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

Hello, first of all, thanks a lot to the community which it’s being mostly helpful with all the material available to learn this great tools!, second sorry for the noob question i’m going to do, this is my first post, and just getting started in 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

And this is the way i’m modeling it.

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:
STUDY ON ENERGY MODELING METHODS OF ATRIUM BUILDINGS
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.

The end of this analysis is to simulate the improvement on comfort from insulation on windows (starting from air tightening, and draught stripping).
This is an actual dying market, with each day fewer customers, and we are group of people trying to save it. It haves a huge problem of comfort, when it’s -5°C outside, inside its -4°, and if its 30° outside, inside its 35°. Also some kitchens exhaust to the interior space and windows are operated anarchically.
I’m trying to see if a very low budget actions could make some improvements.

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.

gh file> rakoczi4simpliefzones.gh (1.0 MB)

@jlgrobe

You are correct that airwalls between zones won’t pass solar, daylight, and long-wave radiation from surfaces and internal gains: ref. Solar and daylight can be achieved with interior windows between zones, but these windows are opaque to long-wave radiation. So I think unrealisitic interzone radiation transfer is ultimately just a limitation of the EnergyPlus engine (I know TRNSY does model interzone radiation). Modeling it as one zone will allow you to achieve a much better radiation model, but then, as you have identified, EnergyPlus will model the single zone as a well-mixed air volume which is the other big limitation here.

This is somewhat outside my traditional area of modeling, so I can’t be of much help, but I would encourage you to post this problem on the https://unmethours.com/questions/ forum, since this building has some unique challenges that will benefit from their insight. Especially regarding the trade-offs between the different methods of modeling atriums (split zones with airwalls, one big zone, split zones with glazing + airflow).

-S

1 Like

Thanks a lot for the reply!
anyway, if you can help me understand this paragraph, (so i can continue doing some tests)

1. Solar gains and daylighting. The only way to pass solar and daylight from one zone to the next is through a window or glass door described as a subsurface on an interzone wall surface. Note that all solar is diffuse after passing through an interior window.

It says that an airwall, doesn’t transmit solar gains? so it’s kind of receiving it and disappearing it?
So it’s better to use windows, but this will produce a bad air mixing between rooms?
can windows be aplied to airwalls? and indoor window should be included one in each adjacent zones as walls?

I had checked TRNSY, thanks for the link! but for the moment i think i’m going to try finish some results from honeybee, as what i primarly want is a comparison between diferent options.

Yes, the airwall is a low-resistance opaque material. Specifically OpenStudio defines an airwall as a single layer of opaque drywall in EnergyPlus. I think in Honeybee (but not in OS?) there is an added airflow rate to promote interzone air mixing.

As for what combinations of windows/air mixing you should use, here’s a good example of an atrium modeled in EnergyPlus (from their examples files) that I have used in the past with really good results:
AirflowNetwork_Multizone_HorizontalOpening.idf (103.3 KB)

This models the atrium using two methods:

First a hole is created as a subsurface fenestration, in which the material in the hole is an Infrared radiation transparent material to model IR exchange between zones. I admit, I had forgotten about this material until I looked up this file - so for the record I should correct my earlier statement to say this is one way you can model IR transfer between stacked zones. The IRT material absorbs and and then re-emits to other zones. EP prevents it from participating in the zone air heat exchange by fixing heat transfer coefficients to zeros, so in this way zone surfaces are linked via IR exchange.

Secondly, there is a Horizontal Opening property specified in the floor to model airflow between zones. However, this property isn’t encoded in Honeybee or last I checked in OpenStudio, so you’ll have to go straight to the EnergyPlus idf to model it. This might have changed with the latest OpenStudio releases.

-S

2 Likes