I need to asses the outdoor comfort, for which I need to obtain the Mean Radiant Temperatures.
My project is an Outdoorsy Canopy with a Radiating Floor.
The Surface temperatures of the Radiating floor were simulated with another software because I don’t know how to simulate the whole SolarThermalPanel-Radiating Floor System in Grasshopper (and by now I don’t have the time to remake it ).
-I have the following questions:
-To enclose the zone, I had to make always open windows, even though in ‘reality’ there would be no windows, I did this so my zone would be closed and able to simulate. Is this an acceptable approach?
-Can I set the surface temperatures I got from the other software on only-one surface? (I tried substituting the temperatures from the specific surface in the excel surf.temps. file generated with the Honeybee_Export to OpenStudio component. Didn’t mange to do it.)
-Would this surface with a fixed temperature also interact with Solar Radiation? Meaning: My surface temperature is of 10c provided by the radiating floor system, if this 10c surface is exposed to direct sun light, it would increase its temperature, right? Is this phenomena simulated in this file?
-Also, can I input a fixed wind speed -given that I can’t make a CFD-? Or would it be safe to simply multiply my Microclimate map results for 1.5?:
“UTCI’s theoretical wind speed at meteorological height and the wind speed at the height of the occupant is simple, involving only a multiplication by 1.5” Jendritzky et al., 2007.
I would really appreciate if someone could give a look to my files. At least the part of setting the given surfaces temperatures is very important.
And I guess that as happens to many others, my deadline is very close so I’d really appreciate if someone could make the time to check this.
Unfortunately I don’t have time to open your file and try and work this out, but here are some brief thoughts to your questions:
-To enclose the zone, I had to make always open windows, even though in ‘reality’ there would be no windows, I did this so my zone would be closed and able to simulate. Is this an acceptable approach?
Interesting question. it seems heavy-handed, as EP will make a lot of assumptions not fit for a canopy:
It may assume a certain infiltration into even unconditioned zones, which technically isn’t the case in your canopy (this depends on how HB models infiltration into unconditioned zones)
coefficients for window edge-conditions, air film convection from your surfaces etc are all based on empirical studies for buildings, and therefore may not map accurately to a canopy
There are more. Personally I would have tried to do this study using the Ladybug MRT, and viewfactor components, which are a bit tricker to use with multiple surfaces but as an academic excercise, allow you to control, and understand the assumptions you are making without having to hack EnergyPlus assumptions. However, if you modeled an unconditioned zone, with open windows, I think for the purpose of your study it should provide a reasonably coarse model of your canopy conditions.
-Can I set the surface temperatures I got from the other software on only-one surface? (I tried substituting the temperatures from the specific surface in the excel surf.temps. file generated with the Honeybee_Export to OpenStudio component. Didn’t mange to do it.)
Yes. You will need to take the output from the existing surfaceIndoorTemp, and then swap the EP-calculated results for that specific surface, with the ones generated from your simulation. The EP-calculated results will return a single temperature for every timestep of your simulation. So make sure you can derive that from your other simulation, then use the Grasshopper data tree components to extract the relevant surface from the EPSurfaceResults component, then overwrite (or swap) those temperatures with your simulated results. Plug in the resulting data stream into the PMV component. If you can’t do this, I can show an example.
Are you only adding the surface temperatures from the radiant slab? Note that by adding the surface temps after the EP simulation, the EP simulation therefore doesn’t account for the heat radiated by this surface, so the surrounding wall surface temperatures will be lower then they should be (because they don’t model radiant heat exchange with the radiant slab). Technically the zone drybulb/operative temperatures will also be lower, but in this case it’s an outdoor space so I think this doesn’t have an impact because that air will be mixed with outdoor conditions.
-Would this surface with a fixed temperature also interact with Solar Radiation? Meaning: My surface temperature is of 10c provided by the radiating floor system, if this 10c surface is exposed to direct sun light, it would increase its temperature, right? Is this phenomena simulated in this file?
Yes, I believe Chris’s HB PMV component integrates a solar-adjusted MRT for it’s radiant calculation.
-Also, can I input a fixed wind speed -given that I can’t make a CFD-? Or would it be safe to simply multiply my Microclimate map results for 1.5?:
“UTCI’s theoretical wind speed at meteorological height and the wind speed at the height of the occupant is simple, involving only a multiplication by 1.5” Jendritzky et al., 2007.
I’m not a comfort expert, but is that saying at the height of occupant the wind speed is higher by a factor of 1.5 relative to the weather station? Shouldn’t it be lower? At any rate, you can plug in the wind values (multiplied by any factor) from the EPW here to approximate the outdoor wind conditions (assuming your canopy isn’t obstructing wind). A fixed wind speed seems an unnecessary simplification unless you are confident your canopy design provides that condition.
Hi Saeran, thank you so much for your soon answer!
All your feedback is very useful and I will take it into account.
I could really use an example of this. Thanks.
Yes, and as you said, as it is outdoors it doesn’t have as much impact.
Oh, I think it means that the comfort results should be multiplied by 1.5, given that the simulation was made with a higher wind speed. At least this is how I understand it, I may have to dig deeper into it.
“Accordingly, a decision was made to “back-convert” wind speeds derived from the CFD studies to the wind
speed at the meteorological height for the UTCI model. Thankfully, the relation between the UTCI’s theoretical
wind speed at meteorological height and the wind speed at the height of the occupant is simple, involving only a multiplication by 1.5 (Jendritzky et al., 2007).”
Taken from “Wind, Sun, Surface Temperature, and Heat Island: Critical Variables for High-Resolution Outdoor Thermal Comfort” by Mackey, et al. Page 4.
The canopy design is supposed to decrease the wind speed but, as I can’t simulate CFD, I would have to assume that it is lower.
Again, thank you for your feed back, it is very very useful. I’d appreciate if you could share the example mentioned before.
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