Where is the Human Body position assumed to be in the HB UTCI Calculation in relation to the sensors Grid?

grasshopper honeybee
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Hello everyone,

I was wondering in the calculation of the UTCI in Honeybee - EnergyPlus, you assign radiance grid sensors to the model for the comfort mapping to occur. And it is mentioned that the Shortwave radiation is calculated by ray tracing from those grid points.

However, where is the human body assumed to be in relation to those sensor points? Because you do not put an input for the position of the standing human.

Let’s say that the sensor grids are placed at a height 1m from the urban canyon ground. In the shortwave radiation calculations, does it account for a person standing at the ground level of the same position, of a height 1.8m (like in ladybug), and calculates the percentage of body exposed to the direct rays?

Thanks.
Regwan

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Hello @charlie.brooker, Would appreciate your thoughts on this.

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Hey @regwan,

I’ve had a bit of a look through the code and components. My understanding is that the analysis point represents the body. I typically set my analysis points at 1.2m as a rough approximation of chest height for external comfort simulations.

My general take is that the human body is small in comparison to the size of objects in the external environment, and so simplifying that experience to a single point is reasonable. I’m sure if you analysed a range of sensor points in the region of human height using the UTCI Map component you would get very similar results.

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Hi @charlie.brooker ,

Thanks for your reply.

I wonder if this simplification would have effect on the shortwave radiation calculation. Because in ladybug outdoor solar MRT, it uses the solarcal method and through using the LB Human to sky relation component, you are able to account for the percentage of body exposed to the solar radiation.

I basically wanted to compare the results of LB and HB UTCI, so I was hoping to keep things similar for a good comparison.

Thanks

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My understanding is that the HB UTCI Map also uses the SolarCal method, but instead of using the lookup here for solar radiation

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It instead uses a radiation value calculated by the Radiance simulation.

Image from here:

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Thanks @charlie.brooker for the references. This is helpful.

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I’m just confirming that your understanding is correct, @charlie.brooker . Thanks for answering the question.

And, yea. Each sensor point is like it’s own tiny human geometry that’s either in direct sun or shade. In other words, the term of the SolarCal model that accounts for the fraction of body exposed to direct sun is either 0 or 1depending on whether the sensor point sees the sun. All of the other SolarCal terms are hopefully pretty self explanatory from the paper.

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Thank you for confirming @charlie.brooker 's answer @chris . And for the clarification.