Hello guys,

I with my colleagues are working in air conditioning sector and step by step we are developing refrigeration systems. Refrigeration is quite new thing for us, so we don't know all the information (factors) that could affect performance of the system. We have made refrigeration system that we are testing in our climate chamber. So shortly about application:

we are using finned air cooled coils (evaporator and condenser), variable speed compressor, eletronic expansion valve and other stuff (like suction accumulator, liquid receiver, filter drier and so on). Our application is reversible, so that means it's able to heat and cool.

coils specification:
- R410A refrigerant
- in summer evaporator capacity 15,3 kw (at 8 C evaporating temperature)
- evaporator inside volume - 8 litres
- in summer condenser capacity 18,9 kw (at 47 condensing temperature)
- condenser inside volume - 15 litres
in winter system is reversed so evaporator works as condenser and condenser contrary (as evaporator).
- in winter evaporator capacity 5,9 kw (at -14 C evaporating temperature)
- evaporator inside volume - 15 litres
- in winter condenser capacity 7,4 kw (at 27 C condensing temperature)
- condenser inside volume - 8 litres

system specification:
- short piping system
- liquid receiver volume - 2 litres

I've made some refrigerant charge calculation according to defra calculator and it says that:
- in summer maximum refrigerant charge approx 10,7 kg and minimum approx 7,1 kg
- in winter maximum refrigerant charge approx 5,9 kg and minimum approx 4,4 kg

Now our system is charged about 8 kg of refrigerant.

The problem is that my colleagues say that system is overdesigned (coils inside volume differs almost 2 times). Also, when we're doing defrost in winter conditions (system is cooling, because evaporator is iced) we're almost working on low pressure limit (with the intense of low system charge).

My questions:
- What do you guys think, if we will add larger receiver (approx 7 litres, because coils inside volume differs of such amount), will our system work more properly?
- If changing liquid receiver won't help, maybe there's only opportunity to reselect new coil that volume would be closer to 8 litres (instead of 15 litres)? What do you think?


If you need any additional information, please write and I'll try to provide it.