Evaluation of Thermal Comfort in Vehicles
- Measuring Thermal Comfort in a Vehicle
Major Breakthrough
Two suppliers of passenger cars in Korea, namely Hyundai Motor Company and Kia Motors have invested in measurering instruments from LumaSense Technologies A/S. The evaluation of the Thermal Environment in Cars is a very complex task. These contracts are considered as a major break through at the Korean market. LumaSense Technologies A/S has a good reputation in this market segment with numerous orders from car manufactures in USA, Europe and Japan.
LumaSense Technologies A/S states: "We are very pleased with these good orders. Thermal Comfort - also in cars - is becomming more and more important, and our measurement instruments are unique for the car-industry."
A more thorougly description of the equipment and system is given below.Read more about evaluation of Thermal Comfort in Vehicles in this application note.
High demand for precision
The thermal environment in a vehicle cabin is very complex and thus difficult to evaluate. These difficulties are due to the influence of convective, radiative and conductive heat exchange created by external thermal loads and the internal heating and ventilation system. Last, but not least, neither driver nor passengers are able to make up for the assymmetric climate conditions which sets high demands for the Instrument and Transducers.
Thermal Comfort
- INNOVA "Flatman" mounted with Dry Heat Loss Transducers
Measurering Methods
The useual method of evaluating the efficiency of the air conditioning system in vehicles is to apply sensors to measure the air temperature at feet and at head level. The main purpose being to investigate how quickly the system will raise or lower the temperature in a warm or cold vehicle and to study the difference between the temperature at feet and head level. However, using this method only one of the three neded parametes (air temperature, mean radiant temperature and air velocity) that concerns the thermal comfort sensation is measured. This fact is especially unfortunate in vehicles as the mean radiant temperature differs more from the air temperature that in buildings and because the air conditioning system can create high local air velocities.
Theory
Man's thermal comfort is a result of the combined effect of six parameters: activity level, clothing, air temperature, air velocity, air humidity and mean radiant temperature which are all described in ISO 7730. This method can be used for whole body evaluation only, however, based on measurement with several transduces at different positions simulating various body parts. The applicable transducer is the INNOVA MM0057, which in shape simulates the body shape of a person, is heated and thus influenced by the air temperatur, mean radinat temperature and air velocity. The activity level, clothing and air humidity are set as constant parameters. The activity level in a car will be sedentary which means that the level will be between 1.2 and 1.6 MET. The clothing in a car can vary from 0.3 to 1.5 Clo in relation to the time of the year. The humidity will depend on the outside climate, the air conditioning system and the number of persons in the car. The dependent parameter for sensation of warm or cool is the water vapour pressure. Normally this may vary from 0.8 to 1.8 kPa.
The Equivalent Temperature
The combined effect of: the air temperature, mean radiant temperature and air velocity can be expressed as the Equivalent Temperature which is related to the dry heat loss from the body. A number of standards are under preparation for the evaluation of the thermal environment in vehicles. ISO/NP 14505 defines the Equivalent Temperature as an integrated physical measurement of the thermal climate in the vehicle and presents methods for its determination.