Hi all,

I am new to this site, so thank you for taking the time to read my post. I have a question on the fundamentals of the vapour compression refrigeration system that hopefully someone can help me with. I'm sure the answer is straightforward but unfortunately all the literature I have found on the internet doesn't seem to answer my question.

In a typical one stage compression cycle, the expansion valve is controlled to regulate the low pressure in the evaporator, whether its a thermal expansion valve or electrically controlled valve it will act on the superheat somehow to optimise the evaporating temperature dependent on the duty (or load). Following the evaporator the vapour is compressed but what I don't understand is what sets the pressure/condensing temperature in the high pressure side?

Is it determined by the temperature of the cooling medium, i.e. ambient air or water? Or is it determined by the compressor?

And finally, if I am using two cooling mediums at different temperatures to provide all the necessary condensation (i.e. some of the refrigerant is condensed in an air cooler and some in a water cooled condenser - either before or after the air cooler), what sets the condensing temperature then? The pressure will be equal throughout the high pressure side (neglecting pressure drops), so the condensing temperature will also be equal throughout.

Many thanks again.