HELP - Approach to measure building pressure loss due to open windows 3

[DennisKmetz]

I need guidance in an area where I have no technical background... so forgive the simple nature of my question.

I am a member of the Home Owners Association of a very large building in Chicago (John Hancock Building). We have engaged an engineering firm to help us with a decision regarding allowing or disallowing residents to continue installing operable windows. The firm says there is no method nor computer simulation program for measuring the effect of open windows on building air pressure, but this seems odd to me (a scientist but not an engineer).

This is an emotional decision and we desire some evidence or empirical data measurements along with mitigation alternatives if we continue to allow additional installations of new windows that can be opened up by the residents.

Is this the proper place to get advice on determining how many windows in our building can be open at any given time before the positive building pressure is adversly affected?

Any guidance on how to approach this issue is appropriated. It almost sounds like a good research project for a local university... or is it simpler than that?

Dennis

 

[IRstuff]

Not sure your question makes sense. Your HVAC is maintaining positive pressure, which means that it supplies a positive air flow into the building. Even if all the windows are open, there is a technical positive air pressure gradient across the building boundaries. The only way to get a negative pressure is if there is something actively sucking air out of the building.

While I don't know about actual computer programs in existence, one would think that your problem should be describable and simulatible, even if it were in lumped parameter form. The only complexity comes in the number of windows, dampers, etc.

TTFN

FAQ731-376

 

[ChrisConley]

The only way to get a negative pressure is if there is something actively sucking air out of the building.

Something like, stack effect, or wind? Buildings that are 'positively' pressurized will frequently have areas of negative pressure due to the above effects. It's not impossible to model, but the complexity would be signficant.

There are some firms that build wind tunnel models of buildings and physically measure intakes and exhausts for contamination: Not cheap, but they give a comprehensize report on all the intakes / exhausts you wish.

 

[DennisKmetz]

IRStuff

With the windows open, if there is a positive wind air pressure the odors from that apartment (the one with the open window) flow into the common areas, and then are forced into other apartments due to the positive air pressure from our HVAC system. This causes complaints.

Each apartment also has air exhausting intakes, and the HVAC positive pressure air flows under the doors keeping odors isolated within the offending unit (unless of course the open window causes a net positive pressure). So in the non-windowed apartments, the HVAC positive pressure flows under the doors, and up the exhaust intakes, and any odors are thus vented up to the roof... rather than being pushed into the halls.

ChrisConley,

Can you tell me how to find a firm that would perform the modeling you suggest. We have struck out using our slate of reputable engineering firms... perhaps we are not asking the right people to perform the study?

Thanks,

Dennis

 

[ChrisConley]

The only firm I know personally that performs work as described is RWDI:

http://www.rwdi.com/

It's a Canadian firm, but they may do work down in the US, or know of a firm.

 

[IRstuff]

I would think that you'd want to be looking for an environmental engineering company, like maybe:

http://www.pbworld.com/bim/projects/computational_fluid_dynamics.asp

TTFN

FAQ731-376

 

[AbbyNormal]

I would say it is hard to pressurize swiss cheese

In the winter time the stack effect is legendary in Chicago. The lobby of the Palmer House gets a gale force in rush of air when people enter, I feel sorry for the doormen.

But if you have some kind of control system trying to maintain a positive pressure in the summer, I think for one, the stack effect will want to reverse itself and the cold air wants to fall to lower levels. It is hard to defeat mother nature, they open any window up high and air is going to rush in.

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[AbbyNormal]

The winds are stronger up higher, and I bet the tendancy is for the upper levels to go negative in the summer.

Do the elevator lobby diffuers tend to sweat in the summer?

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[MintJulep]

Given a suitable model and sufficient processing power and time I think any CFD program could do the job...


for any given set of assumptions applied to the very large set of boundary conditions.

The number of possible permutations of boundary conditions will be a very large number.

 

[ChasBean1]

Even the best model would be subject to compound errors. Assumed leakage rates for suites, leakage floor to floor, whether there are windows open simultaneously on the windward and leeward sides, whether one’s dryer exhaust is on or another’s kitchen exhaust is off, etc. A whole lot of work could go into such a model from which it would be hard to draw conclusions and dictate to high paying residents that they can’t customize their home to their liking; especially if a precedent has been set that it is acceptable for some people.

A better option would be hard data, involving blower door testing, tracer gas testing, evaluating as found pressure differentials, pressures with windows open, etc. It still would be a pretty complex project and would require cooperation from residents, but it would probably give you much better data.

A last point to consider, and possibly the simplest option: a policy where installation of operable windows comes with mandatory sealing of the residence, including entry door gaskets and drop down sweeps and blocking of transfer ducts (if applicable). The entry door undercut is often the design source of make-up air for high rise units. The requirement for mechanical ventilation would become trumped by the operable windows, which by code would typically need an opening area at least 4% of the total floor area to allow a “natural ventilation” alternative. The resident would just need to understand that the building-provided mechanical ventilation would be forfeited with operable window installation. The building would control and maintain front doors; residents would control (and are responsible for) everything inside.

 

[DennisKmetz]

ChasBean1,
Thanks for the practical insight. I will propose these as part of my discussion with the CFD firms I talk with.

ChrisConley and IRstuff and MintJulep... thanks for the specific leads on what type of engineering firm I need to get involved with... CFD... who knew (LOL)

Thanks all for the help! This web site (and this forum) is very helpful.

Dennis