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COP is useful heat moved divided by work supplied, and it exceeds one because the machine moves heat rather than creating it. Shifting 12 kW with 3 kW of electricity gives a cooling COP of 4. As a heat pump the same unit delivers 15 kW to the warm side, so its heating COP is 5 - always exactly one more.
Cooling COP
COP = Q(cold) / W
Heating COP
COP = (Q(cold) + W) / W = cooling COP + 1
Because the compressor's electrical input also ends up as heat on the warm side, so it counts as useful output when heating.
About 3-4 for an air-source heat pump in mild weather, 4-5 for ground-source, dropping towards 2 in hard frost.