semihermetic supermarket rack upgrade with scroll

[coldseek1]

Good afternoon to everyone and thank you for contributing to HVACR knowledge. I hope I can do the same. First post in the forum.
A store owner had us recently retrofitting a low temp semihermetic rack. Now he says that he will be adding soon a few additional cases to the store floor. Logs indicate than since we performed the R-404A to R-407A retrofit, discharge air temp in the cases have been quite similar, but the expected little boost in performace has not been observed. There is this low temp 10hp scroll compressor left from other job, sitting nearby. Is it possible to add up this scroll to the semihermetic rack in order to raise capacity? I know that cranckcase level and supply rate of oil in scrolls are somewhat different from semihermetics, but I remember a Hussmann rack manual that allowed for such a mix of semis and scrolls.Any comments welcomed.

[al]

Before even looking at that, can you condenser take the additional heat rejection needed?

I can't see an issue with adding new scroll so long as oil control can be maintained.

[Glenn Moore]

When retrofitting to a new refrigerant it is necessary to change the expansion valves , to a valve that is designed for the new refrigerant , in this case R407A . If the original R404A valves are being used with the new refrigerant, these valves have most likely had their superheat setting raised to prevent liquid flood back . This in turn will reduce the capacity of the pack . To get an increase in the pack capacity the correct Tevs must be fitted to allow the static superheat setting to be reduced which will raise the suction pressure and increase the packs capacity . Thermostatic expansion Valves are tuned to a specific refrigerant where the static superheat is design to be the same across the evaporating range of the Tev . When the Tev is for a different refrigerant then the static superheat will not be constant and can have a high static superheat at high evaporating temperatures and low or negative static superheats at low evap temperatures . Always reset the Tevs superheat during recommissioning

[coldseek1]

Good afternoon and thank you both for the feedback.
1) Head pressure seems to be ok as now. We changed the original condenser about two years ago with a new one, which has a factory option of adding a water mist system, much like one of those adiabatic condensers used for CO2 in the tropics. We could make this upgrade if necessary.

2) The original TXVs have heads for R-404A. Even though engineering actually believed that these heads should perform ok, as they are removable, we changed them for R-22/R-407A/R-407C heads, and adjusted SH in both med and low temp cases. Very interesting your statement on STATIC SH. That is a concept I did not know until recently.