NBSIR 88-3740

Users Guide to POST - Plant

Operations Simulation Template

George E. Kelly

Daniel R. Clark

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Environment Division

Gaithersburg, MD 20899

March 1988

-QC

100

• U56

#88-3740

1988

c-2

sponsored Dy:

National Bureau of Standards

U.S. Navy Civil Engineering Laboratory

-Research Information Center

fSalionai iiureau of Standards

Gaithersburg, Maryland 20899

USERS GUIDE TO POST - PLANT

OPERATIONS SIMULATION TEMPLATE

NBSIR 88-3740 /\/SS<Lx

Cid'ioo

m.

C-v

George E. Kelly

Daniel R. Clark

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Environment Division

Gaithersburg, MD 20899

March 1988

Sponsored by:

National Bureau of Standards

U.S, Navy Civil Engineering Laboratory

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Stimulating America s Progress

1913-1988

ABSTRACT

A non-proprietary simulation template program named POST (Plant Operations

Simulation Template) has been developed for use with the Lotus 1-2-3*

spreadsheet. The template provides for mathematical simulation of central

heating/cooling plant equipment including boilers, cooling towers, and

centrifugal chillers. It provides methods for configuring a simulation of

a specific physical plant, defining operating conditions and time-dependent

boundary conditions, running simulations, and graphing simulation results.

POST is a flexible and highly portable analytical tool for plant equipment

operators and engineers concerned with efficient operation of physical

plant systems.

This Users Guide provides an overview of POST and its companion template

program SETUP, which is used to define the characteristics of component

models. Information is presented on the menu commands used in POST and

three examples are provided. The examples show how the template program

may be used to simulate the performance of a three-boilers heating plant

and a central cooling plant consisting of two chillers and a cooling

tower. Listings of the actual keystrokes for setting up and running both

simulations are included.

* Release 2 of Lotus 1-2-3 is required. Lotus and 1-2-3 are registered

trademarks of Lotus Development Corporation and are used in this report

as a means of clear identification and neither constitute nor imply

endorsement by the National Bureau of Standards.

iii
TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF TABLES . vi

LIST OF FIGURES vi

CONVERSION FACTORS FROM ENGLISH TO METRIC (Si) UNITS vii

ACKNOWLEDGMENTS viii

DISCLAIMER viii

1. INTRODUCTION 1

2. OVERVIEW 3

3. SETUP AND POST 6

3.1 Setup Worksheet 6

3.2 POST Worksheet 8

The main menu in POST 10

Change 10

Run 14

Display 14

Graph 13

Print 17

Setup 17

Initialize 17

Quit 17

4. EXAMPLE 1: THREE GAS-FIRED BOILERS OPERATING AT IDENTICAL

PART LOAD FACTORS 18

4.1 The Component Models 18

4.1.1 The Boiler Model 18

4.1.2 N-Way Merge [1<N<6] with Heating Load Control Model ... 23

4.2 Setting Up and Running Example 1 25

4.3 Simulation Results 27

Listing 4-1 Complete Procedure for Creating BOILEXPl.WKl .... 28

Listing 4-2 Fuel and Boiler Performance Data 32

Listing 4-3 Simulation Connection Numbers 33

Listing 4-4 User-Defined Variables 35

Listing 4-5 Sample Simulation Outputs and Inputs 36

Listing 4-6 Linear Input Data 37

Listing 4-7 Output Data Set 1 38

5. EXAMPLE 2: SEQUENTIAL OPERATION OF THREE GAS-FIRED BOILERS 39

5.1

The Component Models 3 9

IV
5.2 Setting Up and Running Example 2 40

5.3 Simulation Results 41

Listing 5-1 Outline of Procedure for Generating B0ILEXP2 .WKl . 43

Listing 5-2 Simulation Connection Numbers 45

Listing 5-3 Sample Inputs 47

Listing 5-4 Linear Range for Data Set 1 50

Listing 5-5 Sample Simulation Outputs and Inputs With All

Three Boilers at Full Load 51

Listing 5-6 Data Set 5 52

6.

EXAMPLE 3: TWO CHILLERS AND A COOLING TOWER 53

6.1 The Component Models 53

6.2 Setting Up and Running Example 3 56

6.3 Simulation Results 58

Listing 6-1 Complete Procedure for Creating CHILLEXP.WKl .... 60

Listing 6-2 Simulation Connection Numbers in CHILLEXP.WKl ... 65

Listing 6-3 Periodic Input Range for Data Set 1 in

CHILLEXP.WKl 68

Listing 6-4 Sample Outputs and Inputs 6 9

Listing 6-5 Linear Input 71

Listing 6-6 Output Regions 72

7. CONCLUSION 73

8. REFERENCES 7 5

v
LIST OF TABLES

Table 1. Constants for Determining Temperature Coefficients for

the Heat Capacity of Air and the Products of Combustion

at Constant Pressure 76

LIST OF FIGURES

FIGURE 1. Command Menu Structure in POST Worksheet 76

FIGURE 2. Layout of SETUP Worksheet 77

FIGURE 3. Layout of POST Worksheet 7 8

FIGURE 4. Component Connections for Example 1: Three Gas-Fired

Boilers Operating at Identical Part Load Factors 79

FIGURE 5. Results for Example 1: System Efficiency vs. Building

Load for System of Three Gas-Fired Boilers Running at

the Same Load Factors 80

FIGURE 6. Results for Example 2: System Efficiency vs. Building

Load for System of Three Gas-Fired Boilers Operating

Sequentially 81

FIGURE 7. Comparison of Boiler System Performance for Both Parallel

and Sequential Operation 82

FIGURE 8. Component Connections for Example 3: Cooling Plant System

Consisting of Two Chillers and a Cooling Tower 83

FIGURE 9. Results for Example 3: System COP vs. Chilled Water

Temperature Returning From the Building Load for Two

Different Chiller Operating Strategies 84

vi
CONVERSION FACTORS FROM ENGLISH TO METRIC (Si) UNITS

Physical

Characteristic

To convert from To Multiply by

Length ft m 0.3 048

Area ft 2 m

2 0.0929

Velocity m/ s mph 0.447

Temperature °F °C t c = (t F

- 3 2) /1 .8

Temperature

difference °F °c 0.55535

Energy Btu J 1/055 X 103

Power Btu/hr w 0.293

U-value Btu/hr f

t

2oF W/m2o C 5.678

Thermal

resistance hr ft 2oF/BTu m

2o C/W 0.1761

Pressure in Hg 60°F KPa 3.376

vn
ACKNOWLEDGMENTS

Financial support for this project from NBS and the U.S. Naval Civil

Engineering Laboratory is gratefully acknowledged.

DISCLAIMER

The template programs POST and SETUP described in this report are furnished

by the government and are accepted and used by any recipient with the

express understanding that the United States Government makes no warranty,

expressed or implied, concerning the accuracy, completeness, reliability,

usability, or suitability for any particular purpose of the information and

data contained in these programs or furnished in connection therewith, and

the United States Government shall be under no liability whatsoever to any

person by reason of any use made thereof. These programs belong to the

U.S. Government. Therefore, the recipient further agrees not to assert

any proprietary rights therein or to represent their programs to anyone as other than government programs.

These template programs require the use of Release 2 of Lotus 1-2-3. Lotus

and 1-2-3 are registered trademarks of Lotus Development Corporation and

are used in this report as a means of clear identification and neither

constitute nor imply endorsement by the National Bureau of Standards.

vm
1.

INTRODUCTION

Recent years have seen a tremendous increase in the quantity and quality

of computer programs available to design engineers in all fields. In the

HVAC industry, computer simulation and energy analysis programs have

proven to be valuable tools for improving energy efficiency and comfort

levels, reducing operating costs, and promoting the development of better

heating and cooling system designs and control strategies. Unfortunately,

such programs are often fairly complicated, requiring a long and difficult

learning period to develop the expertise necessary for effective use.

Furthermore, efforts to improve efficiency should not end with system

design. Even the most carefully designed system can be operated inefficiently.

However, little or no assistance has been available to equipment operators

who must make the day-to-day and hour-to-hour decisions on just how to run

a system. Even in large central heating and cooling plants, where minor

inefficiencies can be relatively costly, most decisions still rely heavily

on rules of thumb.

This report describes a computer methodology developed to help central

heating and cooling plant personnel operate a plant more efficiently.

Ideally, such a methodology should exhibit as many as possible of the

following virtues:

1. It should operate on a variety of different microcomputers.

2. It should allow graphical output, so that the numbers generated

can be readily visualized.

3. It should not attempt to take decision-making power out of the

1
plant operator's hands. Rather, it should allow questions to be

posed concerning plant performance and the probable consequences

of operating decisions and provide intelligible answers to these

questions.

4. It should be flexible enough to model the equipment and the

configuration of essentially any physical plant.

5. It should be simple enough to be learned quickly and used

effectively by equipment operators with modest technical

backgrounds and no computer experience.

6. It should be powerful enough to assist in the design of plant

operating strategies.

The methodology described here is a preliminary attempt to meet these

ambitious and sometimes conflicting goals. It is not a free-standing

program, but a template or worksheet for use with a commercial spreadsheet

program. In effect, the spreadsheet program provided a flexible problemoriented language in which the modular simulation program could be

represented easily and compactly (Johansson 1985; Haynes 1985).

Section 2 of this report provides an overview of the two template programs,

SETUP and POST, which are used together to simulate the performance of

heating and cooling plants. The SETUP program is used to tailor generic

models to the specific performance characteristics of actual equipment.

The POST worksheet, whose name stands for Plant Operations Simulation

Template, is used to perform the actual plant systems simulation and to

analyze the simulation results.

2
2 . OVERVIEW

The simulation of a central heating/ cooling plant involves the use of

Release 2 of the spreadsheet program Lotus 1-2-3* and two worksheet files:

a setup worksheet, called SETUP, and a simulation worksheet, called POST.

The first is used to define the characteristics of the system components.

This worksheet file need only be used once to set up models of the

specific equipment found in a given plant. The resulting models are then

moved to the POST worksheet, which is used to run the actual simulations

of the system and to study its behavior under various operating conditions

and strategies.

The component models rely on steady-state equations using a combination of

basic physical laws and polynomial representations. For each type of

component selected, the user is guided through a process of entering data

for a specific piece of equipment. The data required is generally in a

form readily available from equipment manufacturers. For example, the

centrifugal chiller model requires tables of full load capacity and power

consumption at various chilled water and condenser water temperatures, and

\ *Lotus and 1-2-3 are registered trademarks of Lotus Development Corporation

and are used in this report as a means of clear ident if icat iion and neither

constitute nor imply endorsement by the National Bureau of Standards.

3
©

data representing a part-load performance curve. The SETUP worksheet then

uses the spreadsheet program (Lotus 1985) to perform regressions of the

data, inserts the resulting coefficients into the appropriate equations,

and generates "specif ic" equipment models that are tailored to the user's

particular applications.

Once the component models, which represent the equipment in a particular

plant, have been generated, they are transferred to the POST simulation

worksheet. Next, the variables in the system must be identified and the

connections between components must be specified. This is done by

assigning a unique number to each variable in a given category, and the

same number to any two or more variables which represent the same physical

quantity. For example, each temperature has a name consisting of the

characters "TEMP." followed by a number. The inlet and outlet water

temperatures on the condenser side of a chiller might be assigned the

numbers 1 and 2, making their names TEMP.l and TEMP. 2. If the condenser

water flows directly into a cooling tower, the cooling tower inlet water

temperature would also be assigned the number 2 and its name would also

become TEMP. 2. POST would then make the necessary connection to pass

information from the chiller model to the cooling tower model.

When all connections between components have been assigned numbers, POST

names all the variables and generates two lists of variables in alphabetical

order. One is a list of all the simulation inputs or variables which may

be changed freely by the user. This list typically includes weather

conditions, setpoint temperatures, and on/off control settings. The other

4
list contains all the simulation outputs, or quantities which are calculated

by the system model.

The simulation worksheet provides a fairly large set of commands in the

nested menu form, some of which are shown in Figure 1. These allow the

user to examine the simulation outputs at a single operating point, or

under a range or series of input conditions. Up to five inputs may be

varied simultaneously, and POST provides assistance in setting up columns

of input values. New outputs may be defined by the user in terms of existing

variables, and added to the list of simulation outputs. Graphs of

simulation results can be generated to illustrate the effects of a given

set of inputs or to compare the results of several different operating

strategies.

Section 3 discusses the SETUP and POST template programs in more detail,

while sections 4, 5 and 6 contain actual examples of how these worksheets

may be used to simulate central heating/cooling plants. Section 4 models

the performance of three identical boilers run at the same part load

factor to meet the heating requirements of a building. Section 5 is the same heating plant with the boilers run sequentially. A central cooling plant

containing two identical centrifugal chillers and a cooling plant is

simulated in Section 6. Keystroke by keystroke listings are provided in

Sections 4 and 6 to aid the user in learning how to use the SETUP and POST

worksheets.

5
A brief summary of how well POST meets the design goals described above is

#

I presented in Section 7, entitled Conclusion.

3. SETUP AND POST

The SETUP and POST template programs are used together to model and

simulate the performance of plant systems. SETUP is first used to

generate specific component models which match the performance data

supplied by the user. POST is then employed to link these component

models together into a system, perform one or a series of simulations, and

display the results graphically. Both of these worksheets are described

below

3.1 SETUP Worksheet

The SETUP worksheet is initially provided with a set of "generic" mathematical

models for a fossil fuel fired boiler, a centrifugal chiller, a two-cell

cooling tower, and several merge/control models. Each model consists of a

page of descriptive information which identifies the inputs and outputs of

the component and displays their current values. In addition, each model

includes a region of the worksheet where equations are stored for calculating

the outputs from the inputs. These equations initially contain parameter

values and coefficients which were drawn from various sources and are unlikely to represent the equipment in any particular plant. To generate

models of specific pieces of equipment, data characterizing the performance

of the equipment must be supplied by the user.

