modelSmallScaleCHP_L1_idContrMFlow_temp

Information

1. Purpose of model

This model is a small scale CHP plant with a pump with ideal mass flow control to get a given outlet temperature. It can be chosen if the outlet set temperature is constant or given by an input.

2. Level of detail, physical effects considered, and physical insight

The efficiencies are constant.

The mass flow is calculated based on a heat flow rate and a given constant outlet temperature. There is no volume considered.

There are no pressure losses included (pressures at inlet and outlet are given from the outside).

Overheating, i.e. exceeding the set outlet temperature, can be turned on or off.

The model calculates any mass flow that is necessary to reach the given temperature but limits the mass flow so that no flow reversal occurs and that the given maximum mass flow is not exceeded.

If the specific enthalpy at the inlet exceeds the set specific enthalpy, two cases will be distinguished:

• If the set value for the heat flow rate is below the given small value or overheating is not allowed, the mass flow is set to zero and the specific enthalpy is just passed through the fluid ports.
• Otherwise the maximum mass flow rate is set.

The heat flow rate is always calculated according to the actual specific enthalpies and the mass flow rate.

For more details see the equations.

3. Limits of validity

This model is only valid for ideal controls, i.e. ideally tuned controls with no control errors.

4. Interfaces

T_out_set: set point for outlet temperature

Q_flow_set: set point heat flow rate (negative for producers)

fluidPortIn: inlet for fluid

fluidPortOut: outlet for fluid

5. Nomenclature

(no elements)

6. Governing Equations

if inStream(fluidPortIn.h_outflow)>fluidOut.h then

if -Q_flow_set<Q_flow_small or not allowOverheat then

fluidPortOut.m_flow=0;

fluidPortOut.h_outflow=inStream(fluidPortIn.h_outflow);

else

fluidPortOut.h_outflow=Q_flow_set/fluidPortOut.m_flow+inStream(fluidPortIn.h_outflow);

fluidPortOut.m_flow=-m_flow_max; //maximum mass flow to keep the temperature increase at a minimum

end if;

else

fluidPortOut.h_outflow=fluidOut.h;

fluidPortOut.m_flow=-max(0,min(m_flow_max,-Q_flow_set/(fluidPortOut.h_outflow-inStream(fluidPortIn.h_outflow))));

end if;

Q_flow=fluidPortOut.m_flow*(fluidPortOut.h_outflow-inStream(fluidPortIn.h_outflow));

7. Remarks for Usage

The model is only working properly in design flow direction. Reverse flow is not supported!

8. Validation

(no validation necessary)

9. References

(none)

10. Version History

Model created by Carsten Bode (c.bode@tuhh.de), Dec 2018

Model modified by Jan Westphal (j.westphal@tuhh.de), Jul 2019 (added power port, added boolean for using gas port)

Parameters

Connectors

Components

Contents

Name	Description
ProducerCosts