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Technical Paper

Investigation of Airflow Induced Whistle Noise by HVAC Control Doors Utilizing a ‘V-Shape’ Rubber Seal

2011-05-17
2011-01-1615
Doors inside an automotive HVAC module are essential components to ensure occupant comfort by controlling the cabin temperature and directing the air flow. For temperature control, the function of a door is not only to close/block the airflow path via the door seal that presses against HVAC wall, but also control the amount of hot and cold airflow to maintain cabin temperature. To meet the stringent OEM sealing requirement while maintaining a cost-effective product, a “V-Shape” soft rubber seal is commonly used. However, in certain conditions when the door is in the position other than closed which creates a small gap, this “V-Shape” seal is susceptible to the generation of objectionable whistle noise for the vehicle passengers. This nuisance can easily reduce end-customer satisfaction to the overall HVAC performance.
Technical Paper

Practical Approach for Vehicle HVAC Noise Reduction and Comfort Improvement

2011-05-17
2011-01-1592
Comfortable cabin environment from temperature, noise and vibration point of view is one of the most desirable aspects of any vehicle operating in hot or cold environment. Noise generated from HVAC system is one of the most irritating phenomena resulting in customer dissatisfaction and complaints. It becomes absolutely necessary to have low HVAC noise levels when the target market has hot weather all round the year. Balance between control of temperature in desired way with least possible noise and vibration is the key for HVAC performance optimization within constrains posed by design and cost. This paper describes the approach for NVH refinement of front HVAC system proposed for a vehicle with limited off-road capability for which packaging constraints and late changes related to airflow and HVAC unit design for meeting comfort and crash requirements resulted in deterioration of noise and vibrations while operation.
Technical Paper

A/C Moan - its Diagnostics and Control

2009-05-19
2009-01-2054
Air-conditioning (A/C) induced moan is a very commonly observed phenomenon in automotive refrigerant systems. Since most of the automotive A/C systems cycle ON/OFF four to six times every minute, the A/C induced moan is quite readily audible under engine idle and even while driving, especially under lower engine/vehicle speeds. It is not unusual for an A/C compressor to moan or not, on some vehicle/s under certain operating conditions. Most of the OEMs resolve or suppress the A/C moan potential to barely audible levels. However, under some unique and extreme operating conditions, A/C moan is quite readily induced and often results in customer complaints. This paper discusses A/C moan related root-causes, sources and paths of propagation. A systematic diagnostic test-procedure is also described to diagnose and develop the needed most cost-effective design-fixes. Finally, based on this case-study - some objective targets are recommended to suppress the A/C moan to acceptable levels.
Technical Paper

Correlating HVAC Vehicle Interior Noise to Sub-system Measurements

2009-05-19
2009-01-2117
This paper discusses the relationship between the Heating, Ventilation and Air-Conditioning (HVAC) subsystem (module) and vehicle noise levels from test results. Vehicle measurements were performed in semi-anechoic room with a binaural head at driver location. The reverberation room measurements on the subsystem level were performed on modules without ducts and at pre-selected inlet restriction. For a given vehicle segment as defined by the J.D. Power & Associates, the interior vehicle noise levels show a good correlation to the module noise over the entire flow rate range of the HVAC operation. The module and vehicle noise strongly depend on the vehicle segment. The results presented here can provide insight to the vehicle noise trends from module noise measurements and in writing vehicle and module noise level specifications.
Technical Paper

Simulation and Validation of Passenger Compartment Soaking and Cooling under Solar Load

2009-12-13
2009-28-0050
Predicting the thermal comfort of the passenger compartment or the vehicle cabin using computational fluid dynamics (CFD) analysis helps reduce the cost and time of a heating ventilation and air-conditioning (HVAC) system development in any new vehicle program. This paper presents the simulation results of cabin soaking and cooling analysis done on an actual sports utility vehicle (SUV) prototype under constant solar load using the commercial CFD package Fluent™. These results are compared with test results. Cabin cooling and soaking analysis for a closed loop system that would include the HVAC system, the IP duct and the cabin with the air-conditioner (AC) operating in the recirculation mode is simulated. The heat rejected in the evaporator is assumed to be constant and this closed loop system analysis eliminates the need to be dependent on test results for input conditions like air flow rate and air temperature at duct inlet ports.
Technical Paper