6
The SETUP worksheet includes the generic models, storage space for a library of Specific models, and menu-driven procedures for creating

specific models from the generic models and user-supplied data. To

illustrate the process of generating specific models, the setup procedures

for the cooling tower and the centrifugal chiller are described in detail

below.

Figure 2 shows the geography or layout of the SETUP worksheet. Regions

will be referred to by their starting points which correspond to their

upper left-hand corner on the spreadsheet. For example, the index of

previously created specific models starts at region Ql ; it extends to the

right to XI and down as far as required to list all the specific component

models. The generic library, which contains general models of heating/cooling

plant equipment, starts at AA1 , while the specific component model library

starts at EAl . Other regions of the spreadsheet include regions containing

text which describes the information needed to generate specific models

from general models (e.g., the region starting at CA41) , work areas for

intermediate calculations (e.g., the region starting at A1001), and an

area containing macros (region starting at Al). Macros are small spreadsheet

programs which contain sequences of keystrokes and commands which are performed when an item (or command) in a menu is selected.

The SETUP worksheet begins by displaying an index of any previously

created specific models (region Ql) and a menu for selecting a component

whose characteristics are to be specified. When a component (e.g., a

boiler) is selected, the worksheet displays a page of text summarizing the

7
information required to define the component characteristic s, and a menu

allowing the user to either proceed or return to the index menu. If the

user elects to proceed, the general model, stored in region AA1 , is copied

to a transition region starting at CAl . It is then tailored to match the

performance information which the user supplies (e.g., steady state and

part lead efficiency) and the resulting specific model is copied to the

specific library region starting at EAl . The user is also prompted for a

name for this new specific component model which is added to the index in

region Ql . This process may then be repeated for as many specific

component models as the user wishes to generate.

3.2 POST Worksheet

After a suitable library of specific components has been generated using

the SETUP worksheet, the POST worksheet is used to assemble the components

into a model representing a specific plant system. The first step is to

select the desired components by pointing to entries in the library of

specific component models. Models may be used more than once when two or more identical components occur in the system. As each component is

selected, it is copied from the library on the SETUP worksheet into a region starting at FAl of the POST simulation worksheet layout shown in

Figure 3

The next step is to identify the connections among the components of the

system. This is done by assigning numbers (in column EZ) to all the

variables involved in connections, using the same number for any two or more variables which represent the same physical quantity. For example, in

8
a system consisting of one chiller and one cooling tower, three connections

need to be identified. The water temperature leaving the condenser side

of the chiller is assumed to be the same as the water temperature entering

the cooling tower (i.e., piping heat gains are neglected), and these two

variables could both be given the number 1. The water temperature

entering the condenser is the same as the water temperature leaving the

cooling tower, and these temperatures could both be numbered 2. The

condenser water flow rate is the same as the tower water flow rate, and

both could be numbered 3. Alternatively both could be numbered 1. POST

equates variables only when they have the same category name (e.g., TEMP,

FLOW, etc.) as well as the same connection number, so a temperature will

not be equated to a flow rate.

Finally, POST performs an initialization procedure to prepare for carrying

out simulations. Before this procedure, each variable was associated with

a category name consisting of four letters (such as CTRL, FLOW, MISC,

POWR, PRES, TEMP, etc.) followed by a period. During initialization, POST

names each variable by appending a number to the category name, so that

each unique variable has a unique name and variables marked as connections

share the same name. The number supplied by POST is not necessarily the

same as the user-supplied connection number, due to the sorting procedure

that POST uses to assign variable names. POST also generates two lists of

variables, alphabetized by assigned name. One list consists of all the

Simulation Inputs (the region starting at Al), which act as boundary

conditions and may be changed freely by the user. The other list consists

of all the Simulation Outputs (the region starting at II), which are

9
calculated from the input values by the component models. In addition,

#

i # the initialization procedure includes some operations required for

internal bookkeeping purposes.

The Main Menu in Post

The menu commands in POST (see Figure 1) include all the procedures needed

after a system description has been set up and initialized. It allows one

to define sets of varying boundary conditions for driving a simulation, to

run a simulation, to display various categories of information about a

simulation, to define new simulation outputs as functions of existing

variables, and to prepare graphs of simulation results. The top-level

simulation menu of POST is referred to as the main menu. The choices

available from the main menu are Display, Change, Run, Print, Quit, Setup,

and Initialize. These options are discussed, in slightly different order,

in the sections which follow.

Change

In POST, the word "change" refers to modifying the specification of

operating conditions for a simulation. The menu choices under Change are

ErrorTolerance , Linear_Input , Periodic_Input , Output, and Report.

When component connections are specified in a system containing one or more closed loops, iterative calculations are required. In the chiller

and cooling tower example discussed previously, the loop involves the

condenser inlet and outlet temperatures of the chiller and the water inlet

and outlet temperatures of the cooling tower. To achieve a self-consistent

10
solution, the worksheet must be recalculated repeatedly. Before each

recalculation, the current values of all outputs are stored. After each

calculation, the relative change in each variable is computed. Iteration

continues until the largest relative change (Max. Err) is less than the

convergence tolerance (Err.Tol) specified with the Change Error Tolerance

command. A convergence tolerance of 0.01, for example, means that the

largest relative change in any variable from one iteration to the next

must be less than one percent.

The Linear_Input and Periodic_Input commands are used to create columns of

values of selected input variables. In both cases, up to five inputs may

be varied simultaneously. The Linear_Input command generates a column of

values which increase or decrease linearly for each specified variable.

The user must select the inputs to be varied, supply starting and ending

values for each, and set the number of steps from start to end. In

addition to the columns of data, the command writes a column of row numbers ranging from zero to the number of steps.

The Periodic_Input command differs from the Linear_Input command in

several respects. First, it generates a column of "time" values in

addition to the column of row numbers. Second, it generates values which

vary sinusoidally rather than linearly,. The characteristics of each

sinusoid are determined by the maximum and minimum values and the time at

which the maximum occurs. A period of twenty-four hours is assumed.

Third, it also allows values to be entered manually. In the latter case,

for each of the selected input variables, the user can choose either

11
automatic generation of sinusoidal data or manual data entry® This

feature can be used, for example, to specify sinusoidal air temperature

fluctuations in parallel with scheduled setpoint changes and a userdefined load profile or to specify a set of discrete input values, such as different control options, that the user wants to evaluate.

With either command, an output region number must also be specified. The

columns of input data generated by these commands are stored in one of six

regions of the worksheet, determined by a number from 1 to 6

When a simulation is run in Linear_Input or Periodic_Input mode, each row

of inputs is used to calculate all simulation outputs, and some or all of

the output values are written beside the corresponding inputs. The Report

command in the Change submenu is used to specify which outputs are reported. This command permits the use of "wildcards," so that the entry

TEMP* would cause all temperatures to be reported. The default setting

after initialization is the single entry "*", which causes all the outputs

in the simulation to be reported.

The Output command is used to assist the user in processing simulation

results. Its command definitions follow the same form as existing outputs,

consisting of a mnemonic, a name, a formula which generates the value, and

labels representing the units and a verbal definition of the variable.

The Output command provides space for these entries and checks for missing

or illegal entries before adding the new variable to the list of simulation

output s.

12
For example, in the single chiller and single cooling tower system

discussed previously, one might wish to use the Output feature to determine

the system coefficient of performance (COP) under various operating

conditions. System COP can be defined as the cooling power output of the

chiller divided by the total power required to run the chiller, the

cooling tower fan, and the pumps implicitly associated with the system.

Suppose that the cooling power, chiller input power, and cooling tower fan

power have the names P0WR.1, P0WR.2, P0WR.3, respectively, and that pumps

on the evaporator and condenser water lines consume 24 and 20 kilowatts,

respectively. The cooling power is given in tons whereas all other powers

are in kilowatts, so a conversion factor is required for consistent units.

The following spreadsheet expression evaluates to the system COP:

+P0WR.1 *3.516/ (POWR. 2+P0WR.3 +24+20)

The leading plus sign is required to indicate that the expression is a formula rather than an alphanumeric label. When this formula is entered

into a cell of the worksheet, the cell stores the formula but displays its

current value. The Output option allows such a formula to be entered as

the value of a new variable, together with suitable labels describing the

new variable, and takes care of the bookkeeping required to incorporate

the variable into the simulation. Use of this command allows data

analysis to be performed as a simulation is run, rather than after.

13
Run

The Run command invokes a menu of three additional choices: Single_JPoint

,

Linear_Range, or Periodic_Range. The Single__Point option simply iterates

on the current set of simulation inputs until the convergence tolerance is

met. The Linear_Range and Periodic_Range commands iterate on each set of

input values in the appropriate output region, and write the corresponding

output values to the right of the input values.

Display

The Display command is used to bring various portions of the worksheet

into view. The menu choices under Display are Variables, Component,

Linear_Input , Periodic_Input , Output_Region, and Graph. Graph is used for

viewing graphs generated with the Graph command, discussed in a separate

section. The remaining choices are discussed below.

The Display Variables command brings the alphabetical listing of Simulation

Inputs into view (region starting at Al). The user can then examine and

change the current values of one or more inputs, and examine the current

values of the simulation outputs. By "paging right" the user can also

display the Simulation Outputs stored in the region starting at II.

The Component option is used to present the descriptions of the components

which make up the system. Each component is identified by a "page number"

(e.g., *1, *2, etc.) in the top left corner. On selecting Display

Component, the component on page 1 is displayed, and the user is given the

opportunity to enter the page number of any other component in the system.

14
The Display Linear_Input and Display Periodic_Input commands show the

areas where the characteristics of variable inputs are specified when the

corresponding Setup commands are used. Display Output_Region presents an area where the actual values of inputs and outputs for a specific simulation

are stored. Output region 1, 2, 3, and n start, respectively, at A1000,

A1250, A1500, and AX where X=1000 + (n-l)250.

Graph

Graphs of simulation data are invaluable aids to understanding simulation

results and visualizing system behavior. The Graph command yields a

subset of the graph menu options in the host spreadsheet program, with a number of choices made automatically by default. It generates X-Y graphs

from columns of data stored in one or more output regions. The menu

choices under Graph are Use, Edit, Create, SavePic, View, Delete, and

Quit

The Create command sets up a new graph. The user chooses an output

region, and selects columns of data by moving the cell pointer to the

column headings of the independent (X-axis) variable and one or more

dependent (Y-axis) variables. Up to six dependent variables can be

selected, drawing up to six lines on a single graph. Default titles and

legends for the graph are supplied automatically. Two titles appear above

the graph: the title of the simulation, and the output region number.

The X-axis is labeled with the description of the independent variable.

15
Legends below the graph identify each line on the graph by the assigned

name of the dependent variable.

A name for the new graph must also be entered. Any number of graphs can

be created, each with its own name. The Use command allows a graph

already created to be selected by name, and that graph becomes the current

graph. The View command displays the current graph.

The Display command in the Graph menu, mentioned in a previous section, is

equivalent to a combination of the Graph Use and View commands. It

requires a graph to be selected by name before the graph is displayed.

The Edit command allows an existing graph to be modified. The default

titles and legends can be replaced, a Y-axis label can be added, lines can

be erased from a graph or added to a graph, and grid lines can be added to

or removed from a graph.

When a graph is created, all the data must reside in a single output

region. However, the Edit command allows lines to be added using data

from any output region. To compare simulation results stored in different

output regions, the first dependent variable can be selected with Create

and subsequent dependent variables in other output regions can be added

with Edit. This feature could be used, for example, to plot system COP as

a function of wet bulb temperature for two or more simulations involving

different fan speed settings.

16
SavePic stores the current version of the current graph in a file with the

default extension "PIC" for later printing. Delete is used to erase a

graph and its name. Quit returns control to the main menu.

Print

This command causes the spreadsheet program to list the names, values and

definitions of all the simulation input and output variables on a printer.

The user can thus change one or more input values, perform a Single-Point

Run as described above, and use the Print command to obtain a hard copy of

the simulation inputs and outputs.

Setup

The Setup command allows the user to import specific component models

(e.g., boiler, chiller, cooling tower) from the Setup worksheet and to

connect them together to define the desired system simulation model

Initialize

This command initializes the simulation. It appends a number to each

variable's category name and copies all the input variables to the region

of the spreadsheet containing Simulation Inputs and all the output

variables to the region called Simulation Outputs.

Quit

This command on the main menu moves the cell pointer to a page of text and

terminates POST menu control, leaving the user in the host spreadsheet

program "Ready" mode. The page of text provides instructions for re17
starting the main menu of POST, summarizes a few other available POST

commands, and gives the addresses of several regions of potential interest

on the worksheet. Users familiar with the spreadsheet program can then

take advantage of the full set of commands it provides, including graph

options not available in the POST graph menu structure.

4. EXAMPLE 1: THREE GAS-FIRED BOILERS OPERATING AT IDENTICAL PART LOAD

FACTORS

In this example, three identical gas-fired boilers are operated in

parallel to meet a hypothetical building load. Each of the boilers

operates at the same part load factor, which is defined as the boiler's

output divided by its full load capacity or 1, whichever is smaller. All

of the keystrokes required for setting up and running this example are provided in Listing 4-1 along with brief comments. Listings 4-2 through

4-7 provide supplemental information to further assist the user.

4.1 The Component Models

There are only two models used in the simulation—a gas-fired boiler model

and a combination 3-way merge and heating load model. These models are described below.

