Parallel Heat Exchangers

When heat exchangers are connected to give parallel flow, the criterion for flow distribution must be specified. This is done in a direct way by entering a three-way valve in front of the two exchangers and setting the relative mass flow rate for one of the outlets. This is in in principle sufficient for a solution. However, to introduce an automatic adjustment for varying heat exchanger load, it is recommended to control the valve by a Valve control. In such a control, a measurement is performed after one of the heat exchangers. The three-way valve is controlled to achieve a specific temperature (secondary circuits) or superheat/subcooling/vapour fraction (refrigerant circuits) at the measurement connector.

For refrigerant circuits it is commonplace to require the same conditions at exit of the two heat exchangers (evaporators/condensers), one set by a valve control, the other with an enthalpy control.

In the template Actual plant heating a laboratory there are two valve controls.

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