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How to zone a big nave building?… (airflow and solar gain)

asked 2018-10-22 14:42:33 -0500

jlgrobe gravatar image

updated 2019-04-07 10:09:55 -0500

Hello, i'm bringing this question i originally made on the ladybug tools forum. They recommended to take the post to this forum. (i'm using rhino and honeybee)

I’m modeling a 100 year old market hall from Budapest. At first thought it was going to be easy as it’s only one space, but now i have many doubts about how to aproach the zoning of this building, as it’s height and nave section, makes it a lot more complex.

This is the actual market:https://goo.gl/maps/SpxXUABFh5t 3 image description

And this is the way i’m modeling it. image description

I’m splitting the space in different levels, with “air floors”… becouse: it’s said that air stratification is not well modeled with “mixed room air model”. Instead it should be used the “constant gradient room air model” or the “non-dimensional room air model” as is described in this energyplus study: https://www.researchgate.net/profile/...

Becouse i didn’t find a way to imput the “constant gradient room air model” and it’s formula, i’m using this levelled solution, as i readied at recommendation for modelling on other big void. What i'm trying to achieve with this analysis is to simulate the improvement on comfort from insulation on windows (starting from air tightening, and draught stripping).

So my questions are:

It’s modelled right or should i find the way to imput the constant gradient formula? I’m not getting any sun gain on the ground floor, its because of the air walls/floors? If different stories are ok, should i use more zones (splitting each branch in 3 more zones)? I’d also simplified the sloped roofs, i’m going to add them when having this main topic more clear.

thanks a lot!

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AWESOME BUILDING!

__AmirRoth__ gravatar image__AmirRoth__ ( 2018-10-23 09:35:32 -0500 )edit

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answered 2018-10-23 13:00:32 -0500

It’s modelled right or should i find the way to imput the constant gradient formula?

The paper you referenced used the Room Air Model feature of EnergyPlus, which allows the user to specify some kind of air temperature change within a zone instead of the default approach of having the entire zone's volume all at the same air temperature. There are many ways to do this, but the paper used two:

  • Constant Gradient - Temperature changes from floor to ceiling within a zone at the same rate.
  • Non-Dimensional Height - Temperature changes from floor to ceiling within a zone at a user-defined rated. User enters pairs of normalized zone heights with corresponding temperature differences from zone mean air temperature. This would handle the paper's following finding "In general, the air temperature increases gradually along with the height and the temperature gradient becomes fairly large in the region near the top of the atrium."

Note that the paper used temperature results from a CFD simulation (Figures 3-6 in the paper) done as a first step to know what the proper temperature values were to enter into the Room Air Model of EnergyPlus. If you want to repeat their approach, you will need also perform a CFD simulation.

I’m not getting any sun gain on the ground floor, its because of the air walls/floors?

My guess is that Rhino or Honeybee is using the same "Air Wall" approach as OpenStudio -- flagging a surface to be transparent ONLY for a daylighting simulation, not an EnergyPlus simulation. An "Air Wall" is actually 1" of gypsum board. If you have access to the EnergyPlus input file ending in .idf generated by Honeybee, check for the following:

  • Find one upper-level zone using "Air Wall" for its floor surface
  • Search for that zone's name in the IDF to find its floor surface
  • Search for the Construction object with the same name referenced by the floor surface
  • Search for the Material object(s) referenced by the Construction object and examine their heat transfer property inputs

If different stories are ok, should i use more zones (splitting each branch in 3 more zones)?

That seems unnecessary. The paper you mentioned recommends "**... the atrium space can be divided into two sections vertically according to air temperature stratification:

  1. From the floor surface to the plane surface 10m below the roof surface. In this region the air temperature varies little, generally from setpoint to 2$deg$C higher than the setpoint, because the solar radiation has little effect in this region.
  2. From the plane surface 10m below the roof surface to the roof surface. In this region the air temperature gradient is very big due to solar radiation effect.**"
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answered 2019-03-18 04:59:04 -0500

M741 gravatar image

Hey,

if you want to set thermal stratification you can try to take "Infrared Transparent Material (IRT)" for radiation exchange between the zones. https://bigladdersoftware.com/epx/doc...

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Asked: 2018-10-22 14:42:33 -0500

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Last updated: Oct 23 '18