4.1.1 The Boiler Model

As explained previously, the SETUP spreadsheet contains a number of

18
"generic models" which can be tailored to model the performance of

specific equipment. In the case of the Boiler Model, it is assumed that

the boiler runs continuously (does not cycle on and off) during part load

operation. This is equivalent of assuming that the output of the boiler

is reduced from its full load value by reducing the rate at which fuel,

and possibly combustion air, is supplied to the burner. The user must

supply information on the properties of the fuel, the entering combustion

air temperature, and between three and six sets of CO 2 and flue temperature

data at various part load factors. The combustion efficiency at each of

these part load factors is then calculated and the results used to

determine the efficiency versus part load factor performance curve for the

particular boiler being simulated.

In specifying the fuel, the user is asked to give the atomic ratios of the

following elements making up the fuel: carbon, hydrogen, oxygen, nitrogen,

and sulfur. Letting l:h:o:n:s stand for these respective atomic ratios,

normalized to the carbon atomic ratio, the following equations are used to

model the combustion efficiency of the boiler at each of the user supplied

part load factors.

The ratio, RT, of total combustion air to stoichiometric air is given by

(Kelly, 197 8):

RT = A + B/XC0

2

,

where XC0

2 is the concentration of Carbon Dioxide (C0 2

) in dry

19
flue gas, and

A = 1 - BB/ (4.76AA) ,

B = 100/ (4.76AA) , AA = 1 + 0.25h + s - 0.5o,

BB = 1 + s + 0.5n + 3.76AA.

The latent heat loss, QL, in percent, is then:

QL = (100) (9488. 4)h/ ( (12.011 + 1.008h + 16o +

+ 14.008n + 3 2 .066 s) HHV)

where HHV is the higher heating value of the fuel in

units of Btu/lb.

The mass ratio of stoichiometric air to fuel, A/F, is:

A/F = 137 .3 55 AA/ (12.011 + 1.008h + 16o + 14.008n + 32.066s).

This ratio is used to find the sensible heat loss, QS, given in percent

by:

QS = (100/ HHV) E

;=1

[(1 + A/F) CFj + (A/F) (RT - 1) CAj] (T J

' ss T J A ) rm ' ‘

where CAj and CFj are temperature coefficients for the heat capacity at

constant pressure for air and the products of combustion. They are

20
calculated using:

N.

CA. =

J —

y

k=l

l k,j “Ik

“k

N.m

CFj = —

y

(1.8) -> -1

( j)

a k,j ^k

M,. k-1

where mf^ is the mass fraction of the kth constituent, is the molecular

weight of the kth constituent R is the Universal Gas Constant =

1.98726 Btu/(lb-mole R) , N

m

is the number of constituents in the fuel

mixture, is the nxnnber of constituents in the entering combustion air,

and a, . are constants given in Table 1 for each of the different

*» J constituents, k.

Once the latent heat loss, QL, and the sensible heat loss, QS, are

determined, the combustion efficiency, in percent, at a given part load

factor is found using:

Eff = 100 - QL -QS.

After the combustion efficiency of the boiler is found for each of the

part load factors for which the user has supplied CO

2 and flue temperature

data, the efficiency versus part load factor curve for the boiler is

determined. A second order polynomial of the form:

Y = a^ + a2X +

21
where Y = 1/Eff and X = (1/load factor), is put through the 3 to 6 sets of

Eff versus part load factor data using a least square fit method. This

results in the following equations for the regression coefficients a^ # ,

1

C 1 b12 b13

al =

b

c 2 b 22 b23

c 3 b32 b33

1

b ll C 1 b 13

a2 =

b

b 2i c 2 b

23

b31 c

3 b33

1 hi b 12 C 1 ^

=

b

b 21 b22 c 2

b31 b

3 2

c

3

b u b 12 b

13

b = b21 b 22 b

23

b31 b

3 2 b

33

where

i=l i=l

T is the number of (X,Y) data

sets, and Z indicates the determinate of the Z matrix =

^\-i^22 Z33 + Z12 Z

23 Z31 + Z13 Z32Z21 Z13 Z22 Z31 ~ Z23 Z32Z11

~ Z33 Z21 Z12 for a 3x3 matrix

Since the part load boiler performance curve which results from this process

is a second order polynomial in the variable X, which is l/(load factor)

-

^,

the user should try to provide CO

2 and flue temperature data over the

entire range of load factors of interest. This will minimize the possibility

that the resulting efficiency versus part load performance curve could

take on some unusual and erroneous shape outside the range of data

provided (e.g. , go up instead of down as the part load factor goes to

22
zero). In addition, the user must not provide fictitious data for a load

factor identically equal to zero, since this will result in a divide by

zero error in the spreadsheet. (Use instead a partload factor equal to a

very small value, say 0.001).

4.1.2 N-Way Merge [1<N<6] with Heating Load Control Model

The N-Way Merge with Heating Load Control Model is a very simple model

which assumes that there are N boilers, where N equals 2, 3, 4, or 5,

connected in parallel. Since the total output from the merge is the sum

of the individual boiler outputs, the average load factor for the boiler

system, FLFavg, is given by:

FLFavg = LOAD

FL Out put

^

i

where LOAD is the total heating load on the boiler system and FLOutput^ is

the full load output or capacity of the ith boiler. Assuming the loads on

all of the inlet ports, except the port that is to be controlled, are

known, the boiler corresponding to this controlled inlet port (cp) must

have a part load factor, PLFcalc, given by:

LOAD - Output

^ + Out put cp

PLFcalc =

iFLOutput

cp

LOAD - Out put

^

i FLOutput

cp

23
where " ' " indicates that the sum is over all inlet ports except the

controlled port and Output^ and FLOutput C p are the output and full load

output, respectively, of the boiler corresponding to the central port cp.

This follows from the requirement that the total output from the merge must

equal the Load imposed upon the boiler system by the building.

The user specifies the number of inlet ports corresponding to the number

of boilers in the simulation in order to generate a specific Merge and

Heating Load Control Model for a given simulation. For the example being

considered in this section, N equals 3 and the specific model of interest

becomes a 3-Way Merge with Heating Load Control Model.

When identical boilers are operated at the same part load factor (as in

this example), the output PLFcalc from the N-Way Merge with Heating Load

Control Model should be connected to the part load factor, PLF, input on

one and only one boiler. For all the other boilers, the single PLFavg

output from the merge/ load model should be connected to the PLF inputs on

these boilers. In addition, the Ctrl Mod(e) parameters for all the

boilers should be set to 0 in the Simulation Inputs region of the spreadsheet.

This causes the boilers to use the PLF as their part load factor and not

the fixed parameter PLF set. The use of these simulation input parameters

and the proper connections for PLFcalc and PLFavg will allow the simulation

to converge to the proper solution.

24
4.2 Setting Up and Running Example 1

Listing 4-1 contains all the keystrokes necessary to setup and run the

sample simulation entitled "Three Gas-Fired Boilers Operating At Identical

Part Load Factors." Groups of keystrokes will be referred to as steps,

which are numbered and shown on the left-hand side of this listing.

Setting up and running a simulation involves the following tasks:

- Using the SETUP worksheet to generate specific component models from

generic component models and then saving this new worksheet, preferably

with a different name - say SETUP1. This task corresponds to steps 1 through 11 in Listing 4-1 . Listing 4-2 shows typical natural gas

fuel composition data and six sets of CO

2 and flue temperature data.

- Using the Setup command in the main menu of the POST worksheet,

retrieve the specific component models needed. Make a sketch on

paper (see Figure 4) showing how the inputs and outputs on the

various components are connected to form the desired simulation and

transfer this information to the POST spreadsheet by assigning unique

connection numbers to any two or more variables which represent the

same physical or calculated quantity (i.e., the output of one

component is the input to another). Use the Initialize command in

the main menu of POST to generate unique variable names, which depend

upon the variable’s category and connection number, and to copy all

the input variables to the region of the spreadsheet containing

Simulation Inputs and all the outputs to the region called Simulation

25
Outputs. This task is contained in steps 12 through 30 in Listing

4-1 . The connection between the input and output variables in the

various component models comprising this particular simulation are

shown in Listing 4-3 and are partially discussed in section 4.1.2.

Use the Change command in the main menu followed by the Output

command in the submenu to enter a user-defined variable which may be

useful for analyzing simulation results. Enter an Alt-V to incorporate

this new variable in to the list of Simulation Outputs. Repeat this

process for all additional user-defined variables. Steps 31 through

44 in Listing 4-1 and Listing 4-4 illustrate the setting up the userdefined outputs SysCap and SysEff.

Change one or more input variables or parameters in the section

containing Simulation Inputs. Be sure that the Ctrl Mod(e) parameters

for all the boilers are set to 0 as discussed in section 4.1.2.

Listing 4-5 contains a list of Simulation Outputs and Inputs printed

with the Print command in the main menu. Carry out a simulation

with these new inputs by selecting Run in the main menu and Single_Point

in the resulting submenu. Alternatively, use Change in the main menu

and then either Linear_Input or Periodic_Input to setup ranges over

which one or more input variables are to be varied in either a linear

or periodic manner and an Output_Region (e.g., 1, 2, 3, etc.) on the

spreadsheet in which the results are to be stored. After completing

this, select Run in the main menu followed by Linear_Range or Periodic_Range to carry out multiple simulations using the specified

26
variables and ranges. Steps 45 through 51 and Listing 4-6 show how to

setup a Linear_Input range and to carry out the multiple simulations

specified in this Linear_Range . Part of the results which are written to Output Region 1 are displayed in Listing 4-7.

- Use the Graph command in the main menu and the commands in the

various submenus to plot the results. You may also edit a graph to

add or erase lines, change titles and legends, or add grid lines.

When you are satisfied with the looks of a graph(s), it should be

saved for later printing. Before quitting 1-2-3, the spreadsheet

should be saved under a new name, BOILEXPl .WKl for example. This

task is carried out in steps 52 through 7 8 in Listing 4-1.

4.3 Simulation Results

GRAPH 1 in figure 5 contains a plot of System Efficiency versus Building

Load for the three gas-fired boilers running at the same part load

factors. Since all three gas-fired boilers are identical and are running

at identical part load factors, this is the same part load performance

curve for each boiler individually. This would not be the case if another

boiler operating strategy, such as sequential operation, were selected.

The operating strategy and its effect on system efficiency is discussed

in the next section.

27
Listing 4-1 COMPLETE PROCEDURE FOR CREATING BOILEXP1.WK1 IN EXAMPLE 1

BOILEXP1 simulates the use of 3 boilers all operating together at the same part load to meet the building load.

STEP KEYSTROKE ENTRY COMMENT

1 / f cce {esc 5} Entering ccs {esc 5} speeds up

loading of spreadsheets. The notation

{esc 5} means to press the esc key

5 times.

2 r SETUP ~ Load SETUP. WK 1. The symbol ~

should be entered as ~ and is

interpreted as a carriage return.

3 B Select boiler model and read

s cree n.

4 C continue

5 (input/change fuel data, see Listing 4“3)

Information containted in ( ) are instructions to be followed and

should not be interpreted as literal key strokes. Use only arrow keys to input data.

6 -

7 (enter combustion air temperature,

TRA, and up to 6 sets of PLF, XCO2

and TSS, use proper units)

8 ~

9 New Gas Boiler name of specific model

10 q qui t

11 /fs SETUP1 save file as SETUP1.WK1

12 /fr POST ~ retrieve POST.WK1

13 A1 t-M call up main menu

14 S set up new simulation

15 SETUP1 use models in SETUP1.WK1

16 (move cell pointer to cell with *7)~ select boiler model

17 — to place boiler model at FA1

28
18 (move cell pointer to cell with *7)~ select boiler model

19 ~(pgdn)

to place second boiler model at FA21

20 (move cell pointer to cell with *7)- select boiler model

21 -{pgdn} {pgdn}

to place third boiler model at FA41

22 (move cell pointer to cell with *6)

to select 3-way Merge w. Heating L

Control Model

23 -{pgdn} {pgdn} {pgdn}- to place model at FA61

24 ~(with cell pointer over a without an * ) cell to end setup mode

25 Three Gas-Fired Boilers S - simulation title

26 Ctrl-right arrow Ctrl-right arrow means to press

the right arrow key while holding

down the control key.

27 (enter connection numbers.

Listing 4-3)

see to specify how component models

are connected

28 (It is recommended that you also

customize the Mnemonics at this

point to reflect the fact that

there are multiple boilers. For

example: change PLF to FLF1 in

first boiler model, to FLF2 in

second boiler model, to FLF3 in

third boiler model.)

