The principle is that the hot water flow into the top of the heat exchanger and drain at the bottom of the heat exchanger. Best cold water will flow into the bottom of the heat exchanger flow out at the top of the heat exchanger.
The hot water is flowing into the top of the heat exchanger and flows out the bottom of the heat exchanger. The cold water will flow into the bottom of the heat exchanger and flows out through the top of the heat exchanger.