Underfloor ventilation 1

[CptHk]

Our firm will be designing an underfloor supply distribution in an indoor public area that will have some food consumed. It is in a college library where the room will serve as an occaisional reception area (food will be served). When there are no receptions, coffee and other basic foods will be served and consumed. It is not a restaurant or typical cafeteria application.

The air return will be on a wall, so no issue there. But the supplies could get food in them. Are there codes regulating this type of application. Within our office we have not found the text in the IMC or our local building codes, and there is not total agreement among the senior engineers whether the supply registers have to be raised and out of the walkway so no food, dirt, etc... can get swept(or fall) into the supply duct.

Has anyone run into this, if so, any suggestions?

I can provide more details, but I tried to keep it short as possible to kick off the dialogue.

Thanks in advance.

 

[GMcD]

As far as I know there are no Codes specifically related to UFAD systems and spill/debris protection. In fact, there isn't even a requirement to have some kind of emergency floor drain(s) in the UFAD plenum for pipe breaks (and they DO happen...). I assume you've tagged the LBL website at

http://www.cbe.berkeley.edu/research/briefs-website.htm

and done your requisite Google/Yahoo searches for other UFAD design material. My point of view is that the balancing basket in the floor diffusers will contain most of the spillage, and the Owner will have to have a more diligent janitorial service to access and clean the underfloor plenum more often.

That being said, fundamentally is a UFAD the right option for that application? I wouldn't do it. I'd look at low sidewall displacement ventilation style air distribution to avoid the whole floor plenum thing in the first place.

 

[CptHk]

Thanks for the info. I can look deeper into the issue and give better feedback to the Sr. Engineer and my PM.

Right now the design is driven by the existing structure of the building and the way the architect is designing the space. I think my PM knows all the difficulties and is pushing back where he can (No one thinks that the UFAD is the "right" option for this application), but I think this particular area would need many architectural compromises to get the ductwork overhead or even low sidewall. However it is early enough in the Detailed Design that it could be changed if absolutely necessary.

 

[GMcD]

Well, I re-read your original pots, and I guess the mitigating issue is that the space will only be "occasionally" used for food services. So if the Owner is properly informed about the housekeeping issues for when the space is used for food and beverages, the UFAD is at least a whole lot better for comfort and energy compared to an overhead air system.

I have found that the floor diffuser buckets are pretty good at trapping a lot of the spillages unless it's high volume (more than 1/2 litre), and even then as long as it's cleaned up fairly quickly from the floor plenum, before primordial ooze begins it's life, the IAQ won't suffer.

Please make sure the Architect and/or structural engineer has specified concrete floor sealant for the exposed concrete in the UFAD plenum space, and fer gosh sakes, make sure you and the Architect clearly specify the floor plenum sealing around edges, walls, columns, and anywhere that air could potentially leak out of the plenum. Leakage up through the floor tiles is generally acceptable since it's air going into the space being served, but it's the air leaking out through adjacent walls, short curcuiting up walls to the ceiling, and other areas outside the occupied space that you have to be diligent about.

Bottom line- if you point out the plusses and minusses and the housekeeping issues for "occasional" food service use, it should be workable.

 

[atlas06]

UFAD is the worst thing that was ever invented.
It uses as much as 2.5 times more airflow (min, twice the airflow) for very little reduction in static pressure. It acts as a Constant volume system.
This whole UFAD is an archtect's idea gone awry.
We bought that Berkley study from ASHRAE and it is lying like it is breathing to make its case. And if you read carefully and investigate the sponsors, you will find out some guys in the UFAD installation business as the main sponsors.
When that study makes its case it compares two fans at 20,000 CFM each, the one with the UFAD has less static therfore less Horse power. In reality, the study should have compared a 45,000 CFM Vs a 20,000 CFM fan. And then you will see the UFAD actually using more energy.

I will not dwell over the astronomical cost, the maintenance nightmares of teh UFAD VAV's or FCU's, the lack of temperature control (which the Berkley study actually acknowledges as being a problem).

