EN15251 Adaptive Comfort Maps - Methodology

Hi all,

I´m using the indoor adaptive comfort maps (EN 15251) for a research project, and I´d like to get a deeper understanding of what happens under the hood. I´ve made a thorough pass around the forum to collect some information but there are some bits I couldn´t figure out. This may go quite in some depth, but I believe it would also help as future reference.

It would be useful to understand how some variables from Energy+ get distributed/modified spatially (if they do) to compute the results for each point.

  • Air temperature. As far as I know, HB takes the resulting Zone Mean Air Temperature for each zone and modifies it spatially according to Alejandra Menchaca thesis. I found this historical topic :clap: from @chris first release back in 2015. Are those references still applicable?

  • Mean radiant temperature. Surface temperatures from E+ are multiplied by the view factors and the effect of the sun through any window accounted as this paper, again from the original release.

  • Relative humidity. I assume R.humidity is kept constant around the space. Is that the case?

  • Windspeed. Assuming the input is left blank, Is the air velocity assumed by any other mean (Menchaca thesis again?) or just left at a default value?
    Do the WellMixedAirOverride_ and InletHeightOverride_ affect wind speed, or they only play a role in the Air temperature calculation?

  • Clo absorptivity is constant around the space.

At the other end, I´d appreciate if someone knows how these parameters affect the operative temperature that gets compared against the EN comfort thresholds.

  • Air temperature forms part of the operative temperature, straight one.

  • Mean radiant temperature is also already included in the operative temperature.

  • Relative humidity. Does it affect/modify the operative temperature or EN thresholds?
    I´m aware of this paper about the influence of humidity on EN thresholds, but I haven´t seen any other information about the topic.

  • Windspeed. Does it affect the operative temperature? It has an effect, but I wonder how it´s factored in the calculation precisely. I recall a couple of references for this, that I could find if they are helpful for some reason.

  • Clo absorptivity. I suppose this one affects the amount of solar radiation absorbed by the body, hence the MRT.

Some answers will be in the code itself but after a couple of passes I couldn´t get much out of it.
Thanks for any help!


Hi @RafaelA ,

Thank you for asking the questions and sorry for the late response. Here are the answers to your questions:

  1. Everything that you said about the air temperature is correct. The air temperature part of the code really hasn’t been touched since 2015. The only thing that has evolved in my understanding is that most conditioned spaces have diffusers set up to mix the air and get rid of natural convection. So the stratification model should probably only be used in cases of natural ventilation and maybe shouldn’t be the default compared to a well-mixed assumption. That said, I don’t think I’ve ever seen the model produce air temperature differences over a zone more than 2C. So using the air mix override doesn’t change the results much.
  2. Yes, what you said about the MRT is correct. The only thing that has changed since 2015 is the the SolarCal model used to account for shortwave solar has become an official part of the ASHRAE-55 thermal comfort standard.
  3. Yes, relative humidity is constant but this is only used in PMV, UTCI and PET maps. The adaptive comfort model (as it has been published to date) has no input for humidity.
  4. If there is nothing input to windSpeed, the comfort maps default to using the lowest speed possible given the airFlowVol input to the recipe. We basically try to convert the m3/s to m/s by dividing by the “area” of the zone. Thinking over it, this “area” should probably be the zone floor area if we are usually trying to approximate air speed just above the floor of the zone but I think we use a simpler assumption, interpreting the area as the cross section of a sphere with a volume equal to the room volume.
  5. Yes, Clo absorptivity is constant over the whole microclimate map.

For your question about the EN comfort thresholds, your understanding of the air and radiant temperature is correct.

There is no humidity input for the adaptive models in Ladybug Tools and, as far as I understand, there have been no changes in the last 5 years to ASHRAE-55 for EN-15251 to account for it. I know a lot of this is explained by the fact that the data sets used to make the original adaptive models have shown a poorer correlation with all current attempts to account for humidity. But thank you for the link on the paper. I’ll have to give it a read and understand the differences between their method and those used to originally make the model.

You will get the best sense of how air speed affects the adaptive model by changing the windSpeed input on the Adaptive comfort chart:
The CBE tool can also show you this effect if you choose the adaptive method:

Yes, about clothing absorptivity. See the SolarCal paper for how it factors into the calculation specifically.

Thanks for all the detailed answers @chris, I really appreciate your explanations (I´m pretty aware some of the questions dig into bits of the code written long ago). Most of my doubts are clear, just a couple of comments below.

Regarding the humidity and EN-15251, I think that is the only paper I´ve seen attempting a correlation. Nothing has changed on the standards as far as I know.

As for the effect of air movement, I understand that the upper comfort thresholds are modified to account for the cooling effect of air movement. Both the CBE tool and the hydra definition have helped me trace it back in the code to:

Is that the formula for one of the curves described in ISO 7730 annex G (below), or something else?
I haven´t found any source on CBE´s website either.

I found the answer to the last bit remaining, in case this serves for future reference.

The effect for air movement on the upper comfort threshold is included in Annex 2 of EN 15251 (coming from ISO 7730 Annex G) - the formula highlighted in the code above matches both perfectly, the EN and ISO references.