NIST NSRDS 49-2018

CYCLE_D: NIST Vapor Compression 

Cycle Design Program 

Version 6.0

User’s Guide

J.S. Brown

P.A. Domanski

E.W. Lemmon

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NIST NSRDS 49-2018

CYCLE_D: NIST Vapor Compression 

Cycle Design Program 

Version 6.0

User’s Guide

J.S. Brown 

The Catholic University of America

P.A. Domanski

Engineering Laboratory

National Institute of Standards and Technology

E.W. Lemmon

Material Measurement Laboratory

National Institute of Standards and Technology

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September 2018

U.S. Department of Commerce 

Wilbur L. Ross, Jr., Secretary

National Institute of Standards and Technology 

Walter Copan, NIST Director and Under Secretary of Commerce for Standards and Technology

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The National Institute of Standards and Technology (NIST) uses its best efforts to deliver a high-quality copy of the 

Database and to verify that the data contained therein have been selected on the basis of sound scientific judgment. 

However, NIST makes no warranties to that effect, and NIST shall not be liable for any damage that may result from 

errors or omissions in the Database.

___________________________________

NIST Standard Reference Database 23 -(c) 1989, 1991, 1993, 1998, 2003, 2009, 2010, 2012, 2016, 2018 copyright 

by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved. No part of this 

database may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, 

mechanical, photocopying, recording, or otherwise, without the prior written permission of the distributor.

Certain trade names and company products are mentioned in the text to specify adequately the computer products 

and equipment needed to use this software. In no case does such identification imply endorsement or 

recommendation by the National Institute of Standards and Technology of these computer products and equipment, 

nor does it imply that the products are necessarily the best available for the purpose.

Microsoft is a registered trademark, and Windows is a trademark of the Microsoft Corporation. All other brand and 

product names are trademarks or registered trademarks of their respective companies.

National Institute of Standards and Technology 

National Standard Reference Database Series 49-2018

38 pages (September 2018) 

CODEN: NTNOEF

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https://doi.org/10.6028/NIST.NSRDS.49-2018
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ACKNOWLEDGMENTS

Version 1.0 of CYCLE_D, authored by J. Chi, D.A. Didion, and P.A. Domanski, was developed in 1992 under partial 

funding from the Trane Company and the Electric Power Research Institute, with G. Lange and T. Statt managing 

the project. The authors acknowledged helpful suggestions from P. Glamm. J. Wnek made modifications and 

improvements of the graphical user interface in Version 2.0, and J. Schnotale and P.A. Domanski implemented 

thermodynamic charts and line sizing calculations in Version 3.0. For Version 4.0, J. S. Brown extended simulation 

options to include transcritical cycles, cycles with two-stage compression with intercooling, and two and three-stage 

economizer cycles; and E. W. Lemmon provided new thermodynamic charts. The authors acknowledged K. Tchen’s 

assistance in upgrading the graphical user interface, and J. Calm, D. Yashar, B. Dougherty, and T. Watson for their 

testing and comments on the program. For Version 5.0, J. S. Brown upgraded property calculation routines to 

REFPROP 9.0 and made the following program modifications: (1) allow for saturation pressure inputs for both the 

evaporator and the condenser, (2) allow the user to impose refrigerant pressure drops in the evaporator and in the 

condenser, (3) allow the user to specify the compressor isentropic efficiency for each stage for multi-stage cycles, 

(4) allow the user to assign waste heat from motor inefficiency losses to either the evaporator load, suction refrigerant 

vapor, or condenser load, and (5) allow for the optimization of the intermediate pressures for a three-stage 

economizer cycle. Versions 5.1 and 5.1.1 implemented REFPROP 9.1 refrigerant property routines and several new 

single-component and blend refrigerants. For Version 6.0, J.S. Brown implemented blends of up to 10 components 

and upgraded property calculation routines to REFPROP 10.0.
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CONTENTS

INTRODUCTION............................ .....................................................................................................................1

INSTALLATION ........................................................................................................................................................1

System Requirements .......................................................................................................................................1

Installation Procedure........................................................................................................................................1

MODELING APPROACH..........................................................................................................................................1

Refrigerants and Refrigerant Properties ............................................................................................................1

Evaporator and Condenser or Gas Cooler ........................................................................................................1

Compressor ......................................................................................................................................................2

 Economizer(s) and Intercooler...........................................................................................................................3

Suction Line and Discharge Line .......................................................................................................................3

Liquid-Line/Suction-Line Heat Exchanger..........................................................................................................3

Indoor Fan, Outdoor Fan, and Controls ............................................................................................................3

Refrigerant Line Sizing Calculations .................................................................................................................3

Simulation Results ............................................................................................................................................4

Uncertainties of Simulation Results ..................................................................................................................4

USE OF CYCLE_D...................................................................................................................................................5

Specifying User’s Options..................................................................................................................................5

Entering New Input Data....................................................................................................................................7

Refrigerant Tab...........................................................................................................................................7

Cycle Options Tab......................................................................................................................................9

System Specifications Tab ......................................................................................................................11

 Using a Compressor Map .................................................................................................................11

 Entering Data for the Transcritical Cycle ..........................................................................................13

Loading an Existing File with Input Data..........................................................................................................13

Executing a Simulation Run.............................................................................................................................14

Presenting Simulation Results.........................................................................................................................14

Summary Results .....................................................................................................................................14

System Schematic Window .....................................................................................................................15

State Diagram Windows ..........................................................................................................................16

Line Sizing Information ............................................................................................................................17

Saving Input Data ...........................................................................................................................................17

Diagnostic Messages ......................................................................................................................................18

Help Menu ......................................................................................................................................................18

REFERENCES .......................................................................................................................................................19

Appendix A. SINGLE-COMPOUND REFRIGERANTS AVAILABLE IN CYCLE_D..............................................20

Appendix B. PREDEFINED REFRIGERANT BLENDS AVAILABLE IN CYCLE_D..............................................22

Appendix C. COMPRESSOR MAPS....................................................................................................................24

 Compressor Map Formats ...............................................................................................................24

 Preparing a New Compressor Map..................................................................................................25

Appendix D. NOMENCLATURE USED FOR REPORTING SIMULATION RESULTS.........................................27

Appendix E. UNITS, CHECKS AND WARNINGS ...............................................................................................28

Appendix F. CONTACTS .....................................................................................................................................29
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INTRODUCTION

The CYCLE_D model simulates vapor compression refrigeration cycles that use pure refrigerants or blends of 

refrigerants. The model can simulate a basic subcritical or transcritical refrigeration cycle, both with or without a 

liquid-line/suction-line heat exchanger. In addition, the model can simulate a subcritical two-stage economizer cycle, 

a subcritical three-stage economizer cycle, and a subcritical two-stage compression cycle with intercooling.

Calculations are based on refrigerant properties as represented in the NIST Reference Fluid Thermodynamic and 

Transport Properties Program – REFPROP, Version 10.0 [1]. Simulation results are presented in terms of coefficient 

of performance (COP), volumetric capacity, thermodynamic parameters, and thermodynamic charts.