29 A1 t-M to recall main menu

30 I Initialize simulation

31 CO Change Output

32 - (enter a single user-defined

variable, see Listing 4~4

enter Mnemonic, Name, Value, Units,

Definition and use a formula for

Value entry

33 Alt-V to add user-defined variable to

simulation

34 {esc} to accept list of reported

variables and return to main menu

35 CO Change Output

29
36 - (enter 2nd user-defined variable, enter 2nd user-defined variable

see Listing 4~4)

37 A1 t-V to add user-defined variable to

s imula t ion

38 {esc} to accept list of reported

variables and return to main menu

39 D V ~ Display variables

40 ( enter/ change value of input

variables using only arrow keys

to enter data, see Listing 4“5)

41 ~ carriage return when done

42 r s run single point to smooth

feathers ruffled by insertion

43 D V ~ Ctrl-right arrow display output variables (see

Listing 4-5)

44 ~ carriage return when done

45 c L change linear_range

46 e edit

47 (enter linear input data, see Listing 4~6)

48 ~D carriage return when done

49 r L run 1 inear_range

50 DO ~~ to display output region 1 (see

Listing 4~7)

51 carriage return when done

52 g graph

53 C cr ea te

54 ~ to use data set number 1

55 ~

56 u to see Mnemonics associated with

the variable names

30
57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

(position cell pointer over F0WR.4) to select P0WR.4 at x-variable

(position cell pointer over USER. 2)

x ~

GRAPH1

V

E L

A

All at

T

Y

Same Load ~

System Efficiency (%) ~

T

X

Building Load (kBtu/h)~

q

V

q

q

/is B0ILEXP1 ~

(r)

/fcce {esc 6}

to select USER. 2 as first

y-variable

enter x to end selection of

y-variabl

name of graph

View graph

Edit graph legend

select first data range

enter A legend

Title

Y-axis title

X-axis title

qui t

to use GRAFH1 for graph name view

quit graph submenu

quit main menu

same spreadsheet in B0ILEXP1.WK1

(replace old file if one exists)

to get main spreadsheet menu

program and allow for rapid file

loading

31
Listing 4-2 FUEL AND BOILER PERFORMANCE DATA USED IN EXAMPLE 1

FI FJ FK FL FM FN FO FP

1 BOILER

2 Constants

1 Fuel Data

M02 32

5 atomic ratio H/C h 3.6246 MN2 28.016

6 atomic ratio O/C o 0.01896 MC02 44.011

7 atomic ratio N/C n 0.15545 MH20 18.016

8 atomic ratio S/C s 0 MS 02 64.066

9 HHV (BTU/lb) HHV 20120 mf02 0.233

10 mfN2 0.767

11 R 1.98726

12 Performance TRA= 70 F ( 530 R)

14 PLF 0.01 0.2 0.4 0.6 0.8 1

15 XC02 (%) 1 4 6 8 9.5 11

16 TSS (F) 500 400 425 450 47 5 500

17 RT 11.16717 2.859827 1.936788 1.475268 1.256654 1.097661

18 QL (%) 9.420113 9.420113 9.420113 9.420113 9.420113 9.420113

19 QS (%) 85.17809 17.42050 13.05976 10.94253 10.13493 9.583106

20 EFF «) 5.401794 73.15938 77.52011 79.63735 80.44494 80.99677

32
Listing 4-3 SIMULATION CONNECTION NUMBERS IN BOILEXP1 .WK1 , FROM

EXAMPLE 1

*1 Boiler

New Gas

'Boiler Max. Err: 0

I/O Mnemonic Name Value Unit s Definition

6 I FLOutptl POWR.12 1000 kBtu/hr Full Load Output

I PumpPwrl POWR.6 5 kw Pump Power

I CtrlModl CTRL.

4

0 — 0=>use PLF; l=>use PLFset

I PLFsetl CTRL.

6

1 — Setpoint part-load ratio

1 I PLFl CTRL.

8

1 — Part-load factor

3 0 Outputl POWR.9 1000 kBtu/hr Boiler Output

0 EFFl MISC.2 80.7 93 80 — Boiler Efficiency

0 Input

1

POWR.8 1237 .718 kBtu/hr Boiler Input

*2

1/0

Boiler

New Gas

' Mnemonic

Boiler

Name Value Unit s Max. Err: 0

Definition

7 I FL0utpt2 P0WR.13 1000 kBtu/hr Full Load Output

I PumpPwr2 P0WR.2 5 kw Pump Power

I CtrlMod2 CTRL.

3

0 — 0=>use PLF; l=>use PLFset

I PLF set2 CTRL.

5

1 — Setpoint part-load ratio

2 I PLF 2 CTRL.

9

1 — Part-load factor

4 0 Output

2

POWR.10 1000 kBtu/hr Boiler Output

0 EFF2 MISC.3 80.7 93 80 — Boiler Efficiency

0 Input

2

POWR.5 1237 .718 kBtu/hr Boiler Input

*3

I/O

Boiler

New Gas

Mnemonic

Boiler

Name Value Unit s Max. Err: 0

Def inition

8 I FL0utpt3 P0WR.14 1000 kBtu/hr Full Load Output

I PumpPwr3 P0WR.1 5 kW Pump Power

I CtrlMod3 CTRL.

7

0 — 0=>use PLF; l=>use PLFset

I PLF set3 CTRL .1 1 — Setpoint part-load ratio

2 I PLF3 CTRL. 9 1 — Part-load factor

5 0 Out put

3

P0WR.11 1000 kBtu/hr Boiler Output

0 EFF3 MISC.l 80.7 93 80 — Boiler Efficiency

0 Input3 POWR.3 1237 .718 kBtu/hr Boiler Input

33
Listing 4-3 SIMULATION CONNECTION NUMBERS IN BOILEXPl .WKl , FROM

EXAMPLE 1 (Continued)

*4 3-Way Merge Boiler Load Merge

3-Way Merge w. Load Control Max. Err: 0

I/O Mnemonic Name Value Units Definition

I Nset CTRL.

1 — Control Inlet Numb

3 I Outputl POWR.9 1000 kBtu/hr Output of Boiler 1 4 I 0utput2 POWR.10 1000 kBtu/hr Output of Boiler 2

3 I Out put

P0WR.11 1000 kBtu/hr Output of Boiler 3

6 I FLOutptl POWR.12 1000 kBtu/hr Boilerl Full Load Capacity

7 I FLOutpt2 POWR.13 1000 kBtu/hr Boiler2 Full Load Capacity

8 I FL0utpt3 POWR.14 1000 kBtu/hr Boiler3 Full Load Capacity

I Load P0WR.4 3000 kBtu/hr Building Load

I LdPumpPr P0WR.7 7.3 kW Load Pump Power

2 0 PLFavg CTRL.1 — Avg System PLF

1 0 PLFcalc CTRL.1 — Calc PLF for control inlet

34
Listing 4-4 USER-DEFINED VARIABLES IN B0ILEXP1.WK1, FROM EXAMPLE 1

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

79

98

99

100

FA FB FC FD FE FF FG

*5 Additional Outputs Max. Err: 0

I/O Mnemonic Name Value Units Definition

0 SysCap USER. 1 t kBtu/hr Total System Out put

0 SysEff USER. 2 t — Total System Efficiency

t + FD11 + FD31 + FD51

{ + ( (FDll + FD31 + FD51) / (FD13 + FD33 + FD53))*100

35
Listing 4-5 SAMPLE SIMULATION OUTPUTS AND INPUTS IN BOILEXP1 . WK1, FROM

EXAMPLE 1

POST Three Gas-Fired Boilers

Simulation Outputs

Err. Tol = Max. Err = (Page Left for Inputs)

0.001

0

Mnemonic Name Val ue Units Definition

PLFcalc CTRL.

1 — Calc PLF for control inlet

PLFavg CTRL.1 — Avg System PLF

EFF3 MISC.l 80.79380 — Boiler Efficiency

EFF1 MISC. 2 80.79380 — Boiler Efficiency

EFF2 MISC.3 80.79380 — Boiler Efficiency

Input3 P0WR.3 1237.718 kBtu/hr Boiler Input

Input2 P0WR.5 1237.718 kBtu/hr Boiler Input

Inputl PCWR. 8 1237.718 kBtu/hr Boiler Input

Outputl POWR. 9 1000 kBtu/hr Boiler Output

0utput2 POWR. 10 1000 kBtu/hr Boiler Output

0utput3 P0WR.11 1000 kBtu/hr Boiler Output

SysCap USER. 1 3000 kBtu/hr Total System Output

Sy sEf f USER. 2 80.79380 — Total System Efficiency

Simulation Inputs (Page Right for Outputs)

Mnemonic Name Value Units Definition

PLFset3 CTRL.

1 — Setpoint part-load ratio

Nset CTRL.

1 — Control Inlet Number

CtrlMod2 CTRL.

0 — 0=>use PLF; l=>use PLFset

Ct rl Modi CTRL.

0 — 0=>use PLF; l=>use PLFset

PLFset2 CTRL.1 — Setpoint part-load ratio

PLFsetl CTRL.

1 — Setpoint part-load ratio

Ct rlMod3 CTRL.

0 — 0=>use PLF; l=>use PLFset

PumpPwr3 POWR.l 5 kW Pump Power

PumpPwr2 POWR. 2 5 kW Pump Power

Load POWR. 4 3000 kBtu/hr Building Load

PumpPwrl PCWR.6 5 kW Pump Power

LdPumpPr POWR. 7 - 7.5 kW Load Pump Power

FLOutptl POWR. 12 1000 kBtu/hr Full Load Output

FL0utpt2 POWR. 13 1000 kBtu/hr Full Load Output

FL0utpt3 PCWR.14 1000 kBtu/hr Boiler3 Full Load Capacity

36
Listing 4-6 LINEAR INPUT DATA IN B0ILEXP1. WK1, FROM EXAMPLE 1

Edit View Quit Done

Edit linear input settings

AG AH AI AJ A B C D

1 Linear Input Settings 5 Mnemonic Name Value Units

2 6 PLFset3 CTRL. 1 1 --

3 Number of variable inputs: 1 7 Nset CTRL. 2 1 —

4 Number of steps for each: 19 8 CtrlMod2 CTRL. 3 0 —

5 Output Data Set Number: 1 9 Ctrl Modi CTRL.

0 —

6 10 PLFset2 CTRL. 5 1 —

7 Var. Variable First Last 11 PLFsetl CTRL.

6

1 —

8 No. Name Value Value 12 CtrlMod3 CTRL.

0 --

9 === ===== 13 PumpPwr3 POWR. 1 5 kW

10 1 POWR. 4 150 3000 14 PumpPwr2 POWR. 2 5 kW

11 2 15 Load PCWR. 4 3000 kBtu/hr

12 3 16 PumpPwrl POWR. 6 5 kW

13 4 17 LdPumpPr PCWR.7 7.5 kW

14 5 18 FLOutptl POWR. 12 1000 kBtu/hr

15 19 FL0utpt2 POWR. 13 1000 kBtu/hr

16 Current Mode: Line Input 20 FL0utpt3 POWR. 14 1000 kBtu/hr

17 21

18 22

19 23

20 24

37
Listing 4-7 OUTPUT DATA SET 1 IN BOILEXP1. WK1, FROM EXAMPLE 1

B C D E F G H I 999 0 FLFcal c PLFavg EFF3 EFF1 EFF2 Input3 Input2

IOOOPOWR.4 CTRL. 8 CTRL.

9

MISC.l MISC.2 MISC.3 PCJWR. 3 PCWR. 5

1001 150 0.05 0.05 43.67350 43.67350 43.673 50 114.4858 114.4858

1002 300 0.1 0.1 62.42117 62.42117 62.42117 160.2020 160.2020

1003 450 0.15 0.15 69.49426 69.49426 69.49426 215.8451 215.8451

1004 600 0.2 0.2 73.00070 73.00070 73.00070 273.9699 273.9699

1005 7 50 0.25 0.25 75.05535 75.05535 75.05535 333.0874 3 3 3.0 87 4

1006 900 0.3 0.3 76.39393 76.39393 76.39393 392.7013 392.7013

1007 1050 0.35 0.35 77.33117 77.33117 77.33117 452.5988 452.5988

1008 1200 0.4 0.4 78.02235 78.02235 78.02235 512.6735 512.6735

1009 13 50 0.45 0.45 78.55233 78.55233 78.55233 572.8664 572.8664

1010 1500 0.5 0.5 78.97120 78.97120 78.97120 633.1421 633.1421

1011 1650 0.55 0.55 79.31037 79.31037 79.31037 693.4779 693.4779

1012 1800 0.6 0 .

6

79.59049 79.59049 79.59049 753.8588 753.8588

1013 1950 0.65 0.65 79.82565 79.82565 79.82565 814.2745 814.2745

1014 2100 0.7 0.7 80.02584 80.02584 80.02584 874.7174 874.7174

1015 2250 0.75 0.75 80.19827 80.19827 80.19827 935.1821 935.1821

1016 2400 0.8 0.8 80.3 4 833 80.34833 80.34833 995.6646 995 .6646

1017 2550 0.85 0.85 80.48009 80.48009 80.48009 1056.161 1056.161

1018 2700 0.9 0.9 80.59670 80.59670 80.59670 1116.670 1116.670

1019 2850 0.95 0.95 80.70062 80.70062 80.70062 1177.190 1177.190

1020 3000 1 1 80.79380 80.79380 80.79380 1237.718 1237.718

38
5. EXAMPLE 2: SEQUENTIAL OPERATION OF THREE GAS-FIRED BOILERS

In this example, three identical gas-fired boilers are operated sequentially

to meet a hypothetical building load. As the building load increases from

zero, the first boiler is operated at higher and higher part load factors

to meet the load, while boilers 2 and 3 remain off. As the building load

increases past the point where the part load factor of boiler 1 becomes

equal to 1.0, then boiler 2 is fired. Finally, boiler 3 is fired when the

building load has increased to the point where boilers 1 and 2 running at

full capacity (i.e., both have part load factors equal to 1.0) cannot

provide enough heat output to meet the load.

Listing 5-1 provides an outline of the steps necessary to setup, run, and

analyze the results from this example, while Listings 5-2 through 5-6

provide supplemental information. Individual keystrokes are not provided,

since it is expected that a user who has worked through Example 1 successfully

should not encounter serious difficulty.

5.1 The Component Models

The component models in this example are the same as those described in

section 4.1 for Example 1. The only difference that occurs is how they

are linked together and the parameters chosen for some of the Simulation

Inputs.

When the boilers are operated sequentially, PLFavg in the N-Way Merge with

Heating Load Control model is not used. Instead, PLFcalc is connected to

39
the PLF inputs on al

1

the boilers. For a boiler operating at part load,

the CtrlMod(e) parameter in the Simulation Inputs is set to 1 and the full

load output FLOutpt is set to full load capacity of the boiler. For

boilers which are not operating, the CtrlMod(e) should be set to 1, the

PLFset parameters should be set to a very small value (e.g., 0.00001, but

never 0) and the FLOutpt variable should be given the value 0.0. A boiler

that is running at full load should have CtrlMod(e) and PLFset both set to

1 and FLOutpt should be set equal to the full load capacity of the boiler.