The other thing is, often times this system is used for high end goverment buildings, I've seen some with as much as 18" of perimeter window space dedicated to the UFAD diffuser (a $350.00/SF prime real estate space for a diffuser mind you).

Some systems were so badly engineered, GSA has had to insulate the underfloor because it was raining inside (from condensation).

This whole thing is driven by architects with strong pull in decision making to gain one lousy LEED point. ASHRAE indicates this system as experimental and does not endorse it (although it sells the book, tells you how ASHRAE thinks). Time for Engineers to stand up to Architects on this issue, but we can't, they hold the dough.

 

[GMcD]

So, Atlas, get off the fence and tell us how you really feel! I think you are way off base with the overblown rhetoric, and there are enough independent studies that refute all your criticisms. I am not a fan of UFAD systems either, but when properly designed, they DO offer clear measurable advantages over conventional overhead VAV reheat or any other flavour of overhead air delivery systems. There are just as many VAV reheat systems that have had problems percentage-wise as any UFAD system - it's all about proper design and proper construction. All of the UFAD systems in my area were not Architect driven, and were mainly Building Owner, or integrated design team driven for a combination of reasons.

Sure UFAD systems are still an "all-air system" which isn't the greatest, but based on the properly designed systems, it's still better than overhead air delivery.

So what's YOUR ideal system?

 

[STYMIEDPIPER]

I am not discussng the merits of the UFAD.
I am looking at this from a different prespective.
Why do architects use the UFAD?? Because they do not want the supply duct to be exposed and visiable.
As an alternate idea, a college setting is the perfect environment to use the Ductsox. The Ductsox is unique and can be furnished in a rainbow of vivid colors which is ideal for the college setting.
Just thought I would suggest an alternative that you may offer to the architect

http://www.ductsox.com

 

[atlas06]

GMcD
My problem with UFAD is that it is presented as an energy saving system, which it is not and it does not offer the comfort of a VAV system.

There are no ideal systems, for they change from one climatic region to another. I'd say that if you are down south, Cold systems will offer a better comfort, if you are in the rust belt or above, you may consider natural ventilation in some cases (warehouses and such for example). One just needs to adapt.

I side with stymiedpiper's idea with his approach for the problem at hand, I agree that one sould look at the problem from a different angle. Personaly, I'd go with a perforated round spiral duct accross the room perimeter. similar to duct sox but with sheet metal. It can be a decorative exposed structural member, which can be painted in the architect's color of choice. United McGill makes such things.

GMcD, why is it that I sense some nervousness in you response, keep cool man, we are just trying to learn from each other. what do you think of an exposed perforated duct?

 

[GMcD]

Atlas; no nervousness on my part. After 28 years in the business I think I've learned a few things, and I am actually getting away from all-air systems, and especially overhead mixing systems since the IAQ of mixed air and fully mixed room pollution control through dilution is old school.

It's just that your rhetoric and inflammatory adjectives describing UFAD systems from your point of view do not add to the technical discussion at hand. I completely agree that there are no ideal system types and that building occupancy, climate, and local conditions are the driver for some systems being better than others. However, UFAD systems, when designed properly, DO offer better energy efficiency, indoor comfort, and IEQ in many climate zones and applications compared one on one with VAV, fan-coils and hydronic heat pump systems as typical conventional Office Space HVAC systems.

I've spoken with a number of Facilities Managers who deal with a few hundred thousand sq.ft. of UFAD office spaces and all of them, no exceptions, say that the spaces with UFAD are superior in terms of minimizing occupant complaints, energy, and maintenance compared to VAV office buildings they've dealt with prior to, and at the same time as their UFAD buildings. Again, I'm not a proponent of these systems- they are certainly a specific toolbox system that an astute HVAC designer needs to be aware of and how to design properly for the right applications.

