Model for an indirect steam heated absorption chiller based on
performance curves. The model uses performance curves similar to
the EnergyPlus model `Chiller:Absorption:Indirect`

.

The model uses six functions to predict the chiller cooling
capacity, power consumption for the chiller pump and the generator
heat flow rate and the condenser heat flow. These functions use the
performance data stored in the record `per`

. The
computations are as follows:

The capacity function of the evaporator is

capFun_{eva} =
A_{1} + A_{2} T_{eva,lvg} + A_{3}
T^{2}_{eva,lvg} + A_{4}
T^{3}_{eva,lvg}.

The capacity function of the condenser is

capFun_{con} =
B_{1} + B_{2} T_{con,ent} + B_{3}
T^{2}_{con,ent} + B_{4}
T^{3}_{con,ent}.

These capacity functions are used to compute the available cooling capacity of the evaporator as

Q̇_{eva,ava} =
capFun_{eva} capFun_{con}
Q̇_{eva,0},

where *Q̇ _{eva,0}* is obtained from the performance
data

`per.QEva_flow_nominal`

. Let
`TSet`

. Then, the model computes the part load
ratio asPLR
=min(Q̇_{eva,set}/Q̇_{eva,ava},
PLR_{max}).

Hence, the model ensures that the chiller capacity does not
exceed the chiller capacity specified by the parameter
`per.PLRMax`

. The cycling ratio is computed as

CR =
min(PLR/PLR_{min}, 1.0),

where *PRL _{min}* is obtained from the performance
record

`per.PLRMin`

. 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 when the compressor is off and
on.Using the part load ratio, the energy input ratio of the chiller pump is

EIRP = C_{1} +
C_{2}PLR+C_{3}PLR^{2}.

The generator heat input ratio is

genHIR = D_{1}
+
D_{2}PLR+D_{3}PLR^{2}+D_{4}PLR^{3}.

Two additional curves modifiy the heat input requirement based on the condenser inlet water temperature and the evaporator outlet water temperature. Specifically, the generator heat modifier based on the condenser inlet water temperature is

genT_{con} =
E_{1} + E_{2} T_{con,ent} + E_{3}
T^{2}_{con,ent} + E_{4}
T^{3}_{con,ent},

and the generator heat modifier based on the evaporator inlet water temperature is

genT_{eva}=
F_{1} + F_{2} T_{eva,lvg} + F_{3}
T^{2}_{eva,lvg} + F_{4}
T^{3}_{eva,lvg}.

The main outputs of the model that are to be used in energy
analysis are the required generator heat `QGen_flow`

and
the electric power consumption of the chiller pump `P`

.
For example, if the chiller were to be regenerated with steam, then
`QGen_flow`

is the heat that must be provided by a steam
loop. This model computes the required generator heat as

Q̇_{gen} =
-Q̇_{eva,ava} genHIR genT_{con} genT_{eva}
CR.

The pump power consumption is

P = EIRP CR
P_{0},

where *P _{0}* is the pump nominal power obtained
from the performance data

`per.P_nominal`

. The heat
balance of the chiller isQ̇_{con} =
-Q̇_{eva} + Q̇_{gen} + P.

The equipment performance data is obtained from the record
`per`

, which is an instance of Buildings.Fluid.Chillers.Data.AbsorptionIndirectSteam.
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).

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

- November 26, 2019, by Michael Wetter:

Revised implementation and documentation. - July 3, 2019, by Hagar Elarga:

First implementation.

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