The Netherlands Organization for Applied Scientific Research (TNO) has developed a 6kW heat pump that uses acoustic waves to produce both heat and cold air. It achieved this together with Blue Heart Energy, a young company from Alkmaar in the Netherlands.
The novel heat pump measures 55 cm x 55 cm x 55 cm. The device has a service life of more than 15 years, with no moving parts other than the two oscillators. It can be used in combination with rooftop solar generation. A TNO spokesperson explained, ‘The thermo-acoustic heat pump is especially suitable for this given its excellent modulating capability and temperature flexibility. When using the thermo-acoustic heat pump in combination with PV, the energy required to drive the heat pump can be taken mainly from the PV panels, leading to fossil-free heat generation. In the future, smart controls to optimize the efficient use of PV panels and potentially sustainable heat or cold sources are expected.’
According to scientists, the thermoacoustic pump can reach higher temperatures than existing heat pumps without the need for refrigerants. It works with two pistons that oscillate at a frequency of 100 Hz in a closed pressure vessel filled with 50 bar helium. It creates an acoustic wave that can displace the heat from a lower temperature to a higher temperature.
Since the cost of fossil fuels has been rising at an increasingly incalculable rate, heat pumps are experiencing a real boom. They are currently considered one of the most sustainable and cost-effective ways to keep the four walls of a home warm. Most heat pumps work on the vapor compression cycle technology. The refrigerant evaporates and condenses to transfer energy and raise the temperature. Note that the charging point regulates the condensation point of a refrigerant. The technology works efficiently at temperatures around this condensation point, but the farther the input temperature and required power, the lower the efficiency.
Thermoacoustic technology is a new, renewable technology that aims to improve heat pump performance, providing a sustainable solution on the market. The technology is suitable both for residential and industrial applications. However, the Blue Heart Energy solution is focusing exclusively on domestic applications. This thermoacoustic element intends to replace the previous heart of heat pumps in the future and has therefore been designed so that it can be easily integrated into existing systems by original equipment manufacturers. Explaining the four-stage cycle of operation (expansion, displacement, compression, and return displacement), the scientists said,
‘During the expansion phase, the temperature of the gas drops, and the gas in the cold heat exchanger absorbs heat. The gas then moves through the regenerator to the warm heat exchanger. Here, the gas is compressed, the temperature rises, and the heat previously absorbed is released into the warm heat exchanger. Finally, the gas moves back, and the cycle is complete.’
In May 2022, they demonstrated the thermoacoustic technology at HANNOVER MESSE 2022. The heat pump is currently under testing in an advanced climate chamber in Delft, the Netherlands. ‘The climate chamber enables us to mimic reality very closely, so performance in the laboratory can give us a good idea of how the device will perform in people’s homes in the future,’ they said.
Blue Heart Energy plans to test the first devices in real houses in 2023.
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