INSTALLATION

System Requirements

Personal computer capable of running Microsoft Windows 7, 8, 10, or XP with Service Pack 3. A hard disk with eight

megabytes of available space. The screen resolution should be set to 800 x 600 or higher to view images in their

entirety. 

Installation Procedure

Execute the CYCLE_D installation file setup.exe with CYCLE_D Setup.msi residing in the same directory. Follow the 

installation instructions. A NIST CYCLE_D Program Group will be created at the end of the installation.

To run the program, double-click on the NIST CYCLE_D icon.

MODELING APPROACH

The basic subcritical or transcritical system simulated by CYCLE_D consists of a compressor, a discharge line, a 

condenser for the subcritical cycle (a gas cooler for the transcritical cycle), an expansion device, an evaporator, a 

compressor suction line, and an optional liquid-line/suction-line heat exchanger. The other subcritical cycles may 

contain a second compressor, one or two economizers, or an intercooler. These other subcritical cycles, however, 

do not include the optional liquid-line/suction-line heat exchanger. The user of the program has to specify the 

refrigerant and provide input data for the above hardware components, except the expansion device, which is 

modeled as being isenthalpic. The user can also specify the power requirements of the indoor fan, outdoor fan, and 

control unit of the system.

Refrigerants and Refrigerant Properties

CYCLE_D includes 75 single-compound refrigerants, which can be selected as the working fluid. These pure 

refrigerants can also be combined to form blends of up to ten components. In addition, CYCLE_D includes 113

predefined blends. See Appendix A for the list of available pure refrigerants and Appendix B for the list of available 

predefined blends. 

CYCLE_D uses REFPROP 10.0 [1] routines for calculating thermodynamic properties of pure refrigerants and 

refrigerant mixtures and applies the default models recommended in REFPROP for property predictions. 

Evaporator and Condenser or Gas Cooler

The evaporator and condenser are represented by specifying the refrigerant temperature (or pressure) in each of the 

heat exchangers. 

The refrigerant temperature (or pressure) in the evaporator can be specified as either a dew-point temperature (or 

pressure) or an average temperature (or pressure). The average temperature (or pressure) in the evaporator is 

calculated as an arithmetic mean of the dew-point temperature (or pressure) and the temperature (or pressure) of 

the refrigerant entering the evaporator. Additionally, the refrigerant superheat at the evaporator exit can be specified.
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The refrigerant temperature (or pressure) in the condenser can be specified to be either a bubble-point temperature

(or pressure), a dew-point temperature (or pressure), or an average temperature (or pressure). The average 

temperature (or pressure) is calculated as an arithmetic mean of the dew-point and bubble-point temperatures 

(pressures). Additionally, refrigerant subcooling at the condenser outlet can be specified.

In addition to specifying refrigerant saturation temperature (or pressure), the user may specify a refrigerant pressure 

drop (or saturation temperature drop) for the evaporator and/or the condenser. The program assigns the entire 

pressure drop to the two-phase refrigerant.

The gas cooler is represented either by specifying the refrigerant pressure or allowing the program to optimize the 

refrigerant pressure, and by specifying the refrigerant exit temperature. Zero pressure drop is assumed in the gas 

cooler. The gas cooler pressure can be either specified or optimized by the program for the maximum coefficient of 

performance. 

The use of an average temperature (or pressure) in the condenser and evaporator as a mean of refrigerant 

temperatures (or pressures) at the end of two-phase processes is a simplification because temperature profile versus 

enthalpy in a two-phase region is not linear, in particular for large-glide zeotropic mixtures. 

Compressor

For a basic subcritical cycle, CYCLE_D provides two options for representation of the compressor: the "Compressor 

Efficiency" option and the ”Compressor Map" option. For other subcritical cycles and for the transcritical cycle, only 

the “Compressor Efficiency” option is available.

The "Compressor Efficiency" option requires input values of isentropic efficiency, compressor volumetric efficiency, 

electric-motor efficiency, and a target system Cooling Capacity, which is the evaporator capacity adjusted for the 

heat added by the indoor coil fan. If the compression process occurs in stages, the isentropic efficiency for each 

stage can be independently specified. If the cycle includes two compressors, their inputs have to be independently 

specified.

If the value used for the electric motor efficiency is less than unity, the entire heat rejected by the electric motor(s)

can be assigned: (1) as an extra evaporator load reducing the capacity available for cooling duty, (2) as heat 

superheating the suction vapor within a hermetic compressor shell before the compressor’s cylinder inlet, or (3) as 

an extra condenser load in a system with a liquid pump, which pumps the liquid refrigerant from the condenser outlet 

to cool the motor and returns the refrigerant to the condenser inlet.

The "Compressor Map" option uses compressor-map correlations, which are typically derived from compressor 

calorimeter tests. Three types of correlations are allowed. They are described in Appendix C. 

The "Compressor Map" option also requires a value for either the system Cooling Capacity or Capacity Multiplier. 

If Capacity Multiplier is specified, its value is used in the simulation as a multiplication factor for compressor capacity 

(calculated by compressor-map correlations) and for indoor and outdoor fan powers (entered by the user). Power 

input to the system control unit is unaffected. If the system Cooling Capacity is specified, the simulations are 

performed for a system with a compressor of identical efficiency characteristics but with adjusted displacement, so 

that the system can provide the specified capacity. The power input to the indoor and outdoor fans and system 

control unit are unaffected by the specified capacity value. 

Compressor-map equations correlate the compressor performance at certain values of the suction superheat and 

condenser subcooling. To allow simulations at user-specified conditions, the following steps and assumptions are 

employed by the model:

• The isentropic efficiency of the compressor is calculated using the compressor-map correlations at userspecified saturation temperatures (or pressures) and at the superheat and subcooling levels used during the 

calorimeter tests. It is assumed that the isentropic efficiency is not affected by the level of superheat, and the 

calculated efficiency value is used in the cycle calculations.

• When calculating the refrigerant mass flow rate, it is assumed that the compressor volumetric efficiency and 

speed (revolutions per minute, RPM) are not affected by the suction vapor superheat. Consequently, the 

refrigerant mass flow rate at the user-specified superheat equals the value of mass flow rate at the superheat 
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set during the calorimeter tests, adjusted for the different specific volume of the suction vapor caused by a 

different superheat.

Economizer(s) and Intercooler

The economizers and intercooler are represented by the refrigerant pressures for these intermediate components. 

For the economizer cycles, the user can specify the intermediate pressures or have them optimized by the program 

for the maximum coefficient of performance.

Suction Line and Discharge Line

The pressure drop in the suction and discharge lines can be specified by assigning a value of the corresponding 

saturation temperature drop of the refrigerant. CYCLE_D assumes the lines are adiabatic.