5.2 Setting Up and Running Example 2

The starting point for Example 2 is the spreadsheet ( BOILEXP 1 . WKl ) created

and saved in Example 1. This spreadsheet should be retrieved and the

connection numbers changed as described in the previous section and as illustrated in Listing 5-2. The Initialize command in the main menu

should then be used to reinitialize the simulation. The user-defined

variables created in Example 1 will be automatically incorporated into the

Simulation Outputs.

In order to consider the three cases of interest:

Boiler 1 operates at part load to meet the building load with

Boilers 2 and 3 off,

Boiler 1 runs at full load, boiler 2 operates at part load, and

boiler 3 is off, and

40
Boilers 1 and 2 operate at full load while boiler 3 operates at

part load,

the Simulation Inputs and the Linear Input ranges must be changed and the

simulation Run for each of these cases. Listing 5-3 gives sample inputs

for each case, while Listing 5-4 shows how to setup a Linear_Input range

for case 1. The results of cases 1, 2, and 3 should be copied to Output

Regions 2, 3, and 4, respectively. After all three cases have been run,

the results should be combined in Output Region 5 (using the menu commands

in 1-2-3) to give a continuous set of system performance data for all

building loads between 150 and 3000 kBtu/h. Listing 5-5 shows the

Simulation Outputs and Inputs for case 3 and a building load of 3000

kBtu/h, while Listing 5-6 displays part of the combined performance data

from Output Region 5.

5.3 Simulation Results

4 The combined system performance data in Output Region 5 were used to

generate the graph shown in Figure 6 which shows the effect of sequential

boiler operation on System Efficiency. It is interesting to note how the

system efficiency drops as each successive boiler is fired up. Figure 7

is a combination plot showing System Efficiency versus Building Load for

the case where all boilers operate at the same part load factor (the data

in Output Region 1 from Example 1) and the case where the boilers are operated sequentially (same as Figure 6 using Output Region 5). It is

41
clear that for these particular gas-fired boilers it is much more efficient

to operate them sequentially at building loads below 2000 kBtu/h.

42
Listing 5-1 OUTLINE OF PROCEDURE FOR GENERATING BOILEXP2.WK1 IN EXAMPLE 2

BOILEXP2 uses BOILEXP.l and adds three more cases

o boiler #1 operates at part load to meet low building loads

o boiler #1 runs at full load and boiler operates at part load

o boiler #1 and #2 run at full load and boiler #3 operates at

part load.

Load Spreedsheet Program and then retrieve B0ILEXP1

Change connection numbers between component models (see Attachment 1)

Initialize simulation

Change Simulation Inputs so only boiler #1 operates at part load, other

boilers are off

(see Listing 5-3b)

Change Linear__range so that:

Number of variable inputs = 1 Number of steps for each = 5 Output data set = 2

The variable P0WR.5 goes from a first value of

150 to a last value of 900

(see Listing 5-4)

Run Linear_range

Change Simulation Inputs so that boiler #1 runs at full load while #2

operates at part load

(see Listing 5-3b)

Change Linear_range (use output data set =3,6 steps, POWR.5 goes from

1050 to 1950)

Run Linear_range

Change Simulation Input so that boilers #1 and #2 run at full load while

#3 operates at part load

(see Listings 5-3c and 5-5)

Change Linear_range (use output data set = 4, 6 steps, P0WR.5 goes from

2100 to 3000)

Run Linear_range

43
Use 1-2-3 menu to move data in output region #2 to region #5* Append data

from region #3 and region #4 to it so that the building load, P0WR.5,

goes from 150 to 3000 kBtu/h in one data set

(see Listing 5-6)

Plot system efficiency vs. building load for data region #5 in GRAPH2

Edit GRAPHl to include the same results plotted in GRAPH2 and save in GRAPH3

Use Spreadsheet menu commands to change the Y-scale in GRAFH3 and save in

GRAPH4

Save GRAPHl, GRAFH2 and GRAFH3 using SAVEPIC in Graph menu for later printing

Save spreadsheet as B0ILEXP2.WK1

44
J

Listing 5-2 SIMULATION CONNECTION NUMBERS IN BOILEXP2.WK1, FROM EXAMPLE 2

*1 Boiler

New Gas Boiler Max. Err: 0

I/O Mnemonic Name Value Units Definition

6 I FLOutptl PCWR.12 1000 kBtu/hr Full Load Output

I PumpPwrl POWR. 1 5 kW Piomp Power

I Ct rlModl CTRL.0 — 0=>use PLF; l=>use PLFset

I PLFsetl CTRL.

1 — Setpoint part-load ratio

1 I PL FI CTRL.1 — Part-load factor

3 0 Out put

POWR. 9 1000 kBtu/hr Boiler Output

0 EFF1 MISC.2 80.79380 — Boiler Efficiency

0 Inputl POWR. 3 1237.718 kBtu/hr Boiler Input

*2

1/0

Boiler

New Gas Boiler

Mnemonic Name Value Units

Max. Err: 0

Definition

7 I FL0utpt2 PCWR.13 0 kBtu/hr Full Load Output

I PumpPwr2 POWR. 8 5 kW Pump Power

I Ct rlMod2 CTRL.1 — 0=->use PLF; l = >use PLFset

I PLFset2 CTRL.0.00001 — Setpoint pa'rt-load ratio

1 I PLF2 CTRL.

1 — Part-load factor

4 0 Out putPOWR. 10 0 kBtu/hr Boiler Output

0 EFF2 MISC.3 0.000006 — Boiler Efficiency

0 Input2 POWR. 7 0 kBtu/hr Boiler Input

*3

I/O

Boiler

New Gas Boiler

Mnemonic Name Value Units

Max. Err: 0

Definition

8 I FL0utpt3 P0WR.14 0 kBtu/hr Full Load Output

I PumpPwr3 POWR. 4 1000 kW Pump Power

I Ct rlMod3 CTRL. 1 1 — 0=>use PLF; l=>use PLFset

I PLFset3 CTRL. 2 0.00001 — Setpoint part-load ratio

1 I PLF3 CTRL.1 — Part-load factor

5 0 0utput3 POWR. 11 0 kBtu/hr Boiler Output

0 EFF3 MISC.l 0.000006 — Boiler Efficiency

0 Input3 POWR. 6 0 kBtu/hr Boiler Input

45
Listing 5-2 SIMULATION CONNECTION NUMBERS IN BOILEXP2. WK1, FROM EXAMPLE 2

(continued)

*4 3-Way Merge Boiler Load Merge

3-Way Merge w. Load Control Max. Err: 0

I/O Mnemonic Name Value Units Definition

I Nset CTRL. 4 1 — Control Inlet Numb

3 I Out put

1

POWR.9 1000 kBtu/hr Output of Boiler 1 4 I 0utput2 POWR.IO 0 kBtu/hr Output of Boiler 2

5 I 0utput3 POWR.ll 0 kBtu/hr Output of Boiler 3

6 I FLOutptl P0WR.12 1000 kBtu/hr Boilerl Full Load Capacity

7 I FL0utpt2 PCWR.13 0 kBtu/hr Boiler2 Full Load Capacity

8 I FL0utpt3 P0WR.14 0 kBtu/hr Boiler3 Full Load Capacity

I Load POWR.5 1000 kBtu/hr Building Load

I LdPumpPr PCWR.

2

7.5 kW Load Pump Power

0 PLFavg CTRL.

3

1 — Avg System PLF

1 0

*5

PLFcalc CTRL.

9

Additional Outputs

1 Calc PLF for control inlet

Max. Err: 0

I/O Mnemonic Name Value Units Definition

0 SysCap USER. 1 1000 kBtu/hr Total System Output

0 SysEff USER. 2 80 .79380 — Total System Efficiency

46
Listing 5-3 a SAMPLE INPUTS IN B0ILEXP2.WK1, FROM EXAMPLE 2

A B C D

1 POST Three Gas-Fired Boilers

2

3 Simulation Inputs^

4 ============================:====:

5 Mnemonic Name Value Units

6 Ct rl Mod3 CTRL.

1

1 —

7 PLFset3 CTRL.

2

0.00001 —

8 Nset CTRL.

4

1 —

9 PLFsetl CTRL.

5

1 —

10 Ct rlModl CTRL.

6

0 --

11 CtrlMod2 CTRL.

7

1 —

12 PLFset2 CTRL.

8

0.00001 —

13 PumpPwrl POWR. 1 5 kW

14 LdPumpPr PCWR.2 7.5 kW

15 PumpPwr3 POWR. 4 5 kW

16 Load POWR. 5 1000 kBtu/hr

17 PumpPwr2 POWR. 8 5 kW

18 FLOutptl PCWR.12 1000 kBtu/hr

19 FL0utpt2 POWR. 13 0 kBtu/hr

20 FL0utpt3 P0WR.14 0 kBtu/hr

E F G H

Err.Tol = 0.001

Max. Err = 0

(Page Right for Outputs)

Definition

0=>use PLF; l=>use PLFset

Setpoint part-load ratio

Control Inlet Number

Setpoint part-load ratio

0=>use PLF; l=>use PLFset

0=>use PLF; l=>use PLFset

Setpoint part-load ratio

Pump Power

Load Pump Power

Pump Power

Building Load

Pump Power

Full Load Output

Full Load Output

Full Load Output

1 Boiler 1 operates at part-load. Boilers 2 and 3 are off.

47
Listing 5-3 b SAMPLE INPUTS IN B0ILEXP2. WK1, FROM EXAMPLE 2

A B C D

1 POST Three Gas-Fired Boilers

2

o 3 Simulation Input s^* 4

5 Mnemonic Name Val ue Units

6 Ct rlMod3 CTRL.

1 —

7 PLFset3 CTRL.

0.00001 —

8 Nset CTRL.

2 —

9 PLFsetl CTRL.

1 —

10 Ct rlModl CTRL.

1 —

11 Ctrl Mod2 CTRL.

0 —

12 PLFset2 CTRL.

1 —

13 PumpPwrl POWR. 1 5 kW

14 LdPumpPr PCWR.2 7.5 kW

15 PumpPwr3 POWR. 4 5 kW

16 Load PCWR.5 2000 kBtu/hr

17 PumpPwr2 POWR. 8 5 kW

18 FLOutptl PCWR.12 1000 kBtu/hr

19 FL0utpt2 POWR. 13 1000 kBtu/hr

20 FL0utpt3 POWR. 14 0 kBtu/hr

E F G H

Err. Tol = 0.001

Max. Err = 0

(Page Right for Outputs)

Definition

0=>use PLF; l=>use PLFset

Setpoint part-load ratio

Control Inlet Number

Setpoint part-load ratio

0=>use PLF; l=>use PLFset

0=>use PLF; l=>use PLFset

Setpoint part-load ratio

Pump Power

Load Pump Power

Pump Power

Building Load

Pump Power

Full Load Output

Full Load Output

Full Load Output

9 Boiler 1 operates at full load. Boiler 2 operates at part-load.

Boiler 3 is off.

48
Listing 5-3 c SAMPLE INPUTS IN B0ILEXP2. WK1, FROM EXAMPLE 2

A B C D

1 POST Three Gas-Fired Boilers

2

3

4

5

Simulation Input s^

Mnemonic Name Val ue Units

6 CtrlMod3 CTRL. 1 0 —

7 PLFset3 CTRL. 2 1 —

8 Nset CTRL.

4

3 —

9 PLFsetl CTRL. 5 1 —

10 Ct rlModl CTRL.

6

1 —

11 CtrlMod2 CTRL.

7

1 —

12 PLFset2 CTRL.

8

1

--- 13 PumpPwrl POWR. 1 5 kW

14 LdPumpPr P0WR.2 7.5 kW

15 PumpPwr3 POWR. 4 5 kW

16 Load PCWR.5 3000 kBtu/hr

17 PumpPwr2 POWR. 8 5 kW

18 FLOutptl P0WR.12 1000 kBtu/hr

19 FL0utpt2 POWR. 13 1000 kBtu/hr

20 FL0utpt3 PCWR.14 1000 kBtu/hr

E F G H

Err.Tol = 0.001

Max. Err = 0

(Page Right for Outputs)

Definition

0=>use PLF; l=>use PLFset

Setpoint part-load ratio

Control Inlet Number

Setpoint part-load ratio

0=>use PLF; l=>use PLFset

0=>use PLF; l=>use PLFset

Setpoint part-load ratio

Pump Power

Load Pump Power

Pump Power

Building Load

Pump Power

Full Load Output

Full Load Output

Full Load Output

3 Boilers 1 and 2 operate at full load. Boiler 3 operates at part-load.

49
Listing 5-4 LINEAR RANGE FOR DATA SET 1 IN BOILEXP2. WK1. FROM EXAMPLE 2

Edit View Quit Done

Edit linear input settings

AG AH AI AJ A B C D

1 Linear Input Settings 5 Mnemonic Name Value Units

2 6 Ctrl Mod3 CTRL.

1

1 —

3 Number of variable inputs: 1 7 PLFset3 CTRL.

2

0.00001 —

4 Number of steps for each: 5 8 Nset CTRL.

4

1 —

5 Output Data Set Number: 2 9 PLFsetl CTRL.

5

1 —

6 10 Ctrl Modi CTRL.