CFD-Based Design Enhancements in Passenger Vehicle HVAC Module

2009-01-21
2009-26-0058
The Heating Ventilating and Air Conditioning (HVAC) module is a single unit designed to provide passenger comfort and safety in any automotive application. In the present competitive environment cost saving and short turn-around time are two major challenges for the development of automotive HVAC modules and systems. However, to make progress in this area, a good understanding of the flow behavior within the module is essential. Computational Fluid Dynamics (CFD) tool reduces the overall development time and ensure an optimum comfort level to passengers in the vehicle. In this paper, attempt has been made to simulate a passenger SUV HVAC module at different modes to examine flow field development and temperature distribution inside the module. All the CFD results have been compared and validated with wind tunnel obtained test results. A three dimensional model with FLUENT solver and GAMBIT, TGrid meshing software has been used throughout the study.
Technical Paper

NVH Improvement of a Bus Through AC Compressor Drive-Ratio Change

2009-01-21
2009-26-0045
This paper is an outcome of development work done in improving Noise Vibration Harshness (NVH) performance of a bus. A concern from built-up prototypes was high floor vibration levels at higher speeds when Air-Conditioner (AC) was switched on. Running mode analysis of bus-vibrations was performed to visualize exact behavior of its frame. It was revealed that a 4th order vibrations of the AC compressor was matching with a structural resonance of the bus frame on which the AC compressor was mounted. The frame suffered from high amplitudes of torsional vibrations especially near a power-train mount. And these excitations were transferred to the bus-floor. With a change in drive-ratio of the AC compressor, decoupling of its vibrations from the Bus-frame mode was made. This led to a significant reduction of the floor vibrations and increased comfort to the passengers at higher speeds.
Technical Paper

Efficient and Cost Effective Driver for HVAC Blower

2009-01-21
2009-26-0076
The Heating, Ventilation and Air Conditioning system (HVAC) blower is present in every car today. In most vehicles and especially in the mid to low cost segment, typically 250W blower motor is driven by a MOSFET used as a variable resistance. Generally seen as cost effective solution, this linear driving mode will generate a peak power loss of 80W to 100W. A more efficient way to drive a motor is to use PWM control. This solution already exists today but was always seen as too expensive for blower motors and thus reserved for mid to high range vehicles. A PWM controlled solution able to replace the existing linear module will be presented. The system cost is kept similar because no microcontroller is needed in the module embedded in or very close to the blower motor. Electrical, thermal and EMC characterization will also be shown.
Journal Article

Evaluation of Transient Refrigerant Migration Modeling Approach on Automotive Air Conditioning Systems

2011-04-12
2011-01-0649
Automotive air conditioning systems are subject to constantly changing operation conditions and steady state simulations are not sufficient to describe the actual performance. The refrigerant mass migration during transient events such as clutch-cycling or start-up has a direct impact on the transient performance. It is therefore necessary to develop simulation tools which can accurately predict the migration of the refrigerant mass. To this end a dynamic model of an automotive air conditioning system is presented in this paper using a switched modeling framework. Model validation against experimental results demonstrates that the developed modeling approach is able to describe the transient behaviors of the system, and also predict the refrigerant mass migration among system components during compressor shut-down and start-up (stop-start) cycling operations.
Journal Article

Thermal Management System for Electric Vehicles

2011-04-12
2011-01-1336
The thermal management system for electric vehicles is developed. Called the Thermal Link System, it consists of a heat-pump air conditioner, a system recovering waste heat from the electric power train, and a heat exchanger between the air-conditioner refrigerant and the power-train coolant water. The recovered heat is used for interior heating, so the amount of power consumed by the heat-pump air conditioner can be reduced. In this system the refrigerant for the heat-pump air conditioner and the coolant water for electric power trains are thermally linked by the heat exchanger, which can reduce the temperature of the coolant water to less than that of the surrounding air. This enhanced cooling function increases the power of electric power trains, or extends the amount of time at full power operation. Here we describe the Thermal Link System's mechanism and effects on energy efficiency.
Journal Article

Effect of Lubricant on Two-phase Refrigerant Distribution in Microchannel Evaporator

