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:

- A biquadratic function is used to predict cooling capacity as a function of condenser entering and evaporator leaving fluid temperature.
- A quadratic functions is used to predict power input to cooling capacity ratio with respect to the part load ratio.
- A biquadratic functions is used to predict power input to cooling capacity ratio as a function of condenser entering and evaporator leaving fluid temperature.

These curves are stored in the data record `per`

and
are available from Buildings.Fluid.Chillers.Data.ElectricEIR.
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:

- 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`

. - 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. - 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 boiler 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.

- Hydeman, M. and K.L. Gillespie. 2002. Tools and Techniques to
Calibrate Electric Chiller Component Models.
*ASHRAE Transactions*, AC-02-9-1.

- 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.

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