eQuest Boiler Curve Example

Topic: Efficiency performance curves published by equipment manufacturers may not be in a format helpful for energy modeling. This example presents a manufacturers condensing boiler, and derives a set of data points to which a curve can be fit using DOE2 routines.

The following efficiency curve is published by Aerco, representing the thermal performance of KC-1000 Series condensing boilers; the color annotations have been added by the author:

(click on the image to see a larger version)

The three curves on the chart represent firing rates of 37.5%, 75% and 100% from top to bottom. Thermal efficiency can be read on the vertical axis by knowing the firing rate and return water temperature. eQuest/DOE2 however requires input data points for boiler performance curves to be in entering water temp / leaving water temp / heat input ratio (inverse of thermal efficiency) format.

According to the chart, thermal efficiency is independent of both flow and supply water temperature, so the firing rate data curves and entering water temperature points should indicate efficiency regardless of the infinite combinations of flow rates and supply temperatures possible. This produces however, essentially an infinite number of efficiency curve solutions. To solve this problem, we must temper the manufacturer's published data with a measure of sound engineering judgement.

(click on the image to see a larger version)

Realizing that a low firing rate should occur at low load conditions, a high firing rate at high load conditions, and a mid firing rate somewhere in between, let us make the careful assumption that a high firing rate will result in a 40° (100%) ΔT, a mid firing rate in a 30° (75%) ΔT , and a low firing rate in a 15° (37.5%) ΔT across the boiler.

Using these ΔT's, we can now compute a corresponding leaving water temperature for each of the data points on the chart, except for the five at the extreme right. Efficiency is poorest here as entering water temperature approaches that of leaving water temperature. So dispensing with these data points should not detract much from the resultant accuracy of the curve fit, since our control system and operational sequencing should not allow the equipment to operate in this regime anyway.

Following is the BDL code required for a binomial quadratic curve fit of the Aerco KC-1000 condensing boiler's heat input ratio in terms of entering and leaving water temperatures:

"Aerco-KC1000-HIR" = CURVE-FIT
TYPE = BI-QUADRATIC-T
INPUT-TYPE = DATA
INDEPENDENT-1 = ( 80, 80, 80, 100, 100, 100, 120,
120, 120, 140, 140, 140, 160 )
INDEPENDENT-2 = ( 95, 110, 120, 115, 130, 140, 135,
150, 160, 155, 170, 180, 175 )
DEPENDENT = ( 1.010, 1.070, 1.093, 1.058, 1.111, 1.117, 1.093,
1.136, 1.143, 1.130, 1.143, 1.149, 1.136 )

In addition to efficiency, another significant item that needs to be changed when comparing firetube to condensing boilers parametrically is the standby time, which figures directly into standby losses as a percentage of full load capacity.

For example, the default STANDBY-TIME of 0.027 (corresponding to a standby loss of 2.7%) in eQuest may be a bit high for larger firetube boilers; check the manufacturer's data as relative standby losses tend to decrease as boiler size increases. However, condensing boilers do not need to stay warm to avoid thermal shock; hence standby loss factors are on the order of one-tenth that of firetube boilers.

Per Cleaver-Brooks, the standby loss on a 1,000,000 BTU per hour Clearfire condensing boiler is 1810 BTUH or 0.1810%, which translates to a STANDBY-TIME of 0.00181 factor.

eQuest Detailed Editor Checklist

Topic: Miscellaneous notes for using eQuest in detailed edit mode.

eQUEST DETAILED EDITOR

Post-Wizard Shell Editing

• Add note about saving wizard snapshot...
• Add any missing upper level shell exterior walls.
  
• Import the following BDL code fragments from the network library:
• H:\eQuest\Library\Envelope_WSEC_Compliant.inp
  
  and, if doing an ELCCA...
  
  
• H:\eQuest\Envelope_ELCCA_Prescriptive.inp
• Assign the baseline envelope shell components corresponding to WSEC Compliant
  
• Remove the roofs of lower-level shells where upper level shells are placed.
  
