Applications
Flanges for data center chilled water systems
The chilled water plant and facility water mains carry the bulk of a data center's piping. Most joints are carbon steel Class 150, with flat faces at cast iron equipment and large flanges on the main headers.
For a data center chilled water system, a typical flange specification is ASME B16.5 Class 150 (or EN 1092-1 PN16), ASTM A105, weld neck or slip-on, raised face, with flat faces at cast iron chillers and pumps and ASME B16.47 or AWWA C207 flanges on mains above 24 inches.
What the chilled water system includes
Water-cooled chillers, or air-cooled chillers and dry coolers, produce chilled water in a central plant. Primary and secondary pumps move it through headers to the data halls, where it serves computer room air handlers and, in liquid-cooled halls, the coolant distribution units. In ASHRAE's liquid cooling terms, the water delivered to CDUs is the facility water system, classed by its maximum supply temperature from W17 to W45 and W+.
Warmer facility water means more hours of free cooling, so liquid-cooled halls are moving to the higher W classes. Flanges are not affected by these temperatures, but gaskets and the ratings of the lower L grades of stainless should be checked at design temperature.
Flange selection by location
| Location | Flange |
|---|---|
| Chiller evaporator connections | Match the nozzle; FF A105 to cast iron, RF to steel; Class 150 |
| Pump suction and discharge | Weld neck, FF to cast iron casings |
| Headers and mains up to 24 in | B16.5 Class 150 RF, weld neck or slip-on |
| Mains above 24 in | ASME B16.47 Series A or B, or AWWA C207 Class D |
| Branch take-offs for future halls | Blind flange, same class and face as the branch |
| Connections to CDUs | Carbon steel or stainless; check the CDU primary side spec |
A tall building adds static pressure at the lowest floors. Add static head to pump head to find the design pressure, then confirm Class 150 still has margin at the design temperature.
Material choices
Closed chilled water loops run with low oxygen and corrosion inhibitors, which is why carbon steel A105 is the default. Some operators now build the facility water distribution to the CDUs in stainless steel to reduce iron in the water near the white space. Where a carbon steel main meets a stainless CDU connection, see our note on isolating dissimilar metals.
Frequently asked questions
What flange class do data center chilled water systems use?
Class 150 to ASME B16.5, or PN16 to EN 1092-1 in Europe, covers most chilled water plants. Class 300 or PN25 appears where static head is high, typically the lowest floors of multi-storey buildings.
Carbon steel or stainless steel for chilled water?
Closed chilled water loops are commonly carbon steel with chemical treatment. Some operators run stainless steel from the header to the CDUs to reduce corrosion products near the IT equipment. The technology cooling loop after the CDU is stainless.
What happens at the chiller connection?
Match the chiller nozzle. Many chillers have flat-faced cast iron or steel water boxes, sometimes grooved ends. Use a flat face flange and full-face gasket against cast iron.