Cascade is a 200 m² edge data hall — 42 kW of IT held in ASHRAE A1's 18–26 °C band by a CRAH on a 13 °C chilled-water loop — with two 250 m² office floors next door on radiators, one glazed to the south and one facing north with the bigger envelope. The arrangement is the one Danfoss's Impact paper describes at the Westin Building Exchange in Seattle, where two pipes carry the colocation centre's 18 °C return across the street and a heat pump lifts it to 54 °C for Amazon's headquarters: here the CRAH's return water goes to a water-source heat pump's evaporator first, the chiller finishes what the heat pump did not take, and the heat pump's condenser feeds the two floors on a 54 → 35 °C heating curve. Three blocks on one water ring, and the ring conserves: what the chiller makes plus what the heat pump takes is what the CRAH moved, every week of the year.

The A/B is the same heat pump on outside air. The machine is the catalog's Danfoss VZH052 inverter scroll — read from the maker's own selector, its eighteen published speed steps setting what it draws at part load — a 30 kW class unit, and on Seattle's year it puts 55.2 MWh into the offices' radiators either way. On the loop it sees 18 °C water every hour of the year and does it for 7.6 MWh of electricity — a seasonal COP of 7.3; on air it sees Seattle's winter, loses capacity on the cold mornings, and does it for 17.9 MWh at 3.1, leaving the north floor 15 hours short where the loop-source plant leaves it 8. The saving is counted twice, which is the whole economy of the arrangement: the heat pump's own 10.3 MWh, and the 5.1 MWh the chiller no longer spends making the 48.5 MWh of cooling the heat pump took off the loop for it. The site — CRAH fans, chiller and heat pump — reads 100.5 against 115.8 MWh, thirteen per cent, on a hall that rejects 378 MWh a year and hands the offices 13 % of it. Westin's loop was designed to heat almost half a million square metres; the arithmetic per kilowatt is this one.

What it cost to learn. The first draft put the radiators on a trickle — 0.25 kg/s for a 30 kW bank, a 29 K drop at the rating — and two things went wrong at once: the north floor read nine kilowatts short on a 46 °C shoulder-season flow, because a radiator's output is its mean water temperature and a slow flow leaves cool; and the heat pump, handed the sum of two nearly shut valves, spent thirteen hours a week with no converged state to run at. Doubling the flow to a bank's 0.5 kg/s held the floor to one unmet hour and the plant to none. The air-source variant then found the same fault at a larger scale — 705 hours a year on which the radiators' valves handed it a trickle, the condensing temperature ran past the map's 65 °C ceiling even at the compressor's floor, and the hour failed — and the fix is what a real unit does: a high-pressure cutout. The floor read is clipped to the envelope's condensing ceiling and the machine cycles from there; where no capacity sits under the ceiling the switch trips on start, the hour is the machine off with its water passing through, reported short, and the valve opens on the cold return. Zero failed hours on either source. On the loop the offices ride the summer on their windows, 3 air changes an hour when it helps, peaking at 28.4 °C; there is no cooling machine on that side, and the case does not pretend one.

What it reads on Seattle

Heat delivered	55.2 MWh at the offices' radiators — 22.8 south, 32.5 north — on a 54 → 35 °C curve
Heat pump	7.6 MWh on the data-hall loop, seasonal COP 7.3; 17.9 MWh on outside air, COP 3.1 — the same Danfoss VZH052 inverter
Chiller	329.7 MWh of cooling on 51.2 MWh with the heat pump taking 48.5 MWh off the loop; 378.2 on 56.2 without
Site	100.5 MWh against 115.8 — 15.4 MWh (13 %) a year, a third of it the chiller's
Data hall	26.0 °C held on 42 kW of IT, no unmet hour; 378 MWh rejected, 13 % of it recovered
Offices	20.0–28.4 °C south, 19.8–27.7 north; unmet heating 0 / 8 hours on the loop, 0 / 15 on air; summer on the windows

What it taught

• A data centre's return water is a heat source at 18 °C every hour of the year: a heat pump on it never sees a cold morning, never frosts, and never loses capacity where the heat is wanted.
• The saving is counted twice — the heat pump's own electricity and the chiller's, since every kilowatt-hour the heat pump takes off the loop is one the chiller need not make.
• A radiator's output is its mean water temperature: a bank on a trickle reads short at part load, and hands the plant behind it a flow it cannot converge on — which is what a heat pump's high-pressure cutout is for.
• The data hall rejects far more than two office floors can use — 378 MWh against 48 taken. What the neighbourhood can absorb, not what the hall gives off, sizes the arrangement.

The machines

• CRAH, 8 m³/s chilled water — open in the builder
• Water-source heat pump plant, 30 kW class — open in the builder
• Air-cooled chiller, 90 kW class (nine modules) — open in the builder
• Office floor: radiators, 30 kW at ΔT 50 (two of them) — open in the builder

Sources

• Danfoss Impact No. 8, “Data centers: a new lever of flexibility, integration and security” (March 2026) — the Westin Building Exchange / Amazon loop: 18 °C boosted to 54 °C, designed for almost half a million m², 80 GWh projected over 25 years; the Tianjin science park recovering a cluster's cooling-loop heat at 60 % below district heating
• ASHRAE TC 9.9, Thermal Guidelines for Data Processing Environments — the A1 envelope
• EN 442-2 — the radiator law and its exponent
• Danfoss VZH052CJ (R410A) inverter scroll — the polynomial and the eighteen per-speed sets read from Coolselector2, in the catalog
• PVGIS TMY, Seattle

Readings of the shipped model on the building's own PVGIS typical meteorological year; engineering estimates from catalog data and published correlations. The building runs on every plan, including Free, a few times a day.