VFD's and static pressure

Working with a client where we have installed Liebert VFD's on 3 older CRAC units combined with an environmental monitoring system that provides feedback to control the set point on the CRAC's. Client is adamant that he wants to have static pressure sensors in place to control the VFD's as you would for a typical office building. In another discussion thread I see some good information on why static pressure is not the preferred control mechanism but would like some more details or point to reference documents so I can put this issue to rest.