I am trying to model a DOAS system with terminal units hooked up to a ground source heat pump. I have set up my geometry using pollination and then am running both daylight and energy studies within grasshopper. I have successfully modeled a variety of all air HVAC system (e.g. PVAV_PFP HB template and PVAV_DX_Elec IB template) as well as DOAS systems (e.g. DOAS_VRF). When I set up my model to run a ground source heat pump option, I run into errors on both the HB template (DOAS_WSHP_GSHP) and the Ironbug Sys 18 Template (Geothermal + DOAS). I have included the severe errors I received for both options. I have tried various iterations (within Pollination rhino interface, bypassing the daylight study, etc.).
Error with the HB Template:
** Severe ** DualSetPointWithDeadBand: Unanticipated combination of heating and cooling loads - report to EnergyPlus Development Team
Error with IB template:
- ** Severe ** [json.exception.out_of_range.403] key ‘g_functions’ not found
I am hoping that someone might have run into something similar and may be able to help me navigate and fix this so I can ultimately run a GSHP option for my highly conceptual design study. Also if anyone does have a better way to conceptually model a ground source heat pump option that has worked for them I would greatly appreciate it.
Hi @chris and @MingboPeng,
I’m working with @dftraver on this project and we’re running into a real barrier that seems to be a problem with OpenStudio. The above error message might be a false positive, with the real error being lack of convergence in the Zone Heat Pumps. Check out the attached full error report.
Things we’ve tried but didn’t help:
- Increase timesteps per hour from 4 to 6, 10, and 30.
- Increase warmup days from 25 to 40
- Simplify geometry and test again
Do you think these convergence errors with the HeatPump components are related to Ladybug or OpenStudio?
eplusout.err (168.6 KB)
Hi @dftraver @Justin_Shultz, I will check this issue in detail later today, but the GSHP is a very complex and project-specific system. The templates from IB or HB are mostly simplified and use other systems to mimic GSHP (this is what OpenStudio Standards does under the hood).
If you want to use something closer to a real GSHP, you can use this template “GSHP_CentralHeatPumpPlantloops” from the “03_Other” group. Note that this is also a simplified system, and this is an example of plant loops that are connected to the GroundHeatExchanger. You will need to integrate these plant loops into your existing systems.
I have followed your advice to add GHE (Ground Heat Exchanger) to the geothermal + DOAS template. I am trying to have geothermal as the sole HVAC system, and I have removed the DOAS coils. However, I still have heating coil electricity consumption that activates during heating. I understand that this means the geothermal well is undersized, and I need to increase the depth or the number of loops. But when I do the latter, the heating coil electricity load doesn’t change at all.
In principle, I want to use this template in multiple buildings simultaneously in a Dragonfly workflow. How can I automatically size the well or simply set a well depth that would suffice for any building in the study?
Hi @Batiste, as far as I know, there is no way to autosize the well in EnergyPlus/OpenStudio. Please let us know if you found a solution for this.
Thank you for your response @MingboPeng . The only idea that comes to mind right now is to first calculate the load and then use a small script to incrementally change the number of wells. (Taking into account soil properties, etc., it would be possible to determine the theoretical power that, for example, 100m of well could provide and then multiply that well to meet the demand). The other question I had in my previous message was about how to eliminate the substitution system for the geothermal part. I’ve tried it for a house with a maximum load of 8kW and I’ve added 20 or 30 100m wells, but the electrical substitution system still triggers.