2013-04-08
2013-01-1508
This paper presents a model analysis of oil effects on the distribution of two phase refrigerant in a parallel flow microchannel evaporator. A microchannel evaporator model developed and presented earlier (SAE paper 2012-01-0321) is enhanced by inclusion of the thermodynamic and transport properties of refrigerant-oil mixture and their impact on boiling heat transfer and pressure drop characteristics. R134a and PAG oil are selected as the working pair. Viscosity effect and OCR effect on refrigerant distribution are investigated using this model, and the results show that 1) High viscosity is detrimental for refrigerant distribution. 2) As OCR increases, distribution becomes worse; but at very high OCR, distribution becomes better. Some initial experimental results show that distribution becomes worse when OCR changes from 0.1% to 3%.
Journal Article

Smart Rear Defog

2013-04-08
2013-01-1510
Smart Rear Defog can be defined as an optimized control algorithm that sets the state of a vehicle's rear defog relay based on a logical assessment of vehicle parameters and environmental conditions. The use of the optimized control algorithm will minimize the amount of user interaction needed to operate the rear defogger and it will minimize the amount of heat rejected to the environment which in turn will improve the vehicle's real world fuel economy or electric range. This paper provides a detailed description of the smart rear defog control system as well as evidence to demonstrate its robustness to variances in environmental conditions and vehicle usage compared to the traditional rear defog system commonly used in many vehicles today.
Technical Paper

Comprehensive Modeling of Vehicle Air Conditioning Loads Using Heat Balance Method

2013-04-08
2013-01-1507
The Heat Balance Method (HBM) is used for estimating the heating and cooling loads encountered in a vehicle cabin. A load estimation model is proposed as a comprehensive standalone model which uses the cabin geometry and material properties as the inputs. The model is implemented in a computer code applicable to arbitrary driving conditions. Using a lumped-body approach for the cabin, the present model is capable of estimating the thermal loads for the simulation period in real-time. Typical materials and a simplified geometry of a specific hybrid electric vehicle are considered for parametric studies. Two different driving and ambient conditions are simulated to find the contribution and importance of each of the thermal load categories. The Supplemental Federal Test Procedure (SFTP) standard driving cycle is implemented in the simulations for two North American cities and the results are compared.
Journal Article

Internal Heat Exchanger Integration for a Dual Evaporator MAC System

2013-04-08
2013-01-1504
The United States Environmental Protection Agency (EPA) as well as the European Commission (EC) are developing test procedures to regulate mobile air conditioning system (MAC) efficiency to reduce greenhouse gas emissions and reduce global warming. In the United States, air conditioning related MAC credits can be earned by implementing an internal heat exchanger (IHX) into a MAC system. By integrating an IHX into a MAC system the, Coefficient of Performance (COP) can be increased at the same time increasing cooling capacity. This improvement in efficiency reduces the energy and/or fuel consumption of the MAC system. This paper will compare various IHX plumbing configurations for a dual evaporator system with R1234yf refrigerant. A MAC system optimized for efficiency as well as evaporator cooling capacity is used to assess these different IHX plumbing configurations.
Technical Paper

1D Modeling of AC Refrigerant Loop and Vehicle Cabin to Simulate Soak and Cool Down

2013-04-08
2013-01-1502
Simulation has become an integral part in the design and development of an automotive air-conditioning (AC) system. Simulation is widely used for both system level and component level analyses and are carried out with one-dimensional (1D) and Computational Fluid Dynamics (CFD) tools. This paper describes a 1D approach to model refrigerant loop and vehicle cabin to simulate the soak and cool down analysis. Soak and cool down is one of the important tests that is carried out to test the performance of a heating, ventilation and air-conditioning (HVAC) system of a vehicle. Ability to simulate this cool down cycle is thus very useful. 1D modeling is done for the two-phase flow through the refrigerant loop and air flow across the heat exchangers and cabin with the commercial software AMESim. The model is able to predict refrigerant pressure and temperature inside the loop at different points in the cycle.
Technical Paper

