A Danfoss listing, from the manufacturer's published data.

Units: SI · US customary

Published specification

Model	Danfoss VTZ054-G (R407C variable-speed hermetic reciprocating, MT)
Refrigerant	R407C
Performance data	AHRI 540 / EN 12900 10-coefficient map
Reference superheat / subcool	10.0 / 0.0 K
Cooling capacity @ 7.2/54.4 °C	11.50 kW
Input power @ 7.2/54.4 °C	5.75 kW
COP @ 7.2/54.4 °C	2.00

The map across its envelope

AHRI 540 / EN 12900 ten-coefficient polynomials in evaporating and condensing temperature, rated at 10.0 K superheat and 0.0 K subcooling; the solver corrects them to the operating superheat and subcooling. Envelope: the manufacturer's 6-sided polygon. It publishes 12 part-load steps (AHRI 540 §5.3.3), which the solver interpolates between. The mass-flow coefficient set is published too, and the solver checks it against the capacity set.

The rating point and three conditions across the published envelope. The whole map — every condition, the envelope and the curves — is in the builder: open this machine in the app. It solves any point inside the envelope, and warns past it.

Open this compressor in the app — the compressor-map tab, with its rating at any condition, its envelope, capacity and power lines and curves plotted, and the refrigerant's pressure–temperature chart a click away; or open the builder and pick it from the catalog picker — the solver runs it with the catalog's own figures, at your design point or across a year of weather.

Same family

All 21 Danfoss VTZ models

How the model reads against this maker's data

Danfoss compressor maps converted from the maker's own selection database	4 677 maps (186 variable-speed with a step per rated speed, 4 427 with a mass-flow set); 553 nomenclature maps; 400 coefficients against the report	the VZH052's 400 coefficients identical to the report's; eighteen family medians between 0.95 and 1.053 of their model number, 543 of the 553 within 10 % (the ten outside are the smallest Maneurop recips, whose numbers are size codes); the closure median on every family between 0.994 and 1.049 (the R407C scrolls at the top, about 5 % over; nearly every other family within 1 %) over 4 427 sets, the three sets that disagree withheld, and the thirteen HHP heat-pump maps left out because their capacity set is a heating capacity (their closure reads 0.73–0.78, and ṁ·Δh + P reproduces it to 3 %); the polynomials substituted exactly, never refitted
Part-load interpolation between published compressor steps	the envelope between 16 steps	0.04 % mean, 0.21 % worst between the knots
A data centre's cooling loop as a heat source: the water-source heat pump against the same machine on air	a full Seattle year and one winter week, both sources	the same 55.2 MWh into the radiators either way; 7.6 MWh of electricity on the loop against 17.9 on air (seasonal COP 7.3 against 3.1 — the inverter's published steps are what the loop-source machine spends most of the year on, at part speed near its best point), and the chiller 51.2 against 56.2 MWh for the 48.5 MWh the heat pump took off the loop — the site 100.5 against 115.8 MWh, 13 % (re-read on 3 Oct 2026: the chiller now holds its envelope's lowest condensing temperature in mild weather, where it had read an extrapolated COP, and the site saving was 15 %). The ring conserves within 2 % (CRAH duty = heat pump take + chiller duty) with the one-hour lag, both plants converge every hour, and the north floor is held to 8 unmet hours where the air-source machine leaves it 15. Before the high-pressure cutout (the row below) the air-source variant failed 705 hours a year. What the guard cannot say: the paper reports no seasonal COP and no per-kilowatt figure, so the machine is the catalog map on both sides and only the arrangement is the anchor. (Until 4 Sep 2026 the plant was a Copeland ZP91KCE run as a flat-scaling inverter emulation and read 9.9 against 19.2 MWh, COP 5.6 / 2.9, the site 12 % down.)
A maker's inverter scroll read from its own selector: the Danfoss VZH052CJ	eighteen speeds; three selector readings at te −10 / tc 30 (1 002, 3 000, 6 000 rpm); four envelope points for the displacement; the rating point and a grid for the cycle closure	capacity and power at each of the three speeds within 0.3 % of the selector's own rows; the three parameter sets close the refrigeration cycle within 0.5 % at the rating point and 3 % across the grid, each step's own sets within 1 %; the implied volumetric efficiency sits inside the scroll band at every envelope point (the same band the VZH088 entry is held to). The map carries the maker's 65 °C condensing ceiling as a polygon, which is what the cutout rule below reads

From the validation page; every row is held by a test.

Listed from published data; a listing's figures are the manufacturer's, the model that runs them is ours. Solver results never depend on who has claimed what.