Liquid-Line/Suction-Line Heat Exchanger

The liquid-line/suction-line heat exchanger (LLSL-HX) is specified by the user by assigning an effectiveness value of 

the heat exchanger. The assignment of zero effectiveness denotes no LLSL-HX in the cycle.

Indoor Fan, Outdoor Fan, and Controls

The auxiliary powers are specified by the user. The indoor and outdoor fan powers are used in the total power 

calculation and as heat in the capacity calculations for the evaporator and condenser. The control unit power is only 

used in the total power calculation.

Refrigerant Line Sizing Calculations 

After cycle calculations have been completed, CYCLE_D can provide sizing information for the compressor suction 

and discharge lines and for the liquid line connecting the condenser and expansion valve. This information includes 

refrigerant velocity and tube lengths for a range of diameters of straight type L copper tubing. 

CYCLE_D calculates refrigerant velocity and tube length using refrigerant state parameters and the mass flow rate 

determined during cycle simulations, and the predetermined pressure drop in the refrigerant lines. For the suction 

and discharge lines, the pressure drops are those specified by the user in the System Specifications tab in terms of 

the refrigerant dew-point temperature drop. For the liquid line, CYCLE_D calculates the line length for the pressure 

drop that would result in bringing the subcooled refrigerant to flashing. The refrigerant tube length is calculated by 

the following equation:

L= 2∙ΔP∙D∙ρ/(f∙G2)

where:

D - tube inside diameter (m)

f - Darcy friction factor

G - refrigerant mass flux (kg/m2)

L - tube length (m) 

ΔP - pressure drop (Pa)

ρ - refrigerant density (kg/m3)

For the Reynolds number (Re) less than 2000, the friction factor f=64/Re for fully developed laminar flow is used [3]. 

The Petukhov’s correlation for friction factor for turbulent flow, f=1/(1.58∙ln(Re)-3.28)2 [4], is used for higher Reynolds 

numbers. The calculations assume lubricant-free refrigerant flowing in adiabatic tubes, and use refrigerant 

parameters corresponding to the average of the inlet and outlet pressures.
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The refrigerant velocity values presented by CYCLE_D are those at tube inlets. Refrigerant velocity varies in a tube 

because of a pressure drop and change of specific volume. The lowest velocity, critical to oil return, is at the tube 

inlet because of the lowest specific volume.

The program does not provide line length values for zero pressure drops; i.e., for zero condenser subcooling for the 

liquid line, and for zero drop in saturation temperatures for the vapor lines. Also, the program does not provide results 

for the liquid and suction lines if the system employs a liquid-line/suction-line heat exchanger.

Note that CYCLE_D performs refrigerant line sizing calculations using several simplifications. The line sizing 

information is provided by CYCLE_D for general orientation and should not be used as strict design criteria for field 

application.

Simulation Results

Simulation results are generated in two categories: (1) for the thermodynamic cycle and (2) for the compressor and 

system. The cycle category presents the results obtained per unit mass of refrigerant circulated by the compressor. 

These results reflect refrigerant parameters only and are not affected by the auxiliary power input to the indoor fan, 

outdoor fan, and controls. 

If the electric motor efficiency is less than unity, the user’s allocation of the waste heat will affect the simulation 

results. The waste heat is calculated by the following equation:

qcomp motor= (1 – ηcomp motor)(h(3) – h(2))

where:

qcomp motor - compressor motor waste heat (kJ/kg)

ηcomp motor - compressor motor efficiency (fraction)

h(3) and h(2) - refrigerant enthalpy at the cylinder outlet and inlet, 

 respectively (kJ/kg)

 (Refer to page 15 for the Summary Results window.) 

Allocation of the waste heat as an extra evaporator load directly reduces the cooling capacity provided by the 

evaporator to its environment by the amount of the waste heat. Allocation of the waste heat as an extra condenser 

load directly increases the heating capacity provided by the condenser to its environment by the amount of the waste 

heat. In this case, cooling of the electric motor is implemented with the refrigerant pumped by a liquid pump from 

the condenser outlet to the motor, and then returned to the condenser inlet. The flow rate of the refrigerant pumped 

by the liquid pump is controlled so the refrigerant enthalpy after absorbing heat from the electric motor equals the 

enthalpy of refrigerant at the compressor outlet.

The allocation of waste heat as an extra evaporator or condenser load does not alter the state parameters of the 

thermodynamic cycle because cycle simulations are constrained by the specified saturation temperature (pressure) 

for the evaporator and the saturation temperature (pressure) and subcooling for the condenser. However, the state 

parameters of the thermodynamic cycle are altered by allocating the waste heat to the suction vapor, which increases 

refrigerant temperature at the cylinder inlet.

The compressor and system results are calculated for the system based on the Cooling Capacity or Capacity 

Multiplier specified by the user. CYCLE_D calculates line sizing information using the thermodynamic parameters 

identified throughout the cycle and the refrigerant mass flow rate needed to obtain the target system capacity. The 

naming convention used for simulation results is explained in Appendix D.

Uncertainties in Simulation Results

Uncertainties in the simulation results are directly related to the uncertainties of the thermodynamic properties 

calculated by REFPROP 10.0 [1] routines incorporated into the CYCLE_D package. CYCLE_D uses the REFPROP 

default property models, which should provide the most accurate predictions. The user should be aware that the 

uncertainties in these models vary somewhat depending on the refrigerant, property, and thermodynamic state. It is 

thus impossible to give a simple, global statement of uncertainties. Even for the most-studied fluids with equations 

of state based on accurate, wide-ranging data, uncertainties are complicated functions of temperature and pressure. 

For details, refer to the original literature sources listed in [1].
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USE OF CYCLE_D

This section explains how to use CYCLE_D: to specify a cycle/system; to run a simulation; to present simulation 

results; and to manage input/output files. If the user needs additional information after going through this tutorial, he 

or she may refer to CYCLE_D's Help menu. 

Once CYCLE_D is installed on your computer, it can be started by double clicking on the CYCLE_D icon. The 

opening screen is displayed first. Click on the OK button to proceed. After doing so, the main CYCLE_D screen 

appears. Figure 1 shows the main screen after a new session has been started and the user has clicked on the 

‘Options’ pull-down menu. 

Figure 1. Main window with activated Options pulldown menu

Specifying User’s Options

To select either SI or Inch-Pound (I-P) units, click the Options/Units menu item. There are three options for units: 

(1) SI with temperatures specified in K, (2) SI with temperatures specified in °C, or (3) I-P with temperatures specified 

in °F.

To select the reference state for enthalpy and entropy calculations [1], click on the Options/Reference State menu 

item, after which Figure 2 appears. Note: the reference states are completely arbitrary; however, three common 

ones are provided: (1) setting enthalpy and entropy values to zero at the selected refrigerant’s normal boiling point, 

(2) ASHRAE convention, or (3) International Institute of Refrigeration (IIR) convention. The first radio button option, 

if selected, uses the REFPROP 10.0 [1] default reference state for that particular refrigerant. If a blend is selected, 

the reference state is applied to the blend and not to each pure component.
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Figure 2. Selecting reference state for enthalpy and entropy calculations

Figure 3 shows the choices for Startup Preferences. When the user sets the option to load an initial file (which 

could be the last file used or a default file), the units and reference state preferences stored in that file become the 

current preferences for a given session. If desired, these preferences can be changed manually using the Options

pulldown menu. Note that loading any existing file anytime during a simulation session will change the current 

preferences for that session to those stored in the loaded file.