6

0 —

7 Var. Variable First Last 11 Ct rlMod2 CTRL.

7

1 —

8 No. Name Value Value 12 PLFset2 CTRL. 8 0.00001 —

9 === ===== 13 PumpPwrl P0WR.1 5 kW10 1 POWR. 5 1 50 900 14 LdPumpPr POWR. 2 7.5 kW

11 2 15 PumpPwr3 POWR. 4 5 kW

12 3 16 Load POWR. 5 900 kB tu/hr

13 4 17 PumpPwr2 PCWR.8 5 kW

14 5 18 FLOutptl POWR. 12 1000 kB tu/hr

15 19 FL0utpt2 PCWR.13 0 kBtu/hr

16 Current Mode: Line Input 20 FL0utpt3 POWR. 14 0 kB tu/hr

17 21

18 22

19 23

20 24

50
Listing 5-5 EXAMPLE 2 SAMPLE SIMULATION OUTPUTS AND INPUTS IN BOILEXP2.WK1

WITH ALL THREE BOILERS AT FULL LOAD

POST Three Gas-Fired Boilers

Simulation Outputs

Err. Tol =

Max. Err = (Page Left for Inputs)

0.001

0

Mnemonic Name Value Units Definition

PLFavg CTRL.

3

1 — Avg System PLF

PL F cal c CTRL.

9

1 — Calc PLF for control inlet

EFF3 MISC.l 80.793 80 — Boiler Efficiency

EFF1 MISC.2 80.79380 — Boiler Efficiency

EFF2 MISC.3 80.793 80 — Boiler Efficiency

Input

1

POWR.3 1237.718 kBtu/hr Boiler Input

Input3 POWR. 6 1237.718 kBtu/hr Boiler Input

Input

2

POWR. 7 1237.718 kBtu/hr Boiler Input

Out put

1

POWR. 9 1000 kBtu/hr Boiler Output

0utput2 POWR. 10 1000 kBtu/hr Boiler Output

Output3 POWR. 11 1000 kBtu/hr Boiler Output

SysCap USER.

1

3000 kBtu/hr Total System Output

SysEff USER. 2 80.793 80 — Total System Efficiency

Simulation Inputs (Page Right for Outputs)

Mnemonic Name Value Units Definition

Ctrl Mod3 CTRL.

1

0 — 0=>use PLF; l=>use FLFset

PLFset3 CTRL.

2

1 — Setpoint part-load ratio

Nset CTRL.

4

3 — Control Inlet Number

PLFsetl CTRL.

5

1 — Setpoint part-load ratio

Ct rlModl CTRL.

6

1 — 0=>use PLF; l=>use PLFset

Ct rlMod2 CTRL.

7

1 — 0=>use PLF; l=>use PLFset

PLFset2 CTRL.

8

1 — Setpoint part-load ratio

PumpPwrl POWR. 1 5 kW Pump Power

LdPumpPr POWR. 2 7.5 kW Load Pump Power

PumpPwr3 POWR. 4 5 kW Pump Power

Load POWR. 5 3000 kBtu/hr Building load

PumpPwr2 POWR. 8 5 kW Pump Power

FLOutptl POWR. 12 1000 kBtu/hr Full Load Output

FL0utpt2 PCWR.13 1000 kBtu/hr Full Load Output

FL0utpt3 POWR. 14 1000 kBtu/hr Full Load Output

51
Listing 5-6 DATA SET 5 IN B0ILEXP2. WK1, FROM EXAMPLE 2

B C D E F G H I 1999 0 PLFavg PLFcalc EFF3 EFF1 EFF2 Inputl Input3

2000PCWR. 5 CTRL. 3 CTRL.

9

MISC.l MISC.2 MISC.3 PCWR.3 POWR.6

2001 150 0.15 0.15 0.000006 69.49426 0.000006 215.8451 0

2002 300 0.3 0.3 0.000006 76.39393 0.000006 392.7013 0

2003 450 0.45 0.45 0.000006 78.55233 0.000006 572.8664 0

2004 600 0.6 0.6 0.000006 79.59049 0.000006 753.8588 0

2005 7 50 0.75 0.75 0.000006 80.19827 0.000006 93 5.1821 0

2006 900 0.9 0.9 0.000006 80.59670 0.000006 1116.670 0

2007 1050 0.525 0.05 0.000006 80.79380 43.673 50 1237.718 0

2008 1200 0.6 0.2 0.000006 80.79380 73.00070 1237.718 0

2009 13 50 0.675 0.35 0.000006 80.793 80 77.33117 1237.718 •o 2010 1500 0.75 0.5 0.000006 80.79380 78.97120 1237.718 0

2011 1650 0.825 0.65 0.000006 80.793 80 79.82565 1237.718 0

2012 1800 0.9 0.8 0.000006 80.79380 80.34833 1237.718 0

2013 1950 0.975 0.95 0.000006 80.79380 80.70062 1237.718 0

2014 2100 0.7 0.1 62.42117 80.79380 80.79380 1237.718 160.2020

2015 2250 0.75 0.25 75.05535 80.793 80 80.79380 1237.718 333.0874

2016 2400 0.8 0.4 78.02235 80.79380 80.79380 1237.718 512.6735

2017 2550 0.85 0.55 79.31037 80.793 80 80.79380 1237.718 693.4779

2018 27 00 0.9 0.7 80.02584 80.79380 80.79380 1237.718 874.7174

2019 2850 0.95 0.85 80.48009 80.793 80 80.793 80 1237.718 1056.161

2020 3000 1 1 80.79380 80.79380 80.79380 1237.718 1237.718

52
6. EXAMPLE 3: TWO CHILLERS AND A COOLING TOWER

This example consists of a central cooling plant containing a cooling

tower, two identical chillers connected in parallel, and two flow merge

components. Two control strategies are considered—both chillers running

at the same part load factor and sequential operation of the chillers to meet

the cooling load on the plant.

6.1 The Component Models

For the cooling tower, the user must first enter the number of cells in

the tower, the volumetric flow rate per fan at each of three settings

(off, low speed, and high speed), and the power consumption per fan at low

and high speeds. A data entry form is provided for this information.

A second data form is then displayed for entry of initial values of the

inputs to the model. These are the water flow rate and temperature

entering the cooling tower, the off/low/high settings of the fans, the

entering air dry bulb and wet bulb temperatures, and the barometric

pressure. The volumetric air flow rate is determined by the fan settings

and the previously entered fan data. The dry bulb temperature is used

only in converting the volumetric flow rate to a mass flow rate. The

barometric pressure is also used in this conversion and in psy chr ometric

cal dilations.

Cooling tower performance is characterized by a single fixed parameter

called the "factor of merit," F (Whillier 1967). After initial values of

the input variables are supplied, the user is given three choices for

53
specifying F. First, a value of F may be entered. Second, F may be

calculated from a single operating point. In this case the input variables

are used in conjunction with a single value of the water outlet temperature

to determine F. Third, performance data may be entered. In this case a value of F is calculated for each data point, and the average is used.

The standard deviation of F is also displayed.

When the performance data option is selected, the nature of the available

data may be specified. Values of the entering air wet bulb temperature

and the water inlet and outlet temperatures are always required. The

default assumes that all other inputs, including the volumetric air flow

rate calculated from the fan settings, are fixed at their initial values.

A format option permits the data to be entered either as a table of water

outlet temperatures versus a row of wet bulb temperatures and a column of

water inlet temperatures, or as three columns of data. The former is more

convenient for manufacturer's data which is already in tabular form, while

the latter is usually needed for experimental data.

Alternatively, other inputs may be identified as additional variables.

For example, if data are available at more than one air flow rate, this

input may be marked as a variable rather than a constant. Columns of data

would then be entered for each of the four variables. The tabular format

option is not available when additional variables are specified.

The centrifugal chiller model is similar to the one recommended by

Stoecker (1975), the major difference being that capacity and power are

54
correlated with evaporator and condenser inlet temperatures rather than

with the evaporator outlet (chilled water) temperature and the condenser

water inlet temperature. This is to eliminate the need for an iterative

solution under conditions where the chilled water outlet temperature is

not immediately known. When outlet temperatures are provided as performance

data, the inlet temperatures are calculated during the setup procedure.

The centrifugal chiller requires three sets of performance data: full

load capacity versus evaporator and condenser temperatures, and power

ratio (actual power consumption divided by full load capacity) . As with

the cooling tower, the procedure begins with a page of text summarizing

the performance data requirements and a menu allowing the user to either

proceed or return to the menu. The next step requires entry of initial

values for the inputs to the model and then performance data is requested.

The nature of the available data can again be specified. Evaporator and

condenser temperatures are required, but in both cases either inlet or outlet temperatures may be entered. Either a tabular format or a columnar

format for data entry may be chosen.

Once the performance data have been entered, linear regression is used to

generate coefficients for the correlation equations. The resulting

coefficients are inserted into the model in place of the generic coefficients.

A label identifying the specific chiller is requested before the model is

stored in the specific components library.

55
The merge component model simply mixes flow streams having different flow

rates and temperatures to find the mixed flow rate and temperature leaving

the merge. The merge with control is a little more complicated and is

discussed below in the context of setting up the two chillers/ cooling

tower simulation.

6.2 Setting Up and Running Example 3

Figure 8 is a block diagram of the central cooling plant. All variables , which represent connections between components are identified on this

diagram. For example, the temperatures labeled T^ and T2 are outputs from

the two chillers and inputs to the flow merge. Tg is an output from the

merge and an input to the cooling tower, while T^ is an output from the

cooling tower and an input to both chillers. Since no load model is used

in this example, the return temperature from the load, Tg, is a boundary

condition. Temperatures Tg and Tg are setpoints for the two chillers.

The chiller model has two modes of operation, selected by means of the

input called CtrlMode. When CtrlMode = 0, the chilled water temperature

is controlled to a specified setpoint temperature and any value entered

for the part load ratio setpoint, PLRset, is ignored. When CtrlMode = 1,

the chiller operates at a specified part load ratio setpoint, PLRset, and

any value entered for the setpoint temperature is ignored. With the

CtrlMode for the first chiller set equal to 0, this chiller is in the

temperature setpoint mode. If the CtrlMode for the second chiller were 1,

it would operate in a part load setpoint mode at full capacity (with

PLRset = 1) . The "Flow Merge with Setpoint Control" component, which

56
controls the mixed water temperature downstream from the merge, would then

calculate the setpoint temperature Tset for the first chiller such that

the mixed water temperature after the merge will equal the overall

setpoint temperature after mixing, TsetAvg. In this case, the second

chiller would cool the water as long as it could, say to about 38.5 F

(13.1°C) at full capacity, and the first chiller would cool the water to a

Tset = '43.5 F (15.8°C) if the mixed water supply temperature setpoint,

TsetAvg, was 41 F (14.4°C). If the chilled water return temperature or

the ambient wet bulb temperature is changed, the second chiller will still

operate at full capacity but the chilled water supply temperature will

change. The merge and control component will automatically adjust the

temperature setpoint Tset of the second chiller to maintain the mixed

water temperature at the overall setpoint, TsetAvg.

An alternative control strategy is to operate both chillers with a chilled

water outlet temperature equal to the overall setpoint. Since the two

chillers in this example are identical, this means both will run at the

same part load ratio. The simulation can be switched to this strategy

simply by changing the control mode of the second chiller, CtrlMode, from

1 to 0

.

Listing 6-1 is a keystroke-by-keystroke procedure for setting up and

running a simulation which examines how best to operate the cooling tower

(i.e., number of fans on high and low speeds) and compares sequential

operation of the chillers with operation of the chillers at identical

part-load factors. Listings 6-2 through 6-6 provide the user with

57
supplemental information. The System COP, which is a useful measure of

system performance, is added as a user defined output for canparing the

different control strategies.

6.3 Simulation Results

Figure 9 is a graph of System COP as a function of the chilled water

temperature returning from the load. The line denoted by crosses was

generated with the second chiller at full capacity and the first chiller

operating in the temperature setpoint mode. The line denoted by squares

was produced with both chillers operating at the same capacity to meet the

setpoint temperature. The figure shows that for this system under these

operating conditions, the later strategy is slightly more efficient over

most but not quite all of the range of loads examined. The chiller

performance at low return water temperature (below 48 F (8.7 °C) results in

unrealistic by low part load factors for chiller 1, and thus the results

shewn for these low temperature conditions are questionable. To create

this figure, the following steps were taken:

1. The Setup Linear_Input command was used to generate a column of

values of chilled water return temperature from 46 F (17.2°C) to

51 F (20°C) in half-degree intervals in output region 1.

2. The Setup Report command was used to specify a few outputs to be

reported.

58
3. The Run Linear_Input command was used to run a simulation using

these temperatures.

4. The Graph Create command was used to generate a graph of System

COP as a function of chilled water return temperature.

5. The variable CtrlMode for the second chiller was changed from 1

to 0 on the Simulation Input portion of the worksheet.

6. The Setup Linear_Input command was used again to store the same

temperatures in output region 2, and another simulation was run

as before.

7. The Graph Edit command was used to add the second line to the

graph, and to modify the titles and legends on the graph.

8. The Graph SavePic command was used to store the graph in a file

for later printing.

59
Listing 6-1 COMPLETE PROCEDURE FOR CREATING CHILLEXP. WK1 IN EXAMPLE 3

STEP KEYSTROKE ENTRY

1 /f cce {esc 5} r SETUP ~

2 t

3 C

4

5

6 V 0.6~

7 Tower w. F = 0 . 6

8 {r igh t} ~

9 C

10

11 3~

12 C

13 20~

14

15 11~

16

17 400 ton (from ASHRAE da ta ) ~

18 {right 2} ~ C

19 2~

20

21 Condenser Water MergeCOMMENTS

Load SETUP. WK1. If already

loaded, use Alt M to obtain

MENU (note: cce {esc 5}

speeds up loading process.

