Guide · Liquid cooling / hydronic
Liquid cooling & hydronic skills for data centers: pipefitter vs HVAC/R vs OEM
Some newer data centers cool their computers with liquid piped right to the equipment instead of only blowing cold air. When that system leaks or fails, tradespeople fix it, not the computer staff. In trade terms: a pipefitter for the building’s water or glycol pipes into the cooling unit, an HVAC tech (with EPA 608) for anything that holds refrigerant like a CRAH or chiller, and the equipment maker’s trained tech for the rack-side cold plates and specialty coolant behind the unit. IT raises the ticket and protects servers; it does not own the wet work. Manufacturer liquid-cooling classes sit on top of a pipefitter or HVAC ticket; they do not replace either one.
Plain map of who fixes what: facility systems · liquid cooling (also #cooling). Refrigerant credential path: EPA 608 guide. Hire gates: cert checker (HVAC/R). Role compare: Roles. Jobs vs electricity framing: jobs vs power.
Key points
- Who gets the call: Pipefitter for building water/glycol into the cooling unit. HVAC tech with EPA 608 for refrigerant CRAH/chillers. OEM-trained tech for rack-side cold plates and specialty coolant. IT raises the ticket; it does not own the wet work.
- Credential order: Finish the trade baseline first (pipefitting ticket and/or HVAC + EPA 608 where refrigerant is in scope). Manufacturer CDU / cold-plate classes sit on top; they are not a substitute.
- Three loops, one boundary: We follow ASHRAE’s naming: facility water (FWS), technology coolant at the IT gear (TCS), condenser water at heat rejection (CWS), with the CDU as the usual handoff between building water and rack coolant.
- What we do not invent: No wages, campus FTE, gallons or PUE on this page. Those are site-specific or unpublished in the footnotes we cite.
Proof points (footnotes)
- Three named loops: ASHRAE TC 9.9 describes a Technology Cooling System (TCS) at the IT equipment, a Facility Water System (FWS) on the building/campus side, and a Condenser Water System (CWS) at heat rejection. A Coolant Distribution Unit (CDU) is the usual demarcation between TCS and FWS.
- CDU job list: ASHRAE’s water-cooled-servers white paper lists CDU functions: transfer heat from TCS to FWS, circulate TCS coolant, allow a TCS coolant other than water (e.g. refrigerant or engineered fluid), keep TCS supply above room dew point to prevent condensation, hold TCS chemistry separate from FWS, and set a flexible coolant temperature for ITE.
- Dew-point buffer: ASHRAE guidance for CDU temperature control is to keep TCS supply at least 2 °C (3.6 °F) above room dew point so cold plates and manifolds do not sweat inside the server.
- ASHRAE W classes (2021 rename): Thermal Guidelines (5th ed., 2021) renames liquid-cooling facility-water classes with the upper supply limit in the name: W17, W27, W32, W40, W45 and W+. Every class has a 2 °C (35.6 °F) lower limit. W17/W27 are typically chiller/tower with optional water-side economizer; W32/W40 often run without chillers in many climates; W45/W+ target dry cooler / district-heating style rejection.
- Why liquid shows up: ASHRAE TC 9.9’s 2021 liquid-cooling white paper states liquid cooling is becoming a requirement for some high-power SKUs as socket power rises and case temperatures fall, and recommends that future data centers include the capability to add liquid cooling. NREL’s ESIF deck frames traditional air-cooled racks around roughly 1–5 kW and liquid options when rack densities move into the higher tens of kW (their ESIF design target was more than 60 kW per rack).
- EPA 608 boundary: EPA Section 608 / 40 CFR Part 82 Subpart F certifies technicians who maintain, service, repair or dispose of equipment that could release refrigerants. Facility chilled-water, condenser-water and glycol hydronic loops that never open a refrigerant circuit are outside that federal credential; they are pipefitter / steamfitter hydronic work. CRAH coils and chillers that do hold refrigerant stay on the HVAC/R + EPA 608 path.
Numbers below are only what the cited public papers state. Full URLs in Sources.
Skills checklist by trade
Use this to decide who gets the call and what credential to finish first. Cross-check failures on facility systems.
Pipefitter / steamfitter (hydronic & facility water)
- Install and maintain FWS chilled-water / condenser-water / process-water piping, valves, strainers and pumps that feed CDUs and CRAH coils.
- Isolate, drain, flush and pressure-test hydronic branches; leak response on facility loops.
- Glycol / water chemistry handoff with the facility water-treatment plan (FWS quality domain).
- Primary-side (FWS) connections at liquid-to-liquid CDUs: flanges, flexible connectors, isolation valves.
