EP Results: Air temperature in vertical zones

energyplus
#1

Hey,

I don’t understand the results of the EnergyPlus Simulation for the air temperature.
My modell has three vertical zones with air walls as adjacent material.
Usually the highest temperature has to be in the top zone and the lowest temperature in the bottom zone due to thermal buoyancy. My EP results are different to this theory:

It would be very nice, if someone has an explanaition for that :slight_smile:
181116_Mod_DSF_EP_Temp_results_modified.gh (712.7 KB)

Thank you

Marco

Help simulating the stacking effect of air behind panels on a building facade - Honeybee
#2

@Marco ,

The EnergyPlus Reference specifically states that breaking up a continuous vertical volume into different zones is not the correct way to model stratification (even when using a fully detailed airflow network). Not only will this method be unable to model of stratification but you are killing the radiant heat transfer between different surfaces of your atrium by putting air walls in between surfaces that should be exchanging radiant heat.

If you need to get a sense of stratification, the Honeybee Microclimate maps have built-in methods that estimate air temperature variation over individual zones from certain utputs of E+. You will see that stratification is usually only a degree or two different and typically doesn’t drastically change the results that you get when you assume that the air is well mixed in your zone.

If you need to get even deeper into this, EnergyPlus also has several objects that you can add to the model to separate the single air node of the atrium into several sub-nodes:
https://bigladdersoftware.com/epx/docs/8-9/input-output-reference/group-room-air-models.html#group-room-air-models

Whatever method you choose, you should be modeling the atrium as a single continuous zone. You might still want to break the walls of the atrium into different sub surfaces but breaking it up into separate zones is not correct.

#3

Hey @chris,

thanks for your answer and your hints.
It should be possible to create the atrium with multiply zones. Instead of the airwalls, I will test it with internal vertical openings: Open Air connections between zones.

The microclimate maps are nice tool to get an visualization, but you said yourself, the are only estimated.
I want to built a modell with accurate temperature results.

Your tip with several sub-nodes is a possibility, but there’s for e.g. ‘ThreeNodeDisplacementVentilation’ the hint: “The model should be used with caution in zones which have large heat gains or losses through exterior walls or windows or which have considerable direct solar gain.” My modell has big windows and exterior walls.