Also - indicates a carriage

return )

tow er

continue

fan da ta

initial input values

Value of F

Specific name

Chil ler

co nt inue

initial input values

will supply Tevap.out and Tcond. in

columns

# rws of da ta

use default ASHRAE data

# rws part load data

use def aul t da ta

specific name

Merge, continue

# of flowstreams

use existing units label

(gpm) and default input values

specific name

60
22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

{right 3} ~ C Ctrl Merge, continue

2~ # of flowstreams

use existing units label

(gpm) and default input values

Chilled water merge / co ntrol~ specific name

q Qui t /fsSEHJPl- File save SETUP1 (extension

»WK1 supplied by Lotus)

r replace existing copy of

SETUP1 . WK1

/ f rpo st ~ retrieve P0ST.WK1

Alt-M S Begin procedure to copy

components from setup worksheet

SETUPl- Enter name of se tup w orkshee

t

{down 2 } — Select Chiller

Make it 1st page of simulation

{ down 2 } ~ Select Chiller again

~{pgdn}

Make it 2nd page of simulation

{ down} ~ Select Cooling Tower

~{pgdn 2}~ Make it 3rd page of simulation

{down 3} ~ Select Merge

~{pgdn 3}Make it 4th page of simulation

{down 4} ~ Select Merge /Control

~{pgdn 4}~ Make it 5th page of simulation

Quit component entry

Cool ing Tower and Two Chillers~ Enter simulation title

Ctrl-right arrcw Enter connection numbers (see

Listing 6~2)

Alt-M I Initialize simulation

61
46 CO47 Alt-V

Change Output and enter a single user-defined variable

(Mnemonic, Name, Value,

Units, and Definition. Enter

Formula for Value)

Incorporate System COP into

simul ation

4 8 R~ Run in single point mode to

smooth feathers ruffled by

inser tion

49 CRE Change Reported variables

list, Edi t

50 flow.l {down} Report air flow thru cooling

t ower

51 misc.3 {down} Report PLR of 1st chiller

52 misc.6 {down} Report System COP

53 powr.4 {down} Report chiller #1 cooling

power output

54 powr.5 {down} Report chiller #2 cooling

power output

55 temp. 3 — Report chilled water temp,

suppl ied to 1 oad

56 ~ End editing

57 D Done

58 { e sc} Return to Main Menu

59 CP Setup Periodic Inputs for a quick look at effects of

cooling tower fan speed and

chiller control mode

60 E

3 { down} 9{ down} 1{ down} 9{ r igh t}

Ctrl .2 { down} Ctrl . 8 { down} Ctrl . 6 { r i gh t}

L{up}L{up}L—

Fill in

input

se ttings

61 C Continue

62 {pgdn} (enter data) enter data (see Listing 6~3)

62
63 Alt-M Fire up the Main Menu again

64 RP Run simul ation w ith Periodic

input

Conclusions from this simulation:

With this particular load and weather =

1) System COP is highest when both cooling tower fans run at

low speed.

2) System COP is highest when both chillers run at same PLR

(CTRL. 6=0) rather than one chiller at full capacity and

one at part load (CTRL. 6=1) .

65 - ~ ~ Display Variables, enable

( Change NFanHi (CTRL. 2) to 0 ) arrow keys

( Change NFanLo (CTRL. 8) to 2 )

( Make sure CTRL. 3=0 and CTRL. 6=1)

66 Back to Main Menu

67 CLE Change Line_Inputs, Edit

68 l{down}10{aown}2{right}

temp. 8{right}47{right}5 —

D

Vary Tchwi, the temp,

returning from load, from

47 °F to 52 °F in 10 steps

(half-degree intervals)

69 RL

70 CLE

71 { down} {down} 3 — D

72 ~

73 ( Change CTRL. 6 from 1 to 0)

74 RL

75 GC~

76 ~{righ t}~

77 -{right 3}-

78 xSimulation stored at A2000

Prepare to run another

Line_ Input Simulation

Write output to Region 3 (A3000)

Display Variables, enable

arrow keys

Simulation stored at A3000

Create Graph, data in Region

3x-axis variable = temp. 8 = Tchwi

y-axis variable = misc.6 = SysCOP

exi t

63
79

80

81

82

83

84

85

86

87

88

89

90

91

graph 1~

y

e

ts Effect of Chiller

LA CTRL. 6 = 0 ~

ty System COP ~

ab

2 ~

~{r igh t 4

}

LB CTRL. 6 = 1 ~

q~ v

S GRAPH l.PIC r Q Q

/

1 COMMENTS ON GRAPH 1:

enter graph name

view (see hew graph looks)

edit graph

Control StrategyAdd a second line to graph

Data in Region 2

2nd y-variable = misc.6

to use GRAPH 1 and View^

replace GRAPH 1 and Quit

to bring up Lotus 1-2-3 menu

1) At the highest temp, (largest load),

the chillers no longer meet load and

the chilled water supply temp, rises

2) At the lowest temp, when CTRL. 6=1,

Chiller #1 is operating at ridiculously

low capacity (PLR- 5%), which is way

outside the range of data used for

chiller correlation. Thus, the rise in

COP may be an artifact.

64
Listing 6-2 SIMULATION CONNECTION NUMBERS IN CHILLEXP .WKl , FROM

EXAMPLE 3

*1 Centrifugal Chiller

400 ton (from ASHRAE data) Max. Err: 251.5882

I/O Mnemonic Name Value Unit s Definition

4 I FLwChw FLOW.

5

1000 gpm Chilled water flow rate

1 I FlwCdw FLOW.

2

1200 gpm Condenser water flow rate

5 I Tchwi TEMP.

8

52 F Ch.w. return (inlet) temp.

4 I Tcdwi TEMP.

7

87 .646 29 F Entering cond. water temp.

9 I Tchset TEMP. 12 41 .58992 F Setpoint chilled water temp.

I PLRset CTRL . 1 1 KW/kW Setpoint part-load ratio

I CtrlMode CTRL.

3

0 — 0= >use Tset; l->use PLRset

6 0 Tchwo TEMP.

9

42.41007 F Chilled water outlet temp.

1 0 Tcdwo TEMP .4 97 .6 8915 F Condenser water outlet temp.

0 Qact P0WR.4 400.1588 tons Actual cooling power output

0 Pact POWR.7 361 .2212 kW Actual input power

0 Qcond POWR.8 1768.521 kW Condenser heat rej . rate

0 COP MISC.2 3 .895949 kW/kW COP: Qact/Pact

0 PLRout MISC.3 1 kW/kW Part-load Ratio: Qact/Qfull

*2 Centrifugal Chiller

400 ton (from ASHRAE data)

I/O Mnemonic Name Value Unit s Max. Err: 251.5882Definition

5 I FlwChw FLOW.

6

1000 gpm Chilled water flow rate

2 I FlwCdw FLOW.

3

1200 gpm Condenser water flow rate

5 I Tchwi TEMP. 8 52 F Ch.w. return (inlet) temp.

4 I Tcdwi TEMP.

7

87.64629 F Entering cond. water temp.

8 I Tchset TEMP. 11 42 F Setpoint chilled water temp.

I PLRset CTRL.

7

1 kW/kW Setpoint part-load ratio

I CtrlMode CTRL.

6

0 — 0=>use Tset; l=>use PLRset

7 0 Tchwo TEMP. 10 42.41007 F Chilled water outlet temp.

2 0 Tcdwo TEMP.

5

97 .68915 F Condenser water outlet temp.

0 Qact P0WR.5 400.1588 tons Actual cooling power output

0 Pact P0WR.6 361 .2212 kW Actual input power

0 Qcond POWR.3 1768.521 kW Condenser heat rej . rate

0 COP MISC.4 3 .895949 kW/kW COP: Qact/Pact

0 PLRout MISC.5 1 kW/kW Part-load Ratio: Qact/Qfull

65
Listing 6-2 SIMULATION CONNECTION NUMBERS IN CHILLEXP . WK1 , FROM

EXAMPLE 3 (continued)

*3 Cooling

F = 0.6

Tower

Max. Err: 251.5882

I/O Mnemonic Name Value Unit s Definition

I Pbaro PRES .

1

14.6 96 p sia Barometric Pressure

3 I FlwCdw FLOW.

4

2400 gpm Total water flow rate

I Tdb TEMP .1 86 F Entering air dry bulb temp.

I Twb TEMP.

2

77 F Entering air wet bulb temp.

3 I Twi TEMP .6 97 .6891 5 F Entering hot water temp.

I NFanHi CTRL.

2

0 — # cells on high fan speed

I NFanLo CTRL.

8

2 — # cells on low fan speed

0 NFanOff CTRL.

4

0 — # cells with fan off

4 0 Two TEMP.

7

87 .64629 F Leaving cooled water temp.

0 FlwA FLOW.

1

162000 cf m Air flow rate

0 FanPowr POWR.l 14 kW Fan power consumption

0 Qtower POWR.2 3536 .366 kW Tower heat rejection rate

0 RelHum MISC.l 0.670716 — Ambient air Relative Humidity

*4

I/O

2-Way Flow Merge

Condenser water

Mnemonic Name

merge

Value Unit s Max. Err: 251.5882Def inition

1 I Flowl FLOW.

2

1200 gpm Flow rate at first inlet

2 I Flow2 FLOW.

3

1200 gpm Flow rate at second inlet

1 I Tempi TEMP .4 97 .68915 F Temperature at first inlet

2 I Temp 2 TEMP.

5

97 .6 891 5 F Temperature at second inlet

3 0 FlowOut FLOW.

4

2400 Flow rate at outlet

3 0 TempOut TEMP.

6

97 .6 8915 Temperature at outlet

66
Listing 6-2 SIMULATION CONNECTION NUMBERS IN CHILLEXP .WKl , FROM

EXAMPLE 3 (continued)

*5 2-Way Merge with Setpoint Control

Chilled water merge/control Max. Err: 251.5882

I/O Mnemonic Name Value Unit s Definition

I Nset CTRL .1 — Controlled Inlet Number

4 I Flowl FLOW.

1000 gpm Flow rate at first inlet

5 I Flow2 FLOW.

1000 gpm Flow rate at second inlet

6 I Tempi TEMP.

42.41007 F Temperature at first inlet

7 I Temp2 TEMP. 10 42.41007 F Temperature at second inlet

8 I TsetAvg TEMP. 11 42 F Overall Setpoint Temp.

6 0 FlowOut FLOW.

2000 gpm Flow rate at outlet

0 TempOut TEMP.

42.41007 F Temperature at outlet

9 0 Tset TEMP. 12 41.58992 F Setpoint for Inlet # 1

*6 Additional Outputs Max. Err: 251.5882

I/O Mnemonic Name Value Unit s Def inition

0 SysCOP MISC.6 3 .407330 — System COP

67
Listing 6~3 PERIODIC INPUT RANGE AND OUTPUT FOR DATA SET 1 IN CHILLEXP.WKl

FROM EXAMPLE 3

AG AH AI AJ AK AL AM AN

21 Periodic Input Settings

22

oo (PERIOD=24 hours assumed)

Zj

24 Number of variable inputs: 3

25 Number of steps for each: 9

26 Output Data Set Number

1 27 Stopping Time (hours): 9

28

29 Var. Variable Form

30

31

32

No. Name (S or L)

1 Ctrl. 2 L

33 2 Ctrl. 8 L

34 3 Ctrl. 6 L

35 4

36 5 37 (S= sinusoidal

L=piecewise linear)

38

39 Current Mode

Line Input

40

OUTPUT DATA SET 1 IN CHILLEXP.WK1

A B C D E F G H

1000 ROW # TIME Ctrl .2 Ctrl. 8 Ctrl.

MISC.6

1001 0 0 2 0 0 320000 0.803 233 3 .225087

1002 1 1 1 1 0 241000 0.817282 3.323167

1003 2 2 0 2 0 162000 0.838406 3 .3 92 976

1004 3 3 0 1 0 97 000 0.9193 91 3.076503

1005 4 4 0 0 0 32000 1 2.2436 87

1006 5 5 0 0 1 32000 1 2.242043

1007 6 6 0 1 1 97 000 0.8423 51 3.045848

1008 7 7 0 2 1 16 2000 0.678799 3.302174

1009 8 8 1 1 1 241000 0.636020 3 .2236 94

1010 9 9 2 0 1 320000 0.6 06 93 5 3.125238

1011

1012

1013

1014

1015

1016

1017

1018

1019

68
Listing 6-4 SAMPLE OUTPUTS AND INPUTS IN CHILLEXP.WK1 , FROM EXAMPLE 3

POST Cooling Tower and Two Chillers Err.Tol = 0.001

Max. Err =251.5882

Simulation Outputs (Page Left for Inputs)

Mnemonic Name Value Unit s Definition

NFanOff CTRL.

4

0 — # cells with fan off

FlwA FLOW.l 16 2000 cfm Air flow rate

FlowOut FLOW.

4

2400 Flow rate at outlet

FlowOut FLOW.

7

2000 gpm Flow rate at outlet

RelHum MISC.l 0.670716 — Ambient air Relative Humidity

COP MISC.2 3 .895949 kW/kW COP: Qact/Pact

PLRout MISC.3 1 kW/kW Part-Load Ratio: Qact/Qfull

COP MISC.4 3 .895949 kW/kW COP: Qact/Pact

PLRout M1SC.5 1 kW/kW Part-Load Ratio: Qact/Qfull

SysCOP MISC.6 3 .407330 — System COP

FanPowr P0WR.1 14 kW Fan power consumption

Qtower POWR.2 3 536 .366 kW Tower heat rejection rate

Qcond P0WR.3 1768.521 kW Condenser heat rej . rate

Qact P0WR.4 400.1588 tons Actual cooling power output

Qact P0WR.5 400.1588 tons Actual cooling power output

Pact P0WR.6 361 .2212 kW Actual input power

Pact P0WR.7 361.2212 kW Actual input power

Qcond POWR.8 1768.521 kW Condenser heat rej. rate

Tchwo TEMP. 10 42.41007 F Chilled water outlet temp.

