Air conditioning for buildings – there is still room for improvement here

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Klimatisierung von Gebäuden – hier ist noch Luft nach oben

What architects and planning offices can learn from car manufacturers

Image 1 Voith Arena, home of the 1.FCH from a bird’s eye view

The design of ventilation and air conditioning systems in the building sector is still very much in its infancy compared to the complex flow simulations used in the development of vehicles.

In a car, testers would immediately find fault with the air conditioner if it took too long to cool down the vehicle in summer or to defrost the windows and warm up the interior in winter. The whole thing must also not drag or even be too loud.
There are clear criteria that must be met for this.

In contrast, the building sector is much more casual: room volume x air exchange rate equals the required volume flow. What the air does in the room, on the other hand, is a minor matter. Whether there is a draft or whether it gets too cold or too hot in the room is left to subjective perception. It can also happen that the incoming air is immediately exhausted again. Where the temperature sensors are positioned is rather a matter of luck. It can happen that the air conditioner steers back and forth between two extremes. Thermal boredom (nothing happens, same warm, same cold) does not occur here in any case.

The air conditioning units are usually oversized according to standard to ensure that the room can be heated and cooled even if the supply and exhaust ducts are poorly arranged. This is not economical at all, the architect does not care and the air conditioning contractor is paid by kg/sheet. So why save on your own wallet here?

The builder, the real beneficiary of a cheaper and more economical system, often does not have the necessary expertise, even though he is the one who would benefit most from a system half the size, better designed and functioning, with better performance and half the energy costs.

However, the room temperature should not be too uniform either, as a person does not feel comfortable here either (the term thermal boredom actually exists).

How can flow simulation (CFD) help here?

The best way to see this is to look at an illustrative example: the business club of 1st FC Heidenheim in the 2nd Bundesliga.

Why there of all places? Quite simple: The Voith Arena is only 2 km away from our office in Heidenheim and as the bronze sponsor we were provided with the CAD data necessary for a simulation for the following investigation.
Many thanks at this point to Holger Sanwald from FCH as well as to Robert Kohler from ADK-Modulraum.

Perceived differences can be seen in the three construction phases – Business Clubs 1, 2 and 3 of the Voith Arena.
While the 1st Business Club still has teething problems, the ventilation concept at Business Club 3 is much more well thought out.
It is not perfect yet, as you can see for yourself when the FCH soccer team is struggling on the grass in the summer and you are sitting at the wrong table during the break or even before and after the game. There are places where there is a draft and there are places where the air seems to be standing.

Image 1 shows the location of Business Club 3 in the Voith Arena considered in the simulation from a perspective of a bird flying very high.

In image 2 you can see a view from the inside. There are currently no people in the picture because of Corona, although Holger Sanwald and his team have gone to great lengths with a sophisticated hygiene concept. Unfortunately, the political lack of concept was stronger.

Image 2 Businessclub 3, view from the inside

The following two videos show a walk through the building at a steady state flow. The flow velocity is shown once in the form of isosurfaces (same color = same velocity) and once along streamlines. A streamline is the path of an air particle in space, from the entrance duct to the exit duct.

Video 1 Interior velocity distribution
Video 2 Streamlines in the interior

The difference in velocities is what you can perceive. If it is too high, there is a draught; if it is too low, there is not enough flow through the area.

For clarification, the flow conditions in a vehicle are shown in Figure 3. Here one can better imagine the meaning of the streamlines.

Image 3 Air conditioning in a vehicle

So you can define clear criteria how to objectively evaluate the quality of air exchange. The temperatures or the humidity in the room can also be considered and evaluated. For this purpose, an extension of the model is necessary in order to be able to consider effects such as solar radiation and insulation of the room.

When calculating the temperatures, it must also be taken into account that each person in the room is a small oven with 100 W of heat generation.

The current favorite topic of air hygiene can also be better evaluated using these approaches. I will cover this in more detail in one of my next articles.

We are currently working with a startup to be able to see the flow results during a walk-through of the room through augmented reality.
An iPad is already sufficient here. The view through the camera overlaid with the simulation results then shows you where there is a draft or stuffiness.

Are you curious? Feel free to send me a short mail.
We will show you without obligation what is already possible in these areas and how you can also profit from our know-how.

Your Stefan Merkle

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