Gas and diesel boilers have been the most used systems for heating the Domestic Hot Water (DHW), especially in processes where the temperature ranges between 60ºC and 90ºC. With the appearance of the heat pumps which they use as rCO2 coolant, it is possible to reach these temperatures with high performance.
More information:
https://www.caloryfrio.com/calefaccion/bomba-de-calor/bomba-de-calor-para-consumos-elevados-acs-mediante-refrigerante-co2.html