# Desirability of passive evaporative cooling and radiative cooling

Hi everyone, I hope you’re doing fine,
is there any way to calculate the desirability of passive evaporative cooling for outdoor comfort?
also, I have the same question for radiative cooling.

To quantify the benefit of evaporative cooling, you can use the Ladybug Psychometric Chart. The chart will draw out a polygon encompassing the constant maximum and minimum wet bulb temperature lines that bounds the comfort polygon in the psych chart. These indicate the number of hours of in which the latent heat of vaporization will cool the outdoor air to comfortable conditions, without going over or (more rarely) under the comfortable humidity constraints.

IIRC there should also be an option to model the effectiveness of indirect evaporative cooling. That way you can mitigate the humidity constraint by evaporatively cooling a heat exchanger, which “indirectly” cools your supply air without adding moisture.

Quantifying the impact of radiant cooling is a little bit trickier, since radiation is a function of geometry which can’t be captured in your climate file. You can use the psychrometric chart to crudely evaluate the impact of completely blocking solar radiation. But if you want to capture the comfort impact of radiant cooling panels, and/or specific geometries that are driving the radiant exchange, you’ll need to explore workflows that can calculate the mean radiant temperature input for comfort metrics by integrating geometry view factors and corresponding surface temperatures.

There are a lot of different ways to do this in Ladybug/Honeybee with different levels of abstractions that you can explore in hydra. To get you started, you can check out this Radiant Asymmetry Discomfort workflow which models indoor surface temperatures from an energy model, and then calculates comfort as a function of the resulting radiant asymmetry.

S

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@SaeranVasanthakumar,
Thank you for your great clarification,
The Ladybug Psychometric Chart you are referring to, is valid for indoor comfort, is it ok to use that for outdoor studies?
and also could you say what do you mean by IIRC?
Thanks again.

I have to apologize, I missed the fact that you are looking for outdoor thermal comfort. I believe you’re correct, the comfort models used in the LB Psychrometric chart are all indoor comfort models, and therefore make certain assumptions that may not extend to more complex outdoor environments.

I am less certain about modeling evaporative cooling for outdoor thermal comfort, since there’s so much more complexity in outdoor conditions like different sources of humidity, and wind flow that I don’t know how to capture. Hopefully someone else can provide an answer here.

Radiation is a lot easier, here’s an example of how to modify the MRT input for UTCI which you can build on.

and also could you say what do you mean by IIRC?

IIRC = If I recall correctly.

S

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thank you @SaeranVasanthakumar,