Figure 3. Startup Preferences
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Entering New Input Data

To enter new data, the user uses the three tabs titled Refrigerant, Cycle Options, and System Specifications

shown in Figure 1. The sequence of using these tabs does not matter. 

Refrigerant Tab

The Refrigerant tab provides three options: (1) Single-Compound Fluid (Figure 4), (2) Predefined Blend (Figure 

6), and (3) Define New Blend (Figure 8). 

Figure 4. Selecting a single-compound fluid

The user may click the Info button, shown in Figures 4 and 6, to display information for the selected refrigerant. 

Examples are shown in Figures 5 and 7 for a single-compound fluid and predefined blend, respectively. 
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Figure 5. Information for a single-compound fluid

Figure 6. Selecting a predefined blend
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Figure 7. Information for a predefined blend

For the Define New Blend option (Figure 8), refrigerants from the left-hand list can be added to the mixture (righthand list) via the Add button. Refrigerants can be deleted from the mixture by using the Remove button. After 

specifying the mixture and clicking OK, Figure 9 appears. The composition can be modified by typing the appropriate 

values in the boxes and clicking OK. The composition can be specified in terms of mass fractions or mole fractions 

by toggling the combo box. Note that the mass and mole fractions must sum to unity; if they do not, an error message 

will appear. The new mixture can be stored by clicking the Store button. If the mixture is stored in the “~\mixtures” 

subdirectory, it will thereafter appear in the list of predefined blends (Figure 6).

The ‘fluids’ and ‘mixtures’ folders containing REFPROP fluid and mixture files are subdirectories of the folder selected 

for installation of CYCLE_D. For adding new fluids to the program, see Appendix A. 

Cycle Options Tab

The Cycle Options tab presents the following cycle choices (Figure 10):

- Single-stage cycle with or without a LLSL-HX

- Two-stage cycle with an economizer, which includes an option to optimize the intermediate pressure

- Two-stage cycle with an intercooler

- Three-stage cycle with an economizer, which includes an option to optimize the intermediate pressure.

In the example shown in Figure 10, we selected the single-stage cycle with the LLSL-HX of 50 % effectiveness. For 

two-stage economizer cycles, click the Two-Stage Economizer radio button and then click either the Impose 

intermediate pressure radio button or the Optimize intermediate pressure radio button, and either the Impose 

same efficiencies for both stages radio button or the Specify different efficiencies for the two stages radio 

button. The Cycle Options tab will display these options after the Two-Stage Economizer option has been selected
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Figure 8. Defining a new blend

Figure 9. Specifying the new blend composition
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Figure 10. Cycle Options tab

For two-stage compression with intercooling cycles, click the Two-Stage Compression with Intercooling radio 

button and then input the Intermediate pressure.

For three-stage economizer cycles, click the Three-Stage Economizer radio button and then click either the 

Intermediate pressure for high-pressure stage radio button and the Intermediate pressure for low-pressure 

stage radio button, or the Optimize the intermediate pressures radio button, and for both compressors either 

Impose same efficiencies for both stages radio button or Specify different efficiencies for the two stages radio 

button. The Cycle Options tab will display these options after the Three-Stage Economizer option has been 

selected. 

System Specifications Tab

The set of data required for the system specification depends on the simulated cycle type. Figure 11 presents the 

specification input for a single-stage system operating in a subcritical regime. In this example, specify the compressor 

by inputting the compressor isentropic efficiency, compressor volumetric efficiency, and compressor electric motor 

efficiency, all expressed in fractions. The right-hand-side column includes the net system Cooling Capacity, Vapor 

Line Pressure Drop in terms of a drop of dew-point temperature, and Auxiliary Power input.

The gas cooler (transcritical cycle) and compressor maps options shown in Figure 11 are only available for the singlestage, subcritical cycle selected in this example. For multi-stage cycles the System Specifications tab will solicit 

input for intermediate pressure(s), which is not applicable to the single-stage system.

Using a Compressor Map

The compressor map option is available for a basic subcritical cycle. When the Switch to Maps button is clicked, the 

System Specifications window will allow the user to select a compressor from the pulldown menu located in the 

Compressor box, as shown in Figure 12. Once a compressor is chosen, the user selects either the system Cooling

Capacity or Capacity Multiplier option. For simulating a system with a capacity provided by the selected 

compressor, input the value 1 in the Capacity Multiplier input box.

Appendix C explains how to input a new or modify an existing compressor map.
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Figure 11. System Specifications tab for a single-stage, subcritical cycle and efficiency-based 

representation of the compressor

Figure 12. System Specifications tab for a single-stage, subcritical cycle and map-based representation of 

the compressor
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Entering Data for the Transcritical Cycle

If the high-side pressure exceeds the critical pressure of the refrigerant, the high-side heat exchanger will operate as 

a gas cooler. To input data for the gas cooler, click the Switch to Gas Cooler button; a box will appear for specifying 

the refrigerant temperature at the gas cooler exit, and the option to specify the gas cooler pressure or to have it 

optimized by CYCLE_D (Figure 13). Simulating a transcritical cycle is available only for single-stage systems using 

the efficiency-based compressor representation.

Figure 13. System Specifications tab for a single-stage, transcritical cycle and optimization option 

selected for the gas cooler pressure

Loading an Existing File with Input Data

Rather than entering data, the user may opt to open a previously stored input data file and modify it. To open an 

existing file, click on the File/Open menu item, or click the Open File button on the power bar. The window shown 

in Figure 14 will appear. Standard Windows commands are applicable for opening and storing files. After a file is 

selected and opened, the user should modify the input using different tabs, as explained in the previous section for 

inputting new data.
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Figure 14. Opening a previously stored input data file

Executing a Simulation Run

To execute a simulation run, use the Run Simulation pull down menu or click on the Run Simulation button (the 

green arrow located on the power bar). The program will first perform various checks to ensure that the input data 

are valid, and then will proceed with the simulation calculations.

Presenting Simulation Results

Summary Results

When the simulation is complete, the Summary Results window will appear. The corresponding windows showing 

system schematic thermodynamic diagrams and LLSL-HX information can be displayed by using either the Display 

Results pulldown menu or the four buttons located on the right-hand side of the power bar. Figure 15 shows a tile 

with the results windows. The window in the front presents Summary Results for the input data shown in Figures 10 

and 11. This data set is also contained in the file Example 1-stage.mdl, which the CYCLE_D installation module 

places in the RunFiles subfolder. Refer to Appendix D for the nomenclature.
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Figure 15. Results windows 

System Schematic Window

Figure 16 shows an example System Schematic window with simulation results corresponding to the input data 

shown in Figures 10 and 11. To display temperature, pressure, density, enthalpy, or entropy values at the various 

state points, click on the appropriate control button located on the left side of the screen. 