• Verify that the floors of the upper level shells are adiabatic; it may be helpful to separate the shells by temporarily specifying z-coordinates of 100 feet or more between them.
  
• Define air-walls between zones where appropriate.

Post-Wizard Space Editing

• Specify the number of people per square foot under the 'Basic Specifications' tab of the Space Properties dialog box for each space.
  
• Do this or else eQuest will calculate the people density for you, and it will be low
• Specify 31 persons for classroom, multiply the number of classrooms in the space, and divide by the total square footage of the space.
  
• Specify the maximum number of occupants of the school for gymnasiums, cafeterias, auditoriums and multipurpose rooms; scheduling will account for daily diversity.
• Specify 75 SF/person for administrative areas and libraries
  
• Specify 1000 SF/person for restrooms, corridors, and support areas; this will help to moderate outside air demands.
  
• Note that when the area per square foot is specified, and the number of people are reset to the default or 'green' value, this default value is calculated by eQuest to be the total area divided by the people factor per square foot.
• Check daylighting sensors for location and orientation; adjust as required.
  

Renaming Spaces, Zones and Systems

Renaming shells, spaces, zones and systems to improve the interpretability of simulation output and improve the accuracy of internal load factor assignment is best done at the beginning of detailed edit mode. The 15 minutes to half-hour spent doing this will pay great dividends going forward, for even modestly complex projects.

• Rename Shells: By default all shells are named "ELn Ground Flr", where "n" is the sequence number of the shell in the order in which it was added to the project. Rename the shell to something more descriptive like "EL1 Bldg 100" or "EL2 Second Floor" while retaining the shell designation prefix, which is used throughout the project by eQuest for the automatic naming of related components.
• Renames Spaces: In Component Tree view, next rename spaces for each shell to something more descriptive. For example, a group of classrooms may be automatically named "EL2 North Perim Spc (G.N1)"; rename to something like "EL2 Classrooms North Space", retaining the shell designation prefix and adding the "Space" suffix.
• Renames Zones: Switch to the Air-Side HVAC tab. Starting at the top of the component tree, double-click on each zone and rename it corresponding to its space. For instance, continuing the previous example, rename "EL2 North Perim Zn (G.N1)" to "EL2 Classrooms North Zone"; note that the corresponding space is listed in the properties dialog box of the zone for easy reference.
• Renames Systems, Single-Zone: For packaged single zone systems, rename the system to correspond to the zone. For instance, continuing the previous example, rename "EL2 Sys2 (PSZ) (G.N1)" to "EL2 Classrooms North Sys"; note that the corresponding zone is listed in the component tree view below the system for easy reference.
• Renames Systems, Multi-Zone: For multiple zone systems, rename the system to a using a general geographic designation. For instance, continuing the previous example, if the system type of "EL2 Sys2 (PSZ) (G.N1)" is changed from 'packaged single zone' to 'packaged multizone', the automatically assigned system name will not be changed by eQuest. Hence change the system name to something like "EL2 Multizone North System"; with the name selected to enable easy recognition when reading DOE2 reports.

Note: This needs to be integrated into a comprehensive sequential detailed edit checklist.

Post-Wizard System Editing

• Specify minimum CFM per square foot values for each system under the 'Flow Parameters' subtab of the 'Fans' tab of the Air-Side HVAC System Parameters dialog box for each system.
  
• Do this or else eQuest will calculate the value for you, and it will be low
• Specify 1.3 CFM/SF for classroom, administrative and other high-occupancy areas
• Specify 1.0 CFM/SF for gymnasiums, cafeterias, multipurpose rooms and corridors
• For cooling-only systems, remove the drybulb economizer lock-out. The default is 65°F, which is OK if mechanical cooling is provided. However to reduce the number of unmet load hours in natural, displacement and conventional ventilation systems without mechanical cooling, this constraint should be removed.
  

