It is a device used for air conditioning in winter i.e. heating in winter. In heat pump the energy is supplied to the machine. A heat pump operates between the temperature of surroundings and a temperature above that of surroundings. It is just the reverse of air conditioner used for air conditioning in summer. In this, evaporator is kept outside and condenser is kept inside the room to be heated.
(COP)heat pump = Heat effect / Work input
= T1/ (T1-T2)
=1+ T2/ (T1-T2)
=1 + (COP)refrigerator