Figure 16. System schematic window
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State Diagram Windows

Figure 17 shows an example P-h State Diagram, and Figure 18 shows an example T-s State Diagram 

corresponding to the input data shown in Figures 10 and 11. The minimum and maximum tick marks were modified 

for both figures within the CYCLE_D program. To modify (1) the axis labels, (2) the minimum, maximum, and intervals 

between major tick marks, (3) the font size, (4) the number formatting, (5) the presence or non-presence of gridlines, 

(6) the specification of the axes in linear or logarithmic scales, and/or (7) the line/symbol type and color for the 

saturated liquid line, saturated vapor line, or process lines, double-click on the desired figure, after which Figure 19

appears. Note: the P-h State Diagram and the T-s State Diagram have to be modified independently of one another.

Figure 17. P-h state diagram

Figure 18. T-s state diagram
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Figure 19. Modifying the P-h or T-s state diagram

Line Sizing Information

Figure 20 shows the content of the Line Sizing Information window corresponding to the input data shown in Figures 

10 and 11. 

Outside Length Vapor Length Vapor Length Liquid

Diameter Suction line Velocity Discharge line Velocity Liquid line Velocity

 (mm) (m) (m/min) (m) (m/min) (m) (m/min)

==============================================================================

 9.520 (1) 1.835E+03 8.268E+00 6.675E+02 9.284E+02 1.403E+01

 12.700 (1) 9.846E+02 3.670E+01 3.583E+02 4.005E+03 7.532E+00

 15.880 (1) 6.130E+02 1.140E+02 2.230E+02 1.216E+04 4.689E+00

 19.050 (1) 4.106E+02 2.969E+02 1.494E+02 3.102E+04 3.141E+00

 22.220 (1) 2.953E+02 6.520E+02 1.074E+02 6.691E+04 2.259E+00

 28.580 (1) 1.732E+02 2.328E+03 6.300E+01 2.316E+05 1.325E+00

 34.920 (1) 1.138E+02 6.322E+03 4.141E+01 9.296E+05 8.706E-01

 41.280 (1) 8.029E+01 1.449E+04 2.922E+01 1.868E+06 6.142E-01

 53.980 (1) 4.619E+01 5.386E+04 1.681E+01 5.644E+06 3.533E-01

 66.680 (1) 2.994E+01 1.504E+05 1.090E+01 1.343E+07 2.291E-01

 79.380 (1) 2.099E+01 3.490E+05 7.636E+00 2.734E+07 1.605E-01

 92.080 (1) 1.551E+01 7.129E+05 5.644E+00 5.003E+07 1.187E-01

104.780 (1) 1.193E+01 1.325E+06 4.341E+00 8.457E+07 9.128E-02

130.180 (1) 7.658E+00 3.768E+06 2.787E+00 2.053E+08 5.859E-02

155.580 (1) 5.327E+00 8.854E+06 1.938E+00 4.243E+08 4.075E-02

206.380 (1) 3.050E+00 3.282E+07 1.110E+00 1.295E+09 2.333E-02

257.180 (1) 1.964E+00 9.194E+07 7.148E-01 3.120E+09 1.503E-02

307.980 (1) 1.361E+00 2.169E+08 4.951E-01 6.504E+09 1.041E-02

==============================================================================

Refrigerant line length and velocity values are for straight type L tubing for

the refrigerant mass flow rate and pressure drops used in the cycle simulation.

that would result in bringing the subcooled refrigerant to flashing.

Refrigerant mass flow rate: 23.0 kg/h

Pressure drops

 Suction line: 10.8 kPa

 Discharge line: 12.8 kPa

 Liquid line: 60.0 kPa

==============================================================================

(1) - Calculations are not provided for a non-adiabatic suction line

 (liquid line/suction line heat exchanger).

Figure 20. Line sizing information

Saving Input Data

To save the current input data set, use either the Save button located on the power bar or one of the options available 

under the File menu item.
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Diagnostic Messages 

CYCLE_D provides stable solutions if the specified cycle operating conditions do not extend beyond the range for 

which REFPROP 10.0 [1] property routines were validated for a particular working fluid (pure refrigerant or refrigerant 

mixture). If CYCLE_D encounters problems during a cycle simulation, it will write diagnostic messages in the file 

ERREF.TXT located in the default folder. In such cases, the interface will display a note that the messages were 

written and will provide the option to read them. Note that refrigerant property routines can become unstable in the 

neighborhood of the critical point. 

Help Menu

Click on the Help menu item to access online help. The help file consists of two tabs: Index and Search. The Index

tab contains detailed help topics arranged alphabetically. The Search tab allows the user to search the contents 

using keywords. Figure 21 shows a list of help topics in the Index tab. 

Figure 21. List of help topics in the Help Index tab
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REFERENCES

[1] Lemmon, E. W., Huber, M.L., McLinden, M.O., 2018. NIST Standard Reference Database 23, NIST Reference 

Fluid Thermodynamic and Transport Properties - REFPROP, Version 10.0. Standard Reference Data Program, 

National Institute of Standards and Technology, Gaithersburg, MD 20899, U.S.A.

https://www.nist.gov/srd/refprop

[2] Performance Rating of Positive Displacement Refrigerant Compressors and Compressor Units, Standard 

CAN/ANSI/AHRI 540-2015. Air-Conditioning and Refrigeration Institute, Arlington, VA.

 http://www.ahrinet.org/App_Content/ahri/files/STANDARDS/ANSI/CAN.ANSI.AHRI_Standard_540_E_2015.pdf

(accessed on September 6, 2018) 

[3] White, M.F., 2005. Viscous Fluid Flow, 3rd edition, McGraw-Hill.

[4] Petukhov, B.S, Kurganov, V.A., Gladuntsov, A.I. 1973. Heat transfer in turbulent pipe flow of gases with variable 

properties. Heat Transfer, Sov. Res., 5, 109–116.
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Appendix A

SINGLE-COMPOUND REFRIGERANTS AVAILABLE IN CYCLE_D

 Short Name Full Chemical NameTcritTcrit

(

°C)(°F)