Parametric Runs

• Using spreadsheet view, set Daylighting to 'No' for all zones, for the baseline case.
  
• Create the following four parametric runs in the "working copy" of the project after it has been saved with all shell & envelope modifications captured:
  
• Envelope Improvements
• Lighting Improvements
• Daylighting
• Demand Ventilation
• Others may be added, specific to each of the particular systems studied, after the working copy of the project is saved in system-specific versions.
• Any 'Appendix G' baseline generally does not require parametric runs. [more detail]
  

Note: This is a work-in-progress procedure, additional details forthcoming time permitting

Doors & Windows

• Generally custom door and window placement should be accomplished in Wizard mode. The following procedures may be useful when doors and windows need to be defined in detailed edit mode.
  

• Assure that the total area of the windows does not exceed total wall area, else an error will result. This is problem can arise particularly on all glass stair towers, entryways, and corridors where the wall is essentially all glass. To prevent this from happening, the following user expressions may be used for positioning and defining the width and height of "glass wall" windows:
  

X = {PARENT("WIDTH")*0.025}
Y = 0
HEIGHT = {PARENT("HEIGHT")}
WIDTH = {PARENT("WIDTH")*0.95}

• The following expression may be used to center doors and windows in the parent wall:

X = {PARENT("WIDTH")/2-LOCAL("WIDTH")/2}

• The following expression places doors or windows centered on the one third or two thirds points from the origin of the parent wall, respectively:

X = {1*PARENT("WIDTH")/3-LOCAL("WIDTH")/2}
X = {2*PARENT("WIDTH")/3-LOCAL("WIDTH")/2}

• Use the following expression to create windows of a fixed height as wide as the parent wall:

WIDTH = {PARENT("WIDTH")}

• Use the following expression to right-justify doors and windows:

X = {PARENT("WIDTH")-LOCAL("WIDTH")}

• Editing Windows Frame and Spacer:
• In order to eliminate windows frame. first go to the Building Shell mode and click on Spreadsheet.
  
• While on the Component Tree tab, click on one of the windows (i.e E1 South Win).
  
• Change the Frame Width of the window to default (zero) - this can be done easier and faster using multi-edit if you working with thousands of windows.
• Next, change the frame spacer type from the default 'Aluminum' to 'Insulated'
• WRITE-UP MULTIEDIT METHOD USING REGULAR EXPRESSIONS.
• 
  

Schedules

Follow this link for schedule sharing. Implement common schedules now so you don't have to do it 3 or 4 times going forward.

Fan Schedules

After implementing the schedules sharing, the "Fan Schedules" in the Fan Power and Control tab needs to be adjusted. The Cooling should be set automatically to ESM Fan Sch after the schedule input; however, the Exhaust tab will still be empty. ESM Exhaust Fan Sch need to be selected in the Exhaust tab.

Simulations

Change the TITLE, LINE-1 parameter at the beginning of each baseline INP file.

• Rename systems appropriately (e.g. PVVT, PSZ etc.) to for instance, GSHP using MultiEdit (expound).
• Noted if system name is changed via GUI or inp, any reference to the system name in the parametric run definition (.prd) file must be changed manually, most easily via text editor.

Run trial simulation for each system type.

• Eliminate any errors (e.g. 'LOOP has ZERO FLOW') to obtain valid trial simulations.
  

• Examine .SIM output file for each valid trial simulation, and update .INP file to eliminate warnings and errors.
• Exceptions: __ warnings are insignificant (list).
  

Run the 'Annual Energy Consumption by Enduse Report' for the baseline for each system (need graphic).

• The lighting, misc. energy usage, ventilation, domestic hot water and ___? should all be the same.
• If not, there is a variance in the energy densities or scheduling...correction needed.
  

eQuest Graphical Editor Notes

Topic: The eQuest graphical editor is simple, but the documentation for it is difficult to locate. This post is a quick-reference guide.

