SimScale CAE Forum

Q&A Session on HVAC Design and Engineering Simulation

What problems do HVAC designers and engineers have when it comes to energy efficiency and what are the solutions?

What are some creative and functional techniques for introducing ventilation when designing underground structures?

How can you ensure thermal comfort in a building with CFD analysis?

How can I visualize smoke propagation in an underground garage and test the ventilation system?


Which question would you like to find out the answer to? On November 29th you don’t have to choose. The engineers at SimScale and Desanco will answer these questions and all of yours.

Tariq Malik, Business Development Manager at Desanco will lead a Q&A session on the Forum to answer questions about HVAC design, engineering, and simulation.

If you are designing air conditioning, ventilation or heating systems, ducts, fans or even buildings, this is an event you shouldn’t miss. You can find the answers to your questions, solutions to your problems and new ideas for better products. And on top of it, you get the chance to meet fellow engineers.

Just post your question on this dedicated forum topic anytime before the day of the session. If you don’t have a SimScale account yet, register for free here.

On November 29th, between 10:00 A.M. and 12:01 P.M. CET, Desanco and SimScale engineers will be on the forum for two hours, answering questions and engaging in new discussions.

Don’t worry if you can’t attend it live, we promise to answer all posted questions. Just write yours below.

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Has there been any attempt to model the acoustic performance (SIL) of duct attenuators? It would be good to have a method of noise reduction performance based on amount of absorption material and dimensions.

I’ve also been looking at airflow modelling which is quite straightforward, hoping to estimate pressure drop and link turbulence to noise.

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I am interested in simple airflow simulations such as the warm air from a radiant wood heater diffusing through a living space and what happens when windows are opened after a breezy summer cool change. How ceiling fans affect these scenarios might be next. As a beginner I’d be interested to have these ranked by complexity so that I know in which order I ought to attempt them. My students will be learning with me.

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In what phase is MEP design included in the BIM model and at which Level of Detail?
What type of information is fed into the BIM model?
Which of the Stakeholders use this information in post-design phases?

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My name is Mr Folabi Onakanmi, I noticed that some modern vehicles have less active air conditioning systems to save money and to make up for expenses on fuel usage and to meet pass their emissions tests.

What can be done to have a fully functional Air conditioning system in a vehicle which does not compromise quality, to meet the manufacturers vehicular safety standards?
what are the design upgrades which can be carried out to mitigate in such circumstances where there are no alternatives?

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Hi, thanks very much for the question. This is Tariq from Desanco.

In terms of modelling acoustic attenuation in ducts, we would not typically utilise CFD techniques for such an exercise as there are other more appropriate methods that cover acoustic modelling performance.

Pressure drop can be easily calculated using CFD as can the turbulence that leads to noise, however, the latter would be a more involved exercise due to the requirements for a much finer mesh to predict accurate turbulence quantities (for example LES - large eddy simulation). Hope that helps and let me know if you have another question.

Hi arnold1, thanks very much for the interesting question.

The steps you could take (in order of increasing complexity) to model the scenario could be:

  1. Investigate the natural performance with the heater and fans switched off to determine the effect of the airflow when the windows are open.

  2. Switch the heater on by using a surface heat flux (easiest option) or volumetric source with radiation if you need to consider heat transfer to surrounds through radiation (generally not important) since heat convection would be the primary heating mechanism.

  3. Switch the fans on by either A. a numerical representation of a fan i.e. pressure drop profile with flowrate or B. physical fan geometry with MRF or rotating reference frame (which is much more complicated).

Hope that helps. Regards, Tariq.

Do you have to use LES for duct acoustics?
Is URANS+BEM/FEA+statistics not good enough?
Can you use WMLES/DES+BEM/FEA to get broadband noise if URANS+statistics is indeed not good enough…

Hi Mr. Folabi,

Can you please clarify your question in terms of whether you are seeking to optimise airflow within a cabin pre or post design phase and also which vehicular safety standards are you looking to comply with?

Also could you please clarify what you mean in terms of “active air conditioning” systems and whether you’re more concerned about the duct design as well?

Hey Dylan,

To capture acoustics correctly you need an accurate turbulence model and LES / DES would be appropriate (or a minimum standard).

URANS would not be able to provide you with the same accuracy/resolution and may smear the broadband noise profile. From our experience we have found URANS to not be the most capable for broadband noise prediction.

Thanks, Tariq.

Hi Tariq,

Noise predicted by URANS is indeed very tonal, but you can get the broadband part with the help of statistics. If that works and the results are promising, this reduces the computation effort by lots.

Yes you can resolve the broadband part assuming the pressure fluctuations are defined well enough (which is difficult to achieve with the URANS model).

Especially for a (confined) duct flow seeing as URANS models are more suited to free stream flows.

But if you have a fine enough resolution and can resolve the pressure fluctuations then a URANS method might be promising from a cost and time perspective.

Hi @tmalik,

with all press coverage on the need to design more energy efficient buildings (e.g. I recently saw this neat website: https://myheat.ca/) do you see this reflected in the type of projects where CFD / HVAC simulation is being or will be used? We’re all used to seeing CFD being used to design projects of the size of tunnels and parking garages. But do you see it becoming more widely used in such “small scale projects” as normal houses or small office spaces?

Best,

David

And if you don’t mind, another question related to passive ventilation of occupant spaces. It’s a beautiful thing from an energy efficiency perspective but I learned that the real challenge is to make it work reliably all-year-long - otherwise you might end up with too cold / too hot / badly ventilated space at some point of the year.

Are there some design best practices or examples you can share how you make passive ventilation reliably work? Is there often a “fall back” mechanical ventilation system in place? Or are there other methods to reduce the risk of passive ventilation not being sufficient?

Hi @dheiny

Yes we are seeing many more small scale projects utilising CFD / HVAC simulations partly due to the fact that the progression in simulation technology is no longer reserved for bigger companies who design and manufacture larger scale projects.

The other driving factor is the push for more environmentally sustainable design at the smaller scale project level and natural ventilation is a big part of this. We have even used CFD for private residential houses.

@tmalik,

This is very interesting. Following on that, how to do you see the HVAC landscape change in future? Are there any hot topics or new concepts in development?

Re passive ventilation of occupant spaces it is inevitable that at some point in the year it may not work reliably due to the large variation in wind and temperature through different seasons. However, as a general rule we approach it with a probabilistic assessment that considers the annual variation in wind direction, wind speed and ambient temperature.

For example, with previous projects we’ve had we were able to determine the aggregate performance of an apartment complex over a 12 month period and determined that for 9 months of the year the thermal performance was sufficient to provide passive ventilation; but for the remaining 3 months the addition of mechanical systems was necessary. This allowed us to calculate how much energy the building required for the running of mechanical systems.

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Interesting - so this means that you don’t save in purchasing/installing the mechanical ventilation system but operating it.

Do you have a specific/preferred source for the data on wind direction, speed & ambient temperature across the year (If you don’t mind sharing)?

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