Measuring Cabin Temperature, Airflow and Noise for Ultimate Passenger Comfort in Transportation Vehicles

In addition to a vehicle’s continuous development towards improved propulsion technology and modern design, cabin comfort is also becoming increasingly important. For passenger comfort, cabin climate, noise, and vibration have to be regulated but not disturb the vehicle’s operation. Affected by both the external environmental conditions and the HVAC (Heat Ventilation Air Conditioning) system’s performance, the right balance needs to be achieved and maintained.

So, how is this done?

The right temperature balance is usually achieved by cooling or heating the cabin. The challenge here is to keep the outside temperature from propagating inside via the structure. The trim of the vehicle and the thermal blanket act as a shield, and depending on how the ventilation system is positioned, the vehicle cabin’s airflow cools down or heats up slower or faster. Once the right temperature is achieved, it is all about maintaining a uniform and pleasing temperature and airflow in the entire cabin shaft.

However, passenger comfort also depends on acceptable noise levels with noise and vibration measurements playing an important part in cabin comfort validation.

How to Achieve the Ideal Cabin Comfort: Simulation and Physical Testing

Passengers like a uniform overall cabin climate and acceptable noise levels. HVAC systems manage the airflow – and consequently heating, cooling, and humidity – preferably without noise distribution. As comfort has common objective criteria but at the same time is very subjective, manufacturers can individualize their HVAC setups to optimize passenger comfort.

To improve cabin climate and to develop the ideal HVAC system, there are typically different steps that need to be taken during R&D and testing. After developing a design, both simulation and physical testing help to analyse the effects of a HVAC system on the cabin environment.

Three methods are essential in developing and testing cabin comfort:

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Understanding and Improving Cabin Climate

The comfort and health of passengers is fundamental for a new or reworked design of aircraft or railway cabins and compartments, ensuring an optimal, comfortable climate (airflow, temperature, humidity, pressure), acceptable interior noise, and fresh and clean air for the sake of overall health and to fulfil CO2 regulations.

To ensure pleasant cabin climate, air conditioning (HVAC) systems need to consider the following variables:

  • Outside temperature and humidity
  • Direct sunlight affecting window seats
  • Heat sources inside the cabin
  • Flow from outside and through air outtake from climate conditioning
  • In cabin temperature and humidity and its distribution (especially at head and feet)

A perfect balance between all these climate and acoustic parameters is key to success and a comfortable trip or journey – the multi-attribute design optimization, with the minimum material for the maximum effect.

Simulation Using Computational Fluid Dynamics (CFD)

The numerical simulations of the airflow, including heat transfer in solid bodies and convection around structures and passengers, are performed by coupling flow simulations using CFD with FEA (finite element analysis) computations for the thermal aspects.

Based on this, it is possible to simulate and analyse the effects of the HVAC system on the cabin environment, for example, the time to cool down, temperature distribution in the air and in structures, and airflow velocities.

These results can be used to analyse the performance of the HVAC system and passenger comfort to finally improve the cabin climate towards the ultimate comfort level.

RUAG AG: Specialist for Airflow Analysis

HBK customer and partner, RUAG from Switzerland, delivers and operates several wind tunnels, which record, process and evaluate high-quality measurement data with the help of HBK products.

Complementing the experimental data validation, the CFD (computational fluid dynamics) simulation and analysis of physical processes allow for a detailed analysis where wind tunnel testing may not be sufficient. Numerical simulations cover a wide range of applications, including dynamic FSI (fluid structure interaction), and are ideal for preliminary configuration studies.

Learn more about RUAG

Physical Testing of Thermal Flow and Airflow

Physical testing starts with the first cabin interior prototype that needs to undergo a physical validation test program.

This involves performing some experiments in climate chambers, where outdoor, real-world conditions are simulated – for example for aircraft testing: flight heights up to several thousand feet and outside temperature from –60°C to +50°C – with a variance of humidity, artificial sun and the HVAC system’s operational modes.

While performing the tests, hundreds of sensors are installed in a network placed throughout the cabin, measuring temperature, humidity, pressure, and airflow, added by IR (infrared) cameras.

The physical testing can take several hours or even days as the test environment (climate chamber) is often so big that the temperature control and compensation takes some time.

The testing process requires reliable and stable measurement equipment to easily and flexibly acquire data from different sensor types. In order to acquire high precise data insights, unattended testing and recording need to be performed using DAQ systems that can withstand the climate chamber’s harsh conditions, for example HBK’s SomatXR DAQ. Post-processing tools for tests with high-channel count help with the extraction, visualization and analysis of large amounts of measurement data.

Acoustic Analysis

Cabin comfort is also affected by the impact of noise and vibration. Targets and objectives of the overall noise level for, for example, a newly designed aircraft are based not only on simulation, but also physical testing and the measurement and analysis of existing cabins. Data is then translated into propulsion levels, overall acoustic levels, and acoustic isolation material in the fuselage.

For aircraft interior noise, every aircraft manufacturer has its own guidelines instead of fixed regulations or standards to follow. The type of different propulsion (jet turbine, turbo prop, electric) also needs to be considered as they all have different noise signatures.

In acoustic modelling as in physical testing, engineers need to understand noise paths and distribution from the outside source to the inside. The turbulent airflow creates a broadband noise inside, which becomes the most dominant factor. Isolation is then adjusted in the optimal compromise of noise, thermal climate, weight, and cost. The spectrum is best analysed during ground testing but is also part of flight testing.



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Choose Comprehensive Measurement Excellence with an HBK Setup

HBK offers the ideal setup not only for cabin thermal and air flow testing, but also for acoustic analysis. High-precision data acquisition systems and software for excellent data evaluation help you with the final design of the ideal cabin comfort.

Your benefits: accurate measurements, scale to any number of channels – distributed or centralized, powerful data validation.

Measurement & Analysis

Powerful and flexible data integration: QuantumX and SomatXR data acquisition systems measure thousands of channels with parallel data acquisition and control.­

catman Enterprise software can visualize and acquire all physical measurement data.
All data can then be used to optimize the HVAC system in the cabin and adapt the simulation models.­

Acoustic Camera

HBK's Acoustic Camera, a setup of microphone arrays and LAN-XI DAQ systems, enables reliable noise source identification, measurements and data acquisition.­

Going the Extra Mile: Supplementary Service and Support

Our service and support team will assist you in all issues regarding test and measurement applications. We offer: 

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