R-11 trichlorofluoromethane 198.0 388.3 

R-12 dichlorodifluoromethane 112.0 233.6

R-13 chlorotrifluoromethane 29.2 84.6

R-13I1 trifluoroiodomethane 123.3 253.9

R-14 tetrafluoromethane -45.6-50.2

R-21 dichlorofluoromethane 178.3 353.0

R-22 chlorodifluoromethane 96.2 205.1

R-23 trifluoromethane 25.9 78.7

R-32 difluoromethane 78.1 172.6

R-40 methyl chloride 143.2 289.7

R-41 fluoromethane 44.1 111.4

R-50 methane-116.7-82.7 

R-113 1,1,2–trichloro–1,2,2–trifluoroethane 214.1 417.3 

R-114 1,2–dichloro–1,1,2,2–tetrafluoroethane 145.7 294.2 

R-115 chloropentafluoroethane 80.0 175.9

R-116 hexafluoroethane 19.9 67.8

R-123 1,1–dichloro–2,2,2–trifluoroethane 183.7 362.6

R-124 1–chloro–1,2,2,2–tetrafluoroethane 122.3 252.1 

R-125 pentafluoroethane 66.2 151.1

R-134a 1,1,1,2–tetrafluoroethane 101.1 213.9 

R-141b 1,1–dichloro–1–fluoroethane 204.2 399.6

R-142b 1–chloro–1,1–difluoroethane 137.1 278.8

R-143a 1,1,1–trifluoroethane 72.9 163.2 

R-150 dichloroethane 288.5 551.2

R-152a 1,1-difluoroethane 113.3 235.9

R-161 fluoroethane 102.2 215.9

R-170 ethane 32.2 89.9

R-218 octafluoropropane 161.5 72.0

R-227ea 1,1,1,2,3,3,3–heptafluoropropane 102.8 217.0

R-236ea 1,1,1,2,3,3–hexafluoropropane 139.3 282.7

R-236fa 1,1,1,3,3,3–hexafluoropropane 124.9 256.9

R-245ca 1,1,2,2,3–pentafluoropropane 174.4 346.0

R-245fa 1,1,1,3,3–pentafluoropropane 154.1 309.3

R-365mfc 1,1,1,3,3-pentafluorobutane 186.9 368.3

R-290 propane 96.7 206.1

R-C318 octafluorocyclobutane 115.2 239.4

R-600 butane 152.0 305.6

R-600a isobutane or 2–methylpropane 134.7 274.5

R-717 ammonia 132.3 270.1

R-744 carbon dioxide 31.1 87.9

R-1123 trifluoroethylene 58.9 137.4

R-1150 ethylene 9.2 48.6

R-1216 hexafluoropropene 85.8 186.4

R-1224yd(Z) cis-1-chloro-2,3,3,3-tetrafluoroprop-1-ene 155.5 312.0

R-1233zd(E)1-chloro-3,3,3-trifluoroprop-1-ene 166.5 330.1

R-1234yf 2,3,3,3-tetrafluoroprop-1-ene 94.7 202.5

R-1234ze(E) trans-1,3,3,3-tetrafluoropropene 109.4 228.9

R-1234ze(Z) cis-1,3,3,3-tetrafluoropropene 150.1 302.2

R-1243zf 3,3,3-trifluoroprop-1-ene 103.8 218.8

R-1270 propylene or propene 92.4 198.4

R-1336mzz(Z) cis-1,1,1,4,4,4-hexafluoro-2-butene 171.3 340.3

R-E143a methyl-trifluoromethyl-ether 104.8 220.6

R-E170 dimethylether (DME) or ethylene oxide 127.2 260.9

R-E245cb2 methyl-pentafluoroethyl-ether 133.7 272.6

R-E245fa2 2,2,2-trifluoroethyl-difluoromethyl-ether 171.7 341.1

R-E347mcc methyl-heptafluoropropyl-ether 164.6 328.2

CH3CH2CH=CH21-butene 146.1 295.1

Cyclo-C3H6 cyclopropane 125.2 257.3

C2H6O ethanol or ethyl alcohol 240.8 465.4

CH(CH3)3 isobutene or 2-methyl-1-propene 144.9 292.9
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 Short Name Full Chemical Name Tcrit Tcrit

(°C) (°F)

(CH3)2CH(CH2)2CH3 isohexane or 2-methylpentane 224.6 436.2

(CH3)2CHCH2CH3 isopentane or 2-methylbutane 187.2 369.0

CH3OH methanol 239.5 463.0

CH3-3(CH2)-CH3 pentane 196.6 385.8

C3H6O acetone 235.0 454.9

C4H8 cis-butene or cis-2-butene 162.6 324.7

C4H8 trans-butene or trans-2-butene 155.5 311.8

C5F12 perfluoropentane or dodecafluoropentane 147.4 297.3

C5H12 neopentane or 2,2-dimethylpropane 160.6 321.1 

C6H6 benzene 288.9 552.0

C6H12 cyclohexane 280.5 536.9

C6H14 hexane 234.7 454.4

C7H16 heptane 267.0 512.6

C12H26 dodecane 385.0 724.9

SF6 sulfur hexafluoride 45.6 114.0 

The user can add new fluids to CYCLE_D by placing new fluid files into the “fluids” folder. The fluid file must be 

compatible with REFPROP [1], and its name must start with “R” or “r” (e.g., Rnew2.fld or r754.fld will be recognized 

by CYCLE_D as fluid files). The ‘fluids’ folder is a subdirectory of the folder selected for the installation of CYCLE_D.
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Appendix B

PREDEFINED REFRIGERANT BLENDS AVAILABLE IN CYCLE_D

ASHRAE CompositionTcritTcrit

Designation Components (mass %)(°C)(°F)

