Extensive testing ensures optimal comfort

When developing a comprehensive low energy heating and cooling system like the one we are developing in the JOSPEL project, it is important to make sure that all components are working as intended – i.e. that they are making the car hotter or colder to ensure the comfort of the driver and the passengers. This is known as HVAC testing (heating, ventilation and air conditioning).

Before launching new car models, automotive manufactures expose the cars to various types of tests, including HVAC tests where heating, ventilation and air conditioning systems must prove their worth. Some of the earlier tests typically take place in a lab, while some of the later tests are road tests, where engineers travel the word with a test vehicle to examine if the car’s climate system can handle any conditions – from excruciating desert heat to freezing arctic temperatures. So, if you spot a curious-looking camouflaged car in traffic, there’s a good chance that it is undergoing tests.

In the JOSPEL project, the heating and cooling systems are still at an early stage, so the current HVAC tests are carried out in a lab. This is taking place in the Galicia region of Spain, where JOSPEL partner CTAG has a full-vehicle climatic chamber with solar radiation available.

Preliminary simulations pre-optimize the systems

In a development process like the one taking place in JOSPEL, where multiple components and technologies are being developed and configured asynchronously, it will be a while before all components are installed in the test vehicle together and are working as a system.

However, it is still beneficial to run preliminary tests to get an idea of how the system will be performing in the vehicle, so it is possible to adjust and optimize the components during the development phase. But how do you run such a test if you don’t have the system available? In the JOSPEL project, Spanish partner CTAG has developed a numerical simulation model, where they are able to do preliminary simulations of the Joule and Peltier devices, even though these are not yet integrated in the final vehicles. That way, the project is prepared for when the devices are installed and will be undergoing the real HVAC tests. In addition, the project partners can use the results of the simulations to pre-optimize the Joule and Peltier devices and get a better idea about how they will perform when they are ready.

 

Thorough HVAC tests ensure passenger comfort

When car manufacturers are running HVAC tests, it is of course to ensure that the heating and cooling systems are working properly, so the driver and passengers will have a pleasant driving experience. This is no different in the JOSPEL project – except the heating and cooling systems also play an integral part in reducing the energy consumption of the vehicle and thus optimizing its performance and range. And by means of these tests, it is possible to fine tune the Peltier cooling devices and the Joule heating devices to perform even better.

As mentioned, the JOSPEL HVAC tests are carried out in a climatic chamber, which provides a completely controlled environment that allows CTAG engineers to simulate weather condition from anywhere in world – be it African desert heat or freezing Siberian winter.

During the tests, several sensors are installed in key locations around the vehicle cabin, and they record a myriad of data such as temperature, humidity, power consumption and airflow. With this data, the engineers can objectively determine the thermal comfort of the cabin, and by using human subjects in the tests as well, the objective data will be supplemented by a subjective perception of that comfort. To merge the subjective and objective readings, sensors are also placed on the human subjects to register e.g. heart rate and clothes surface temperature.

With the tests being a mix between subjective and objective evaluations of the heating and cooling systems, the engineers and test personnel can take the data from the sensors and immediately compare it with how they feel inside the car. Subsequently, they are able to calibrate and fine tune the system, explains Carlos Bandrés Diéguez, R&D Engineer at CTAG.

Simulating the extremes

As mentioned, the vehicle should be able to endure varying weather conditions, so the tests need to reveal how the heating and cooling systems handle these conditions. To cover this spectrum, the tests include a high temperature pull down test, a low temperature warm up test, a test for comfort at high temperature and a test for comfort at low temperature.

  • High temperature pull down test
    Here, the vehicle is soaked in the sun (simulated with infrared lamps) until the temperature in the cabin reaches 55°C. Then the vehicle is operated at about 25km/h (simulated with a blower fan) with maximum AC and fan speed control settings. The aim of the test is to evaluate how long it takes to get back down to a chosen comfort point.
  • Low temperature warm up test
    The vehicle is soaked in a cold ambient until the temperature in the cabin is stabilized at minus 20ºC. Then the vehicle is operated at about 25km/h (simulated with a blower fan) with maximum AC and fan speed control settings. The aim of the test is to evaluate how long it takes to get back up to a chosen comfort point.For health and safety reasons, these first two tests are performed autonomously with no technician inside the vehicle cabin. 
  • Comfort at high temperature
    A technician is inside the cabin controlling the HVAC settings, measuring the air flow and air flow temperature, and taking notes about the subjective comfort level. During the test, seven cooling options are tested with – six with pre-established levels of cooling power and airflow output, and one where the technician adjusts the cooling power and the airflow output until it finds the most comfortable setting.
  • Comfort at low temperature
    This test is identical to the comfort at high temperature test, except here it seven heating options that are being tested.

In the end, the tests will not only ensure that the heating and cooling systems provide a comfortable indoor climate in the vehicle – they will also validate that the requirements of the project have been reached.