What is N+1 Sparing?
Sizing a system so that N units supply the required flow and capacity and a third of the same size is added for redundancy. Discussion: Redundancy is a basic principle of sizing of any process equipment. The idea is to always be able to take at least one process unit out of service and still be able to maintain production. Hence, if you have two process units, one should be able to handle full production. If you have three process units, two should be able to handle full production. The expectation is to have one spare unit or N+1. The use of N+1 sparing in water softeners. Let us consider a required flow of 600 gpm. Case 1, N=1: The flow could be provided by one unit at 600 gpm and then for redundancy, an additional 600 gpm softener can be installed. In this first case, N = 1 and N+1 = 2. The required capacity per unit is 600/1 = 600 gpm. Case 2, N=2: In this case, the flow is provided by two units at 300 gpm with an additional 300 gpm softener. In this case, N = 2 and N+1=3. The capa