R-401A R-22/152a/124 53/13/34 106.9 224.3

R-401B R-22/152a/124 61/11/28 104.6 220.0

R-401C R-22/152a/124 33/15/52 111.7 233.1

R-402A R-125/290/22 60/2/38 74.8 166.6

R-402B R-125/290/22 38/2/60 82.1 179.7

R-403A R-290/22/218 5/75/20 84.0 183.2

R-403B R-290/22/218 5/56/39 75.4 167.8

R-404A R-125/143a/134a 44/52/4 72.1 161.8

R-405A R-22/152a/142b/C318 45/7/5.5/42.5 104.3 219.8

R-406A R-22/600a/142b 55/4/41 115.5 239.8

R-407A R-32/125/134a 20/40/40 82.3 180.1

R-407B R-32/125/134a 10/70/20 74.8 166.6

R-407C R-32/125/134a 23/25/52 86.1 187.1

R-407D R-32/125/134a 15/15/70 91.6 196.9 

R-407E R-32/125/134a 25/15/60 88.6 191.5

R-407FR-32/125/134a 30/30/40 82.6 180.7

R-407GR-32/125/134a 2.5/2.5/95 99.5 211.0

R-407HR-32/125/134a 32.5/15/52.5 86.5 187.8

R-408A R-125/143a/22 7/46/47 82.9 181.3

R-409A R-22/124/142b 60/25/15 110.1 230.1

R-409B R-22/124/142b 65/25/10 107.6 225.7 

R-410A R-32/125 50/50 71.3 160.4

R-410B R-32/125 45/55 70.8 159.5

R-411A R-1270/22/152a 1.5/87.5/11.0 88.9 191.9

R-411B R-1270/22/152a 3/94/3 95.7 204.2

R-412A R-22/218/142b 70/5/25 107.1 224.8

R-413A R-218/143a/600a 9/88/3 95.3 203.6

R-414AR-22/124/600a/142b 51/28.5/16.5 111.4 232.5

R-414B R-22/124/600a/142b 50/39/1.5/9.5 110.7 231.3

R-415A R-22/152a 82/18 96.7 206.0

R-415B R-22/152a 25/75 109.9 229.9

R-416A R-124/R134a/600 39.5/59.0/1.5 106.3 223.3

R-417A R-125/134a/600 46.6/50.0/3.4 85.4 185.8

R-417BR-125/134a/600 79.0/18.3/2.7 74.1 165.3

R-417CR-125/134a/600 19.5/78.8/1.7 94.6 202.2

R-418A R-290/22/152a 1.5/96/2.5 95.6 204.2

R-419A R-125/134a/DME 77/19/4 83.5 182.3

R-419BR-125/134a/DME 48.5/48/3.5 91.1 196.0 

R-420A R-134a/142b 88/12 104.8 220.6

R-421A R-125/134a 58/42 82.8181.0

R-421B R-125/134a 85/15 72.4 162.3

R-422A R-125/134a/600a 85.1/11.5/3.4 70.7 159.3

R-422B R-125/134a/600a 55/42/3 82.0 179.6

R-422C R-125/134a/600a 82/15/3 72.1 161.7

R-422D R-125/134a/600a 65.1/31.5/3.4 78.2 172.8

R-422E R-125/134a/600a 58/39.3/2.7 81.1 178.0

R-423A R-134a/227ea 52.5/47.5 99.1 210.5

R-424A R-125/134a/600a/600/601a 50.5/47/0.9/1/0.6 84.7 184.4

R-425A R-32/134a/227ea 18.5/69.5/12 93.9 210.4

R-426A R-125/134a/600/601a 5.1/93/1.3/0.6 99.0 210.2

R-427A R-32/125/143a/134a 15/25/10/50 85.5 185.9

R-428A R-125/143a/290/600a 77.5/20/0.6/1.9 68.0 154.4

R-429A DME/152a/600a 60/10/30 122.0 251.5

R-430AR-152a/600a 76/24 107.0 224.6

R-431AR-290/152a 71/29 91.8 197.2

R-432AR-1270/DME 80/20 97.3 207.1

R-433AR-1270/290 30/70 94.4 201.9

R-433BR-1270/290 5/95 96.3 205.4

R-433CR-1270/290 25/75 94.8 202.6

R-434AR-125/143a/134a/600a 63.2/18/16/2.8 74.1 165.5

R-435A DME/R-152a 80/20 123.1 253.5

R-436AR-290/600a 56/44 115.9 240.6
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ASHRAE CompositionTcritTcrit

Designation Components (mass %)(°C)(°F)

R-436BR-290/600a 52/48 117.4 243.4

R-437AR-125/134a/600/601a 19.5/78.5/1.4/0.6 95.5 203.9

R-438AR-32/125/134a/600/601a 8.5/45/44.2/1.7/0.6 83.8 182.9

R-439AR-32/125/600a 50/47/3 70.3 158.6

R-440AR-290/134a/152a 0.6/1.6/97.8 112.7 234.8

R-441AR-170/290/600a/600 3/55/6/36 118.5 245.2

R-442AR-32/125/134a/152a/227ea 31/31/30/3/5 82.1 179.9

R-443AR-1270/290/600a 55/40/5 96.0 204.8

R-444AR-32/152a/1234ze(E) 12/5/83 106.3 223.4

R-444BR-32/152a/1234ze(E) 41.5/10/48.5 95.7 204.2

R-445AR-744/134a/1234ze(E) 6/9/85 106.1 222.9

R-446AR-32/1234ze(E)/600 68/29/3 86.1 186.9

R-447AR-32/125/1234ze(E) 68/3.5/28.5 85.3 185.5

R-447BR-32/125/1234ze(E) 68/8/24 78.9 174.1

R-448AR-32/125/1234yf/134a/1234ze(E) 26/26/20/21/7 82.7 180.8

R-449AR-32/125/1234yf/134a 24.3/24.7/25.3/25.7 82.1 179.7

R-449BR-32/125/1234yf/134a 25/24/23/27 82.2 180.0

R-449CR-32/125/1234yf/134a 20/20/31/29 86.8 188.3

R-450AR-134a/1234ze(E) 42/58 104.5 220.0

R-451AR-1234yf/134a 89.8/10.2 94.4 201.9

R-451BR-1234yf/134a 88.8/11.2 94.3 201.8

R-452AR-32/125/1234yf 11/59/30 75.1 167.1

R-452BR-32/125/1234yf 67/7/26 77.1 170.8

R-452CR-32/125/1234yf 12.5/61/26.5 74.1 165.3

R-453AR-32/125/134a/600/601a 20/20/53.8/0.6/0.6 88.0 190.3

R-454AR-32/1234yf 35/65 81.7 179.1

R-454BR-32/1234yf 69/31 78.1 172.6

R-454CR-32/1234yf 21.5/78.5 79.3 174.7

R-455AR-744/32/1234yf 3/21.5/75.5 85.6 186.1

R-456AR-32/134a/1234ze(E) 6/45/49 102.7 216.8

R-457AR-32/1234yf/152a 18/70/12 91.3 196.3

R-458AR-32/125/134a/227ea/236fa 20.5/4/61.4/13.5/0.6 91.5 196.8

R-459AR-32/1234yf/1234ze(E) 68/26/6 79.6 175.3

R-459BR-32/1234yf/1234ze(E) 21/69/10 87.5 189.4

R-460AR-32/125/134a/1234ze(E) 12/52/14/22 83.6 182.5

R-460BR-32/125/134a/1234ze(E) 28/25/20/27 88.1 190.5

R-500 R-12/152a 73.8/26.2 102.1 215.7

R-501 R-22/12 75/25 95.9 204.5

R-502 R-22/115 48.8/51.2 81.5 178.7

R-503 R-23/13 40.1/59.9 18.3 64.1

R-504 R-32/115 48.2/51.8 62.2 144.0

R-507A R-125/143a 50/50 70.6 159.1

R-508A R-23/116 39/61 10.2 50.3

R-508B R-23/116 46/54 11.2 52.2

R-509AR-22/218 44/56 68.5 155.2

R-510A DME/600a 88/12 125.7 258.2

R-511AR-290/DME 95/5 97.0 206.6

R-512AR-134a/152a 5/95 112.8 235.1

R-513AR-1234yf/134a 56/44 94.9 202.8

R-513BR-1234yf/134a 58.5/41.5 94.8 202.6

R-515AR-1234ze(E)/227ea 88/12 108.2 226.7
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Appendix C

COMPRESSOR MAPS

Compressor Map Formats

CYCLE_D uses three types of compressor maps for representing the compressor performance. Their format is give 

below.

