This study looked at how heat pumps can be used in older apartment buildings to reduce carbon emissions from heating. By studying data from over 50 heat pumps in homes, they found that the temperature of the building and the heat pump system affect how well the heat pump works. They tested a heat pump system in a 30-dwelling apartment building that used both air and ground heat sources. The system had a good performance with a seasonal performance factor of 3.25 in its first year, and only needed a gas boiler for 27% of the time. This research shows that it is possible to upgrade older buildings with heat pump systems, even if they need high temperatures.