"HVAC" starts to sweat

When the sun beats down mercilessly on the facades in midsummer, the interiors of buildings with unshaded windows or poor insulation heat up mercilessly. If even the open window does not provide a cooling draught, it starts to get uncomfortable from a room temperature of 26 degrees. If the room temperature rises even further, even less physically strenuous activities such as office work become a burden. Fans and air conditioning systems run hot. Switzerland is sweating.

Energy consumption for air conditioning units and air conditioning systems in Switzerland is now in the terawatt range every year, i.e. in the order of billions of kilowatt hours. It is uncertain whether the desired cooling in the room can be achieved at all. Empa researcher Agnes Psikuta has therefore set herself the task of generating reliable data on the indoor climate in the workplace. Her goal: to air-condition buildings much more sustainably - while at the same time maintaining people's health and performance. Her work colleagues: "ANDI" and "HVAC", smart dummies that measure the indoor climate. Thanks to sensor technology and mathematical modeling, they recognize how workplaces can be sustainably brought to a comfortable temperature.

Sweating in the virtual office

The futuristic-looking "HVAC", short for "Heating, Ventilation, Air Conditioning", is well equipped: However, sensors for air temperature, humidity and air movement alone are not enough. A total of 46 measuring fields break through the plastic shell of the manikin, which it uses to quantify the heat radiation from the environment and, for example, to differentiate between solar heat and heating air.

Its partner with the simple name "ANDI" complements "HVAC's" data perfectly: "'ANDI' is the type for the big picture, it absorbs the heat balance that a person has under the given conditions," explains Agnes Psikuta from Empa's "Biomimetic Membranes and Textiles" laboratory in St. Gallen. To this end, "ANDI" keeps its operating temperature constant at 34 degrees, which corresponds to the skin temperature of a person in the comfort zone. Comfort zone here means that the body of a healthy adult can maintain a constant core temperature of 36.5-37.5 with minimal effort. "In the comfort zone, people don't sweat, they don't shiver from the cold and their hands and feet don't freeze because they can maintain their thermal balance with ease," says the researcher.

The mathematical modeling of this combined data ultimately results in a virtual thermal model of a person at work. In a project funded by the Swiss National Science Foundation (SNSF), Agnes Psikuta is now working with partner institutes at EPFL and the Silesian University of Technology in Poland to investigate how "HVAC" and "ANDI" cope with the parameters of real office conditions over the course of the year.

Ultimately, it should be possible to optimize the energy requirements of buildings based on this work. "At the height of summer, air conditioning systems run at full speed to completely cool open-plan offices, for example. However, it is unclear how effective the situation is for the respective workplace," says the Empa researcher. Structural elements directly at the workplace, such as cooling wall panels or ventilated office chairs, could provide more energy-saving and efficient solutions. The same could apply to the winter heating period: "HVAC" and "ANDI" could determine whether, for example, a room temperature of 17 degrees is sufficient if the workplace is heated to 22 degrees locally.

Dangerous hypothermia

However, the two manikins are also used in completely different situations - namely on the operating table. During a surgical procedure lasting several hours, it is important that the patient's body does not cool down too much, while the surgeon must not start sweating. If the patient loses too much heat, the risk of complications increases and the chances of recovery worsen. "Previous options for keeping the patient warm enough, however, have consisted of unsustainable disposable solutions or cumbersome set-ups that are difficult to disinfect," says Agnes Psikuta.

In a project with the Warsaw University of Technology, "HVAC" and "ANDI" are therefore investigating how easy-to-disinfect infrared lamps should be positioned in the operating room without obstructing the complex spatial conditions during the procedure. In addition, the heat radiation must not heat up the healthcare staff or even cause skin burns on the patient. While "HVAC" measures the heat flow from the lamp to the body with its dense matrix of sensors, "ANDI" calculates the entire heat balance of a patient, including the current room temperature. "The modeled data will be used to determine the position and output of the heat lamps for a wide variety of situations," says the Empa researcher. "In this way, we hope to be able to create ideal operating conditions without the risk of hypothermia."

Source: Empa