Model a cool Slab in the UTCI calculation

Hi @chriswmackey I would like to replicate a cool slab system within my model and run the UTCI analysis to understand the impact of this system on a selected amenity area.
Is there a way I can assign a selected temperature to the slab geometry? If yes, would this temperature be influenced by the weather or will it be fixed?
I’m wondering what would be the best way to run this scenario.

Thank you in advance for your support on this topic.

Hi @mateang ,

I might need more information about the specific case that you are trying to model in order to recommend the best simulation process.

If you really just wanted to assign a temperature to a particular surface, you could try using the HB Other Side Temperature boundary condition for your slab. But how you assign it is going to very a lot depending on whether you are modeling your area of interest inside a Honeybee Room or outside of it.

Do you have a visual of what your setup looks like? Is the sun beating down on this cooled slab or is it shaded? And is there any control to prevent condensation from happening on it? Or are we just assuming that it’s the outdoors and condensation is ok since we have drainage for rain anyway?

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Hi Chris,
thank you for your advice.
I have attached an image of the scenario I’m analysing. The aim is to run the UTCI on the external area underneath the canopy, considering that the slab will be cooled.
At the moment I’m running the script using Ladybug UTCI Comfort. Should I use HB UTCI Comfort Map instead?


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Hi @mateang ,

The graphic is helpful. The space is relatively enclosed such that, even though you’ll be loosing a lot of cooling energy through convection losses to the outdoor air, the fact that it’s shaded should mean that the radiant temperatures of the balcony underside are lower thanks to the radiant exchange between the balcony and the slab. And things like the transmittance of the upper canopy will make a huge difference (I’d really push the team to make it opaque and insulated if they really wanted to go with the radiant slab strategy).

There are several different ways of analyzing this situation and a lot of this comes down to what exactly you’re trying to show here. The UTCI comfort map is going to be the most detailed and it will account for the most factors but there are ways of approximating the results with just a simple UTCI analysis.

Are you looking for just single number here to quantify the impact of the slab and, if so, what is the metric of that number? Or are you looking for a few different metrics and maybe a visual that shows the impact of the slab spatially over the area?

It would also just be helpful to know the motivations for looking into this. For example, are you trying to illustrate that this might not be the best decision from an energy perspective because you’re cooling the outdoors? Or is this just an idea that the client and the design team are committed to and you’re trying to give them recommendations for how to make it more effective and maybe use less energy? Or am I way off and we’re not concerned about energy use at all (eg. maybe this is some type of “waste cooling”) and you’re just trying to show how much more comfortable people will be if you design an outdoor radiant system like this?