[Sbse] ASHRAE Lowdown Showdown Modeling Competition

Alexandra Rempel arempel at uoregon.edu
Mon May 10 13:40:20 PDT 2021


This is fascinating, everyone! I would love to see anything that’s been validated for air flow reductions due to fly screens or security grilles. This would affect the effectiveness of ceiling fans as well. Thank you for the discussion!

---
Alexandra Rempel, Ph.D., M.Arch.
Assistant Professor of Environmental Design
Environmental Studies Program
University of Oregon, Eugene OR  97403

From: Susan Roaf <s.roaf at btinternet.com>
Sent: Monday, May 10, 2021 9:15 AM
To: Matthias Haase <mathaase at gmail.com>; Nathaniel Jones <nathanieljon at gmail.com>
Cc: Alexandra Rempel <arempel at uoregon.edu>; SBSE List <sbse at uidaho.edu>
Subject: Re: [Sbse] ASHRAE Lowdown Showdown Modeling Competition

Nathanial,



Really - I was talking about windows - not ducts, they are different you know?



How lose a grill do you need as a security feature on a window? not that small.. umm has anyone papers on that? A simple screwed in security on the no opening side of a window would work well on higher floors. Of course sash windows are perfect.. but expensive. Actually there has been some good work n the reduction in flow across a fly screen or door - c. roughly 50% I seem to remember - I will look the paper up. Or anyone please send one they have for reference.



Re extreme winds - this is about loosing windows etc like the Austin Texas building or the Katrina hotel? I have a fairly good paper i did on designing for high winds for the Scottish Architects if anyone wants a copy - the nice thing about windows is that you can shut them...so you can dictate the windspeeds they should operate in for everyday use. Like temperature - put the control back into the hands of the occupants. Noone designs HVAC buildings to work optimally in 100 klm windws? the problem is different - trying to stop the windows flying out - especially in ever windier parts of america.



Anyone who pretends they have the correct answer to three decimal places is pretty well doomed to failure, but good clean common sens will get you a long way. May the force be with you - wind driven of course.



Let me know if you want the paper ...



Sue






------ Original Message ------
From: "Nathaniel Jones" <nathanieljon at gmail.com<mailto:nathanieljon at gmail.com>>
To: "Matthias Haase" <mathaase at gmail.com<mailto:mathaase at gmail.com>>
Cc: "SBSE List" <sbse at uidaho.edu<mailto:sbse at uidaho.edu>>; "Alexandra Rempel" <arempel at uoregon.edu<mailto:arempel at uoregon.edu>>
Sent: Monday, 10 May, 21 At 15:49
Subject: Re: [Sbse] ASHRAE Lowdown Showdown Modeling Competition
Hi Sue and Matthias,

Of course ASHRAE has a method for calculating the pressure loss/speed reduction through screens and grills. It's in the ASHRAE Handbook of Fundamentals (in my 2009 edition it's chapter 21, tables CD6-1 and CR6-1). The chapter is on duct design, but since this is just physics we're talking about, it is applicable to other settings as well.

As for pressure distributions around buildings, ASCE has methods that can be applied to fairly normative building geometries for wind loading calculations. However, more complex geometries and surrounding structures result in unique wind pressure distributions that can only be analyzed with wind tunnel or CFD tests (although there are some promising results from reduced order models, i.e. machine learning). Matthias, if you are interested in adding buoyancy (i.e. convection) to outside pressure calculations, then I assume you are concerned with exhaust plume re-entrainment, as this is the only case I can think of where the temperature difference might be enough to counteract the force of wind. In that case, CFD is really the only option. Given the possible harm to occupants when exhaust is re-entrained into building air supply, I would be hesitant to use a simplified or generic model in such a case.

Nathaniel

On Mon, May 10, 2021 at 7:04 AM Matthias Haase <mathaase at gmail.com<mailto:mathaase at gmail.com>> wrote:
Dear all,

I agree that we need guidelines for pressure drops of screens and other devices (e.g. shading). But we also need more research on pressure distribution around buildings and within districts. These have to be measured and calculated taking local solar radiation, absorption and convection into account. Many models I have seen are not detailed enough and often make simplifying assumptions. Measurements of airflow around buildings is often very generic and static. Any hint to work that has focused on this is much appreciated! UHI is going in the right direction but often asks for UHI mitigation instead of designing with pressure differences. Again, hints to promising work in this direction are most welcome.

best regards

Matthias Haase
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On Sun, May 9, 2021 at 11:28 PM Alexandra Rempel <arempel at uoregon.edu<mailto:arempel at uoregon.edu>> wrote:
Hi Sue,
It’s great to hear your thoughts on this! I sure hope you’re right that natural ventilation will be a prominent strategy here, supplemented by ceiling fans, of course! Passive heating and cooling have not been as popular in the past few years as one might hope, but they’re gaining ground.
And no, I’m not aware of any ASHRAE strategy for calculating air speed reductions for screens and grills. We definitely need something like that!
Intriguingly, the teams are required to choose and defend their own indoor air temperature setpoints; in the past, the adaptive comfort zone has been used sporadically, and the air speed expansion to both standard and adaptive comfort zones has not been fully exploited. I’m hoping this program is an irresistible invitation to do that this year, though!
I would love copies of all of the papers you mention; thank you so much. I’ll look at the HVLS website, as well.
Have you thought about coaching a team for this? There’s plenty of time!
Take care, and thank you again so much for your input!
Alex
---
Alexandra Rempel, Ph.D., M.Arch.
Assistant Professor of Environmental Design
Environmental Studies Program
University of Oregon, Eugene OR 97403
From: Susan Roaf <s.roaf at btinternet.com<mailto:s.roaf at btinternet.com>>
Sent: Saturday, May 8, 2021 5:33 AM
To: Alexandra Rempel <arempel at uoregon.edu<mailto:arempel at uoregon.edu>>; sbse at uidaho.edu<mailto:sbse at uidaho.edu>
Subject: Re: [Sbse] ASHRAE Lowdown Showdown Modeling Competition
Dear All,

In that lovely climate there will be many who will want to run their building complexes for as much of the day and year as possible using natural ventilation which is the main way to reduce heating and cooling and ventilation costs in buildings (that is obviously a no-brainer).

Question - Does ASHRAE have a standard methodology for calculating reductions in air movement due to insect screens and security grills?

Ceiling fans will also be key to genuinely low energy buildings.

This begs the question of what temperatures are inbuilt into the models use for acceptable temperatures for fan and natural ventilation use.

Fergus Nicol and I did a paper last November for the Dutch HVAC journal for acceptable temperature ranges for naturally ventilated building - I would be happy to send a copy to anyone interested.

I also have a great paper by Dick Aynsley on calculating fan power etc he did for a book I edited - I can send that too if you are interested. He was an early expert for Big Ass Fans who also have a great resource site on fan design: HVLS Design Guide (bigassfans.com)<https://urldefense.com/v3/__https:/guide.bigassfans.com/__;!!C5qS4YX3!V41rAjKP6Hk9Rq1ESdqV4dV1e9n8wW_XSG8e9PrhE-JSCmsyeAeSunkm3yED2mIrFw$>

In that climate a great idea is to use simple roof space extract fans to pull air through the building from cooler / garden type places - where planting and water etc can lower temps by up to 5C - from a shiny hot sunny equivalent space with hard reflective surfaces - if not more.

I have no doubt that such issues will dominate the submissions - or is this for high energy buildings that need energy 24/7/365 - that cant be....

Good luck with the interesting project.

Best wishes

Sue
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