Biogas / Kraft-Wärme Kopplung?

Power heat coupling means that not only the electrical energy generated by a power plant is used, but also the remaining heat energy.

In conventional power plants, the remaining heat energy is referred to as “waste heat” and how waste is disposed of: with river water and through the cooling towers.

In the case of power plants with KWK, the remaining heat energy is passed on as useful heat, e.g. through a district heating network to heat houses or to heat industrial plants.

If the power plant Biogas is driven, it works as well.

How is heat obtained from cold?

That sounds as if not a power plant is meant, but a Heat pump. This is a technique for itself and has nothing to do directly with power heat coupling.

Of course you can do both: with a biogas power plant with KWK generate useful heat and electricity, and with this power drive heat pumps with which you gain additional heat from the environment.