Wish: Psychrometric chart - shading strategy

I have a wish and it is to include the potential of a shading strategy to provide comfort.
Assuming the lower limit will be the left part of the comfort polygon, the shading contribution will be all the data point to the right of this limit. It should not be affected by any humidity constraints.
If you consider this wish makes sense, I’ll appreciate if at some point this important strategy will be implemented.


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Hi @AbrahamYezioro ,

I’m not sure that I understand the proposed behavior of this strategy but, based on your description, it doesn’t sound like shade. Are you suggesting that this shading strategy polygon able to make any dry bulb temperature to the right of the comfort polygon comfortable regardless of how hot or humid it is? That sounds more like active cooling than shade.

Or maybe I’m misunderstanding what temperatures you are plugging into the psychrometric chart that would make a shading polygon behave like that since plugging in the EPW dry bulb temperature already assumes that the human subject, whose comfort we’re evaluating, is experiencing temperatures in shade.

If you want to demonstrate the impact that shade can have on getting more conditions inside a comfort polygon, you can compare the operative temperature in the sun to that in the shade like so:

psychrometric_chart_shade_benefit.gh (36.5 KB)

And it’s obviously a big impact.

Am I misunderstanding that, for your shade polygon, you’re starting with an assumption that solar-adjusted operative temperatures have been plugged into the psychrometric chart?

Hi @chris,
Thanks for your response.
The truth is that i was looking for something much more simple.
I was looking at the ClimateConsultant psychrometric chart and how they deal with the “potential” contribution of the shade in buildings. They show the following:

As i can see they take all hours to the right of the left line of the comfort polygon that are not included in the comfort itself.
For a basic exercise i’m preparing for the students they will see how much each strategy can contribute to the possible comfort on buildings. The assumption is that shading of windows is recommended for all hours to the right of the comfort polygon.
I think it will be great if they can see the shading of windows as another strategy but also being able to quantify its potential. For this purpose i’m not sure your example will make the point, but maybe can cause a bit of confusion.

I’m taking indeed the EPW dbts. I get what you say that the temperature sensors in the weather stations are in shade, … but the expected contribution of shading of windows is on blocking the direct radiation.
In short, my wish/intention is intended for something much simpler that summarizes the amount of hours that can be considered summer hours and for them shading of windows is recommended.

Makes sense for you?

Thanks again,

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In addition to the previous, just wanted to post a couple of images relating to what is called the “shade line” on both psychrometric and bio-climatic charts.:


Thanks, @AbrahamYezioro . I appreciate providing sources and examples since this gives us something that we can discuss and try to understand.

Understanding the Existing Sources

It seems like both cases are not adding a shade “strategy polygon” but are instead trying to draw a “shade line” on the chart, which is just trying to say “shade can be helpful here” and it doesn’t actually make any of the hours more comfortable. So, this at least helps me see that, if we were to try implement something similar in LBT, we probably shouldn’t be doing it with a polygon and we should instead find a way to draw a line on the chart that doesn’t really add to the the total number of comfortable hours.

I’m also at a bit of a loss to understand how this shade line tells us something that we don’t already know. If we just wanted to figure out the number of hours that are in the comfort polygon or warmer, we don’t need to have a line on the psych chart labeled “shade” to do this.

This leads me to a bigger point of confusion, which is that I can’t figure out why these two sources decided to put this “shade line” where the did. Technically, any temperature above the building balance point is one where the solar gain combined with a lack of building shade could make conditions too warm to be comfortable. So I don’t see any satisfactory explanation for why the shade line is at the lower boundary of the comfort polygon and not the lower boundary of the “Internal Gains” polygon. All of this kind of underrepresents how powerful shade is as a strategy since, as my comparison above shows, it can be REALLY helpful and we risk having people walk away with a false sense that “shade is not really that important” when we under-represent it like this.

Lastly, as I said earlier, climate consultant and the strategy polygons in LBT already assume that the building is shaded for all hours above the building balance point (as long as you’re plotting outdoor dry bulb temperature in LBT). So it’s not like shade it something that can be added on top of the existing strategy polygons.

It all makes me think that the creators of the “shade line” might have gotten a little carried away with wanting to represent all of passive design in a single temperature/humidity plot that they didn’t think enough about how informative, useful, or accurate their implementation was.

Proposal for LBT

What do you think about trying to implement “shade” in the following way on the psychrometric chart?