Compressor map # 1 (based on the ANSI/AHRI Standard 540 [2])

X = B1 + B2∙Ts + B3∙Td + B4∙Ts

2 + B5∙Ts∙Td + B6∙Td2 + B7∙Ts3 + B8∙Td∙Ts2+ B9∙Ts∙Td2 + B10∙Td3

where

B1-B10 = correlation coefficients

Ts = compressor suction dew-point temperature, °C (°F)

Td = compressor discharge dew-point temperature, °C (°F)

X = represents (as designated): refrigerant mass flow rate, kg/s (lb/h) or power input W, (W)

Compressor map # 2 (pressure-based correlation)

X = B1 + B2∙Pd + B3∙Ps + B4∙Pd0.9 + B5∙Ps

0.89 + B6∙Ps∙Pd

where

B1-B6 = correlation coefficients

Ps = suction pressure, kPa (psia)

Pd = discharge pressure, kPa (psia)

X = represents (as designated): cooling capacity, W (Btu/h) or power input W

Compressor map # 3 (modified temperature-based correlation)

X = B1 + B2∙Td + B3∙Td2 + B4∙Ts + B5∙Ts∙Td + B6∙Ts∙Td2 + B7∙Ts

2 + B8∙Td∙Ts2 + B9∙Ts2∙Td2

where

B1-B9 = correlation coefficients

Ts = compressor suction dew-point temperature, °C (°F)

Td = compressor discharge dew-point temperature, °C (°F)

X = represents (as designated): cooling capacity, W (Btu/h) or power input kW
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Preparing a New Compressor Map

In the System Specifications tab, click the Switch to Maps button, and then click the Create New

button shown in Figure C1. 

Figure C1. System Specifications tab showing the Create New and Edit Selection compressor map options 

after a click on the Switch to Maps button

Click the Create New to have the input window displayed for compressor maps (Figure C2). The window has radio 

buttons for selecting one of the three compressor maps and their units. The units selected in the window are 

applicable to the compressor map output, coefficients and temperature unit for which the coefficients were developed. 

This unit selection does not override the units the user selected outside of this window for the input data and output 

of simulation results.

The refrigerant selection in this window will override the prior selection of the refrigerant within the Refrigerant tab 

(Figure 1). The refrigerants available for selection in this window are those available within the Refrigerant tab as 

Single-Compound Fluid or Predefined Blend. If the compressor uses a blend that is not available, the user needs 

to define this blend first using the Define New Blend (Figure 1) button before inputting compressor coefficients. 
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 Figure C2. Input data window for compressor map data (CAN/ANSI/AHRI Standard 540-2015 map 

selected [2])
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Appendix D

NOMENCLATURE USED FOR REPORTING SIMULATION RESULTS

This appendix presents the symbol convention used for simulation results in the order they appear on the printout. 

Self-explanatory output is omitted here. Note that the printout varies somewhat between simulation options.

Thermodynamic Cycle Results

T = temperature

P = pressure

h = specific enthalpy

v = specific volume

s = specific entropy

XQ = mass-based quality

Work = compressor motor energy consumption per unit mass of 

 circulated refrigerant; Work = (h(3)-h(2))/ ηcomp motor

 where ηcomp motor - compressor motor efficiency (fraction)

Qevap = specific evaporator capacity

Qcond = specific condenser capacity

COPc = coefficient of performance in the cooling mode

COPh = coefficient of performance in the heating mode

Two-phase glide, evaporator = temperature difference between saturated vapor and evaporator inlet

Two-phase glide, condenser = temperature difference between saturated vapor and saturated liquid

Condenser superheat = temperature difference between condenser inlet and saturated vapor

P(3)/P(2) = compression pressure ratio

Volumetric capacity, cooling = Qevap/v(2)

Volumetric capacity, heating = Qcond/v(2)

Compressor and System Results

m^3/h or cfm = compressor volumetric output

m^3/h/kW or cfm/ton = (compressor volumetric output) /(cooling capacity 

 of evaporator) {1 ton = 12000 Btu/h}

Total power = sum of powers of compressor, indoor fan, outdoor 

 fan, and controls

COPc,sys = (system cooling capacity)/(total power)

COPh,sys = (system heating capacity)/(total power) 
28

This publication is available free of charge from http://dx.doi.org/10.6028/NIST.NSRDS.49-2018

Appendix E

UNITS, CHECKS AND WARNINGS

There are a number of built-in checks and warnings in CYCLE_D. Efforts have been made in developing the system 

to make the checks self-explanatory. Presented below are: (1) an explanation of consistency in units and (2) some 

examples of the run time checks and warnings.

(1) Systems of Units

Users may select either I-P or SI units.

I-P Units:

By selecting "I-P units," temperatures are entered in °F.

SI Units:

By selecting "SI units," temperatures are entered in °C (SI – Celsius option) or K (SI – Kelvin option).

Common Bases:

In both systems, mass composition and efficiency values are entered as decimals not greater than unity. 

(Note, decimals, not percentages)

(2) Checks and Warnings

The following are examples of checks and warnings built into the CYCLE_D system: 

1. In selecting the number of refrigerants in a new mixture, the number must be from 2 to 10. 

2. If the sum of refrigerant mass (or mole) fractions is greater than unity, an error message is issued. 

3. Compressor isentropic efficiency values must be greater than or equal to 0.05 and less than or equal to unity.

4. Compressor volumetric efficiency values must be greater than or equal to 0.05 and less than or equal to unity.

5. Compressor motor efficiency values must be greater than or equal to 0.05 and less than or equal to unity.

6. The evaporator saturation temperature drop specification is unrealistic.

7. The bubble-point temperature (or pressure) of refrigerant in the condenser must be greater than the dew-point 

temperature (or pressure) of refrigerant in the evaporator.

8. The condenser temperature (or pressure) must be greater than the evaporator temperature (or pressure).

9. The condenser saturation temperature (or pressure) must be less than the refrigerant critical temperature (or 

pressure).

10. The gas cooler refrigerant pressure must be greater than the critical pressure.

11. The intermediate pressures for the two-stage economizer cycle, the two-stage compression with intercooling 

cycle, and the three-stage economizer cycle must fall between the evaporator and condenser pressures.

12. For the three-stage economizer cycle, the intermediate pressure of the low-pressure stage must be below the 

intermediate pressure of the high-pressure stage.
29

This publication is available free of charge from http://dx.doi.org/10.6028/NIST.NSRDS.49-2018

Appendix F

CONTACTS

If you have comments or questions about the database, the Standard Reference Data Program would like to hear 

from you. Also, if you should have any problems with the CDs or installation, please let us know by contacting:

Cindy McKneely

National Institute of Standards and Technology

Office of Data Informatics (ODI)

100 Bureau Drive, MS 8550

Gaithersburg, MD 20899-8550

Phone: 301-975-4332

E-mail: data@nist.gov

If you have questions or problems pertaining to the use of CYCLE_D, contact:

Piotr A. Domanski

National Institute of Standards and Technology

Engineering Laboratory

100 Bureau Drive, MS 8631

Gaithersburg, MD 20899-8631

E-mail: piotr.domanski@nist.gov