Method and system for heating

A system for heating a structure, wherein the system comprises

• a first heat pump and a first heat exchanger, the first heat pump being a liquid-to-liquid heat pump, the first heat exchanger being arranged to deliver heat, in a first heating process, from a hot side of the first heat pump to a first hot-side external liquid, the first heat pump being arranged to receive heat from a cold-side external liquid circulating in the ground or a water body;
• and
• a second heat pump and a second heat exchanger, the second heat exchanger being arranged to deliver heat, in a second heating process, from a hot side of the second heat pump to a second hot-side external liquid, the first and second hot-side external liquids possibly being the same and possibly circulating in a common circuit;
• wherein
• the system is arranged to heat the structure via heat exchange with at least the first hot-side external liquid,
• wherein,
• the second heat pump comprises an internal loop in which carbon dioxide is circulated as an internal-loop heat medium, and wherein
• the system comprises a third heat exchanger being arranged to, in said second heating process, cool the internal-loop heat medium to below a critical point of the internal-loop heat medium by heat exchanging the internal-loop heat medium to the cold-side external liquid, the cold-side external liquid as a result being heated.