DOE/ORNL Heat Pump Design Model

Notes on Updated Web Interface and Capabilities:

Over the fall and winter of 2000/2001, a number of improvements were made to the Web model to improve functionality and usability. These changes were beta tested in the spring by a selected group of users. Further adjustments, improvements, and navigation changes were made as a result of their feedback.

This model supercedes the previous official version (Oct. 24, 2000). User saved data sets should work with this new version. (If you find this isn't the case, please let us know so we can try to resolve any remaining backward compatibility issues.)

The listing below summarizes the Web model improvements. This is followed by further discussion of  the changes by category.

Summary of Updated Web Model Interface and Capabilities

The new interface features and capabilities include:

  1. improved page layouts for compressor data, indoor and outdoor units, refrigerant lines, and accumulator,
  2. simplification of required compressor input to use more readily available rating information (capacity and EER) and new checks to make sure the refrigerant used for the system is the same as for the compressor map,
  3. capability to scale compressor capacity and EER levels (in addition to the existing option of scaling to the desired system capacity),
  4. option to specify fan power per unit airflow,
  5. a second output page summarizing HX and compressor performance, flow control, HX, and compressor sizing calculations, and charge inventory information;
  6. option to save calculated flow control and compressor sizing and charge info for off-design calculations,
  7. an ambient control option under parametrics which lets users specify condenser subcooling and/or superheat as a function of outdoor ambient, and
  8. two-variable parametrics with contour or 3-D (surface) performance plotting capability, such as capacity and EER vs outdoor ambient and indoor airflow rate.
The example case has been changed to use an R-22 scroll compressor of 10.9 EER with a default indoor fan power of 365W/1000 cfm. Previously we used a 10.6 EER reciprocating compressor of similar capacity (28 kBtuh) and a fixed indoor fan power of 293W.

Further Description

The following is a more detailed description of the new interface features that have been added from the previous official version of the Web model.


CONTINUE, JUMP, and DONE buttons (as appropriate) were added to the upper rightmost corner of input pages to have one consistent location for moving from page to page. We also included a second set of these buttons at the bottom center. One can now alternately "continue" to the next page by just using the Enter (or Return) key (if no selections are made on the page).

Selecting the CONTINUE button proceeds to the next input page.

Using the JUMP button allows one to "jump" to a new section -- either ahead or back.

Choosing the DONE button skips to the end of the input data.

The first page of a New Case lists all the data input sections and allows the user to jump to any section as does the Revise Input Data button at the end of the data input.

Compressor Data

We made a number of changes in the compressor map and sizing pages. On the compressor data page, the rated compressor capacity, EER, and refrigerant are now required (items previously included in the comment line on the sample data sets). Harder to obtain data like the compressor motor size, displacement, and nominal speed are now optional. If not user specified, motor size is calculated using the rated compressor capacity and the assumption of one horsepower per ton of cooling capacity.

We now use the specified refrigerant for the map to prevent a user from using a (refrigerant-specific) compressor map with the wrong refrigerant. On the preconfigured compressor map page, all the compressor model choices available for the selected system refrigerant are displayed in Bold text. If a map for another refrigerant is selected, the system refrigerant is automatically changed as well.

For older user data sets which do not have the compressor refrigerant, EER, and capacity specified, we use the system refrigerant and somewhat arbitrarily set the EER to 9.999 Btu/W-h and the capacity to 29999 Btu/hr. If possible, these default values should be replaced with the appropriate rated levels.

The compressor field adjustment factors were moved to the sizing page which is now called the Compressor Performance Calibration & Scaling page. Here, users can scale both the capacity and EER of the compressor or just use the field calibration factors based on lab data from one rating point. Scaling the compressor capacity scales the displacement and motor size while changing the EER level adjusts the compressor power draw. The system capacity can also be set here as before but now the provided compressor capacity is used to determine the initial scaling guess for compressor displacement to reach the specified system capacity.

Heat Exchanger Data

The layouts of the indoor and outdoor coil pages were extensively revised per suggestions from an industry user to present this information more compactly for easier viewing with less scrolling.

The option of specifying fan power per unit flow (Watts / 1000 cfm) for either or both coils was added to the coil input screen. This feature applies for single point runs and for parametrics when the indoor and/or outdoor airflows are changed. The ARI indoor default value of 365 Watts / 1000 cfm is now used as the sample setting for the indoor coil and a value of 75 Watts / 1000 cfm is the default on the outdoor coil, if selected (although the sample setting for the outdoor coil fan power is still 220W independent of airflow).

As part of the HX layout simplification, we no longer include the fin choice of specific zig-zag pattern. Previously saved data sets of this type should still work if users don't go back to the HX coil data pages. We plan to provide an equivalent replacement for this in the Mark VI Web version planned for later this year where more surface types and geometries will be covered.

Refrigerant Lines Data

On the refrigerant lines page, we simplified the word descriptions, reorganized the bottommost elements and reduced the page size a bit.

Accumulator Data

The accumulator input page was improved with a diagram and input labels similar to the coil pages.