Use the following list of keyboard and mouse combinations within the eQuest graphical model editor window:

• 'W' changes to wireframe view mode
• 'S' changes to surface view mode (default)
• Ctrl+ left mouse button allows 3D model orbiting with the mouse
• Ctrl+ right mouse button allows 3D model zooming with the mouse
• Right-clicking with the mouse deploys a context menu with additional options

If the building model "disappears" in the process of orbiting and zooming, click out of the 'Building Shell' on the toolbar, for instance to 'Internal Loads', then back to 'Building Shell'. Then right-click within the graphical display window and select 'Reset Camera'.

Contents of eQuest Project/Runs List

Topic: In Reports Output mode, what controls the contents of the list in the Project/Runs tab, and how can that list be edited?

The Project/Runs list is populated by the simulation results that are contained in the "Projects" folder of your eQuest program directory.

If it is desired to prevent items from showing up, one alternative is to make a new folder (for example, "Projects Archive") in the eQuest program file directory and move the unused files to that folder.

For eQuest projects stored in a network folder, the results viewer will show the results for all projects in the "Projects" folder of eQuest along with all of the results that are in the folder for the currently active project. Thus copies of known good baseline projects may be stored locally, for use in comparison to network projects under development.

It may also be necessary to edit feed the .pdh file with a text editor. For example, if parametric runs are renamed, the .pdh file may continue to list the old names; in this case the old names contain 'DCV' resulting in an erroneous project/runs list:

1,"Garfield ES - GSHP" ,
1,"4 - Classroom, Admin & Library DCV" ,"Garfield Elementary - GSHP - 5" ,1172020623,
1,"3 - Gym & Cafeteria DCV" ,"Garfield Elementary - GSHP - 4" ,1172020604,
1,"2 - Lighting Improvements" ,"Garfield Elementary - GSHP - 2" ,1172020568,
1,"1 - Envelope Improvements" ,"Garfield Elementary - GSHP - 1" ,1172020551,
1,"Baseline Design" ,"Garfield Elementary - GSHP - Baseline Design" ,1172020536,
1,"4 - Demand Ventilation" ,"Garfield Elementary - GSHP - 4" ,1172012402,
1,"3 - Daylighting" ,"Garfield Elementary - GSHP - 3" ,1172012385,
-1,

Simply delete the lines containing old parametric run names from the .pdh file, replacing them with the lines containing the new names:

1,"Garfield ES - GSHP" ,
1,"4 - Demand Ventilation" ,"Garfield Elementary - GSHP - 4" ,1172012402,
1,"3 - Daylighting" ,"Garfield Elementary - GSHP - 3" ,1172012385,
1,"2 - Lighting Improvements" ,"Garfield Elementary - GSHP - 2" ,1172020568,
1,"1 - Envelope Improvements" ,"Garfield Elementary - GSHP - 1" ,1172020551,
1,"Baseline Design" ,"Garfield Elementary - GSHP - Baseline Design" ,1172020536,
-1,

Be sure to do this with eQuest closed; upon reopening eQuest the project/runs list should now meet or exceed expectations.

eQuest Analysis Project Structure

Topic: How best to structure an eQuest analysis project?

The following is a suggested file naming convention for eQuest analysis projects:

• project_name_baseline
• project_name_baseline_envelope
• project_name_baseline_electrical
• project_name_alternate_#1
• project_name_alternate_#2
• project_name_alternate_#n

In order to work with the eQuest limit of analyzing up to five ECM groups side by side, the following procedure is suggested for separating envelope and electrical ECM groups from mechanical ECM group alternates.

• Fully develop the mechanical baseline run analysis without ECM's, using code-minimum windows, walls and roofs.
  
• Save as the envelope and electrical options as shown in the file naming convention above.
• Add proposed envelope and electrical ECM's to the respective analysis run, and
  
• Determine the recommended ECM package for each using the baseline mechanical equipment.
  
• Analyze the mechanical ECM groups in the baseline and alternates, with the selected envelope and electrical ECM packages "rolled up", into a single ECM group.