Modern buildings, especially when constructed in cities like London with a great heritage and with the need to meet requirements of millions of modern day inhabitants, face a lot of challenges. Buildings must look good, sleek and modern from the outside and provide suitable space for shops, offices or flats. Huge glass surfaces let the sunshine in because nobody wants to live and work in a cave any more. But modern day comfort like temperature and humidity control require high-tech heating, ventilation and air conditioning (HVAC) machinery to be built in as well.
These machines have to handle surprisingly large amount of air. As rain and in other parts of the world sand are a regular additives to air, HVAC engineers use louvres to keep the unwanted bits out of the delicate machinery.
So louvres must keep rain and sand out but at the same time these should not mean too much resistance to air flow. Of course there are standardised ways to measure, test and calculate louvre performance as described in BS EN 13030 (for pressure loss and simulated rain) and in BS EN 13181 (for pressure loss and simulated sand). But what if the HVAC engineer has a louvre design that combines an aesthetic and a performance louvre into a non-standard setup?
Do not go for the looks only
It looks awesome but pressure loss of the combined system should be low enough to fit the air flow rate of the machinery it is supposed to supply. How to make sure it will work fine? Test it? Sure, but what if it needs to be changed because pressure loss is too high? Test again after a design change? Well, fluid dynamics simulation that reproduces the standardised testing process is a much smarter move.
This is why Conttego UK, a professional supplier of architectural facade systems got in touch with us. They wanted to know how big the pressure loss of an aesthetic and a performance louvre placed behind each other would be.
The aesthetic louvre was not previously tested, no information was available about its pressure loss figures. However, the supplier of the performance louvre was known and we could find its data sheet showing the most important parameters. The pictures below demonstrate the standardised 1m x 1m test louvre assemblies in their designed orientation.
When a louvre is tested in real-life, the test piece must comply with the rig’s own features. Louvres must have a frame so that the test assembly can be mounted on the rig. We did not need such intricacies. We could use the whole 1m x 1m standard cross section for the louvre blades if we wanted to.
It is called performance because its job is to let as much air in as possible while keeping some of the rain out. Conttego was interested in pressure loss only, water protection performance was not part of this project.
The simulations were made the exact same way as a real-life test would be carried out.
Simulated according to BS EN 13030
The 1m x 1m test geometries were placed in the 3D CAD model of the test rig and loaded up into the CFD simulation tool. We applied the same boundary conditions as a real-life test would have used. We simulated entry and discharge conditions, simulated each louvre layer separately and behind each other to have the full scope of results.
For the entry condition, the performance louvre had a Ce=0.457 pressure coefficient catalogue value. Based on simulation data, our setup resulted in a Ce=0.43 pressure coefficient for the entry case, which gives us 94% accuracy. Not bad at all.
Apart from the entry and discharge coefficients, it was a matter of minutes to calculate K-factors and to visualise pressure loss dependency on flow rate.
These curves show that the entry setup has higher pressure loss than discharge one. The bigger air velocity is, the bigger the difference between the two setups will be. For this project it was a challenge because behind one section of the facade there was an air inlet, in need of loads of fresh air.
Having all the performance characteristics of this non-standard louvre setup within a day, HVAC engineers can decide how to handle the situation if the original louvre system geometry did not bring in good enough results.
Besides being accurate, fast and being able to provide full performance testing scope including water or sand protection, a fluid dynamics simulation of non-standard building elements has the flexibility to run several design changes in a matter of days. So just let the sunshine in, machines can handle the rest.
Dr Robert Dul