Considering your blanket opinion of UFAD systems, I can't wait to hear what you think of low level displacement ventilation coupled with radiant cooling/heating systems.....which HAVE been proven in many diverse climate types to offer better energy efficiency, better IEQ and lower first costs than conventional "all-air" systems.

 

[ChrisConley]

low level displacement ventilation coupled with radiant cooling/heating systems.....which HAVE been proven in many diverse climate types

I've done radiant cooling and heating, I've done displacement ventilation, I've never heard of both concepts being used simultaenously successfully. In fact most case studies I found recommended not using them together.

Have you combined them GMcD? How did it work out?

The problem, as I understand it, is that displacement ventilation relies on stratification, and radiant overhead cooling works directly against that concept.

 

[GMcD]

Chris: there are over 2 million sq. meters of combined radiant cooling ceiling/DV systems in Germany and Switzerland alone right now, so yeah, it works....

I'm not sure what case studies you've been reading, but my library is full of case studies of radiant cooling ceilings (NOT chilled beams) combined with low level DV and their operation and how successful they are for comfort and energy.

Yes, DV relies on stratification, but how, in your mind does a cool ceiling at a 17C surface temperature work against that concept? The ceiling boundary layer of air that is at some temperature "x" between the stratified air layer temperature and the 17C ceiling surface temperature does not start to depart and "fall" from the ceiling unless you get below 14C, but most radiant cooling ceilings are generally operated at 17C or above, so that layer of air next to the cool ceiling does NOT affect the stratified air layer.

Perhaps the information is coming from the "chilled beam" concept where those things are purposely run at fairly cool temperatures to induce the denser cool air falling down into the space to supplement an overhead air distribution system approach?

The Swiss have patented the system now- check the Zent-Frenger folks at:

http://www.zentfrenger.de/Download/prospekte/Englisch/Zent_Frenger_Batiso_E.pdf

And this is the quote used in their brochure:

"Optimal thermal comfort is
nowadays obtained through a
combination of chilled ceilings
and displacement ventilation.
This proven combination gives
a high level of output performance
per area of ceiling,
together with individual room
temperature control."

They have the same, or better occupant thermal comfort standards over there that compares to ASHRAE-55, so it's been tested and proven.

The real secret for energy efficient HVAC systems? It's the building envelope - high performance facades with solar control, so the thermal loads in the space are reduced to a low enough level so all the sensible thermal heating/coolingloads are handled by the radiant system (radiant cooling surfaces of 17C and above), and the DV system is simply 100% outdoor air supplied at a degree or two below room temperature, and it removes half of the room cooling loads you'd normally accout for in a "fully mixed" mode room condition calculation. The DV air system is where any humidification/de-humidifation occurs, and the system must be climate adapted, mainly via the high performance envelope.

Heck- the system works at the new Bangkok airport if you want an extreme example of radiant cooling and DV in a hot'n'humid climate, and as well, this system is being installed in the new Manitoba Hydro headquarters in Winnipeg (-40C winter design, +36C summer design). These combined radiant/DV systems date back 20 years in Switzerland and Germany, and are now the "go-to" system of choice for Office, institutional, and other occupancies.

 

[atlas06]

"Considering your blanket opinion of UFAD systems, I can't wait to hear what you think of low level displacement ventilation coupled with radiant cooling/heating systems.....which HAVE been proven in many diverse climate types to offer better energy efficiency, better IEQ and lower first costs than conventional "all-air" systems."

GMcD
To answer your question about my opinion on the satement above, I am in full agreement with that. I have many problems implementing such a system in the US. Lack of US manufacturers being the main reason for its rejection by clients.

PS: I, too have been in the business for 28 years. so peace pal, I'd hate to irritate any member of this forum that takes that much time explaining his case so scientifically. That being said, I still maintain that the UFAD does not save energy compared to VAV. The system you described above (DV with radiant cooling) does use less energy, because it reduces the amount of airflow substantially and with less static. We have commissioned 1,000's of SF of UFAD systems, and they all operate as CV, their VFD's just wouldn't throttle down.

