Liquid-cooling retrofit economics in an existing hall

Reading order

Start with the hall that already exists, not with a new-build density slide. Write whether the file is about rear-door exchangers in an air hall, a cold-plate loop that needs a coolant-distribution unit, or a full plant replacement. IEA 4E’s February 2026 report says the most significant capital advantage of liquid cooling in a new plant is densification — a smaller building footprint — and then says that advantage does not apply in a retrofit. Do not paste a new-build “capex per megawatt” bar onto an existing Kista or Akalla floor.

Then name the density the existing plant can actually reject. ASHRAE’s 2021 paper writes that a 40 to 50 kilowatt rack can ask for up to 5,000 cubic feet per minute, while a best-in-class raised-floor tile is 1,900. It also writes that fan power, once below 2 percent in many servers, is again 10 to 20 percent on some denser machines, and that socket power moving through 300 watts toward 400 watts makes standard 1U and 2U air servers more difficult. Those are physics cells. They are not a Swedish invoice.

Only then open the economic papers and the Swedish reporting door. IEA 4E publishes a modelled 8 / 30–40 / 10–21 percent savings stack and a private-discount-rate threshold around 20 kilowatts per rack. The IEA’s April 2026 Key Questions paper publishes a global 40,000 to 50,000 US dollars per kilowatt capital band that includes IT equipment. Lag (2025:570), already owned on the reporting page, is a 500 kilowatt installed-IT filing duty from 1 July 2025. A filing duty is a compliance cost. It is not a retrofit payback.

• Name retrofit, hybrid row or full plant replacement before any payback.
• Keep the 20 kW IEA 4E private-rate cell off a Swedish invoice.
• A 5,000 cfm ASHRAE airflow is not a raised-floor guarantee in Kista.
• The parent adoption page already owns the Nordic liquid path.

What a retrofit-economy cell actually is

A retrofit-economy cell is a dated comparison between the hall you already have and the loop you would add. IEA 4E writes that current use of liquid cooling remains low, that 48 percent of operators who use it apply it in less than 10 percent of their racks, and that the most cited barriers are lack of standardisation (39 percent), high initial costs (38 percent) and concerns about long-term reliability (35 percent). Those survey shares are not a Swedish contractor quote.

The same report separates new-build densification from retrofit. A modelled 10 percent data-centre capital reduction when rack density doubles from 10 to 20 kilowatts is written as a new-build example. The retrofit paragraph says capital offset and densification do not apply, so the private-rate threshold around 20 kilowatts per rack is the remaining economic sentence. At societal discount rates the report says liquid cooling is likely economical well below 20 kilowatts, but it also says that gap has not been quantified for a named hall. Do not print the societal sentence as a Swedish subsidy.

ASHRAE’s 2021 paper is a physics and product paper. It writes that liquid-cooled solutions allow a reduction of PUE to less than 1.1 and that warm-water cooling minimises or eliminates chillers. That is committee language about a design family. The Green Grid’s WP#49 and ISO/IEC 30134-2, already in this register, remain the PUE definition door. A PUE below 1.1 is not a measured Swedish retrofit result and not a licence to skip the water-and-cooling file.

The IEA’s April 2026 Key Questions paper is a later global capital and density paper. An advanced rack the size of a large refrigerator could, by 2027, have peak power demand equivalent to 65 households. AI data centres need to evacuate heat equivalent to 30 natural-gas boilers per server rack, and a single rack can weigh more than a pick-up truck. Those images are IEA teaching sentences. They are not a Swedish floor-loading certificate and not a municipal elevator rating.

What named primary sources show

IEA 4E’s February 2026 EDNA report shows the retrofit sentence, the private-rate 20 kilowatt cell, the 8 / 30–40 / 10–21 percent savings stack, the 39 / 38 / 35 percent barrier shares and the 48 percent “less than 10 percent of racks” row. The IEA’s 16 April 2026 Key Questions paper shows the eleven-times and fourfold density sentences, the 65-household peak image and the 40,000 to 50,000 US dollars per kilowatt capital band including IT.

ASHRAE’s 2021 white paper shows the requirement language, the 40–50 kilowatt / 5,000 cfm versus 1,900 cfm tile pair, the 10 to 20 percent fan-power return and the 300-to-400 watt socket inflection. The Green Grid WP#49 and ISO/IEC 30134-2 show what PUE is. Lag (2025:570) and Energimyndigheten’s reporting page show the 500 kilowatt Swedish filing duty. atNorth’s SWE01 page and Meta’s Luleå careers page remain two operator plants, not a controlled retrofit experiment.

A matrix instead of one payback month

The table is a permission table. A filled cell is a claim the named URL can carry. An empty cell means this page will not invent the missing Swedish retrofit quote.

Do not add the IEA 4E 10-to-21 percent savings stack to the 40,000 to 50,000 dollar capital band and call the sum a Kista payback. Those remain different objects from different letterheads.

Common misreads

The first misread is to treat the IEA 4E new-build densification example as a retrofit saving. The report itself separates those sentences. The second is to treat the private-rate 20 kilowatt cell as a Swedish statutory threshold. It is a modelled operator-discount sentence. The third is to treat a PUE below 1.1 as a measured Swedish hall result after a weekend pipe job.

The fourth is to paste the 40,000 to 50,000 dollar IEA capital band, which includes IT equipment, onto a cooling-only contractor quote. The fifth is to treat Meta’s outdoor-air Luleå campus or atNorth’s SWE01 liquid sentence as a controlled before-and-after. The sixth is to treat the 500 kilowatt reporting duty as the economic case for the loop.

What to ask next

If a brief prints one Swedish retrofit payback, ask which named URL uses that month for an existing hall, a hybrid row or a full plant replacement. If the URL only shows a global capital band, a modelled 20 kilowatt cell or a new-build densification example, the brief has already left the source.

Then open the parent liquid-cooling page, the water-and-cooling page and the energy-performance reporting page. Those pages already own the adoption path, the water door and the 500 kilowatt filing. This page only asks whether the economic cells stay on their own rows.

1. Is the file a retrofit of an existing air hall, or a new-build density slide?
2. Which IEA 4E sentence is in play — private-rate 20 kW, retrofit-no-offset, or new-build densification?
3. Has anyone treated USD 40,000–50,000/kW including IT as a cooling-only Swedish quote?
4. Is a PUE below 1.1 being treated as a measured Swedish result?
5. Has a hall payback month been invented?

What this does and does not prove

This page proves that IEA 4E already publishes a retrofit sentence that strips densification out of the capital story, and that ASHRAE already publishes airflow and socket cells that can break an existing raised floor. It proves that the April 2026 IEA capital band includes IT equipment.

It does not prove how many months a named Swedish hall will take to recover a pipe job. It does not invent a Swedish statutory 20 kilowatt threshold. It does not treat a reporting duty as a payback.

Empty cells stay empty. Until a later primary source names a Swedish hall’s retrofit with dated invoices and a boundary, the economy stays a method, not a census.