ACS Door Heat Exchanger Requirements for Open Rack, Revision 1.0

Overview

This is a requirements document from the Open Compute Project's Advanced Cooling Solutions group (authors from Facebook and nVent) covering active and passive rear-door heat exchangers on Open Rack. It defines mechanical integration with ORV3, the electrical and communication interfaces of active doors, facility air- and water-side operating conditions, and the performance parameters a vendor must declare. Test methods are also in scope: pressure and leak tests, and air-sealing tests. Leak tightness is verified by gas pressure-decay or helium testing, with 'water tight' defined as a leak rate of 1e-2 mbar.l/s. For water quality the document points to ASHRAE liquid-cooling guidelines (Table 5.3 for the FWS loop, Table 6.2 for the TCS loop) with VDI 2035 Part 2 as further guidance.

On the water side, the recommended minimum coolant supply temperature to a door HX is 16 C to avoid excessive condensation (within ASHRAE W1); this is a floor, not a fixed setpoint. The coolant temperature difference across the door HX should be maximised for facility efficiency unless the site defines it (an example of at least 8 C is given). As general guidance a floor-level CDU may operate in a 140-450 kPa range, while a direct facility-water connection may impose higher pressures in multi-storey buildings.

Electrically, active doors take 230 VAC via C14/C20 inlets (or DC from the Open Rack busbar, in which case the PSU/BBU shelves and busbar must account for the load) and should support Modbus RTU/IP, SNMP v2/3 or HTTP. On the air side, OCP Ready gear should meet ASHRAE Class A1 allowable conditions.

Key points

1. Recommended minimum coolant supply temperature to a door HX is 16 C (within ASHRAE W1); a floor, not a fixed setpoint.
2. Coolant temperature difference across the door HX should be maximised unless the site defines it (example: at least 8 C).
3. A floor-level CDU may operate in a 140-450 kPa range; direct facility-water connection may impose higher pressures in multi-storey buildings.
4. Water quality: ASHRAE Table 5.3 (FWS loop) or Table 6.2 (TCS loop), with VDI 2035 Part 2 as further guidance.
5. Active doors take 230 VAC via C14/C20 (or DC from the busbar) and should support Modbus RTU/IP, SNMP v2/3 or HTTP.
6. OCP Ready gear should meet ASHRAE Class A1 allowable conditions on the air side.
7. Leak tightness is verified by gas pressure-decay/helium testing; 'water tight' is 1e-2 mbar.l/s.

Using it in design

• Give rear-door HX catalog entries rated kW, fan power, coolant inlet temperature, flow, pressure drop and active/passive type.
• Raise a condensation warning when door-HX supply temperature is set below 16 C or below the room dew point.
• For DC-fed active doors, add the fan load to the rack busbar and PSU budget.
• In the liquid-loop calculator, validate facility pressure against the door rating for multi-storey buildings.
• Set water quality per the ASHRAE and VDI 2035 Part 2 guidance.

Who should read it

Cooling engineers selecting rear-door heat exchangers and designing liquid loops for Open Rack environments, and equipment vendors.

Related standards

• ASHRAE Liquid Cooling Guidelines for Datacom Equipment Centers
• VDI 2035 Part 2
• OCP Open Rack V3 Base Specification

Publication details

Authors

Open Compute Project Foundation

Publisher

Open Compute Project Foundation

Year

2021

Document number

Rev 1.0

Document language

English

Source type

Industry body

Access

Free to read

Licence

Bibliographic reference only — the document is not redistributed here; confirm reuse terms at the original source

Citation