Thank you for taking the time to write a very good lengthy post.

 

[GMcD]

Atlas: Well, I guess there is hope for you yet!

I still disagree with you about the UFAD energy savings since interior zone VAV systems generally act as CV systems as well. Many of the UFAD systems that I'm familiar with use VAV boxes and underfloor "air dams" for underfloor zoning perimeter vs interior, as well as CV interior zone, with 4-pipe fan-coil perimeter zoning systems. The UFAD "saving energy" arguement comes from both the lower fan Hp required, as well as the fact that over the course of the seasons, a UFAD system, using 63F nominal SAT, can use more free cooling over the year compared to VAV systems that typically supply air at 55F. So that 55F to 63F "extra" free cooling band is available to the UFAD system as compared to the VAV system.

Regarding the "lack of US Manufacturers" for DV and radiant systems: I tend agree somewhat, but...- EH Price has a nice line of DV stuff like Halton's line, plus a full test lab for it in Winnipeg that will provide some nice video smoke tests for convincing clients. Radiant stuff is all over the place - there are at least five or six PEX tubing manufacturers, and a few manufacturers of the suspended radiant panels (expensive!!). I'm waiting for the capillary tubes to start coming into North America- we already have one local Sales/Supplier bringing in the Karo capillary tubes, and they have already got them installed in a couple large local projects so it's a start.

 

[lilliput1]

Note that the UFAD also acts like a radiant floor for cooling. The largest temperature rise occur within 6" off the floor then the temperature rise gradient becomes approroximately linear. See Trox for graphical method of determining airflow.

It would require less airflow if you have high ceilings that would allow you to stratify the air temperature to 82°F and above. You would have to make sure the plenum is reasonably airtight. One way of accomplishing this is to use carpet tiles with resilient backing and laying them in a pattern so the 2'x2' carpet tile grid falls at the middle of the floor tile grid, thus the carpet overlaps the tile seams. Then you would need to put automatic dampers at the root of the branch air distribution ducts to regulate and maintain the design underfloor plenum pressure. You can gang duct dampers in same air system zone to be controlled off a plenum static pressure sensor. If properly designed & with plenum reasonably airtight, supply air should be approximately 68% of that with conventional overhead air distribution. Architects should note however that ceiling space must still be provided for return air duct. You have to have good return air duct distribution particularly if you don't have much ceiling height to make sure you remove the stratified hot return air out of the conditioned area.

To produce the 60-63°F supply air consider using AHU with return air bypass. Make sure the unit bypass only the return air, that OA does not get bypasses but instead always go through the cooling coil.

 

[CptHk]

Thanks for all the feedback.

Apparantly, I did not qualify the job enough. We were not going to design a typical UFAD with all the design requirements that go with it. We need to feed the air from below at the perimeter, but it will not have any other of the UFAD traits. The supply distribution is underfloor and the registers will be at floor level, but that is where the similiarties to the UFAD end. I originally stayed away from calling it a displacement ventilation or typical UFAD design for that reason.

I am not a senior level designer and my background was more hydronic than air, so my PM directs me on almost all air side systems at this point. He is dealing with the compromises with the air flow and comfort, etc... of the ground level air distribution. I justed wanted to check about the practicality of floor registers where food was present.

Thanks.

 

[atlas06]

GMcD
We are probably not about to agree on this point but heh, If two peoples agree 98% of the time, one of them is not necessary?
Agree somewhat that if the UFAD air handler is provided with air-side economizer capabilities, the additional economizer hours will be there, BUT, and BIG BUT here

Reality check:
Most of the UFAD's I've seen are high end, top dollar projects, with nice looking facades, not the 60's architecture where you see louvers at each floor. Typcally, they tend to use a unit bringing in 100% OA, since they don't have air-side economizers, the argument for more free cooling hours is eliminated 90%+ of the time in real applications.