[BCreekDave]

If you already have a good functioning 5HP, why not just add another 5HP that you can fire up when needed? That way you aren't running extra HP when not really needed. At the factory where I work, we do this on a larger scale; 2 50's and a 100. we alternate the 50's on off shifts and run the 100 plus an automatic kick in to one of the 50's during day shift. The nice thing about this is if one of the 5's need some work, you aren't out of air completely. The downside is it does take twice the floor space. You can also stagger the cut-in pressure to lighten the electrical load. A compressor takes most of the energy during start-up.