What is heat pumpin construction?

The difference is where the unit exchanges heat. Air-source units trade heat with outdoor air and lose capacity in extreme cold. Water-source units trade heat with a building loop kept in a workable temperature range by a boiler and cooling tower, which is why they suit multi-tenant buildings. Ground-source (geothermal) units use the stable temperature of the earth through a buried loop or wellfield, trading higher first cost in drilling for lower operating cost.

Yes. A reversing valve flips the direction of the refrigeration cycle, so the same coil that rejects heat in summer absorbs it in winter. That is the core appeal of heat pump buildings: one piece of terminal equipment per zone covers both seasons. Air-source units in cold climates often pair with electric or hydronic backup heat for the coldest hours, and that backup is a separate takeoff line.

Sometimes. A ground-source system can eliminate the chiller and most of the boiler plant. A conventional water-source heat pump building still carries a boiler and a cooling tower or fluid cooler to keep the loop in range, just no chiller. Read the plant side of the mechanical drawings before assuming scope has disappeared, because the loop equipment and the hydronic piping that serves it usually remain.