Hi Piwoslaw,
Most heat pump manufacturers are really just assemblers. They don't have extensive engineering departments. In the US they depend on the engineering departments of the compressor manufacturers, Copeland and Tecumseh. Attempts to use multiple compressors with a common condenser, expansion valve and evaporator are usually very tricky.
The evaporator, condenser and Freon charge will be sized according to the displacement of both compressors running simultaneously.the condenser will be mostly filled with Freon gas which will be releasing its heat of vaporization. A small amount of Freon liquid will be in the bottom of the condenser. The expansion valve will be sized to allow sufficient Freon liquid to flow to the low-pressure side. The evaporator will mostly be filled with Freon liquid absorbing its heat of vaporization. A small amount of Freon gas will be in the top of the evaporator.
when you switch off one of the compressors a lower body among Freon wolfs, the expansion valve throttles back, releasing less Freon liquid into the evaporator, more Freon liquid accumulates in the bottom of the condenser, and less Freon liquid accumulates in the bottom of the evaporator. The condenser releases heat by condensing the gas, not by cooling the liquid. The increased liquid in the evaporator results in less heat being released. Similarly, the evaporator absorbs heat by vaporizing the liquid, not by heating the already vaporized gas. The increased liquid in the condenser results in less heat being absorbed.
I think that you're probably better off with one compressor. The chief reason for using multiple compressors would be to limit starting current if your electric service is not capable of delivering the high in Russia current. The two compressors would start sequentially a few seconds apart.
( how are things in Warsaw. My grandmother came from Bialystok, my grandfather from Kraków.)
Paul_L
(Pavel)
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