  1. We can add an option to the Passive Strategies List called “Remove Shading.” Using this “Remove Shading” option will require the user to plug in hourly solar_data_ just like the “Passive Solar” polygon.
  2. Checking this “Remove Shade” option will draw a “shade line” on the chart at the building balance point, above which shade is considered helpful and a lack of shade can make conditions uncomfortable.
  3. Using methods similar to the “Passive Solar” polygon (with the user-input Solar Heat Capacity and Time Constant), the “Remove Shading” option will try to figure out how much warmer the building is at each hour as a result of not having shade.
  4. If the temperature delta from the removed shading would put a point outside of all comfort and strategy polygons, these hours will be removed from the “total comfort data” and the total comfort percent output form the component.

I’m open to other suggestions if anyone else has a proposal that would be more helpful or informative. This is just the best one that I could think of that doesn’t mis-represent how important shade is.

Hi @chris,
This is getting interesting … :slight_smile:

Agree. In my opinion shading is the one (and only) strategy (let’s keep calling it so) that is more wishful thinking and a good/necessary to have in the building. This as opposed to the other strategies that you can have a more solid base to justify and really assess their contribution to the comfort sensation. I justify this as “common sense” that when you are hot you want to be in shade. Don’t fully agree with you that it doesn’t make any of the hours more comfortable. One thing is to find a way to consider its contribution and another is saying it doesn’t contribute.

Can be. In CC they count the hours to the right of the line excluding those inside the comfort polygon. Which i think is a good way to go because that tells you the number of hours (and the percentage of time) that can get use of shade.

Not fully. Not sure how you can get this data. Not all the hours fall inside certain polygon(s) but still can have a benefit from the shade. The shade line itself, for me, is just informative and educational and can help for a better understanding.

Kind of agree. I believe that for this initial analysis the balance temperature is unknown (many times you don’t even have a building to check that). About the internal gains themselves, they are like a black box. Didn’t find how they are defined and how/why they define the polygon. Seems to me that the range of the polygon is too wide (even when i rise the balance temperature to values that are not real). Can’t see how to differentiate a residential building from an office building).

As for the Proposal for LBT, let me think a little bit. I need to go now for a meeting … :slight_smile: … But i’ll be back.

Thanks @chris,

Hi again @chris,
As for Proposal for LBT:

If i understand your previous comments, you say that the shade is already embedded in the cooling strategies, right? If so, this point means “see what you really get from the strategies if you don’t implement shades”. Is this correct? Maybe i like better to add in the strategies list “Account for shade”. If you check this one you get what you are getting with the existing component. If you don’t check it, it will show you what you suggested. Makes sense?
What is this input solar_data_? Something from the EPW or a value the user sets?

I like better the other way around. For me to be more consistent and intuitive, The “shade line” should be in the chart when the shade strategy is ON.

Here i’m a bit torned. It means that shade is only recommended inside the limits of the cooling polygons. But what happens when you have 35C and 90% Rh?It is not comfortable at all, but been in shade can be useful. I’ll be uncomfortable … but less than if i were exposed to the sun. Makes sense?


Hey @AbrahamYezioro ,

I just wanted to say that I haven’t forgotten about this and I’ve been mulling it over in the back of my head.

It looks like we’re mostly in agreement with what I proposed but we don’t like the fact that adding the shade strategy line and then removing previously comfortable hours seems counter intuitive.

I’m not really buying the idea that a strategy is meant to show that something “can help”. It shows when a strategy “can make things comfortable”. Or at least that’s how all of the other strategies work right now. It’s not like the “occupant use of fans” takes over the whole right side of the chart because higher air speed can always help when people are hot. We just draw the region that’s comfortable up to a speed that a typical ceiling fan can go.

I could just try to do something like what I proposed previously but it wouldn’t change the overall comfort percentage. I’ll just add a data collection for shade that includes all of the cases across the current strategy polygons that require shade to make them comfortable.

What do you think?

Also, what do you think about having the shade line at the building balance point? Do you know of any reason why the sources you cited put it at the lower boundary of the comfort polygon?

Hi @chris,
No worries. I know your plate is pretty full.

Kind of agree. The thing is, that opposed to all strategies, the shade line is the only one that is not “measured” in the references i know. It is like an “obvious” to implement and as such the argument is that it “helps” or contributes to comfort sensation.

Continuing the previous sentence, the ventilation with fans or natural, is limited by high temperatures. At some level that t is not recommended anymore. Shade, on the contrary, is good at all temperatures.