New Output Page - Component Sizing, Charge, and Performance

The model output screen now shows two cycle summary diagrams,

"Equipment Operating Conditions and Performance" and

"Component Sizing, Charge, and Performance",

and various selection buttons. The View Page 1 & 2 selections let you display the output pages individually for printing without the navigation buttons. New "View Extended Text" and "Revise Input Data" buttons have been added here as well.

The new "Component Sizing, Charge, and Performance" diagram shows:

  1. heat exchanger sizes and performance,
  2. compressor size, scaling, and performance,
  3. specified or assumed flow control characteristics and calculated sizes, and
  4. charge inventory distribution and total required charge.
This page also has a "Save Sizes and Charge" button at the top that lets the user save flow control and compressor sizes and the calculated refrigerant charge for subsequent use in an off-design simulation. This button works like the "Revise Input Data" button except that the calculated sizes for all flow control alternatives are used to update the input sizes and the required refrigerant charge is set to the input value. To run off-design cases, one now only needs to select how charge is to be balanced and the type of flow control. (In the earlier version, one had to dig out these flow control and charge values from the extended text output listing and manually specify them on various input screens for off-design cases.)

The "Save Sizes and Charge" button also updates the compressor displacement and motor size if the compressor was scaled in the previous run. (Note that if one goes back to the compressor selection, data, or scaling pages and then uses the "Continue", "Jump", or "Done" buttons, the compressor data reverts to the originally selected compressor.)

New Output Option

Users can now choose to have the summary and parametric output shown in either absolute or gauge pressure. This is set in the Output/Convergence section and is retained as a setting along with the saved user data file.

New Parametric Capabilities

Regarding parametrics, the following new capabilities were added: Whereas the previous Web version provided for one-variable parametrics and x-y plots, we have now enabled two-variable parametrics and 3-D or contour plotting. The default setup is for two-variable parametrics, varying outdoor ambient temperature and indoor airflow rate, as an engineer might do to generate a range of performance values for a specified set of indoor conditions. (One-variable parametrics are still possible by selecting "None" for the second variable under "None of the Above" at the bottom of the list on the Available Operating and Design Parameters page.)

The resulting output data sets are presented in tables of values that correspond directly to the locations of the varied independent parameters on the plots. As in the case of the previous 1-D parametrics, one can select any of the numbered buttons to view the summary cycle and performance diagrams for any individual run. The shaded items under the "Selected Results" are the minimum and maximum values for each dependent variable.

The user can view the results as 3-D (surface) or contour plots. For the 3-D plots, contours of constant z-values (the dependent values) are also shown. As in the one-parameter case, the generated performance data can be exported in spreadsheet format for use in Excel or engineering plotting packages for making more publication quality plots.

The parametrics are limited to 7 values in each independent variable (for a maximum of 49 runs of the model at one time).

A new ambient control option was added to the parametric choices of Available Operating and Design Parameters under Outdoor Air Inlet Temperature. This option allows compressor inlet superheat and/or condenser exit subcooling to be given as linear functions of ambient whenever outdoor ambient is chosen as the parametric variable. Minimum and maximum levels can also be set.

The ambient control option can be used in lieu of a charge inventory balance to predict off-design performance for a system where superheat and/or subcooling trends are known from experimental tests on a unit with the same heat exchanger sizes, or for a family of units of similar heat exchanger design that scale up and down linearly in size and capacity. In cases where the HX designs are changing, the approach might be expected to remain the most applicable for systems where the flow control is a TXV or other type of variable opening device that maintains a fairly constant level of superheat. Further advice is given on the use of this option for predicting off-design performance, at this link, in lieu of or in conjunction with other system balancing approaches.

For purposes of model simplification, the previously allowed choice of void fraction model was removed. We still select the Hughmark method as the default for all charge calculations. (Users wishing to try other void fraction models can select them from within the Expert Mode under the Revise Input Data button, using the online heat pump data specification file as a guide to selecting from among ten available choices as described in the related online 1987 ASHRAE paper by Rice.)

New Input Data Requirements

As noted earlier, the only new input data you need to add to existing data sets are the compressor EER and capacity. The default values of EER = 9.999 Btu/W-h EER and capacity = 29999 Btu/hr will be assigned otherwise. If neither the correct compressor capacity or displacement are given, the calculated volumetric efficiency will be incorrect but the system performance calculations should be unaffected. As the compressor capacity is now used to estimate the motor size if not specified directly, the estimated motor operation point and efficiency will also be off if the correct compressor capacity is not given.

Closing Comments

We hope you find the updated Web version to be easier to use while providing helpful new capabilities. Please continue to let us know if the program is of benefit to you and/or how it could be made more useful.

We plan to upgrade the computational engine from the current Mark V version to Mark VI over the coming months. The Mark VI version has improved R-410A properties and is more HFC-capable in general. Let us know if you would like to be a beta tester for this version.


Many thanks to Bill Jackson (wlj) of ORNL, the originator and keeper of the Web model, for his capable implementation of the many interface and feature improvements and for his able management of the Web site. For further information on his Web applications of FORTRAN programs, select this link.