ASHRAE Journal, Oct. 2016, by Ron Jarnagin.

"Standard 90.4 is a code-intended energy standard designed to work in concert with Standard 90.1. In developing Standard 90.4, the basic structure matched that of Standard 90.1, which enables Standard 90.4 to simply refer to Standard 90.1 for requirements such as envelope, lighting and service water heating, which are within the scope of Standard 90.4 but are already well-covered by Standard 90.1. Standard 90.4 also references Standard 90.1 for mechanical equipment efficiencies, some of which are linked to U.S. Department of Energy legislation. So, if you are building or expanding a data center, you need to use both standards."