Incorporating Chilled Slab using Ironbug

Hi all,

Does anyone have experience in defining a chilled slab using ironbug? Any guidance is much appreciated.


cc @MingboPeng should be able to help

Hi @SaketSarupria
There is an example to do radiant ceiling for cooling and heating: image

You can start working on this by changing “RadiantSurfaceType” to “Floors”, and limit heating capacity by setting HotWaterFlow to 0.

Meanwhile, you will also need to assign the radiant construction to floors instead of ceilings.


Awesome! @MingboPeng Thank you very much for the details. Will try it out.

Hi @MingboPeng,

The radiant panel seems not working. When I check the node mass flow, the chilled water through the compensate coil is always 0. Could you please help?

20200305 test radiantpanel_to (665.3 KB)

Thank you

Hi @XavierZhouLadybug ,

This is a big topic to discuss. Here are two categories that I would typically check:

  1. System design flaws: is this hvac system really going to work? Things like control logic (setpoint temperature, flow, control types, etc) would dramatically affect how hvac performs. Solution: make sure all manual overridden inputs make sense by system itself, and also check if these numbers make sense in this climate, and your building.

  2. Simulation problem: this is related to how to model a system in a software interface, simulation engine, etc. This require one understands the HVAC in terms of energy simulation, and how to build this HVAC in a software that properly reflects to the system in the real world.

Now back to your system:

  1. One of the first thing that I noticed that you changed the DOAS to a typical AHU with full cooling capacity with supply air temperature 12.5C. From this point, I can almost say any zone that is connected to this AHU doesn’t really need any additional cooling system, in your case: radiant panel. Because all cooling load has been taken care in AHU.
  2. You have connected to your secondary chilled water loop to the main chilled water loop via heat exchanger. The main chilled water supply temperature is set to 8C, and secondary loop takes 19C. This is impossible to do without any heat source to raise the water temperature from 8C to 19C.

    I think what you might want to do is take the returned chilled water from cooling coil, which is typically a radiant system will do. In this case: you will need to move your heat exchanger to a place after cooling coil to take its return water. It can be right after coil in the demand branch or the main return loop.

    But even after you changed to this design, I still see a design flaw: currently there is only one cooling coil using chilled water, and it is serving the airloop with 12.5C supply air temperature. The physically highest temperature of return water is 12.5C if I understand your design and how this system works correctly. This might sill be a problem for your 19C input water temperature for radiant panel. Basically all water will bypass your secondary loop even if you have cooling demand from this loop.

These are just my comments purely from by looking at your file without really running it. I might be mis-checked on some other details, but please let me know if didn’t understand your design correctly.


Hi @MingboPeng, first of all, thank you so much for taking time to answer my question!

My first question is, if you look into my script, I set the panel’s control temperature to mean radiant temperature. So I was expecting the AHU to cool down the room to the setpoint 23C, but the radiant panel to work further to bring down to radiant temperature, i.e., to cool down the floor surface temperature. (the zone has a big skylight)

@XavierZhouLadybug have you tested this system individually in OpenStudio? Does it work as what you expected?