Some other points to consider include
Three phase versus single phase. Three phase motors are cheaper to run, suffer less vibration
and don’t have start capacitor problems hence are more reliable, however they are more expensive up front to buy
and to supply power to.
Rotary scroll type compressors are quieter, cheaper to run, best in stop start situations as
the start inertia is lower and head pressure build-up is more linear, more efficient per unit power and
longer lasting, they are however are more expensive up front than reciprocating piston type.
After-coolers are a must in the tropics. They fit between the
compressor and treatment system or receiver and when fitted with an auto drain they can remove up to
70 % of water vapour before it has a chance to condense in the receiver.
Desiccant dryers are cheaper to run but have higher repairs costs than refrigerant dryers as
the only consumable is the desiccant as opposed to the continual power use. There is a cost with the
desiccant which has to be replaced periodically and the unit will need a service periodically. They are
capable of achieving far lower dew points than a refrigerant dryer which is paramount when air temperatures
go below freezing. Refrigerant dryers are far more reliable giving upwards of 15 years trouble free service
life and are cheaper to buy.
With filters, points to consider include whether they have flow indicators, ease of cartridge
change and cost of cartridges replacments.
Always work on the actual Free Air Delivery (FAD) of a compressor and not the displaced volume
as its is the Free Air Delivery which gives you the actual volume the unit can deliver at