[Sbse] ASHRAE Lowdown Showdown Modeling Competition

Nathaniel Jones nathanieljon at gmail.com
Mon May 10 07:49:50 PDT 2021


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> 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
> Professor for Building systems at Institute for Facility Management - ZHAW
> Zurich University of Applied Sciences
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>
> On Sun, May 9, 2021 at 11:28 PM Alexandra Rempel <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>
>> *Sent:* Saturday, May 8, 2021 5:33 AM
>> *To:* Alexandra Rempel <arempel at uoregon.edu>; 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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