This can be great. This is what ClimateConsultant does (see image above). I would take out the hours inside the comfort polygon.

I’m not sure about this one. The balance point in a"normal" building can be 15C or less. I can’t imagine recommending the use of shades in winter time just because the building is well insulated or otherwise. This is an argument that MAYBE can fit a closed building, where you don’t open windows if hot … even in winter time.
I didn’t find resources explaining why the shade line is at the lower boundary. It seems to be just “logic” (not a very academic argument, but still).

Makes sense for you?

Thanks @chris,

It looks like we’re still a little further away than I thought about this. Let me first summarize what we seem to agree on and then we’ll see if we can come to a consensus about a couple of things that are necessary to implement shade as a strategy.

What We Agree On

  1. We can represent “Shade” as a strategy on the Psych Chart using a line (in lieu of a whole polygon).
  2. Adding the Shade strategy should come with another data collection out of polygon_data showing hours when the shade is relevant.
  3. The addition of shade probably shouldn’t affect the total_comfort all that much (though I think there’s still a lot of specifics to work out here).

What We Need a Consensus On To Implement Shade

1. Does a psych chart strategy represent the hours that are made comfortable by the strategy or the hours helped by it? Alternatively, does it matter that we enforce a consistent definition for what a strategy is?

So far, all of the current strategies that you can plot in the LBT plugin show the hours that would be made comfortable by a given strategy. That is, implementing the strategy in a manner that obeys the assumptions of the Passive Strategy Parameters would move the point from where it currently is on the chart to be inside the comfort polygon(s). We were using “Occupant Use of Fans” as a means to demonstrate this since the polygon currently shows the hours that would be made comfortable by increasing the air speed to the _fan_air_speed_ of the “Passive Strategy Parameters” (default value is 1 m/s). However, increased air speed is helpful for occupants any time that they’re hot and they have sweat to evaporate. Granted, this air speed might not be enough to lower PPD to less than 10% and put conditions inside the comfort polygon. But it will lower PMV to something closer to zero/neutral from where it originally was because increased air speed leads to increased sweat evaporation. So it’s helpful anywhere on the right side of the chart. Maybe the only case where increased air speed wouldn’t be helpful is if the air temperature were warmer than the radiant temperature but this isn’t a nuance that we can capture on a psychrometric chart that only has one temperature axis for operative temperature.

All of this is to say that many of the strategy polygons would change significantly if we wanted them to show that a strategy can help instead of when it makes occupants comfortable. Granted, I could possibly be convinced that it’s not important to have a consistent definition for what a psych chart strategy represents. But I just feel that we have an opportunity to keep things consistent here and so I don’t really understand why we should make an exception for Shade and not some other strategies.

2. What type of shade does the Shade Line represent? Is it Shading on a passive building in which the occupant sits? Or is it more like a beach umbrella that directly blocks sun falling on the occupant?

I think a lot of our disagreement about where the shade line is might come down to this. I keep thinking of shade as something that is applied on top of the other strategy polygons and that these other strategies together represent a hypothetical passive building in which the occupant sits. So the shade is essentially like an awning or overhang on this hypothetical passive building. This is why I only want “Shade” to affect the hours that are already inside the existing comfort/strategy polygons since these strategies effectively need a low solar load in order to work correctly. It’s also why I feel the shade line should be at the building balance point since this is the temperature at which the sun switches from being a benefit to the building (Passive Solar Heating) to something harmful (Shade). And the logic follows that, even if it’s 15 C outside, conditions within an insulated all-glass greenhouse blasted by the sun can be so warm that it’s just not comfortable for people.

I have to imagine that this “building shade” interpretation is not what the original authors of the “Shade Line” thought. I’m guessing they were imagining that this Shade was more like a beach parasol that was applied directly to the human and not the the passive building in which they were sitting. And so they put the line at the “human balance point” of the comfort polygon instead of the “building balance point”. Granted, I can understand the appeal of either interpretation but I struggle with the fact that we know today that sitting in shade vs. sun has a huge impact on perceived temperature. So much so that the “delta C” you experience by sitting in the sun can easily change you from being too cold to too hot, skipping over the whole comfort polygon in the process. It’s just a tough thing to represent with a strategy on the psych chart and it’s the type of comparison that’s better done by adjusting the temperature plotted on the chart (as I did above).

