications at the initial design stage.
Numerical simulations are widely used to predict the performance of products in the automotive development process. In particular, ventilation and defrost performances of automotive HVAC system are developed according to design variables and environmental conditions based on CFD (Computational Fluid Dynamics). Recently, as improvement on both computer hardware performance and analysis technology continues, the usage of simulation has been increasing accordingly. However, the cost of software license also increases in such development environments. In this paper, we introduce our CFD program with OpenFOAM, which is the free, open source CFD software, to simulate flow characteristics of ventilation and defrost in automobile. This program includes self-developed GUI similar to commercial CFD code, two-layer realizable κ-ε turbulence model to secure numerical stability, and fluid film model to check the defrost phenomena with time dependence from OpenFOAM libraries.
SAE J3078 provides test methods and criteria for the evaluation of the operator enclosure environment in earth-moving machinery as defined in ISO 6165. SAE J3078/1 gives the terms and definitions which are used in other parts of SAE J3078. It is applicable to Off-Road Self-Propelled Work Machines as defined in SAE J1116 and Agricultural Tractors as defined in ANSI/ASAE S390.
Car air conditioners operate in all seasons to keep the cabin temperature cool in summer and warm in winter. In summer, for air conditioning systems without humidity sensors, the system cannot maintain a comfortable humidity level because the dehumidification function stops when the compressor stops. However, a system with humidity sensors can maintain a comfortable level because the system operates with on/off switching control of the compressors based on the information of humidity sensors, even when the engine is stopped. In winter, to reduce the heating load, the air conditioning system, in conjunction with the engine, controls defogging of the windshield using humidity sensors in addition to reducing ventilation loss by increasing the recirculation rate. By adding humidity information, the control of humidity in summer and defogging in winter can minimize the operation of compressors and the engine, and lead to improved fuel consumption without loss of comfort. In particular, in order to prevent energy loss, it is necessary to sense the humidity around windshields to prevent windshields from fogging up in winter.
Microfabricated, silicon-based capacitive actuator/sensor devices have been developed as prototypes of compact, low-power transducers that would be used to detect the presence (and perhaps eventually measure the thickness) of ice on aircraft lift and control surfaces. These transducers would be mounted flush with surfaces, so that they would not perturb airflows. Transducers of this type could also be used in such diverse applications as detecting ice in refrigerators for triggering defrosting cycles and detecting ice on roadways to trigger warning signals for drivers.
The scope of this SAE Recommended Practice is to establish uniform test procedures for passenger cars, to determine whether the system is defined as a defroster or defogger, and to establish minimum performance requirements for each system. A defroster for purposes of this practice is a system which will remove moisture and/or frost from the interior surface of the backlight at 0°F (−18°C). A defogger is a system which will remove moisture and/or fog from the interior surface of the backlight at 40°F (4°C). The test procedure is intended to simulate actual conditions by utilizing either a cold room with an appropriate device to introduce air flow over the backlight or a sufficiently large wind tunnel with ambient temperature control. The test procedure and the minimum performance requirements are based on currently available engineering data.
This SAE Recommended Practice establishes uniform test procedures for the defrosting systems of enclosed cab trucks, buses, and multipurpose vehicles. It is limited to tests that can be conducted on uniform test equipment in commercially available laboratory facilities. Current engineering practice prescribes that for laboratory evaluation of defroster systems an ice coating of known thickness be applied to the windshield to provide more uniform and repeatable test results, even though under actual conditions such a coating would necessarily be scraped off before driving. The test condition, therefore, represents a more severe condition than the actual condition, where the defroster system must merely be capable of maintaining a cleared viewing area. Because of the special nature of the operation of most of these vehicles (where vehicles are generally warmed up before or garaged in preparation for road operations) and since defrosting under steady state, over-the-road operation is the main concern, test conditions have been adopted which eliminate the engine warmup phase of vehicle operation. This recommended practice will be reviewed and revised as technological progress in vehicle defroster test procedure requires.
This SAE Recommended Practice establishes uniform test procedures for the defrosting systems of enclosed cab trucks, buses, and multipurpose vehicles. It is limited to tests that can be conducted on uniform test equipment in commercially available laboratory facilities. Current engineering practice prescribes that for laboratory evaluation of defroster systems an ice coating of known thickness be applied to the windshield to provide more uniform and repeatable test results, even though under actual conditions such a coating would necessarily be scraped off before driving. The test condition, therefore, represents a more severe condition than the actual condition, where the defroster system must merely be capable of maintaining a cleared viewing area. Because of the special nature of the operation of most of these vehicles (where vehicles are generally warmed up before or garaged in preparation for road operations) and since defrosting under steady state, over-the road operation is the main concern, test conditions have been adopted which eliminate the engine warmup phase of vehicle operation. This recommended practice will be reviewed and revised as technological progress in vehicle defroster test procedure requires.
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