This would depend on the capacity (CFM) of your air compressors, the required pressure and the total length of piping in the system. By knowing those three factors, standard tables can be used to determine the size of pipe required to minimize pressure drop. It is also important to know the number of valves and elbows in the system, as each one counts as an equivalent length of straight pipe. Size piping for the maximum CFM required and include the current system capacity and possible future expansion in your piping plan.
Only stored air above the pressure being used is defined as useful free air. Majority of pneumatic tools and work processes only require 90 to 100 PSI. Storing compressed air above this working pressure provides a surplus of useful air that can accommodate work demands. A 120-gallon receiver at 175 PSI stored provides 193 cubic feet of compressed air.
This depends on the application and required dewpoint. For most applications, a 35° F dewpoint is sufficient, which can be provided by a refrigerated air dryer. For outdoor applications, a desiccant dryer will be necessary to provide a -40° F dewpoint. Filters will provide various levels of contaminant removal and can be selected according to the application requirements.
One 100 CFM compressor operating at 100 PSI will generate 18 gallons per day at 90° F and 50 percent RH. About 60 percent of this moisture will be removed by the aftercooler. The remainder will pass into your compressed air system if a dryer is not installed.
Hot air holds more water. Every 20° F increase in temperature doubles the amount of moisture suspended in air. Every 20° F decrease in temperature reduces the amount of moisture suspended in air in half. An aftercooler or air dryer can eliminate this fluctuation. Air entering a 10hp compressor at 75° F and 75 percent relative humidity would produce 6.3 gallons of water per day. An air-cooled aftercooler with a separator would remove 4.3 gallons per day and a refrigerated air dryer would remove an additional 1.7 gallons. Only .3 gallons would be left within the 50,400 cubic foot of compressed air.