After writing on Google's post regarding ASHRAE's standard 90.1 and requirement for economizer and talking to Google's Chris Malone, I decided to find the documents.

Here is the proposed Addendum bu.

6.5.1 Economizers. Each cooling system that has a fan shall include either an air orwater economizer meeting the requirements of Sections 6.5.1.1 through 6.5.1.4.

There are a through k in just section 6.5.1

j. Systems primarily serving computer rooms where
1) the total design cooling load of all computer rooms in the building is less than 3,000,000 Btu/h (880,000 kW) and the building in which they are located is not served by a centralized chilled water plant, or

And Addendum cy

What is hard to figure out is why ASHRAE is making economizers a requirement for cooling systems instead of a performance based solution, but if you meet an efficiency improvement in table 6.3.2 you are allowed you to eliminate economizers.

Does addendum cy supersede addendum bu? addendum cy doesn't have the above section j.

DataCenterKnowledge references addendum bu.

ASHRAE, for its part, says it welcomes the feedback on the proposed changes. “ASHRAE is committed to excellence in the consensus standard development process and encourages anyone with comments regarding the proposed addendum regarding data centers (addendum bu) to participate in the public review process,” it said.

Are you confused? I am.