Studies on AC Suction Line Pressure Drop using 1D Modeling

2013-04-08
2013-01-1503
In an automotive air-conditioning (AC) system, the amount of work done by the compressor is also influenced by the suction line which meters the refrigerant flow. Optimizing the AC suction line routing has thus become an important challenge and the plumbing designers are required to come up with innovative packaging solutions. These solutions are required in the early design stages when prototypes are not yet appropriate. In such scenarios, one-dimensional (1D) simulations shall be employed to compute the pressure drop for faster and economical solution. In this paper, an approach of creating a modeling tool for suction line pressure drop prediction is discussed. Using DFSS approach L12 design iterations are created and simulations are carried out using 1D AMESim software. Prototypes are manufactured and tested on HVAC bench calorimeter. AC suction line pressure drop predicted using the 1D modeling co-related well with the test data and the error is less than 5%.
Technical Paper

Compressor Body Temperature and Lubrication

2013-04-08
2013-01-1501
The paper addresses compressor body temperature (crankcase) importance to the vehicle AC system long-term durability. Majority of OEM vehicle test evaluation is to see if AC system can pass compressor discharge temperature and discharge pressure targets. Most OEMs adopt 130°C max compressor discharge temperature and 2350 kpag head pressure as the target. From the field, although some of the compressor failure results from a high compression ratio, and compressor discharge temperature that are caused by the poor front end airflow, etc., high percentage compressor failed systems exhibit not too high compression ratio and compressor discharge temperature, but having the trace of high temperature in the shaft area, gasket area, etc. With introducing more and more variable swash plate compressor applications, OEMs start to see more and more compressor failures that are not related to a high compressor discharge temperature but the trace of high compressor body temperature.
Journal Article

Periodic Reverse Flow and Boiling Fluctuations in a Microchannel Evaporator of an R134a Mobile Air-Conditioning System

2013-04-08
2013-01-1500
This paper presents experimental study of periodic reverse flow and induced boiling fluctuations in a microchannel evaporator and their impacts on performance of R134a mobile A/C system. Simultaneous flow visualization and pressure measurements revealed that reverse flow due to confined bubble longitudinal expansion caused periodic oscillations of the evaporator inlet pressure and the pressure drop, and their oscillation magnitude and frequency increase with ambient air temperatures because of higher average refrigerant mass flux and heat flux. Three potential impacts of vapor reverse flow reversal on evaporator performance are identified: 1) mild liquid maldistribution; 2) increased the evaporator pressure drop; 3) reduced heat transfer coefficient. Finally, to mitigate vapor reverse flow impacts, revised flash gas bypass (FGBR) method is proposed: vent and bypass backflow vapor trapped in the inlet header.
Technical Paper

Development of a S-FLOW System and Control (S‑FLOW: Energy Saving Air Flow Control System)

2013-04-08
2013-01-1499
This paper focuses on the development of the centralized air flow system S-FLOW (Energy Saving Air Flow Control System). The S-FLOW system directs thermal energy to each seating position in the vehicle based on occupancy, thus prioritizing the energy usage based on the particular scenario. The thermal environment in a vehicle's cabin is non-uniform. If the climate control system is used to direct airflow exclusively to any one region of the cabin, without special considerations, comfort may be adversely impacted. To solve this concern, a non-uniform evaluation method was developed to evaluate comfort at each body region of the occupant using the SET* (Standard new effective temperature) method. SET* is a parameter that combines the effects of temperature, airflow velocity, humidity, and other parameters to quantify thermal comfort. Next, a method was established that correlated each body region's SET* value to the occupant's overall thermal comfort.
Technical Paper

Experimental and Analytical Investigation of Two-Phase Ejector Air-Conditioning Cycles Using Low-Pressure Refrigerants R134a and R1234yf

2013-04-08
2013-01-1495
Two-phase ejectors have received increased attention in recent years because of their ability to improve the performance of automotive air-conditioning cycles by means of expansion work recovery. Much attention in recent years has been given to how high-pressure fluids, such as carbon dioxide, perform with ejector cycles; high-pressure fluids tend to have higher throttling loss, making them more attractive for expansion work recovery cycles, such as the two-phase ejector cycle. However, low-pressure fluids, such as those commonly used in automotive air-conditioning applications, tend to offer significantly lower work recovery potential. Nonetheless, the limited previous work on low-pressure refrigerants in ejector systems has shown that there is some improvement potential when using these fluids with ejector cycles.
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