Some questions about designing a building

Bernd · Posts: 2

Hello,

I’m new in energy plus and DesignBuilder. I have to simulate an office building for University and after trying E+ and DB a bit; there are some questions I need some help to answer.

1. There are special windows which shall be used in this building. These kind of window has a prismplate between the normal glaspanels. So when the sunlight hits the window under a defined angle range the complete direct Sunlight will be reflected. I have a study about the variation of the SHGC and the Light transmission depending on the position of the sun. My Idea was to design a Window with the worst values and then use a midpane shade with a schedule to simulate this type of windows. The problem is I don’t know how E+ calculates the SHGC, the direct solar transmission and the Light transmission, so I can’t calculate which characteristics the shade needs and how much percent I have to define in the schedule to get the SHGC etc. at a specific sun position.

Is my idea to simulate that windows correct or am I totally wrong? And how could I calculate the settings?

2. My second problem is, that I’m not sure how to build the Floor. The Problem is that there is a 0,7m thick air layer between the concrete and the Floor. I can’t design this as an extra layer in the construction data of the Floor, because the concrete layer isn’t completely horizontal (please look at the detail I posted). My thought was to design it as two zones, but I shall design the concrete as a thermally activated structural component to heat the rooms above and below the concrete and I’m not totally sure if a two zone solution will give correct results or if E+ wouldn’t use the total potential of the activated concrete. (Or is there a way to draw horizontal partitions?)

3. Out of the thermally activated concrete comes my next problem. The building has 18 levels and to minimise the simulation time I was planning to design only three Levels at special positions and use component blocks for the other levels. The question is, can I design the component blocks in a way that it isn’t full adiabatic, so that the heat transfer from the concrete in the not designed zone would be considered? Or must I design the complete building?

4, When I draw a sub-surface witch goes to the boundaries of the surface in DB there is a border between the surface edge and the sub-surface. How can I design a wall which has for example the first 1,5m concrete and the rest bricks?

5. How can I design a detail like the assembly between the concrete and the glassfacade?

I hope you can help me with these questions, and I hope you’ll have right a sunny day like me here.

Thank you very much,

Bernd

Bernd · Posts: 2

Hello again,

I´m still looking for some help with the questions I posted above. Isn`t anyone here who could help me with this questions?

regards,

Bernd

AOG · Posts: 85

Hi Bernd, welcome to DesignBuilder!

It seems we all are very busy right now Smile

. Well, here is my modest attempt:

1. I have not much experience in this field, but... you can find detailed information about daylighting and window calculations in the EnergyPlus Engineering Reference document, which could help you to develop your own calculations. And of course, Mr. Mahabir could help us whit his great experience.

2. As far as I know, DesignBuilder offers three alternatives to model this situation:

a) Using separate constructions (Model options > Construction and glazing data), where you can define a slab construction and a floor construction fitted above it. It’s also possible to define the fitting height.
b) Using combined construction, where you can define a floor construction which includes all the required layers, the air gap inclusive.
c) Modeling the entire system as a zone-block by itself. The slab is defined as the internal floor construction of this zone, while the fitted floor is defined as the internal floor construction of the zone above.

Neither of these options allows modeling the inclined part of the slab. So, I think the more advisable strategy is to define an ‘equivalent’ fitting height (some like the average height). In the other hand, I think the more accurate option is c), as it can better take into account conductive, convective, and radiant heat flows. Also, please note that in DesignBuilder, when you use a radiant floor heating system, the radiant heat is distributed directly and uniformly through the zone floor.

3. You can only define totally adiabatic or totally not adiabatic surfaces, and in the second option, if there is an adjacent space, it should be a thermal zone (not a component block). So, if you need to simplify your model, what I could advice is to include the bottom and top stories, as well as a representative number of intermediate stories (so you can find an ‘average’ thermal performance of most intermediate stories).

4. You can model this situation precisely with subsurfaces. I assume that borders you mention are related with the fact that openings and subsurfaces are drawn over the internal surfaces of the zones, so wall thickness remain in the corners. However, it is just a visualization issue, because DesignBuilder-EnergyPlus, as I understand, only take into account heat transfer trough the internal area (not the corner lines).

5. I’m afraid it’s not possible right now, so it is necessary to simplify the detail.

I really hope this helps you at least a little.

Arturo

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