- Does not replace EPA 608: pipefitters do not open refrigerant circuits unless they separately hold 608 and are assigned that work.
HVAC/R technician (refrigerant CRAH / chiller + EPA 608)
- Service CRAH/CRAC units, chillers and any other appliance that contains regulated refrigerants: leak repair, recovery, charging, gauges.
- Hold EPA Section 608 (Type matching the equipment, or Universal) under 40 CFR Part 82 Subpart F.
- Airflow, containment and supply-air temperature control on the air side of hybrid halls.
- May own or share CDU work when the unit uses a refrigerant-bearing heat pump / DX circuit, or when the site assigns mechanical techs to CDU controls; still 608 for any refrigerant open.
- Does not own server cold plates, rack manifolds or OEM TCS chemistry by default.
OEM / liquid-cooling specialty (on top of a trade ticket)
- Vendor or manufacturer courses for a specific CDU, cold-plate manifold, dielectric fluid or immersion tank.
- TCS loop fill, filtration change-out and chemistry to the ITE maker’s spec (stricter than typical FWS).
- Rack-level quick-disconnect service, TCS leak response inside the white space, and IT-side commissioning with the OEM.
- Sits on top of a pipefitter or HVAC/R baseline; it is not a substitute for apprenticeship, state license or EPA 608 where those apply.
How to line up the cooling path
Map the loops on your site
Name which pipes are FWS (facility/campus water), which are TCS (technology / IT coolant behind the CDU), and which appliances still hold refrigerant (CRAH/chiller). ASHRAE’s three-loop naming keeps ownership clear.
Match the failure to the trade
Refrigerant alarm or gauge work → HVAC/R with EPA 608. FWS leak, valve or pump → pipefitter. CDU heat-exchanger / TCS chemistry / cold-plate manifold → typically HVAC or pipefitter plus OEM specialty, never IT alone.
Get the baseline credential first
EPA 608 for any refrigerant circuit (see the EPA 608 guide). Pipefitting apprenticeship / state rules for hydronic FWS work. State electrical license is a separate path for power, not a cooling substitute.
Add OEM liquid-cooling training second
Manufacturer CDU, cold-plate and dielectric courses sit on top of the trade ticket. They do not replace 608 or a pipefitting ticket.
Keep IT out of the wet work
IT owns servers, switch config and software. Cold plates inside a sealed OEM assembly may be OEM/IT vendor service; the facility FWS, CWS and refrigerant circuits stay with the trades.
FAQ
Who works on liquid-cooling CDUs in a data center?
The facility side (FWS piping into the CDU) is pipefitter / steamfitter hydronic work. The mechanical tech path covers refrigerant-bearing CRAH/chillers and any CDU circuit that opens refrigerant. OEM specialty training often covers TCS chemistry, filters and rack manifolds. IT does not own the wet loops.
Do pipefitters need EPA Section 608 for chilled-water loops?
No. EPA 608 covers equipment that could release refrigerants. Facility chilled-water, condenser-water and glycol hydronic loops without a refrigerant open are outside Section 608. If the same person also services CRAH/chiller refrigerant circuits, they need 608 for that work.
What is a CDU, and why does ASHRAE treat it as a boundary?
A Coolant Distribution Unit uses a liquid-to-liquid heat exchanger to separate the Technology Cooling System (TCS) at the IT equipment from the Facility Water System (FWS). ASHRAE lists heat transfer, TCS circulation, optional non-water coolants, dew-point control, chemistry isolation and flexible supply temperature as CDU jobs.
What are ASHRAE W17, W27, W32, W40, W45 and W+?
They are liquid-cooling facility-water supply classes from Thermal Guidelines for Data Processing Environments (5th ed., 2021). The number is the upper supply temperature in °C; every class bottoms out at 2 °C (35.6 °F). They describe what the facility water plant can deliver, not a technician license.
Does liquid cooling replace CRAH units and EPA 608?
No. Many halls stay hybrid: liquid for high-density racks, air handlers for the rest of the load and for humidity control. Any refrigerant work on CRAH/chillers still needs EPA 608.
Who owns server cold plates and rack manifolds?
Those sit on the TCS / OEM side. Facility pipefitters own the FWS into the CDU; HVAC/R owns refrigerant appliances; OEM or vendor-trained techs typically service cold plates, quick disconnects and TCS chemistry. IT raises tickets and protects hardware; it does not become the hydronic or refrigerant crew.
Is OEM liquid-cooling training enough to get hired?
It is a specialty layer, not a substitute. Employers still expect the trade baseline (pipefitting apprenticeship and/or HVAC/R with EPA 608 where refrigerant is in scope) plus site-specific OEM courses for the CDU and TCS they run.