The Heat Pump uses a process that is basically the opposite of a regrigerator compressor to heat up a reservoir of water that is then pumped around the house to heat the rooms. The photo below shows the grey plastic coils laid in a special egg-crate sub-floor which is covered by a screed. There is also a thick layer of insulation below the red plastic sheets to direct the heat upwards. Once the screed is in place almost any form of standard flooring (tiles, carpet, etc.) can be laid on top.
Most underfloor heating designs are restricted to the ground floor. Ours is also built in to the upper floors as well.
This is part of an ongoing series, the earlier parts of which can be seen here and here.