Milo,
Apart from losses to environment and transient conditions, the heat removed from the hot side, is the same as the heat received by the cold side. However to calculate the Uactual you need at least either:
- One Flow
- 4 Temperatures (in fact, the thermodynamic variables that allows to calculate the entalphy difference between inlet and outlet, that for no phase change and known composition it is usually temperature)
- Both Flows
- 3 Temperatures
Or if you have a pure condensing stream on one side (like steam) you need:
- The other side flow, inlet and outlet temperature.
- Operating pressure on the condensing side.
So wonder what it is being calculated "only from one side".