"World's largest heat pump" is a 🇫🇮 lämpöpumppu (the only Finnish word I know, don't ask)And in the competition for largest heat pumps, it is a bit like the Olympics: with many subcategories (heat source), there are many winners

'Europe's largest heat pump' to be installed in Vienna

(: sewage)

Not one, but 6 giant heat pumps will harvest heat from the Vienna waste water treatment plant to provide 90°C heat to the district heating (that also uses waste heat from a candy factory)

https://www.derstandard.at/story/2000143180017/europas-groesste-waermepumpe-holt-energie-aus-wiens-abwasser

more on heat pumps in combination with district heating:

https://www.bbc.com/future/article/20230131-can-city-dwellers-ever-have-heat-pumps

I've been to Drammen in Norway where they use the ice cold water from the Oslo Fjord as heat source for the district heating. I didn't freeze.

https://www.bbc.com/news/business-31506073

Helsinki has a 126 MW heat pump in operation since 2006:

https://www.helen.fi/en/about-us/energy/energy-production/power-plants/katri-vala-heating-and-cooling-plant

and there's another one under construction in Helsinki that should be operational by the end of next year:

https://www.hel.fi/fi/uutiset/helen-rakentaa-eiranrantaan-uuden-lampopumppulaitoksen

Aalborg has tendered for a 100 - 125 MW seawater heat pump for its district heating:

https://dbdh.dk/aalborg-forsyning-puts-denmarks-largest-seawater-heat-pump-out-to-tender/

Stockholm a combination of heat pumps harvesting heat from purified waste water totalling a whopping 225 MW,
PLUS 6 sea water heat pumps - add another 180 MW!

https://smartcitysweden.com/best-practice/401/stockholm-innovates-district-heating-with-new-solutions-and-renewable-sources/

a modest 3,2 MW waste water heat pump in Vancouver , being expanded to 9,9 MW

http://www.falsecreeksouth.org/2021/02/17757/

A 25 MW waste water heat pump in Utrecht
https://www.eneco.nl/en/about-us/what-we-do/sustainable-sources/heat/heat-pump-at-utrecht-sewage-treatment-plant/

The examples are multiplying - as with heat pumps, which use 1 unit of electricity to produce 3-4 units of heat to supply the district heating:
Helsinki is a world leader, with a 500 MW seawater heat pump system under construction:

https://www.bloomberg.com/news/articles/2022-10-18/helsinki-utility-finds-a-surprising-heat-source-icy-seawater

Water works with heat pump in Frederiksberg (don't know the capacity, yearly output is 40 GWh of heat)

https://www.frb-forsyning.dk/om-os/nyheder/byggeriet-af-danmarks-foerste-hoejhusvandvaerk-starter?PID=18090&M=NewsV2&Action=1

Hamburg : 60 MW heat pump (4 x 15 MW) using waste water to heat district heating

https://www.pv-magazine.com/2023/06/01/hamburg-to-deploy-large-scale-heat-pumps-in-wastewater-heat-project/

50 MW heat pump system for Esbjerg using the Wadden Sea as a heat source to heat the district heating system - and with its flexibility in electricity use helps integrate wind power & balance the grid

https://www.man-es.com/discover/esbjerg-heat-pump

Mannheim, (for now) leading in the 'river' heat source category with a 20 MW heat pump

https://www.mvv.de/ueber-uns/unternehmensgruppe/mvv-umwelt/aktuelle-projekte/mvv-flusswaermepumpe

Berlin : 75 MW waste water heat pumps under construction:

https://www.linkedin.com/pulse/heat-pumps-action-berlins-sustainable-future-karim-amin-scqif

Kiel using sea water in the Kieler Fjord:

https://www.stadtwerke-kiel.de/privatkunden/nachhaltigkeit-soziales/waermewende-kiel/dekarbonisierung-der-kieler-fernwaerme

Köln / Cologne getting ready for some 'chaleur de cologne' and to take over the lead from Mannheim (from the same river) with the world's largest river heat pump: 150 MW

https://www.rheinenergie.com/de/unternehmen/newsroom/nachrichten/news_71240.html

25 MW heat pump now in operation in Stuttgart

https://www.enbw.com/presse/grosswaermepumpe-liefert-fernwaerme-fuer-10-000-haushalte.html

"Wrompa" is Poland's largest heat pump: once operational, it will be able to transfer 12.5 MW of heat from wastewater to the district heating system (which is currently 100% coal-based)

https://www.gov.pl/web/climate/wrompa---heat-pump-in-wroclaw

60 MW heat pump for Flensburg’s district heating, using sea water as heat source

https://www.stadtwerke-flensburg.de/foerdepost/presse/grosswaermepunpe-johanson-controls
https://www.ndr.de/nachrichten/schleswig-holstein/Stadtwerke-Flensburg-bestellen-riesige-Meerwasser-Waermepumpe,waermepumpe204.html