Tset TEMP. 12 41 .58992 F Setpoint for Inlet # 1 TempOut TEMP. 3 42.41007 F Temperature at outlet

Tcdwo TEMP .4 97 .68915 F Condenser water outlet temp.

Tcdwo TEMP.

5

97 .6 8915 F Condenser water outlet temp.

TempOut TEMP .6 97 .68915 Temperature at outlet

Two TEMP.

7

87 .646 29 F Leaving cooled water temp.

Tchwo TEMP. 9 42.41007 F Chilled water outlet temp.

69
Listing 6-4 SAMPLE OUTPUTS AND INPUTS IN CHILLEXP . WK1 , FROM

EXAMPLE 3 (continued)

Simulation Inputs

Mnemonic Name Value Unit s PLRset CTRL . 1 1 kW/kW

NFanHi CTRL.

2

0 —

CtrlMode CTRL.

3

0 —

Nset CTRL. 1 —

CtrlMode CTRL.

6

0 —

PLRset CTRL.

7

1 kW/kW

NFanLo CTRL.

8

2 —

FlwCdw FLOW.

2

1200 gpm

Flow2 FLOW.

3

1200 gpm

Flowl FLOW. 5 1000 gpm

Flow2 FLOW.

6

1000 gpm

Pbaro PRES .

1

14 .6 96 p sia

Tdb TEMP.l 86 F

Twb TEMP. 2 77 F

Tchwi TEMP.

8

52 F

Tchset TEMP. 11 42 F

(Page Right for Outputs)

Definition

Setpoint part-load ratio

# cells on high fan speed

0=>use Tset; l=>use PLRset

Controlled Inlet Number

0=>use Tset; l=>use PLRset

Setpoint part-load ratio

# cells on low fan speed

Condenser water flow rate

Flow rate at second inlet

Flow rate at first inlet

Flow rate at second inlet

Barometric Pressure

Entering air dry bulb temp.

Entering air wet bulb temp.

Ch.w. return (inlet) temp

Setpoint chilled water temp.

70
Listing 6-5 LINEAR INPUT RANGE IN CHILLEXP. WK1, FROM EXAMPLE 3

AG AH AI AJ AK AL AM AN

1 Linear Input Settings

z

3 Number of variable inputs: 1 4 Number of steps for each: 10

5 Output Data Set Number: 3 o

7 Var. Variable First Last

8

9

10

No. Name Value Value

1 TEMP. 8 47 52

11

2

12 3

13 4

14 5

15

16 Current Mode: Line Input

17

18

19

20

71
Listing 6-6 OUTPUT REGIONS IN CHILLEXP. WK1, FROM EXAMPLE 3

A B C D E F G H

1000 ROW # TIME Ctrl. 2 ct rl . 8 Ctrl. 6 FLOW.l MISC.3 MISC.6

1001 0 0 2 0 0 320000 0.803233 3.225087

1002 1 1 1 1 0 241000 0.817282 3.323167

1003 2 2 0 2 0 162000 0.83 8406 3.392976

1004 3 3 0 1 0 97 000 0.919391 3.076503

1005 4 4 0 0 0 32000 1 2.243687

1006 5 5 0 0 1 32000 1 2.242043

1007 6 6 0 1 1 97000 0.842351 3.045848

1008 7 7 0 2 1 162000 0.678799 3.302174

1009 8 8 1 1 1 241000 0.636020 3.223694

1010 9 9 2 0 1 320000 0.606935 3.125238

A B C D E F G H

1250RCJW # TEMP. 8 FLCW.l MISC.3 MISC.6 P0WR.4 POWR. 5 TEMP. 3

1251 0 47 162000 0.054520 2.999102 21.57314 395.6922 42.00005

1252 1 47.5 162000 0.159560 2.952600 63.15725 395.8195 42.00024

1253 2 48 162000 0.264272 2.974857 104.6635 396.0435 42.00020

1254 3 48.5 162000 0.368379 3.038046 146.0286 396.4080 42.00017

1255 4 49 162000 0.471933 3.123 506 187.2935 396.8639 42.00024

1256 5 49.5 162000 0.575129 3.216370 228.5290 397.3524 42.00028

1257 6 50 162000 0.678233 3.302918 269.8047 397.8051 42.00026

1258 7 50.5 162000 0.781343 3.370238 311.1339 398.2039 42.00025

1259 8 51 162000 0.884666 3.406227 352.5517 398.5136 42.00025

1260 9 51.5 162000 0.988439 3.400861 394.0916 398.7007 42.00025

1261 10 52 162000 1 3.408575 400 . 27 57 400.2757 42.40727

A B C D E F G H

1500RCW # TEMP. 8 FLOW.l MISC.3 MISC.6 POWR.

4

PCWR. 5 TEMP.

3

1501 0 47 162000 0.527972 2.814210 208.6351 208.6351 42

1502 1 47.5 162000 0.57 9 57 2 2.951709 229.49 86 229.49 86 42

1503 2 48 162000 0.631595 3.074360 250.3621 250.3621 42

1504 3 48.5 162000 0.6 83 47 4 3.181964 271.2256 271.2256 42

1505 4 49 162000 0.735228 3.272224 292.0891 292.0891 42

1506 5 49.5 162000 0.786907 3.342945 312.9526 312.9526 42

1507 6 50 162000 0.838563 3.392285 333.8161 333.8161 42

1508 7 50.5 162000 0.890254 3.418931 354.6796 354.6796 42

1509 8 51 162000 0.942043 3.422221 375.5432 375.5432 42

1510 9 51.5 162000 0.993994 3.402220 396.4067 396.4067 42

1511 10 52 162000 1 3.408641 400.2819 400.2819 42.40712

72
7 . CONCLUSION

Of the six program design goals listed in the introduction, the first two,

limited hardware dependence and graphical output capabilities, were

achieved by basing the method on an existing spreadsheet program which

already has these features. The third, not usurping the decision-making

power of a plant operator, was met by developing a simulation methodology

which makes no attempt to optimize system performance of its own accord

but instead encourages the user to evaluate different alternatives and to

select what he believes is the best mode of plant operation. The fourth,

flexibility, was achieved by using a modular method with provisions for

linking components together into the configuration of a specified plant.

The fifth, simplicity, was partially achieved by developing procedures for

turning general-purpose component modules into models for specific

equipment without demanding that the user understand the mathematics

behind the models.

It should be noted that these last two goals of flexibility and simplicity

are not independent and tend to conflict. The tradeoffs made in developing

POST have tended to favor flexibility at the expense of simplicity. The

developers of the spreadsheet program upon which POST relies have attempted

to make their program both flexible and easy to use, and POST owes its

existence to the success of their efforts. Hopefully, POST will be judged

easy to use for the same reasons that spreadsheet programs are, since it

takes advantage of the same menu-driven command structure.

73
Finally, the sixth design goal was to produce a powerful method which would

be useful to persons with a wide range of technical sophistication. The

authors believe that the power of the technique has been demonstrated, but

its usefulness will depend largely on its success in actual plant applications.

At present, the utility of POST in an actual heat ing/cooling plant environment

remains to be tested.

74
8. REFERENCES i

Haynes, J. , 1985. "Circuit Design with Lotus 1-2-3." BYTE , Vol. 10,

No. 11.

Johansson, J. , 1985. "Simultaneous Equations with Lotus 1-2-3."

BYTE , Vol. 10, No. 2.

Kelly, G.E. , 1978. "Recommended Testing and Calculation Procedures

for Determining the Seasonal Performance of Residential Central

Furnaces and Boilers." NBSIR 78-1543.

Lotus, 1985. 1-2-3 Reference Manual . Massachusetts; Lotus Development

Corporation.

Stoecker, W.F. , ed. 1975. Procedures for simulating the performance

of components and systems for energy calculation . New York;

American Society of Heating, Refrigerating, and Air-Conditioning

Engineers, Inc.

Whillier, A., 1967. "A fresh look at the calculation of performance

of cooling towers." ASHRAE Transactions . Vol. 82, pt. 1, p.

269.

75
Table

1.

Cbntants

for

Determining

Temperature

Cbefficients

far

the

Heat

Capacity

of

Air

and

the

Products

of

Combustion

at

Constant

Pressure

ON T1 ’© '© '© '©

tH rH rH rH X X X X

m 00 «n d

d §

tH

53

t~* aco

co

c—

5n

in r» co tT cs

T—

1

© © co vo

cs rH rH vo rH

«r» fp

ON

1 -12 '© '© o © rH rH rH rH X X X X

cs 00 vo co a §

vorCOr* a § a

cs «n cs co

cs vo <s rH CO «n T

cs

2

s

VOS

8

x

VO

OvVO

Ov'o

a

«nT

csr.

mVO

coa

? ? © ©

o

Tl TL

00

- VO S?* 3 03 vo

co

cs•n 8rHco

CO © §

co «n VO

co vo r>

rH cs ON

X

S’

csr*a

<N

«T> ON Y

1 '© '© '© '©

rH rH rH rH X X X X $ §8 £R 3 8

ON cS co rH

«N ON c- c— 00 CS o

00

rH VO

rH 83 On

On

00©

03 t~; >n n CS CO 00 00

1 cs

. rH CS CO «n

76
COMMAND

MENU

STRUCTURE

77

Figure

1.

Command

Menu

Structure

in

POST

Worksheet
SETUP

WORKSHEET

GEOGRAPHY

78

Figure

2.

Layout

of

SETUP

Worksheet
POST

WORKSHEET

GEOGRAPHY

>0

z0

LL0

X

LL

CL

LL

, FA

FH,

#1

First

worn pon

ent

#2

etc.

N

UJ

#5 >

UJ

QCUJ

Con

#

Rudiment Instruct

0

<

LL<

o

cl

a «i ® —

— 3 —

o a. £

g- 3 -1 £ o

> « 1 §

® UJ

J2 a . i £

in

«5 3 If

55

O </) 1 1

1

® — ®

CL CO c * — CO

o> - 2 ® >- ^ Q. ® w 3 35 = a;

J5 ® 3 M 3 Q O

=

a _ </> V.

v; Q. CM

</> ^

g * ©*-(/> r => o o o. © . ii«

05 O

05

"T 1/5 CM CM

*3

" 1/5 CM CM

CM CM

79

Figure

3.

Layout

of

POST

Worksheet
3

Q_

h”3O

C\l

h~3

CL

h”3o ©

coH3

CL

h"3O o

o©

LL0I

(0J 3

CL

h"3O

CM

h“3

CL

h“3O

coh—3

CLH3o

80

Figure

U.

Component

Connections

for

Example

1:

Three

Gas-Fired

Boilers

Operating

at

Identical

Part

Load

Factors
i 00

oj

c\i

q

oj

CD

C\J

oo

d

o

in

co

o

oo

_L

LO o

JL

LO

CD

O

CD

LO

LO

_L

o

LO

_L

LO o,3"

(%) AONdlOlddd IAI31SAS

T3

0)

Ct.

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c3 O

0)

0)

5-1 -CH

4-1O

a

s

COX

td

e u

0J <u

4-J —I M m-4 O

CO CO

in

CD

5-1 a

bO

•H

81

BUILDING

LOAD

(kBtu/h)
00

c\i

c\i

o

c\j

u.

I(0

CQ u

O CN

<u

J-I <uS3

X

CM

CO

e o

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C/5 mH ^ o

00 30 O

<u

i-i 3

30

I O 00 CO CM

co h- r^

o

o

(%) A0N3l0ldd3 IAI31SAS

82

BUILDING

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Figure 8. Component Connections for Example 3: Cooling Plant System

Consisting of Two Chillers and a Cooling Tower

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TEMP.
NBS-114A irev. 2»8C> U.S. DEPT. OF COMM.

e.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

4. TITLE AND SUBTITLE

PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date NBSIR 88^37 40 MARCH 1988

Users Guide to Post - Plant Operations Simulation Template

5. AUTHOR(S)

George E. Kelly and Daniel R. Clark

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8 . Type of Report & Period Covered

WASHINGTON, D.C. 20234

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City » State, ZIP)

U.S. Navy Civil Engineering Laboratory

Port Hueneme, CA 93043

10.

SUPPLEMENTARY NOTES

j~ Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here)

A non-proprietary simulation template program named POST (Plant Operations

Simulation Template) has been developed for use with the Lotus 1-2-3*

spreadsheet. The template provides for mathematical simulation of central

heating/cooling plant equipment including boilers, cooling towers, and

centrifugal chillers. It provides methods for configuring a simulation of a specific physical plant, defining operating conditions and time- dependent

boundary conditions, running simulations, and graphing simulation results.

POST is a flexible and highly portable analytical tool for plant equipment

operators and engineers concerned with efficient operation of physical

plant systems.

This Users Guide provides an overview of POST and its companion template

program SETUP, which is used to define the characteristics of component

models. Information is presented on the menu commands used in POST and

three examples are provided. The examples show how the template program

may be used to simulate the performance of a three-boilers heating plant

and a central cooling plant consisting of two chillers and a cooling

tower. Listings of the actual keystrokes for setting up and running both

simulations are included.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key

boilers; central heating/cooling plant; centrifugal chillers; cooling

words by semicolon s) towers

equipment performance; heating/cooling equipment; operating strategies,*

simulation; spreadsheet template

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

[XX Uni imited

1

I For Official Distribution. Do Not Release to NTIS

' Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

94

15. Price

X

-’ Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $13.95

USCOMM-DC 6043-P80