Appendix E: Ground-Source Heat Pump Modeling using ApacheHVAC and Gaia Geothermal Ground-Loop Design (GLD)

Capability for transferring hourly equipment loads and final results between the IES Virtual Environment and Gaia Geothermal’s Ground Loop Design (GLD) provides for comprehensive and detailed modeling and design of ground-source heat pump HVAC systems. For more information on GLD software, go to: www.gaiageo.com   If you are interested in using this coupling of Gaia Geothermal and the IES VE, be sure to check with the distributor of Gaia GLD, Thermal Dynamics Inc., at sales@groundloopdesign.com for discounts that have been and may still be available to licensed IES-VE users.

 

Modeling Ground-Source Heat Pump HVAC Systems

There is not yet an explicit ground-source heat pump model within ApacheHVAC; however, loads results can be read into Gaia Geothermal’s Ground-Loop Design tool. This provides detailed modeling of heat pump equipment and bore fields.

Begin by modeling the building as you would otherwise in the VE and the appropriate HVAC system in ApacheHVAC, including all controls, air-side components, coils, terminal units, hydronics, water loops, etc. and a boiler and chiller to provide the hot and cold supply water with suitable water loop flow rates and temperatures. Include any loop temperature rest schemes that will be used with the ground-source heat pump (GSHP) system. The ApacheHVAC boiler and chiller components are a placeholder that will simply record loads for the GSHP, ground-source loops and pumps, geo-exchange bore fields, backup heating and cooling equipment (boiler and cooling tower), and time-of-use (TOU) demand-based heat pump controls that can be modelled in GLD 2010.

Prior to running the simulation, set the ApacheSim reporting interval to 60 minutes. Having completed up to a full year of simulation in the IES Virtual Environment, instructions from Gaia Geothermal are as follows:

Import the .aps results file from the VE into GD via either of the GLD Loads modules (Average Block or Zone Manager).  Clicking the Import button (arrow that goes down to the left) opens a dialog that allows import of .aps or .csv files into the Loads module. The .csv option allows for manipulation of loads between the VE and GLD using a spreadsheet to account for an uncommon heating or cooling source or scheme that is not yet available in either the VE or GLD, and thus which would reduce the load passed on to the GSHP.

Do not use the Loads > Import Loads Menu item in GLD to import .aps files, as Gaia Geothermal have not set this up yet to work with .aps files.  The .asp file import for boiler and chiller loads from the VE must be done through one of the Loads modules (Average Block or Zone Manager).

Create a Borehole Design project and make sure it is properly linked to the correct Loads project—i.e., it is populated from the .aps or .csv file that contains the loads from the VE.

From this point forward, use GLD as you would otherwise to model the complete GSHP system, including detailed bore field design and manufacturer heat pump performance data.

Once the analysis in GLD is complete, you can export from GLD to an .aps file that IES VE can then read for display and further analysis of results.  The steps for that are as follows:

1.       Completed the Hourly simulation in GLD

2.       Go to the main File menu > Export File > Export APS and save the data generated by GLD as an .aps file that can be read by IES VE.

The following requirements must be adhered to for exporting APS files from GLD for use with the IES VE:

A.      Make sure you run the GLD program as an Administrator on Windows Vista or Windows 7

B.       Must run an Hourly Simulation in the BoreHole Designer

C.       Do not exceed a 1-year modelling period (Prediction Time)

D.      Make sure that the "APS FIles" Folder exists in the GLD2010 directory.

Note:  A quick way to test the Hourly simulation and the ability to export the .aps files is to use a very short prediction time in GLD, such as 0.1 years, so that you don’t have to wait a long time for the full year analysis.

GLD results exported to the IES VE .aps file should appear in Vista Results as in the screen capture above.

If you have followed the steps above without success, first check that the .aps file from the VE does in fact include boiler and/or chiller loads to be addressed by the heat pump system. If you have confirmed these loads are present in the file, but are still having difficulty, Gaia Geothermal has expressed willingness to provide technical assistance to GLD users to address any import/export issues.