The Dutch national energy bureau ECN has build the prototype of a heat pump that is smaller than conventional heat pumps and potentially could become even a lot smaller. What is special about this heat pump is that it operates on sound. Sound is a pressure wave. If air is compressed it gets warmer. The ECN heat pump is a closed tube with speakers.
Core parameters: heat pump is a wall-mounted box of 40x50x10 cm. You need electricity for an air pump and speakers. Electricity of 1 kWh returns 4 kWh of heat. Air is pumped from outside and led through the (inaudible) “sound heat pump” and finally pumped into the living space, providing ventilation as an extra.
Within the Dutch context that means that you get the same heat performance from 2 kWh (40 cent) as from 1 m3 gas (64 cent). Eventually that heat pump can be powered by electricity from renewable sources. The heat pump should cost ca. $1,000 including installation.
At [1:00] the sound-heat conversion is demonstrated. Sound in the tube pumps heat from lower to higher temperatures.
The thermo-acoustic principle in reverse: use heat to generate standing sound waves and create mechanical work.