  Improving the rates and distances over which quantum secure keys are
generated is a major challenge. New source and detector hardware can improve
key rates significantly, however it can require expensive cooling. We show that
Twin Field Quantum Key Distribution (TF QKD) has an advantageous topology
allowing the localisation of cooled detectors. This setup for a quantum network
allows a fully connected network solution, i.e. one where every connection has
non zero key rates, in a box with sides of length up to 110km with just 4
cooled nodes, while Decoy state BB84 is only capable of up to 80km with 40
cooled nodes, and 50km if no nodes are cooled. The average key rate in the
network of the localised, cooled TF QKD is more than 30 times greater than the
uncooled Decoy BB84 solution and 0.9 those of cooled Decoy BB84. To reduce the
cost of the network further, switches can be used in the network. These
switches have losses ranging between 1 to 2dB. Adding these losses to the model
shows further the advantages of TF-QKD in a network. Decoy BB84 is only able to
generate fully connected solutions up to 20km if all nodes are cooled for a 40
node network for 1dB losses. In comparison, using TF QKD,70km networks are
possible with just 4 cooling locations for the same losses. The simulation
shows the significant benefits in using TF QKD in a switched network, and
suggests that further work in this direction is necessary.
