Sir Humphrey – thank you. Looks like the next step is to ask for 2 compressors to be on common property. Could they just say no? Where do I find the information to present to the OC that it is necessary to have the compressors so as to fit the amount of KWs available?
You would need an electrician to tell you the available supply capacity into each unit. Doing load calculations is something an electrician should be able to do. That said, be a bit careful. Some will, for example, incorrectly calculate as if an electric hob will draw its full rated current, when in practice nobody ever has every ring on full power at the same time.
Then the key thing to understand with a heat pumps, whether for space heating/cooling (ie an air conditioner) or for water heating is that a system rated at (say) 3kW heat output only requires 1kW or less electrical input. This is because the electrical energy is only being used to move heat from the air outside into the space or water. Even when it is subjectively cold outside, the air still contains heat. This is what makes heat pumps so much more efficient than converting the electrical energy into heat, which is necessarily using 3kW of electrical energy input to produce heat output at 3kW.
As for ‘Can they say no?’. ‘They’ is you. You and your neighbours are the Owners Corporation. You are all in the same boat. I think you need to work with your committee and/or some neighbours to develop an energy plan to work out the best solution for getting the building off gas that can work for every unit and be given permission for. If that means two compressors, then the OC as a whole might want to decide on a uniform solution about where they may and may not be put.