Validating Outdoor Mean Radiant temperature

Hi all.

I’m working on modelling a shading canopy throuygh Ladybug & Honeybee to understand the effect of different design parameters on thermal comfort (e.g material properties such as transparancy, emissivity or geometry such as canopy height). Right now i’d like to justify the Mean Radiant Temp i’m getting through the use of the LB Outdoor Solar MRT component (pictured below)

I’m using just one test point situated directly underneath the canopy at a height of 1.2m.
Relating to the surface temperature input, I’ve read here “ladybug_comfort.collection.solarcal — ladybug comfort documentation” that ‘When the temperature of these individual surfaces are known, the input here should be the average temperature of the surfaces weighted by view-factor to the human’

So to calculate the weighted surface temp I’m using two legacy components (effectively calculating longwave mean radiant temp) - Surface View Analysis and MRT Calculator (as pictured) and turning the resulting MRT into an hourly data collection to plug into surface temp (analysis period is 24 hours).

I think the two legacy components take care of long wave radiation from the ground and canopy, while the Outdoor Solar MRT adds the radiant exchange with sky and direct solar radiation.
Two questions:

1 - Does this make sense? The other method I was looking into was using the LB View Percent Analyis to calculate view factors but then I’m not quite sure how I can seperate the overhead canopy, sky and ground so I can weight each by their respective temperatures. Plus then am I just duplicating what’s happening in the Outdoor Solar MRT component?

2- Can anyone suggest an alternative method to calculate MRT and thus validate the results from LB (i’m trying to write a paper on this). I started with calculating the view factors numerically so i can compare against the Ladybug outputs and I’ve written something in python to calculate the view factor between a surface representing a person and the canopy surface based on what i found here (Radiation Configuration Factors C-158.html), thanks to this discussion [discussion] Sky View Factor - #3 by AymericDELABACHELERI, but this is getting a bit out of my depth!


1 - Yes, it does make sense and this is a valid way to compute at the influence of the surrounding surfaces on longwave MRT.

2 - Yes. The thermal mapping recipes in the LBT Honeybee plugin are generally going to be more accurate than trying to build everything up from scratch with the Ladybug components. This is because the thermal mapping recipes use Radiance to model the shortwave solar, which means that you can account for shortwave solar reflections (unlike the Ladybug components). The thermal mapping recipes also use Radiance to compute surface view factors and they uses EnergyPlus to compute surface temperatures, which allows you to factor in lots of properties of the surrounding surfaces (eg. their heat capacity, conductivity, emissivity, and absorptance). The only catch is that you’ll have to find a way of modeling any surface for which you want to compute temperature as a Honeybee Room (aka. EnergyPlus Zone). I know it feels weird to model a canopy as a Room but, if you know what you’re doing and you set the Room to have no loads with the HB Plenum component, you can usually get surface temperatures that are really close to what you’d find in reality.

Hi Chris, thanks for your reply

I was actually doing as you suggest and modelling the canopy as a room although I found I had to model the canopy as the roof of the zone (with walls 95% glazing and ‘open’ all the time) rather than the entire zone to get reasonable results for canopy surface temperatures.

I would like to be able to use the UTCI Comfort Map, but I need to extract surface temperatures, view factors and mean radiant temperature which I can’t find a way to do. Can you suggest anything?

Also I’m having problems when visualising the results of the UTCI matrix output. The map values seem mixed up with the outer edges cooler than the inside and the temperatures from one pixel to the next arent continuous where i’d expect them to be. I’ve attached some images to show what I mean. Any idea what I’m doing wrong?

Look in the simulation folder. You’ll find most of these available in the earlier steps of the recipe simulation. Surface temperatures are in the EnergyPlus SQL file, View Factors are in the longwave sub-folder, MRT can be calculated by summing the longwave and shortwave MRTs.

The results don’t seem unreasonable to me for an indoor simulation. Remember glass is a radiant barrier so its surface temperature will influence the comfort.