HVAC Geothermal Heat Pump with Floor Radiant ASHRAE 90.1

Hi all,

I have been modeling an HVAC system GSHP + Floor Radiant with IronBug.
I think there is something of wrong in my workflow, operative temperature is very high.
Comparison of three scenario with max operative temperature values for the three thermal zones:

GSHP + Floor Radiant

Packaged VAV with reheat

Plenum zones test

General details:

  • Heating System: Zone 0-1-2; Radiant panel supply by 1 Central Geothermal Heat Pump - no DOAS
  • Zone Serice Water: Only Zone 0; BoilerTank (mixed) + Hot Water by Geothermal Hot Water Loop

a) Do you have any idea? @mingopeng and HVAC experts.
b) How can I set “heating only” in this case?

Ironbug_HVAC_test00_GSHP.gh (823.3 KB)


@AntonelloDiNunzio I would take a closer investigation to the system.

  1. is the system big enough for your building.

A couple tests to verify this by: check the supply water flow rate and temperature to see if they are able to keep its maximum value relative constant throughout the year. You can add a probe at the end of supply side of water loop.

if you are seeing a pattern that temperature of supply water is increasing month by month, it might be an indicator that the your Central heat pump is overloading.
If this is the case, you just just do a simple test by replacing the central heat pump by district heating and cooling system to provide unlimited hot/chilled water to test if the rest system is working correctly.
If this improves your situation dramatically, then you should be looking into how to design and use a Central Heat Pump correctly. I will leave this up to you unless you want to discuss about this in detail if this is the case.

  1. to increase your testing speed, you can just use one simple zone, no window, all surfaces adiabatic, but the same space program type to ensure you have only internal load for system to deal with.
    Make sure your system work for this room first, and then apply it to your building. We want to isolate the problem with minimum variables.

Hi @MingboPeng,

I had a test.

  1. I have set a simple box with all adiabatic surfaces, space type “Office::OpenOffice”.
  2. I have added a probe to check supply exit node.
  3. I have added a switcher to change supply type: Geothermal Heat Pump or District Heating cooling.

GSHP Results:

  1. Series of warning because inner air temperature is extreme.
  2. Probe results:

District Heating/Cooling results:

  1. Series of warning because inner air temperature is extreme.
  2. Probe results:

Other tests:

  1. Plenum zone test:
  2. Packaged VAV with reheat

At this point, I am pretty sure there are some errors in how I have modeled plant loops and setpoint.
Could you take a look at this new file and give me a feedback about results above?

Ironbug_HVAC_test00_GSHP_probe_test.gh (818.2 KB)


Hi @AntonelloDiNunzio,

I looked at your file, one thing that I found is not correct is your construction setting for radiant floor. You have an insulation layer next to radiant source layer at inner side, which prevents heat exchanges between room and radiant system.

Here is I moved the insulation layer to outside of radiant source:

In terms of radiance system, to simplify the question problem here, I am only including the equipment and lighting loads here to be the only internal load for radiant system to deal with. More importantly, they are sensible loads, which is the type of load that radiant system only takes care of.

Here is indoor temperature I got with radiant system.

Here is data from chilled water loop’s pump, which is return water temperature/flow from room. These are all making sense.

Now set the capacity of Cooling source to 0, to see if it has direct impacts to room. And the room temperature goes up to crazy 100C.

Here is file I simplified your file for above tests. Hope this will get you started.
Ironbug_HVAC_test00_GSHP_probe_test_MP.gh (631.1 KB)

Thanks, and stay safe.

Hi @MingboPeng

Thanks for review and fixing my mistake.

Is it possible to set it in way it works also with other kind of loads? E.g. People loads contain also a fraction of sensible heat.
I have enabled it and inner temperature goes up to 100C.


Is it possible to set it in way it works also with other kind of loads? E.g. People loads contain also a fraction of sensible heat.

Hi @AntonelloDiNunzio
You can try to add a DOAS system, or other types of air system that could deal with humidity.

Thanks @MingboPeng,

So the problem is because radiant system handle only sensible loads. For this reason, it is usually combined with an air system that can handle latent loads and ventilation.
Here is hybrid system, radiant panel + DOAS: