Letters to the Editor
Not everyone sold on the benefits of UFADThe January article on underfloor air distribution ("Undervalued?" Jan. 2002, p. 28) raised a question: "... whether this is a legitimate trend or a case of a client or designer falling in love with a particular technology?" and then very strongly answered it for me.
Not everyone sold on the benefits of UFAD
The January article on underfloor air distribution ("Undervalued?" Jan. 2002, p. 28) raised a question: "... whether this is a legitimate trend or a case of a client or designer falling in love with a particular technology?" and then very strongly answered it for me.
I have designed HVAC systems for over 35 years, and I can say without hesitation that UFAD is strictly a case of puppy love. It is great for data centers and probably for a few rare other cases, but not for general applications. I can rebut every advantage stated, except for the comments as they relate to data centers. For example, how do we reduce the supply air volume by using 63°F air? How do we do latent cooling with 63°F? How does UFAD reduce chiller capacity? How do we do away with the ceiling and still take care of the return and exhaust? How does UFAD reduce equipment costs unless we sacrifice control—which is where we were with the original VAV designs?
Fortunately, the P.E.'s comments in the article were based mostly on engineering reality, and not on "what's in fashion this year."
DAVIE LLOYD, P.E., Askew Hargraves Harcourt & Assocs. Memphis, Tenn.
Where's the fire?
Several important issues relating to fire and life safety were not discussed in the "Undervalued?" (Jan. 2002, p. 28) underfloor air distribution article:
Section 607 of the Uniform Mechanical Code regulates the use of underfloor space as an HVAC supply plenum in single-family residences only. The code does not regulate, nor does it address under-floor supply plenum in other types of occupancies, such as office buildings.
If it is proposed to use a raised access floor system as a supply plenum—in an office building, for example—an alternate method of design (equivalency) is required to be submitted to the Authorities Having Jurisdiction.
The flexibility provided by a raised access floor may be affected by the provision of required fire-rated corridors, or by separations that are required to be continuous through the raised-floor space.
JOHN YOUNGHUSBAND, Project Director, Schirmer Engineering El Segundo, Calif.
As a manufacturer of cellular floors— a competitive system to access floor systems—I felt compelled to ask your roundtable panel ("Wiring Underfloor, Not Underfoot" Jan. 2002 p. 24), who generally praised access-floor systems as ideal for delivering electrical wire and conditioning air, the following:
How do you handle the possibility of a fire spewing toxic gases out of the access-floor plenum at workstation occupants?
Is fire detection and suppression equipment necessary for plenums that contain large amounts of combustible, plastic-coated cables?
Should access floors be covered by the NEC?
Are abandoned cables as dangerous in access floors as they are in ceiling plenums, and should they be removed?
In shallow, non-adjustable floors, how do you achieve and maintain a level floor? Can shims be used under pedestals or will they fall out of place?
In addition, just to be certain I have it right, let me review what makes a good access-floor installation:
First, build a shell with heavier beams, girders and foundations to carry the extra dead load of the access floor and extra height dead load.
In the shell, elevate the rest rooms, elevator lobbies and other areas that will not have the access floor system.
Install the access floor and the higher-cost carpet squares it requires.
Add a cable tray or duct system for cable management.
Lay steel conduit, as required by code, for all live-power wires.
Add smoke detection.
Add a sprinkler or halon system under the floor—optional, but highly recommended if large amounts of cabling are anticipated.
Now what does this all cost? Please excuse the sarcasm, but I'm frustrated reading article after article praising access floor.
On top of the cost, combustible plastic coated cables are a fuel for fires and their unlimited use under access floors and in ceiling plenums is recognized as a severe life-safety threat. Are you aware that NFPA and NEC are now mandating the removal of abandoned cable in ceiling and access floor plenums?
In my opinion, life safety, not convenience, flexibility or scalablity is—and must be—the primary design issue for architects and engineers.
I agree with some of what the panel expressed, and access floor is an "ideal" system if money is no object. But I find that it is, and in such cases more conventional air and wire-delivery systems can often outperform an access floor.
JOHN J. MICHLOVIC, P.E., Centria/H.H. Robertson Floor Systems Ambridge, Penn.
Editor's Reply: The questions raised in the preceding letters are indeed valid and form a good basis for future discussions of underfloor systems in the magazine. In fairness to our panelists, they could only answer the questions we asked.
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