modelElectricEIR

Information

Model of an electric chiller, based on the DOE-2.1 chiller model and the EnergyPlus chiller model Chiller:Electric:EIR.

This model uses three functions to predict capacity and power consumption:

These functions take the same form as documented in EnergyPlus v22.1.0 Engineering Reference section 14.3.9.2 (equations 14.231 through 14.233). These curves are stored in the data record per and are available from Buildings.Fluid.Chillers.Data.ElectricEIR. How they are used to compute the adjusted capacity and compressor power can be found in the documentation of Buildings.Fluid.Chillers.BaseClasses.PartialElectric. Additional performance curves can be developed using two available techniques (Hydeman and Gillespie, 2002). The first technique is called the Least-squares Linear Regression method and is used when sufficient performance data exist to employ standard least-square linear regression techniques. The second technique is called Reference Curve Method and is used when insufficient performance data exist to apply linear regression techniques. A detailed description of both techniques can be found in Hydeman and Gillespie (2002).

The model takes as an input the set point for the leaving chilled water temperature, which is met if the chiller has sufficient capacity. Thus, the model has a built-in, ideal temperature control. The model has three tests on the part load ratio and the cycling ratio:

1. The test

     PLR1 =min(QEva_flow_set/QEva_flow_ava, per.PLRMax);
   

   ensures that the chiller capacity does not exceed the chiller capacity specified by the parameter per.PLRMax.
2. The test

     CR = min(PLR1/per.PRLMin, 1.0);
   

   computes a cycling ratio. This ratio expresses the fraction of time that a chiller would run if it were to cycle because its load is smaller than the minimal load at which it can operate. Note that this model continuously operates even if the part load ratio is below the minimum part load ratio. Its leaving evaporator and condenser temperature can therefore be considered as an average temperature between the modes where the compressor is off and on.
3. The test

     PLR2 = max(per.PLRMinUnl, PLR1);
   

   computes the part load ratio of the compressor. The assumption is that for a part load ratio below per.PLRMinUnl, the chiller uses hot gas bypass to reduce the capacity, while the compressor power draw does not change.

The electric power only contains the power for the compressor, but not any power for pumps or fans.

The model can be parametrized to compute a transient or steady-state response. The transient response of the chiller is computed using a first order differential equation for the evaporator and condenser fluid volumes. The chiller outlet temperatures are equal to the temperatures of these lumped volumes.

Optionally, the model can be configured to represent heat recovery chillers with a switchover option by setting the parameter have_switchover to true. In that case an additional Boolean input connector coo is used. The chiller is tracking a chilled water supply temperature setpoint at the outlet of the evaporator barrel if coo is true. Otherwise, if coo is false, the chiller is tracking a hot water supply temperature setpoint at the outlet of the condenser barrel. See Buildings.Fluid.Chillers.Examples.ElectricEIR_HeatRecovery for an example with a chiller operating in heating mode.

References

• Hydeman, M. and K.L. Gillespie. 2002. Tools and Techniques to Calibrate Electric Chiller Component Models. ASHRAE Transactions, AC-02-9-1.
• EnergyPlus v22.1.0 Engineering Reference

Parameters

Connectors

Components

Revisions

• March 12, 2015, by Michael Wetter:
  Refactored model to make it once continuously differentiable. This is for issue 373.
• Jan. 9, 2011, by Michael Wetter:
  Added input signal to switch chiller off.
• Sep. 8, 2010, by Michael Wetter:
  Revised model and included it in the Buildings library.
• October 13, 2008, by Brandon Hencey:
  First implementation.