I guess there’s also the question of whether these strategy polygons are trying to help us design passive buildings or are the just reiterating something simple that we already know like “people shouldn’t sit in the sun if they’re already comfortable or hot.”

Thinking this over, maybe this isn’t as black and white as I originally made it out to be. Maybe we could just change where the shade line is based on the other strategies plotted on the chart. So, if “Capture Internal Gains” is plotted on the chart, we can show the shade line at the building balance point. Otherwise, we can show it at the human balance point on the lower part of the comfort polygon. What do you think?


On another note, I forgot to answer this earlier:

Check out this sample file for what I mean. You have to plug in solar radiation data to the solar_data_ input of the PMV Polygon component in order to plot a “Passive Solar Heating” strategy polygon (otherwise the component turns red). You’ll see in the sample that this solar data can be for any orientation of windows on the theoretical passive building that’s being assumed under the hood of the strategy polygons. You’d just have to use the LB Directional Solar Irradiance component to convert the EPW irradiance components to be irradiance on a window surface facing any direction you want. This solar data is used to determine which particular points inside the “Passive Solar Heating” polygon are actually comfortable since you can see that not all of them are this way:

The assumption is that, if a given hour is too cloudy, then passive solar heating doesn’t make the hour comfortable. I was thinking that shade should have to abide by a similar rule.

Hi @chris,
We are getting closer, i think. You are convincing me … and i want to propose something.

  1. What we agree on: This is fine. :white_check_mark:
  2. What we need a consensus:

I believe we can agree that the former is the right one. This is the accepted approach so we don’t need to challenge that at this point.

I see your point and i’m for keeping consistency.

I would say that it is a combination. I’ll try to explain after the next quote.

You are right on this BUT you are denying the possible use of ventilation. When you check winter time in the chart, the cooling options are off. What you suggest is provide shading as an option, which is fine, but not the only option i can apply. I’m trying to think what i would do in the case that in mid january i get lots of sun in the space i am in. Open a window or close the shades? Myself will probably open the window.

Exactly. So here is what i propose, based on what i just found in the Lechner’s book (Heating, Cooling, Lighting: Sustainable Design Methods for Architects):

The key part is

… to the right of the vertical shade line, the sun should be prevented from entering windows

So maybe this should be the approach: the shade line is not a strategy but rather a recommendation. The counting of the hours that fall to the right of it (not counting the comfort polygon ones) represent the potential severity of the situation (i know you don’t like the potential word in this context … :slight_smile: ) and not a strategy by itself.

This can be a good option, you can explain that to people and makes sense.

Saying that, what do you think about the quote of the book. Right now i can live with either of the options.

Thanks @chris. I see the intellectual effort you are putting here and the responsibility you feel towards this. This is great!! I appreciate it very much.


In case this fell into the cracks, I bring it up to the surface again

Hey @AbrahamYezioro ,

Sorry for the late response here. It’s on my radar and I have it pinned in my personal agenda but it would take me a couple of days to implement this and there have been other things that have taken priority. So that’s the only reason why I have not been responding here and you can rest assured that I will eventually get to it.

From what I can tell, I think we came to a consensus if you are alright with the shade line moving depending on whether “Capture Internal Gains” is already plotted. I also think maybe some of this difference between “strategy” and “recommendation” will go away when you see the implementation that I have in mind, which I’m imagining is an idealized version of what shade can do. It’s probably going to be closer to some type of dynamic shade that is deployed to block all of the sun at the times when it’s helpful, thereby showing the overall potential for shade as a strategy.

I also agree with the statement that “the sun should be prevented from entering the building when conditions are to the right of the shade line” just like I agree with the statement “the ceiling fans should be turned on whenever conditions are to the right of the comfort polygon.”

I just don’t want to present hours as comfortable if they aren’t ultimately going to be able to make it inside the comfort polygon between all of the currently-applied strategies.

What do you think of this:

In addition to adding a “Shade Line” I’ll also add some strategy lines for “Active Cooling” and “Active Heating”. Turning on the “Active Cooling” line will get the Shade line to behave almost exactly how you originally described it. Basically, we will model shade as something that is applied on top of all the other strategies and, if one of those strategies is “Active Cooling”, then virtually all of the sunny hours to the right of the shade line are going to merit the deployment of shade to help keep conditions inside the comfort polygon.

Could this work well for you?

Hi @chris,
Absolutely this can work for me!
Thanks. It is/was a good discussion, and don’t worry about the implementation right away. I am fine knowing it is on the “to do” list.


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