Simulation results challenged by common sense

Hi all,

Today I presented some Honeybee OSM simulations to my boss, but the results were critiqued and I couldn’t think of an explanation. I’d appreciate it if someone could help!

The model was a 14-story, 2.2m-per-floor high-rise apartment. I set the period to 6/21, 0-23. The results show that the higher the floors, the lower the operative temperature. Also, the higher the rooms, the lower the cooling EUI (images shown below).

My boss critiqued that, based on common knowledge, higher floors should have a higher radiant temperature, and therefore, they should demand more cooling than the lower floors. The simulation results seemed opposite to him.

Any comments about it? Or maybe my simulation was wrong?

Ps. Does Openstudio consider wind speed and height? Maybe the highr floor gets higher wind speed so that the thermal got dispel more than lower floors?

The files and EPW file are attached below.
Apartment (126.6 KB)
467571_TMY3.epw (1.4 MB)

I think the main factor here might be the surrounding buildings as shades. Did you model them in your simulations?

Hi @MingboPeng

No, nothing surround it at all.

That’s the difference between your model and “common sense”

Can you explain a little bit more?

In fact I trust the simulation result but just don’t know how to explain and persuade to someone else.

Probably such high-rise buildings won’t exist in a context of no surrounding buildings, and that is different than what “common sense” thinks why such buildings “should” have a higher solar heat gain on the higher floors and lower floors get less solar heat gains because of the surrounding buildings cast shades on them.

I guess what I was trying to say is: why do you think the following statement is correct, and if it is correct, have you thought about the reason?

“common knowledge” thinks higher floors should have a higher radiant temperature, and therefore, they should demand more cooling than the lower floors.

Just my pure guess: (you can check the load balance to better understand the cooling load)

The top and bottom floors are easy to understand.
The middle part might because of the reflection of radiation from the ground.

@MingboPeng Thank you once again for your response.

To be honest, I cannot deduce why the temperature is higher on higher floors; this is purely based on a subjective judgment from third parties of my side. They simply believe that, based on common experience, drying clothes on the balcony of higher floors results in faster drying, and the indoor temperature on higher floors is “perceived” to be warmer than on lower floors.

However, regarding the reason for “the higher the floor, the lower the temperature,” I can think of a few possibilities:

  1. You are correct in saying that typically, tall buildings are surrounded by other structures. The shadows cast by these structures at certain times partially shade the lower floors, making their temperature lower than that of the higher floors. However, in the current simulation scenario (which also the actual site conditions), there are no other buildings nearby. Perhaps this is one of the reasons causing a contradiction with the third parties’ preconceived notions.

  2. As you mentioned, lower floors are closer to the ground, so they receive more “reflected radiation” from the ground than higher floors, leading to higher temperatures.

  3. Wind speed tends to increase with height. This means higher floors experience higher air convection, accelerating heat convection and resulting in lower temperatures compared to lower floors. I believe this point aligns with another preconception: the higher you live, the colder it is in winter. However, I need to confirm whether, after importing the EPW file, OpenStudio’s simulation incorporates data on wind speed and pressure. If it does, this assumption about wind can be validated.

So I did a Outside Face Temperature shown as below, still try to find the possible cause …

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I think I found the clue, I ran a custom result of “Outside Face Outdoor Air Wind Speed”, and the result shown as below…


@tutu7931, I think you’ve found the main reason - I’ve seen the same behaviour in IES VE driven by increased air speeds at higher levels, so it’s likely E+ is doing the same (no guarantees though)

Yes @charlie.brooker ,
E+ calculates a wind profile using the the power law equation and the profile used depends on the terrain defined in the setting.

Thanks @charlie.brooker @AbrahamYezioro for confirm the outdoor wind speed impact.

However, the result raises another concern: why do all the surfaces in a specific room have the same velocity? Shouldn’t they be somewhat varied due to their orientation?

That is the wind speed, not the wind velocity. Depending on what convection algorithm is used, EnergyPlus may also factor in the wind direction, albeit typically at a rudimentary level (leeward sides 1/2 weighted in the TARP algorithm, for example). See Section 3.5.5 of the Engineering Reference for some details.

Without a CFD, there is no way reliable way to accurately estimate the wind flow around the facade, particularly if there is concave geometry, but your geometry does not look complicated enough for the EnergyPlus convection coefficients algorithms to be way off either.

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